Tweet1. Introduction The economic development of any region, state or country, depends not only on its natural resources and productive activities, but also on the infrastructure that account for the exploitation, processing and marketing of goods. Irrigation systems, roads, bridges, airports, maritime, land and air transport, school buildings, offices and housing, industrial installations are affected […]
The economic development of any region, state or country, depends not only on its natural resources and productive activities, but also on the infrastructure that account for the exploitation, processing and marketing of goods. Irrigation systems, roads, bridges, airports, maritime, land and air transport, school buildings, offices and housing, industrial installations are affected by corrosion and therefore susceptible to deterioration and degradation processes.
Corrosion is a worldwide crucial problem that strongly affects natural and industrial environments. Today, it is generally accepted that corrosion and pollution are interrelated harmful processes since many pollutants accelerate corrosion and corrosion products such as rust, also pollute water bodies. Both are pernicious processes that impair the quality of the environment, the efficiency of the industry and the durability of the infrastructure assets. Therefore, it is essential to develop and apply corrosion engineering control methods and techniques.
Other critical problems, that impact on infrastructure and industry are climate change, global warming and greenhouse emissions, all interrelated phenomena.
This post presents important aspects of corrosion in industrial infrastructure, its causes, impacts, control, protection and prevention methods.
1. Materials in industry
Metallic materials play a key role in the development of a country and its sustained growth in the context of the global economy. Table 1 shows a classification and the properties of different types of materials used in the industry. During the course of the metal production it undergoes various types of processes: mining of minerals, manufacturing and application and generation of gases, liquids or solids that are released into the environment. In the industrial development, production and use of materials in general, economic cycles are due to take effect that influence the environment (Raichev et al., 2010). The selection of a predominant group of materials depends on the particular industries; they determine to a greater or lesser extent the pattern of consumption of a given product, inducing the market to adapt itself to this new reality. The materials industry follows two general strategies: re‐ search the materials and the available technology recommended for their. Recycled materi‐ als typically require less capital and energy consumption, but need more manpower, for primary processing. Also, the costs of pollution control are lower than those required for primary processing of minerals. Recycling becomes more intense, as economies tend to be more sophisticated, since viable quantities of recycled material must be available for reuse (Garcia, R., et al, 2012, Lopez, G. 2011, Schorr, M., 2010).
In the production of a material waste is generated: for example, parts of material that was left aside, through the production steps. There are called effluent, which consist of waste that comes from the processes linked to the technology involved in each step of production, although not necessarily with the main material. Industrial processes for the recovery of ore from the mine to produce a metal, are related to technological development and therefore varies from one country to another, including regulatory laws, financial aspects etc.. Therefore, the environmental impacts vary widely. A low grade or poor quality of the ore, with low metal content, increase the cost of recovery, requiring large amounts of mineral raw material and en‐ ergy invested for the recovery of small amounts of metal. Also important is the feasibility of the mineral that can be worked out e.g., the cost of physical removal of rock, accessibility to the mines, thickness and regularity of the ore zone, and its hardness. Figure 1, shows the material cycle, which involves processes from raw material, extraction from natural sources, processing and conversion into industrial materials, their processing and application, the deterioration rate effects, its mechanical properties, environmental behavior, corrosion, disposal and possible recovery of some of these through the use of recycling methods.
There are many examples of recovery of metals, which could help to describe step by step the various interactions with the environment itself. A mineral submitted to a production process will impact the environment, during four steps: extraction, processing, fabrication and manufacturing, of goods as seen in the cycle of materials. (Figure 1)
In the mineral extraction step, the effluents of N, C, S, NOx, SOx and COx, from machinery and equipment, operation process water, particulate matter and ground movement in landfills.
The processing stage, chemical operations or extractive metallurgy for converting the concentrate into metal apply selected technologies. The effluents are gases such as SO2, NO2 and CO2, water contaminated with heavy metals, and hazard sediments.
In the manufacturing step the material undergoes operations that transform it into rods, bars, sheets; losses are scrap metal, such as cuts, burrs, mill scale, which recycled with no net loss of metal. In the manufacturing stage the metal is formed by stamping, machining and forging.
Focus on good operations management involves control of air emissions, water management and treatment, solid waste disposal and good land use, will greatly help to maintain a good balance with the environment. It is also necessary to analyze the production area to identify what improvements or measures should be implemented. The role of hydrometallurgist is particularly important and so he is responsible for the design of environmentally friendly processes in each of his steps, to promote sustainable production.
2.1 Processes of materials biodeterioration in industrial systems
In addition to the common processes of deterioration of materials by chemical reactions and mechanical fracture, there are others who are concerned with the participation of various types of microorganisms that adhere in colonies or develop on their surfaces.
Biocorrosion and biodeterioration of metallic materials and nonmetallic materials are two important processes that cause serious problems to the infrastructure of various industrial systems. Generally, microorganisms do not deteriorate or corrode metals directly, but modify the conditions of interface material / environment and surroundings, favoring the degradation of these materials in such a way that induce or influence the development process.
Biofouling is a common term that indicates the presence of microbiological growth on the surfaces of structures built of different materials favoring the formation of biofilms with the colonies of various types of microorganisms.
In the case of metal, biocorrosion occurs due to corrosion electrochemical processes and bio‐ logical agents due to the action of microorganisms and / or bacteria present in the system. The knowledge of these biological processes and their effects is necessary in order to establish preventive measures and control measures in industrial systems.
An industrial plant containing several biocorrosion environments is a potential risk:
In a heat exchangers system, usually dust accumulates biological waste; biocorrosion could occur, leading to corrosion film formation on walls surface. Therefore, it will be energy loss by increasing the resistance to fluid flow and heat transfer. Loss by evaporation of water favors the increase of the concentration of nutrients, the residence time, the water temperature and the surface / volume ratio, which leads to higher rate of microbial growth (Stoytcheva et al., 2010, Carrillo M. et al., 2010).
Until the early 80′s of the twentieth century, we used mixtures of anodic and cathodic inhibitors, such as chromium, zinc and phosphates, to lessen the effects of corrosion in water systems. In some cases we added a polymer, as is still done to date, to avoid or eliminate the problems of fouling on the metal walls. On the other hand, to prevent microbiological growth, we added biocides such as chlorine and quaternary ammonium compounds under acidic conditions.
In the early 90′s, the strategies for industrial water treatment changed because of pressure from laws for the preservation of the environment. Chromates and acid pH values are replaced by the use of organic phosphonates as corrosion inhibitors, while for the control of fouling polycarboxylate type polymers are used. However, this change brought about an increase in the amount of suspended solids, a greater number and variety of microorganisms and therefore a greater amount of inorganic deposits on the heat exchangers walls.
2.2. Biodeterioration of metallic and nonmetallic materials
The metal nature has an effect on the distribution and development of microbial films on its surface. These films influence on the wear and corrosion of the metal substrate. The lack of homogeneity in the biofilm is a precursor of differential aeration processes with formation of differential cell concentration, for example, stainless steels (SS) and nickel-copper (Ni-Cu) alloys in seawater. The oxides passive films or hydrated hydroxides (corrosion products) are a good place for the establishment and growth of bacteria, especially when these products are at a physiological pH values (pH ≈ 7.4)
- Carbon Steel (CS)
CS are very active metals in aggressive media, such as seawater. In this case, the action of microorganisms involves the dissolution of films of corrosion products, by processes of oxidation and reduction. This creates new metal active areas, exposed to the aggressive medium and suffers corrosion processes. In the case of sulfate-reducing bacteria (SRB), the species generated by their metabolism (sulfides) are corrosive to the metal. Figure 2 shows the final state pitting outside a CS pipe, which was affected by microbial growth inside, prompting a process of microbial corrosion with not uniform localized attack.
- Stainless steel
The presence of chromium and molybdenum as alloying elements, enable passive behavior of stainless steels in different environments. However, the passive surface of these SS provides an ideal location for microbial adhesion and therefore are susceptible to corrosion pit‐ ting, crevice corrosion under stress or in solutions containing chlorides, as sea water.
In marine environments, the generation of peroxides during bacterial metabolism causes an ennoblement of the pitting potential of SS, thus promoting corrosion. Obviously, not all SS have the same behavior, but in general they tend to deteriorated in the presence of colonies of microorganisms.
- Copper and nickel alloys
Alloys of Cu with Zn, Sn and Al, brasses, bronzes, aluminum bronzes; also the nickel alloys: Monel, Hastelloy, nickel superalloys: Ni-Mo, Ni-Cr-Mo, Ni-Cr-Fe- Mo; the traditional nickel alloys: Ni-Cr-Fe, Ni-Fe-Cr, Fe-Ni-Cr-Mo), and the Cu-ni alloys CuNi\70/30, CuNi\90/10, have shown great corrosion resistance in different environments, so they have found a wide use in different industries and environments. However, despite these skills, there are reports that these alloys are colonized by bacteria after several months of exposure in seawater (Acuña, N. et al., 2004).
- Aluminum and its alloys
Al is an active metal which is passivated rapidly in some neutral and acid media, thus offer‐ ing a good resistance to corrosion. Al alloys with copper, magnesium and zinc, are widely used in the aviation industry. However, there have been cases of biocorrosion on fuel tanks of jet aircraft made of Al alloys by microbial contaminants in turbo combustibles. The presence of water (moisture), even in minimal amounts, allows growth of microorganisms (typically fungi), when these are able to utilize hydrocarbons as a carbon source.
Ti is considered as the most resistant metal to biocorrosion, according to the results of tests carried in different conditions, due to its passive behavior that is reinforced in the presence of oxidizing agents. This is the reason why Ti is the material of choice, for example, for the manufacture of tubes in cooling systems that use seawater.
- Nonmetallic materials
Non-metallic materials such as fiberglass reinforced polyester (FGRP), concrete and wood, are also affected by biodeterioration processes in the presence of microorganisms
In the case of FGRP, bacteria and algae are able to use the polyester matrix as a carbon source, consuming and considerably reducing the mechanical strength of composite material, ultimately causing its failure. This is easily observable in screens of this material in cool‐ ing towers or tanks containing fresh water or salt water. Wood suffers biodeterioration by the presence of fungi in moist environments that promote the delignification of this material (Valdez B., et al., 1996, 1999, 2008).
2.2. Facing the problems of biodeteriorationThe inevitable presence of microorganisms in the feed water causes a sequence of biofouling, biocorrosion and biodeterioration of the materials component of the structures. This sequence depends on the degree of microbial contamination and the system operating characteristics.
The most common methods of controlling these problems involve the application of continuous or metered biocides such as chlorine. Currently, we use substances more compatible with the environment, since the use of chlorine is limited to certain concentrations. Such is the case of ozone, which is also ascribed with passivating effects on certain metals and alloys commonly applied in industry, and also in antifouling action.
In order to tackle a biodeterioration problem it is required a prior analysis of the problem, to know when conditions are suitable for the development of this process. In industrial systems we need to know some parameters: temperature, pH, nutrients; carbon, phosphorus, nitrogen, sulfate ion levels and flow rates. The places where we find biodeterioration are: biofouling deposits, under any deposit, zones of localized metal corrosion. to check their presence it is necessary to utilize sampling techniques, isolation and identification of micro‐ organisms. It is interesting to note that there are commercial devices for in situ measurements that are practical and useful for the plant engineer.
1. Corrosion in the electronics industry
Corrosion of device components, manufactured by the electronics industry, is a problem that has occurred during a long time. Often, especially corrosion of one or more of the metallic ele‐ ments of an electronic component is the primary cause of failure in various electronic equip‐ ments. The high density of components required to reduce the size of electronic equipment, also for a better signal processing, leads to the generation of enclosed corrosion between thin metal sections. Furthermore, when electronic devices are in more severe environments such as tropical, subtropical, contaminated deserts, etc., they have high failure rates. Problems, due to the aggressiveness of the medium in electronic equipment for military use, have also occurred in aircraft and submarine guidance systems. Another common problem is corrosion damage suffered by components music players, when exposed to humid environments contaminated with chlorides, for example, during transport by ship, from the manufacture location to the consumer place. Thin layers of corrosion products on the surface of the metal component change their electrical characteristics: resistance, capacity and lead to partial or total failure of the electronic system. There are reported cases where small amounts of moisture have caused corrosion in tablets with printed circuits, nichrome resistors, fittings, electrical connectors and a wide range of components, and micro-electronic components, which have been coated with metallic films (Valdez B. et al., 2006, G. Lopez et. al., 2007)
Corrosion of metal components in the electronics industry may occur at different stages: during manufacture, storage, shipping and service. The main factors in the onset of corrosion and subsequent development are moisture and corrosive pollutants, such as chlorides, fluorides, sulfides and nitrogen compounds, organic solvent vapors, emanating from the resins used as label, or coatings formed during the curing process and packaging of microcircuits.
The sources providing aggressive pollutants are diverse, from flux residues used for welding processes, waste and vapors from electrolytic baths, arising volatile organic adhesives, plastics and acidification of their environment. Assays in artificial atmosphere, which simulates an in‐ door environment of an electronic plant have shown that the surface of the silver undergoes browning or tarnishing and the formation of dendrite whiskers due to corrosion (Figure 3).
The elemental chemical analysis of the surface (EDX – Scattered Electron Spectroscopy and XRD – X-rays) shows that the corrosion product formed on the silver surface is silver sulfide (Ag2S), due to the action of pollutant gases such as SO2 and H2S present in a humid environment (Figure 4). Moreover, the micrograph of the silver surface (SEM) shows a dendritic growth of corrosion products, characteristic for silver components.
The design of electronics equipment requires a great variety of different metals, due to their different physical and electrical features. Metals and alloys used in the electronics industry are:
- Gold (Au) coating and / or foil in electrical connectors, printed circuits, hybrid and miniature circuits.;
- Silver (Ag) for protective coating in contact relays, cables, EMI gaskets, etc..;
- Magnesium (Mg) alloys for radar antenna dishes and light structures, chassis brackets, etc..;
- Iron (Fe), steel and ferroalloys for guide components, magnetic shielding, magnetic coatings memory disks, processors, certain structures, etc..;
- Aluminum (Al) alloys for armor equipment, chassis, mounting frames, brackets, trusses, etc..;
- Copper and its alloys for cables, tablets printed circuit terminals, nuts and bolts, RF pack‐ aging, etc..;
- Cadmium (Cd) for sacrificial protective coating on iron and safe electrical connectors;
- Nickel (Ni) coating for layers such as barrier between copper and gold electrical contacts, corrosion protection, electromagnetic interference applications and compatibility of dis‐ similar material joints;
- Tin (Sn) coating for corrosion protection of welding; for compatibility between dissimilar metals, electrical connectors, RF shielding, filters, automatic switching mechanisms;
- Welding and weld coatings for binding, weldability, and corrosion protection.
Many of these metals are in contact with each other, so that in the presence of moisture, galvanic corrosion / bimetallic corrosion occurs. When using similar metals, due to design the following requirements must be taken into account.
- Designing the contact of different metals such that the area of the more noble cathodic metal should be appreciably smaller than the area of the more active anodic metal. The area of the cathode can be decreased by applying paint or coating.
- Coating the contact area of a metal with a compatible metal.
- Interpose between dissimilar metals in a metal compatible packaging.
- Sealing interfaces to prevent ingress of moisture.
- Set the electronic device in a hermetically sealed arrangement.
Other corrosion problems can occur due to the characteristics of electronic components such as electromagnetic interference, electromagnetic pulse, flux residues, finishes and materials component tips, organic products that are used for various purposes and emitting gases during curing, whiskers, embrittlement inter-metallic electrical contacts.
Metal components may corrode during manufacture and storage prior to assembly, needing protection against corrosion. In plants and warehouses, air conditioning systems must operate efficiently, removing moisture and suspended particulate matter. Filters and traps should be cleaned and replaced regularly. For closed containers, we recommend the installation of dryers with visual indicators, and the use of volatile vapor phase corrosion inhibitors. In the case of sealed black boxes, the temperature inside these drops should never be below the dew point (Veleva L. et al., 2008, Vargas L. et al., 2009, Lopez G. et al., 2010).
1. Corrosion in water
Abundant water sources are essential to a country’s industrial development. Large quantities of this precious liquid are required for cooling products, machinery and equipment, to feed boilers, meet health needs and provide drinking water to humans. Estimates of water consumption for each country are different and depend on the degree of industrial development thereof. In first world countries like the United States, these intakes are as high as several hundred billion liters per day. These countries have implemented water reuse systems with certain efficiency due to the application of appropriate treatment for purification. Water, a natural electrolyte is an aggressive environment for many metals / alloys, so that they may suffer from corrosion, whose nature is electrochemical.
As raw water or fresh water we mean natural water from direct sources such as rivers, lakes, wells or springs. Water has several unique properties and one of these is its ability to dis‐ solve to some degree the substances found in the earth’s crust and atmosphere allowing the water to contain a certain amount of impurities, which causes problems of scale deposition on the metal surface, e.g. in pipelines, boiler tubes and all kinds of surfaces that are in con‐ tact with water (Valdez, B. et al., 1999, 2010).
Oxygen is the main gas dissolved in water, it is also responsible for the costly replacement of piping and equipment due to its corrosive attack on metals in contact with dissolved oxygen (DO). The origin of all sources of water is the moisture that has evaporated from the land masses and oceans, then precipitated from the atmosphere. Depending on weather conditions, water may fall as rain, snow, dew, or hail. Falling water comes into contact with gas‐ es and particulate matter in the form of dust, smoke and industrial fumes and volcanic emissions present in the atmosphere.
The concentrations of several substances in water in dissolved, colloidal or suspended form are low but vary considerably. A water hardness value greater than 400 parts per million (ppm) of calcium carbonate, for example, is sometimes tolerated in the public supply, but 1 ppm of dissolved iron should be unacceptable. In treated water for high pressure boiler or where radiation effects are important, as in nuclear reactors, impurities are measured in very small amounts such as parts per billion (ppb).
In the case of drinking water the main concern are detailed physicochemical analysis, to find contamination, and biological assays to detect bacterial load. For industrial water supplies it is of interest the analysis of minerals in particular salts. The main constituents of water are classified as follows:
- Dissolved gases: oxygen, nitrogen, carbon dioxide, ammonia and sulfide gases;
- Minerals: calcium, sodium (chloride, sulfate, nitrate, bicarbonate, etc.), Salts of heavy metals and silica;
- Organic matter: plant and animal matter, oil, agricultural waste, household and synthetic detergents;
- Microbiological organisms: include various types of algae, slime forming bacteria and fungi.
The pH of natural waters typically lies within the range of 4.5 to 8.5; at higher pH values, there is the possibility that the corrosion of steel can be suppressed by the metal passivation. For example, Cu is greatly affected by the pH value in acidic water and undergoes a slight corrosion in water releasing small amounts of Cu in the form of ions, so that it’s corroded surface because green stained clothing and sanitary ware. Moreover, deposition of the Cu ions on surfaces of aluminum or galvanized zinc corrosion cells leads to new bimetallic con‐ tact, which cause severe corrosion in metals.
The mineral water saturation produces a greater possibility of fouling on the metal walls, due to the ease with which the insoluble salts (carbonates) can be precipitated. To control this effect it is necessary to know and use the Saturation Indices. Water saturation refers to the solubility product of a compound and is defined as the ratio of the ion activity and the solubility product. For example, water is saturated with calcium carbonate when it is no more possible to dissolve the salt in water and then it begins to precipitate as scale. In fact, it is called supersaturated when carbonate precipitation occurs on standing the solution. The most common parameters that must be known to characterize the water corrosivity, be it raw or treated, for operation in an industrial facility are shown in Table 2.
There six formulas to calculate Saturation Indices and embedding: Langelier index (LSI), Ryznar stability index, Puckorious index of scaling, Larson-Shold index, index of Stiff- Davis and Oddo-Tomson index. There is some controversy and concern for the correlation of these indices with the corrosivity of the waters, particularly regarding the Langelier (LSI).
A LSI saturation index with value “0″ indicates that the water is balanced and will not be fouling, while the positive value indicates that the water may be fouling (Table 3). The negative value of the LSI suggests that water is corrosive and can damage the metal installation, increasing the content of metallic ions in water. While some sectors of the water management industry uses the values of the indices as a measure of the corrosivity of the water. Corrosion specialists are alerted and are very wary of issuing an opinion, or extrapolate the use of indices to measure the corrosivity of the environment.
Sometimes the raw water is contaminated with chemicals such as fertilizers and other chemicals coming from agricultural areas (Figure 5).
In these cases, ionic agents such as nitrites, nitrates, etc., in water causes an accelerated process of localized corrosion to many metals and the consequent failure of equipment.
Raw water contaminants can be quite varied, including both heavy metals and organic chemicals, referred to as toxic pollutants. Among the heavy metals may be mentioned arsenic (As), mercury (Hg), cadmium (Cd), lead (Pb), zinc (Zn) and cadmium (Cd), which are sometimes at trace levels, but they tend to accumulate over time, so that priority pollutants are to be treated.
Pesticides, insecticides and plaguicides comprise a long list of compounds, for which we should be concerned: DDT (insecticide), aldrin (an insecticide), chlordane (pesticide), endo‐ sulfan (insecticide), diazinon (insecticide), among others.
Contaminants, such as polycyclic aromatic organic compounds, include what is known as volatile organic compounds such as naphthalene, anthracene and benzopyrene. There are two main sources of these pollutants: petroleum and combustion products found in munici‐ pal effluents. On the other hand, there are polychlorinated biphenyls or PCBs, which are mainly used in transformers for the electrical industry, heavy machinery and hydraulic equipment. This class of chemicals is extremely persistent in the environment and affects human health.
From the viewpoint of corrosion, these contaminants which are present even at low concentrations or trace in the raw water, favor the corrosivity the metals which are in contact with. The combination of the corrosive effects of these contaminants together with the oxidation by oxygen, minerals and other impurities, leads to consider raw water as a natural means capable of generating corrosion of metals. It is recommended at least, to carry out a process of treating raw water, to reduce significantly the hardness and remove suspended solids, which will help greatly in preventing subsequent problems of corrosion and fouling on metal surfaces, curbing economic losses and maintaining the industrial process in good operating condition.
4.1. Corrosion in potable water systems
Corrosion is a complex phenomenon that arises as a result of the interaction between water and the surface of metallic pipes or the equipment of storage and handling. The process is invariably a combination of oxidation and reduction, as already described in previous chapters. In drinking water, it should be noted that the corrosion products which are partially soluble in water in ionic form are toxic at certain concentrations, e.g. copper and lead. The existence of high concentrations of lead in water carried by copper tubing, indicate that the source of lead may be tin-lead solder at the junctions of the copper pipes. The consumption of domestic water contaminated with toxic metal ions (Pb+2, Cu+2, Zn+2, Cr+3), gives rise to acute chronic health problems. The regulations have set the following limits allowable concentration in drinking water: Cr (0.05 ppm), Cu (0.01 ppm), Pb (0.05 ppm) and Zn (5 ppm). These regulations are made in order to protect the public user and consumer of drinking water and are continuously striving for a reduction in the maximum allowable limits. Some concentrations reach zero as is the case of Pb in the United States due to the concerns Pb about poisoning of children. Still, many sources such as wells and springs are outside the control of law and toxic substances, bacteria and pathogens. Damage caused by corrosion of household plumbing may be accompanied by unpleasant aesthetic problems such as soiled clothing, unpleasant taste, stains and deposits in the toilets, floors of bathrooms, tubs and showers. To prevent corrosion of pipes, we recommend the use of PVC pipes for drinking water, replacing the metal, as a preventive measure.
Corrosion can occur anywhere on the pipes that carry drinking water, mainly at sites of con‐ tact between two dissimilar metals, thus forming a corrosion cell. In general, the metals will corrode to a greater or lesser degree in water, depending on the nature of the metal, on the ionic composition of water and its pH. Waters high in dissolved salts (water hardness), favor the formation of scale, more or less adherent, in different parts of the equipment (Figure 6). These deposits may be hard or brittle, sometimes acting as cement, creating a physical barrier between the metal and water, thereby inhibiting corrosion. Calcium carbonate (Ca‐ CO3) is the most common scale; its origin is associated with the presence of carbon dioxide gas (CO2) in water. Sometimes these deposits are filled with pasty or gelatinous hydrated iron oxides or colonies of bacteria (Valdez, B. et al., 1999, 2010).
Usually, groundwater CaCO3 saturated (calcareous soils), due to the presence of dissolved CO2, whose content depends on its content in the air in contact with the water and on temperature. These waters are often much higher in CO2 content, so they may dissolve substantial amounts of calcium carbonate. These waters are at pressures lower than they had in the ground, so CO2 gas lost with consequent supersaturation of carbonates. If conditions are appropriate, the excess of CaCO3 can precipitate as small agglomerates deposited in muddy or hard layers on solid surfaces, forming deposits. An increase in temperature is an important factor and also leads to supersaturation of carbonates, with the consequent possibility of fouling. To a lesser extent fouling can precipitate more soluble Mg carbonates (MgCO3) and Mn (MnCO3), and also oxides / hydroxides, dark colored and gelatinous. Except in very exceptional cases in sulfated water, it is normal to find deposits of gypsum (CaSO4•½ H2O) because their solubility is high, but decreases with increasing temperature. Hard silica scale (SiO2) may appear with oversaturated waters or appear as different silicates (SiO44-) trapped in the carbonate deposits. Generally, the silica appears trapped in other types of scale and it is not chemical precipitation.
Waters often carry considerable amounts of iron (ferrous ion, Fe+2), which may be often precipitated by oxidation upon contact with air as hydrated iron oxide (ferric, Fe+3) but sometimes can be Fe+2 form black sludge, more or less pasty or gelatinous and sometimes very large. The voluminous precipitate occupies the pores, significantly reducing the permeability of the fouling. Sometimes the Fe ions can come from corrosion of the pipe giving rise to simultaneous corrosion and scaling (Figure 6). Common bacteria of the genera Gallionella, Leptothrix Cremothrix are known as Fe bacteria, can give reddish-yellow voluminous precipitate and sticky ferric compounds from ferrous ion, which drastically reduce the permeability of the deposit, in addition to trap other insoluble particles.
The cost for impairment of domestic water systems and the impact on health, involves several consequences: premature corrosion and failure of the pipes and fittings that carry water in a house or building, a low thermal efficiency (up to 70%) of water heaters (boilers), which can cause their premature failure. High levels of metals or oxides, which usually are not properly, treated in drinking water cause red or blue-green deposits and stains in the toilets sinks. In addition to concerns about the aesthetic appearance, a corrosion process can result in the presence of toxic metals in our drinking water. For evaluating water quality and their tendency corrosive and / or fouling, LSI can be used. This analysis must be accompanied by measurements of water pH and conductivity, and corrosion tests applying international standards.
4.1. Anticorrosive treatment of water Corrosion control is complex and requires a basic knowledge of corrosion of the system and water chemistry. Systems can be installed for water pretreatment, using non-conductive connections, reducing the temperature of hot Cu water pipes employed and copper installing PVC or other plastic materials. It is important to note that the corrosiveness of water can be increased by the use of water softeners, aeration mechanisms, increasing the temperature of hot water, water chlorination, and attachment of various metals in the water conduction system. A proper balance between the treatment systems and water quality, can be obtained with acceptable levels of corrosivity. Thus, the lifetime of the materials that make the water system in buildings, public networks, homes and other systems will be longer.
1. Soil corrosion
A large part of steel structures: aqueducts, pipelines, oil pipelines, communications wire ropes, fuel storage tanks, water pipes, containers of toxic waste, are buried, in aggressive soils. Large amounts of steel reinforced concrete structures are also buried in various soil types. In the presence of soil moisture it is possible to have humid layer on the metal sur‐ face, whose aggressiveness depends on soil type and degree of pollution (decaying organic matter, bacterial flora, etc.). Thus, the soil can form on the metal surface an electrolyte complex with varying degrees of aggressiveness, a necessary element for the development of an underground electrochemical corrosion. The corrosion process of buried structures is extremely variable and can occur in a very fast, but insignificant rate, so that pipes in the soil can have perforations, presenting localized corrosion attack or uniform.
Metal structures are buried depending on their functionality and security. Most often they traverse large tracts of land, being exposed to soils with different degrees of aggressiveness exposed to air under atmospheric conditions (Figure 7).
When pipes or tanks are damaged by corrosion, the formation of macro-and micro-cracks can lead to leaks of contained products or fluids transported, causing problems of environmental pollution, accidents and explosions, which can end in loss of life and property (Guadalajara, Jalisco, Mexico, 1992). In the case of pipes used to carry and distribute water, a leak may cause loss of this vital liquid, so necessary for the development of society in general and especially important in regions where water is scarce, so the leakage through aqueducts pipes should be avoided. An important tool needed to prevent the most serious events, is the knowledge of the specific soil and its influence on the corrosion of metal structures.
5.1. Types of soils and their mineralogy
A natural soil contains various components, such as sand, clay, silt, peat and also organic matter and organisms, gas, mineral particles and moisture. The soils are usually named and classified according to the predominant size range of individual inorganic constituent particles. For example, sandy soil particles (0.02 – 2 mm) are classified as fine sand (0.02 – 0.2 mm) or thick (0.20 -2.00 mm). Silt particles (0.002 to 0.02 mm) and clay, which have an average diameter 0.002 mm, are classified as colloidal matter. A comparison of the sizes of these typical soils is done in Figure 8.
Currently exists in the U.S. and in over 50 countries worldwide, a detailed classification for soils, which includes nine classes with 47 subgroups.
The variation in the proportion of the groups of soil with different sizes, determines many of its properties. Fine-textured soils due to high clay content, have amassed particles, so they have less ability to store and transport gases such as oxygen, that any ground-open e.g. sandy soil. The mineralogy of both clay types and their properties, are closely related to the corrosivity of the soil. Silica (SiO2) is the main chemical constituent of soils type clay, loam and silt, also in the presence of Al2O3. Common species in moist soil are dissolved ions H+, Cl-, 2- -SO4 , HCO3 . The chemical composition and mineralogy of the soil determine its corrosive aggressiveness; poorly drained soils (clay, silt and loam) are the most corrosive, while soils with good drainage (gravel and sand type) are less aggressive to metals. Vertically homogeneous soils do not exist, so it is convenient to consider the non-uniformity of ground, formed of different earth layers. To understand the corrosion behavior of a buried metal is very important to have information about the soil profile (cross section of soil layers). The physicochemical and biological nature of soil, corrosive aggressiveness and dynamic interactions with the environment, distinguishes the ground like a very complex environment and different from many others. Climate changes of solar radiation, air temperature and relative humidity, amount of rainfall and soil moisture are important factors in corrosion. Wind, mechanical action of natural forces, chemical and biological factors, human manipulation can alter soil properties, which directly affects the rate of corrosion of metals buried in the ground. Conditions may vary from atmospheric corrosion, complete immersion of the metal, depending on the degree of compactness of the soil (existence of capillaries and pores) and moisture content. Thus the variation in soil composition and structure can create different corrosion environments, resulting in different behavior of the metal and oxygen concentrations at the metal / soil interface.
Two conditions are necessary to initiate corrosion of metal in soil: water (moisture, ionic conductor) and oxygen content. After startup, a variety of variables can affect the corrosion process, mentioned above, and among them of importance are the relative acidity or alkalinity of the soil (pH), also the content and type of dissolved salts.
Mainly three types of water provide moisture to the soil: groundwater (from several meters to hundreds below the surface), gravitational (rain, snow, flood and irrigation) and capillary (detained in the pores and capillary spaces in the soil particles type clay and silt). The mois‐ ture content in soils can be determined according to the methodology of ASTM D 2216 (“Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass”), while its permeability and moisture retention can be measured the methods descri‐ bed in ASTM D2434 and D2980. The presence of moisture in soils with a good conductivity (presence of dissolved salts), is an indication for high ion content and possible strong corrosive attack.
The main factors that determine the corrosive aggressiveness of the soil are moisture, rela‐ tive acidity (pH), ionic composition, electrical resistance, microbiological activity.
5.1. Corrosion control of buried metals
Given the electrochemical nature of corrosion of buried metals and specific soils, this can be controlled through the application of electrochemical techniques of control, such as cathodic protection. This method has been universally adopted and is appropriate to protect buried metallic structures. For an effective system of protection and cheaper maintenance, pipelines must be pre-coated, using different types of coatings, such as coal tar, epoxies, etc. This helps reduce the area of bare metal in direct contact with the ground, lowering the demand for protection during the corrosion process. The purpose of indirect inspection is to identify the locations of faulty coatings, cathodic protection and electrical Insufficient shorts (close- interval, on/off Potential surveys, electromagnetic surveys of attenuation current, alternating current voltage gradient surveys, etc..), interference current, geological surveys, and other anomalies along the pipeline.
1. Corrosion under thermal insulation
One of the most common corrosion problems in pipes, ducts, tanks, preheaters, boilers and other metal structures, insulated heat exchange systems, is the wear and corrosion occurring on metal (steel, galvanized steel, Al, SS, etc.), below a deposit or in its immediate neighbor‐ hood. This corrosion is known as corrosion under deposit. The deposit may be formed by metal corrosion products and / or different types of coating applied for protection. For ex‐ ample, in the case of a calcareous deposit, formed in the walls of galvanized steel pipes which carry water with a high degree of hardness (dissolved salts), it might develop corro‐ sion under deposit. These shells may be porous, calcareous deposit and / or partially detach‐ ed from the metal surface, so that direct contact between metal, water and oxygen (the oxidizing agent in the corrosion process) allows the development of metal corrosion. For this reason the pipes could be damaged severely in these locations up to perforation, while in parts of the installation corrosion might occur at a much lower level.
There is a considerable amount of factors in the design, construction and maintenance, which can be controlled to avoid the effects of deterioration of metal by corrosion under de‐ posit. In general, under these conditions the metal is exposed to frequent cycles of moisture, corrosivity of the aqueous medium or failure in the protective coatings (paint, metal, ce‐ ment, fiberglass, etc.). Figure 9 shows a conductor tube steam in a geothermal power plant, where CS corrosion happened beneath the insulation.
Seven factors can be controlled on the ground, to prevent this type of corrosion: design of equipment, operating temperature, selection of the insulation, protective coatings and paints, physical barriers from the elements, climate and maintenance practices of the facility. Any change in any of these factors may provide the necessary conditions for the corrosion process to take place. The management knowledge of these factors help explain the causes of the onset conditions of corrosion under deposits, and it will guide a better inspection of existing equipment and the best design.
6.1. Equipment design
The design of pressure vessels, tanks and pipes, generally includes accessories for support, reinforcement and connection to other equipment. Details about the installation of accessories are the responsibility of the engineers or designers, using building codes to ensure reliability of both insulated and non insulated equipment. The protective barrier against the environment surrounding the metal structure in such designs often breaks donor due to an inappropriate insulation, loss of space for the specified thickness of insulation or simply by improper handling during installation of the equipment. The consequence of a rupture or insulation failure means greater flow water ingress to the space between metal and coating hot-cold cycle, generating over time a buildup of corrosive fluid, increasing the likelihood of corrosive damage. Moreover, wet insulation will be inefficient and also cause economic loss‐ es. The solution of this factor is to meet the thickness specifications and spacing, as indicated in the code or equipment-building specifications and characteristics of the coating used.
The operating temperature is important for two reasons: a high temperature favors the wa‐ ter is in contact with the metal for less time, however, also provides a more corrosive environment, causes fast failures of coatings. Usually a team operating in freezing temperatures is protected against corrosion for a considerable life time. However, some peripheral devices, which are coupled to these cold spots and operating at higher temperatures, are ex‐ posed to moist, air and steam, with cycles of condensation in localized areas, which make them more vulnerable to corrosion. For most operating equipment at freezing conditions, the corrosion occurs in areas outside and below the insulation. The temperature range where this type of corrosion occurs is 60 °C to 80 °C; however, there have been failures in zones at temperatures up to 370 °C. Also, in good water-proof insulation, corrosion is likely to occur at points where small cracks or flaws are present, so that water can reach the hot metal and evaporate quickly. On the other hand, in machines where the temperature reach‐ es extreme values, as in the case of distillation towers, it is very likely to occur severe corro‐ sion problems.
6.2. Selection of insulation
The characteristics of the insulation, which have a greater influence on the corrosion proc‐ esses deposits, are the ability to absorb water and chemical contribution to the aqueous phase. The polyurethane foam insulation is one of the most widely used; however, in cold conditions they promote corrosion due to water absorption present. The coatings of glass fi‐ ber or asbestos can be used in these conditions, always when the capacity of absorbing wa‐ ter do not becomes too high. Corrosion is possible under all these types of coating, such insulation. The selection of insulation requires considering a large group of advantages and disadvantages regarding the installation, operation, cost, and corrosion protection, which is not an easy task. The outside of the insulation is the first protective barrier against the ele‐ ments and this makes it a critical factor, plus it is the only part of the system that can be readily inspected and repaired by a relatively inexpensive process. The durability and ap‐ pearance, melting point fire protection, flame resistance and installation costs are other im‐ portant factors that must be taken into account together with the permeability of the insulation. Usually the maintenance program should include repairs to the range of 2 to 5 years. Obviously the weather is important and corrosion under thermal insulation will more easily in areas where humidity is high. Sometimes conditions of microclimate can be ach‐ ieved through the use of a good design team.
1. Corrosion in the automotive industry
One of the most important elements of our daily life, which has great impact on economic activity, is represented by automotive vehicles. These vehicles are used to transport people, animals, grains, food, machinery, medicines, supplies, materials, etc. They range from com‐ pact cars to light trucks, heavy duty, large capacity and size. All operate mostly through the operation of internal combustion engines, which exploit the heat energy generated by this process and convert it in a mechanical force and provide traction to these vehicles.
The amount and type of materials used in the construction of automotive vehicles are diverse, as the component parts. They are usually constructed of carbon steel, fiberglass, aluminum, magnesium, copper, cast iron, glass, various polymers and metal alloys. Also, for aesthetic and protection against corrosion due to environmental factors, most of the body is covered with paint systems, but different metal parts are protected with metallic or inorganic coatings.
Corrosion in a car is a phenomenon with which we are in some way familiar and is perhaps for this reason that we often take precautions to avoid this deterioration problem.
A small family car, with an average weight of 1000 kg, is constructed of about 360 kg of sheet steel, forged steel 250 kg, 140 kg cast iron mainly for the engine block (now many are made of aluminum), 15 kg of copper wires, 35 kg and of plastic 50 kg of glass that usually do not deteriorate, and 60 kg for rubber tires; which wear and tear. The remaining material is for carpets, water and oil. Obviously, that is an advanced technology in the car industry, with automobiles incorporating many non-metallic materials into their structure. However, the problem of corrosion occurs at parts where the operation of the vehicle is compromised. Corrosion happens in many parts of the car (mostly invisible) it is not only undesirable for the problems it causes, but also reduces the vehicle’s resale value and decreases the strength of the structure. To keep the car in good condition and appearance, its high price, it is neces‐ sary to pay attention to the hidden parts of the vehicle.
The main cause of corrosion of the car body is the accumulation of dust in different closed parts, which stays for a long time by absorbing moisture, so that in these areas metal corrosion proceeds, while in the clean and dry external parts it does not occur (Figure 10).
The corrosion problem that occurs in the metal car body has been a serious problem that usually arises most often in coastal environments, contaminated with chlorides and rural areas with high humidity and specific contaminants. Many countries use salt (NaCl, CaCl2 or MgCl2) to keep the roads free of ice; under these conditions these salts, in combination with the dust blown by the car, provide conditions for accelerated corrosion. Therefore, it is recommended as a preventative measure, after a visit on the coast or being on dirty roads, to wash the car with water, and also the tires and the doors, especially their lower parts. In urban environments, the corrosion problem has been reduced due to the new design and application of protective coatings, introduced by major manufacturers in the early nineties of the twentieth century. The areas most affected are fenders, metal and chrome bumpers views which are used in some luxury vehicles as well as areas where water and mud are easily accumulated e.g. auctions of funds windshield and doors (Figure 11).
In regions with high incidence of solar radiation and the presence of abrasive dust, paint vehicles deteriorate rapidly. The hot, humid weather, combined with high levels of SO2 and NOx emissions that come from burning oil, chlorides salt. In the Gulf of Arabia, the blowing sand from the nearby desert, creates a very aggressive environment; statistics reveals that one in seven cars is damaged and due to corrosion the car life is estimated to an average of 8 months, also the car corrosion resistance decreases in the following order: manufactured in Europe, USA and Japan. White paints generally have shown a significantly better corrosion protection than other colors. Initially, corrosion defects appear as a kind of dots and spots of corrosion products formed under the paint and subsequently emerge from the steel sheet, leaving a free entry for moisture and air (oxygen), accelerating the corrosion process; in these cases reddish metal corrosion products.
7.1. Corrosion in the cooling systemThe cooling system of a car combustion engine consists of several components, constructed of a variety of metals: radiators are made of copper or aluminum, bronze and solder couplings with tin water pumps; motors are made of steel, cast iron or aluminum. Most modern automobiles, with iron block engine and aluminum cylinder head, require inhibitor introduced into the cooling water to prevent corrosion in the cooling system. The inhibitor is not antifreeze, although there are in the market solutions which have the combination of inhibitor-antifreeze. The important thing is to use only the inhibitor recommended in the automobile manual and not a mixture of inhibitors, since these may act in different ways and mechanisms. The circulating water flow should work fine without loss outside the system. If the system is dirty, the water should be drain and filling the system with a cleaning solution. It is not recommended to fill the system with hard water, but with soft water, introducing again the inhibitor in the correct concentration. If there exhaust at the water cooling system, every time water is added the inhibitor concentration should be maintained to prevent.
In small cars, it is common for water pumps; constructed mainly of aluminum, to fail due to corrosion, cavitation, erosion and corrosion, making it necessary to replace the pump (Val‐ dez, B. et al., 1995). Accelerated corrosion in these cases is often due to the use of a strong alkaline solution of antifreeze. On the other hand, in heavy duty diesel trucks, the cooling system is filled with tap water or use filters with rich conditioner chromates that can cause the pistons jackets to suffer localized corrosion. After 12 or 15 months, the steel jackets are perforated and the water passes into the cavity through which the piston runs, forcing tocarry out repair operations (Figure 12).
Corrosion causes great economic losses to the transport industry, since it must stop to repair the truck and abandon to provide the service with all the consequences that this entails. Fur‐ thermore, the use of chemical conditioning is now controlled by environmental regulations, so chromates and phosphates are restricted and novel mixtures of corrosion inhibitors have been produced to control the problem of corrosion in automobile cooling systems.
7.1. Corrosion in exhaust pipes and batteries
Exhaust pipes made of SS (0.6 – 0.8 mm thick) have a better resistance to chemical corrosion at high temperatures, which is why we are now using SS in many popular models. This SS resists corrosion much more than conventional CS and thus their long life covers the higher price. An‐ other alternative is to use conventional CS tube, zinc coated or aluminum (Figure 13). These ex‐ haust pipes are less expensive than stainless steel, but less resistant to corrosion.
The acidic environment which is generated on the surface of accumulators supplying the energy necessary for starting the engine, favors conducting corrosion processes in the lead terminals, where the cables are connected by bronze or steel clamps. Thus, this environment and these contact zones predispose cells to a process galvanic corrosion, which gradually deteriorates the contact wires, generating bulky corrosion products. This phenomenon is called sulfation of the contacts due to the sulfuric acid containing the battery, thus forming white sulfates on the corroded metal surface. These products introduce high resistance to current flow and cause failure to the engine ignition system, and impede the battery charge process. This problem has been eliminated in batteries that have airtight seals, or are manufactured with new technologies as well as bases covered with organic coatings that prevent corrosion.
Some years ago it was common for starters to fail, because the moisture or water penetrated into the gear area preventing it sliding motion and causing burning of the electric motor. Currently, new designs avoid contact with moisture and other foreign agents, preventing the occurrence of corrosion problems in these devices. As a preventive measure is recommended to prevent spillage of battery acid, to periodically clean the battery terminals (with a brush of wire or a special instrument), also coat them with petroleum jelly to prevent corrosion in these contact areas. A fat based composition which contains several components: alkaline salts and oxides of lithium, sodium bicarbonate and magnesium oxide are applied to the terminals and the connector. In general, in wet weather, the contacts of the accumulators have a tendency to more accelerated corrosion, thus requiring greater care to disconnect the terminals when not being used.
7.1. Corrosion prevention
To keep the vehicle for a longer time without the appearance of corrosion, it always requires washing with running water and, the use of very soft brush or cloth-like material, with a special detergent (not household detergents, which are very corrosive) and finally wash the vehicle with plenty of water. The floor carpet should be maintained clean and dry. A car should not be left wet in a hot garage, since under these conditions accelerated corrosion takes place since the water does not dry and can condense on the cold parts of the vehicle. In these cases, it is best not to close the garage door or use a roof space, to protect it from rain, and not allow moisture condensation. However, if the vehicle is left unused for a long time in a closed garage, it should be protected from dust, moisture and contaminants.
1. Corrosion control in thermoelectric plantsElectricity is a key element in ensuring economic growth and social development of a country. Many conventional power plants in recent years are being installed in combined cycle power plants, also called cogeneration. The latter, simultaneously generate electricity and / or mechanical power and useful heat, sometimes using thermal energy sources that are lost in conventional plants.
A power station is a thermoelectric energy conversion system, starting with the chemical energy of fuel that during combustion is converted into heat energy accumulated in the steam. This thermal energy generates mechanical energy from the hot steam, which expands in a turbine, turning on electricity in the generator. In this process of low energy thermal efficiency is lost in the hot gases that escape through the chimney and the cooling steam in the condenser.
Electricity generating plants burn fossil fuels such as coal, fuel oil and natural gas. These fuels containing as minor components sulfur compounds (S), nitrogen (N), vanadium (V) and chloride (Cl-). These are corrosive chemicals attacking the metal infrastructure; and polluting the environment by becoming acid gas emissions, also affecting the health of the population.
The three central equipment of a thermoelectric plant are the boiler, which converts the wa‐ ter into steam, the steam turbine to whom the pressure imparts a rotary motion and the con‐ denser that condenses the vapor released by the turbine and the condensed water is returned to the boiler as feed water. The turbine itself transmits rotary motion to the genera‐ tor of electricity, which will be distributed to industrial, commercial and homes in cities.
Corrosion in steam plant equipment occurs in two parts of the boiler: on the water side and the steam side, with the fire temperature up to 700 ° C, depending on the type, size and ca‐ pacity of the boiler. The boiler feedwater must be treated to eliminate the corrosive components: salts such as chlorides and sulfates dissolved oxygen (DO); silicates and carbonates, producing calcareous scale on the boiler walls, regarded as precursors for the formation of corrosion under deposits. The water is softened by eliminating salts and treated to remove oxygen; the pH is controlled by addition of alkaline phosphate to reach a pH range of 10 to 11, and inhibitors are added to the feedwater to prevent corrosion.
The flue gases and ash solid particles reach temperatures up to 1000 to 1200 °C, impinging on the outer surface of the boiler water tubes and preheater, creating an atmosphere for aggressive chemical corrosion. The damaged tubes lose its thickness generating metal corrosion products; they often are fractured, suffering a stress corrosion due to the combined effects of mechanical stress and corrosion (Figure 14). Since the tubes lose steam and pres‐ sure, the operation of the plant is interrupted and the tubes or its sections should be changed incurring severe economic losses. For example, in the United States has been concluded that the costs of electricity are more affected by corrosion than any other factor, contributing 10% of the cost of energy produced.
A study reveals that in 1991 there were more than 1250 days lost in nuclear plants operating in the United States, due to failure by corrosion, which represented an economic loss of $250.000 per day. Such statistics indicate that the power generation industry needs to obtain a balance between cost and methods for controlling effectively corrosion in their plants. It is sometimes advisable to add additives to the fuel, for example, magnesium oxide which prevent the deposition of the molten salts on the boiler tubes. Corrosion occurs also in the combustion air preheater, by sulphurous gases which react with condense and form sulfuric acid. Metal components of the turbine rotor: disks and blades suffer from corrosion by salts, alkali and solid particles contained in the vapor. In these cases, it is common to observe the phenomena of erosion-corrosion, pitting and stress corrosion fracture; their damage can be ameliorated through a strict quality control of boiler water and steam.
Efficient maintenance and corrosion control in a power plant is based on the following:
- Operation according to mechanical and thermal regime, indicated by the designer and builder of the plant;
- Correct treatment of fuel, water and steam;
- Chemical cleaning of the surfaces in contact with water and steam, using acidic solutions containing corrosion inhibitors, passivating ammoniacal solutions and solutions;
- Mechanical cleaning of surfaces covered with deposits (deposits), using alkaline solutions and water under pressure;
- Perform an optimum selection of the materials of construction for the components of the plant, including those suitable as protective coatings.
- The installation of online monitoring of corrosion in critical plant areas will be one of the most effective actions to control corrosion. In addition, it is recommended same use and document to use corrosion expert system software and materials databases for the analy‐ sis of the materials corrosion behavior.
Corrosion in power plants can be controlled by applying the knowledge, methods, stand‐ ards and materials, based on corrosion engineering and technology.
1. Corrosion in geothermal environments
The development of alternative energy sources represents one of the most attractive challenges for engineering. There are several types of renewable energies already in operation, such as wind, solar and geothermal. Geothermal environments can lead to aggressive environments, e.g. the geothermal field of “Cerro Prieto”, located in Baja California, Mexico.
The physical and chemical properties of the vapor at “Cerro Prieto” make it an aggressive environment for almost any type of material: metal, plastic, wood, fiberglass or concrete. The typical chemical composition of a geothermal brine, is shown in Table 4. Many engineering materials are present as components of the infrastructure and field equipment, required for the steam separation, purification and posterior operations for the generation of electricity. This entire infrastructure is a costly investment and therefore, failure or stoppage of one of them, means economic losses, regardless of how vital it is to maintain constant production of much-needed electricity.
In the process of the geothermal fluid exploitation, corrosion of metal structures occurs from the wells drilling operation, where the drilling mud used, causes corrosion of pumping and piping equipment. Subsequently, when the wells pipes are in contact with the steam, they can also suffer from corrosion-erosion problems, where the corrosive agent is hydrogen sulfide. Steam separators and the pipes are exposed to problems of fouling and localized corrosion due to the presence of aggressive components such as H2S and chloride ions (Cl-), present in the wells fluid. These agents lead to the deterioration of reinforced concrete foundations supporting steel pipes, or other concrete structures used to separate steam from water and to operate steam silencers. The reinforced concrete deterioration due to steel corrosion in this aggressive environment, and the steam pressure mechanical forces lead to concrete damage with formation of cracks and fractures.
In the power plants, the observed corrosion affects components of the steam turbines, condensers and pipelines, and also the cooling towers and concrete structures inside and outside the building that houses the plant. In these cases, the effects of corrosive attack appears in the form of localized corrosion in metal walls and gas piping) or as corrosion fatigue or stress corrosion, caused by cyclic mechanical forces or residual stresses, in turbines and other metal equipment. Table 5 shows a list of equipment and materials used for construction,which are part of the infrastructure of a geothermal power (Valdez, B. et al., 1999, 2008)
The combination of an aerated moist environment with the presence of hydrogen sulfide gas (H2S) dissolved in water provides a very aggressive medium (Figure 16), which promotes the corrosion of metals and alloys, such as CS and SS. The presence of dust, from the geothermal field and condensation cycles favor the failure of protective coatings applied to steel, so that developed corrosion leads to constant repairs and maintenance of metal installations: pipes, machinery, cooling towers, vehicles, tools, fences, warehouses, etc.
Cooling towers constructed of wood, steel and fiberglass in the presence of flowing and stagnant water and air currents (induced to complete cooling fans), suffer a serious deterioration of the steel by corrosion and biodeterioration, involving a variety of microorganisms. The timber is subjected to oxygen delignification under the effect of colonies of fungi and algae, as well as fiberglass reinforced polyester screens, which deteriorate due to colonies of aerobic and anaerobic bacteria e.g. sulfate reducers.
Furthermore, carbon steels corrode in the form of delamination due to sulfate reduction processes which induce the oxidation of iron, while the SS nails and screws undergoes localized corrosion, forming pits (Figure 17)
The deterioration by microorganisms capable of living in these conditions is one of the processes that have provided more information to the study of corrosion induced by microorganisms. In “Cerro Prieto”, for example, have been isolated and studied various bacteria capable of growing even at temperatures of 70 ° C under conditions of low nutrient concen‐ trations, while in the geothermal field of “Azufres” bacteria have been isolated to survive at temperatures of 105 °C and pressures of downhole (Figure 18).
1. Corrosion in the paper industry
Corrosion of the infrastructure used in the pulping and paper industry, is another serious problem for corrosion specialists. The wide experience, gathered from cases of corrosion in the various infrastructure components of the paper industry, has provided an extensive literature on mechanisms, types and control of corrosion in this environment.
In the early 60′s of last century, when the continuous digester process was adopted, the paper industry had limited knowledge about caustic embrittlement. Currently, it is known that the digesters are subjected to caustic levels and temperatures too close to the fracture caustic range where the total relieves of stresses in the material are essential. To elucidate the mechanism of this phenomenon, it was necessary to conduct serious investigations, which subsequently provide solutions to the problem of corrosion and caustic embrittlement. Technology in the paper industry has evolved over the last forty years and in parallel we can talk about the solution of corrosion problems in different parts of its infrastructure. Components with high failure rate due to corrosion are those built of bronze, SS, cast iron. Corrosion occurs in the papermaking machinery, where the white water equipment is subjected to an aggressive environment. The metal surfaces are exposed to immersion in this water; to steam that promotes the formation of cracks, which favor the deposit of pulp and other compounds. CS undergoes rapid uniform corrosion, while the copper alloys and SS (austenitic UNS S30400 L: 18% Cr8% Ni, UNS S31600 L: 16% Cr10% Ni 2% Mo) develop localized pitting corrosion. In the mill bleach plants the pulp equipment has traditionally been made of SS which has good general corrosion resistance and weldability. The use of chlorine gas (Cl2) and oxygen in the bleach plant and pulp bleaching, favors a very aggressive oxidant and SS, as type 317 L (18% Cr14% Ni3.5% Mo). However, in the last 25 years the environment in these plants has become much more corrosive due to the wash systems employed for the paper pulp, which increased the emission of oxidizing and corrosive gas‐ es; so type “317 L” SS is not resistant and has a shorter service life. Many mills in the paper industry have opted for the use of high-alloy SS, nickel (Ni) and titanium (Ti), for better corrosion resistance in these particular environments. In general, SS exposed to corrosive environment of bleach plants are benefited by the share of chromium, nickel and molybdenum as alloying elements, which increase their resistance to the initiation of pitting and crevice corrosion. The addition of nitrogen (N) increases its resistance to pitting corrosion, particularly when it contains molybdenum (Mo). Furthermore, to avoid waste of elements such as carbon (C), where a concentration greater than 0.03%, can cause sensitization at affected by heat areas in the solder, causing the SS to be less resistant to corrosion. Other waste elements, such as phosphorus (P) and sulfur (S) can cause fractures in the hot steel, formed in the metal welding area. The corrosive environment of bleach plants contain residual oxidants such as chlorine (Cl2) and chlorine dioxide (ClO2), these are added to resists the effects of temperature and acidity, maintaining a very aggressive environment.
Corrosion also occurs in the pulping liquor facilities by sulfites, chemical recovery boilers, suction rolls and Kraft pulping liquors. The Kraft process is the method of producing pulp or cellulose paste, to extract the wood fibers, necessary for the manufacture of paper.
The process involves the use of sodium hydroxide (NaOH) and sodium sulfite (Na2SO3) to extract the lignin from wood fibers, using large high pressure digesters. High strength is obtained in the fiber and methods for recovery of chemicals explain the popularity of the Kraft process. The black liquor separated, is concentrated by evaporation and burned in a recovery boiler to generate high pressure steam, which can be used for the plant steam requirements for the production of electricity. The inorganic portion of the liquor is used to regenerate sodium hydroxide and sodium sulfite, necessary for pulping. Corrosion of metals in the facilities used in this process may occur during the acid pickling operation for the removal of carbonate incrustations on the walls and black liquor pipe heaters. It has been found that SS 304 L presents fracture failure and stress corrosion. In the recovery processes of chemical reagents, known as stage re alkalinization, metals can fail due to caustic embrittlement or corrosion-erosion under conditions of turbulent flow. Corrosion also occurs in the equipment used for mechanical pulping, such as stress corrosion cracking, crevice corrosion, cavitation and corrosion-friction.
B. Valdez1, M. Schorr1, R. Zlatev1, M. Carrillo1, M. Stoytcheva1, L. Alvarez1, A. Eliezer2 and N. Rosas3
1 Instituto de Ingeniería, Departamento de Materiales, Minerales y Corrosión, Universidad Autónoma de Baja California, Mexicali, Baja California, México
2 Sami Shamoon College of Engineering Corrosion Research Center, Ber Sheva, Israel 3 Unversidad Politécnica de Baja California, Mexicali, Baja California, México
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 Stoytcheva, M., Valdez, B., Zlatev, R., Schorr, M., Carrillo, M., Velkova, Z., Microbial‐ ly, Induced., Corrosion, in., The, Mineral., Processing, Industry., Advanced, Materi‐ als., & Research, . (2010). Trans. Tech publications, Switzerland, 95, 73-76.
 Raicho Raichev, Lucien Veleva y Benjamín Valdez, Corrosión de metales y degrada‐ ción de materiales.Principios y prácticas de laboratorio. Editorial UABC, 978-6-07775-307-0(2009). pp
 Santillan, S. N., Valdez, S. B., Schorr, W. M., Martinez, R. A., Colton, S. J., Corrosion, of., the, heat., affected, zone., of, stainless., steel, weldments., Anti-Corrosion, Meth‐ ods., Materials, United., & Kingdom, Vol. (2010). (4), 180 EOF-184 EOF.
 Schorr, M., Valdez, B., Zlatev, R., Stoytheva, M., Santillan, N., Phosphate, Ore., Proc‐ essing, For., Phosphoric, Acid., Production, Classical., And, Novel., Technology, Min‐ eral., Processing, , Extractive, Metallurgy., & Vol, . (2010). (3), 125-129.
 Valdez, B., Guillermo Hernandez-Duque, Corrosion control in heavy-duty diesel en‐ gine cooling systems, CORROSION REVIEWS Vol.Nos. 2-4, (1995). , 245-260.
 Valdéz, Salas. B., Miguel, Beltrán., Rioseco, L., Rosas, N., Sampedro, J. A., Hernan‐ dez, G., & Quintero, M. Corrosion control in cooling towers of geothermoelectric power plants. Corrosion Reviews, (1996). England., 14, 237-252.
 Valdez, B., Rosas, N., Sampedro, J., Quintero, M., Vivero, J., Hernández, G., Corro‐ sion, of., reinforced, concrete., of, the., Rio, Colorado., Tijuana, aqueduct., Materials, Performance., & May, . (1999). USA., 38, 80-82.
 Valdez, B., Rosas, N., Sampedro, J., Quintero, M., Vivero, J., Influence, of., elemental, sulphur., on, corrosion., of, carbon., steel, in., geothermal, environments., Corrosion, Reviews., & Vol, . Nos. 3- 4, October (1999). England, 167-180.
 Valdez, S. B., Zlatev, R., , K., Schorr, M., , W., Rosas, N., , G., Ts, Dobrev. M., Monev, I., Krastev, Rapid., method, for., corrosion, protection., determination, of. V. C. I., Films-Corrosion, Anti., Methods, , Materials, United., & Kingdom, Vol. Noviembre (2006). (6), 362-366.
 Valdez, B., Carrillo, M., Zlatev, R., Stoytcheva, M., Schorr, M., Cobo, J., Perez, T., & Bastidas, J. M. Influence of Actinomyces israelii biofilm on the corrosion behaviour of copper IUD, Anti-Corrosion Methods and Materials, United Kingdom, N0. 2, 55-59, (2008). , 55
 Valdez, B., Schorr, M., Quintero, M., Carrillo, M., Zlatev, R., Stoytcheva, M., Ocampo, J., Corrosion, , scaling, at., Cerro, Prieto., Geothermal, Field., Anti-Corrosion, Meth‐ ods., Materials, United., & Kingdom, Vol. N0. 1, (2009). , 28 EOF-34 EOF.
 Valdez, B., Schorr, M., Corrosion, Control., in, The., Desalination, Industry., Ad‐ vanced, Materials., & Research, . (2010). Trans. Tech publications, Switzerland, 95, 29-32.
 Valdez, B., Schorr, M., Quintero, M., García, R., Rosas, N., The, effect., of, climate., change, on., the, durability., of, engineering., materials, in., the, hydraulic., & infra‐ structure, . An overview. Corrosion Engineering Science and Technology(2010). , 45(1), 34-41.
 Valdez, B., Schorr, M., So, A., Eliezer, A., Liquefied, Natural., Gas, Regasification., Plants, Materials., Corrosion, M. A. T. E. R. I. A. L. S. P. E. R. F. O. R. M. A. N. C. E., & Vol, . December (2011). (12), 64-68.
 Vargas, O. L., Valdez, S. B., Veleva, M. L., Zlatev, K. R., Schorr, W. M., Terrazas, G. J., Corrosion, of., silver, at., indoor, conditions., of, assembly., processes, in., the, micro‐ electronics., industry-Corrosion, Anti., Methods, , Materials, United., & Kingdom, Vol. N0. 4, (2009). , 218 EOF-225 EOF.
 Veleva, L., Valdez, B., López, G., Vargas, L., Flores, J., Atmospheric, Corrosion., of- Electronics, Electro., Metals, in., Urban-Desert, Indoor., & Environment, . Corrosion of Electro-Electronics Metals in Urban-Desert Indoor Environment. Corrosion Engineering Science and Technology(2008). , 43(2), 149-155.
This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), original found here:http://www.intechopen.com/books/environmental-and-industrial-corrosion-practical-and-theoretical-aspects/corrosion-control-in-industry
Tweet Care and maintenance instructions for the Ultrapen PT4 Free Chlorine and Temperature pen. MAINTENANCE I. Routine Maintenance 1. ALWAYS rinse the FCE sensor with clean water after each use. 2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent the sensor from drying […]
Care and maintenance instructions for the Ultrapen PT4 Free Chlorine and Temperature pen.
I. Routine Maintenance
1. ALWAYS rinse the FCE sensor with clean water after each use.
2. ALWAYS replace the soaker cap half filled with Sensor Storage Solution to prevent the
sensor from drying out after each use.
3. Do not drop, throw, or otherwise strike the PT4. This voids the warranty.
4. Do not store the PT4 in a location where the ambient temperatures exceed its specified Operating/Storage Temperature limits.
II. Battery Replacement The PT4 display has a battery indicator that depicts the life
remaining in the battery. When the indicator icon is at 3 bars, the battery is full. When the indicator icon falls to 1 bar, replace the battery with an N type battery.
Align groove in battery housing with guide bump in pen case.
1. In a clean/dry environment,
unscrew the pen cap in a counter-clockwise motion.
2. Slide the cap and battery housing out of the PT4.
3. Remove the depleted battery out of its housing.
4. Insert a new battery into the battery housing oriented with the negative end touching the spring.
5. Align the groove along the battery housing with the guide bump inside the PT4
case and slide the battery housing back in.
6. Screw the PT4 cap back on in a clockwise direction. Do not over tighten.
III. Sensor Cleaning
Cleaning the sensor:
Clean your sensor every two weeks, however this depends on application and frequency of use. Indications of a dirty sensor are slower and/or erroneous readings.
There are three critical components in your PT4 sensor; a very sensitive glass pH sensor bulb, a platinum ORP electrode, and a temperature sensor encapsulated in a small glass noid. Use extreme caution when cleaning your PT4 sensor.
To clean your sensor, select one of the following methods:
• Basic Cleaning: Using a solution made of dish soap mixed with water and a cotton swab, gently clean the inside of the sensor body and platinum electrode, rinse thoroughly with clean water, then recondition the sensor.
• Cleaning the pH Sensor Bulb: If the sensor becomes dirty, clean the sensor surface with an isopropyl soaked cotton swab. Then rinse thoroughly with clean water.
• Deep cleaning the platinum ORP electrode: Using the ORP electrode cleaning paper and water, gently clean the platinum electrode, rinse thoroughly then recondition the sensor.
To recondition the sensor: Rinse the sensor thoroughly with clean water, then allow it to soak in Storage Solution for a minimum of 1 hour (for best results allow the sensor to soak in Storage Solution overnight).
A. Calibration preparation
For maximum accuracy, fill 2 clean containers with each pH Buffer and/or ORP Standard Solution. Arrange them in such a way that you can clearly remember which is the rinse solution and which is the calibration standard/buffer. If you don’t have enough standard/ buffer, you can use 1 container of each standard/buffer for calibration and 1 container of clean water for all rinsing. Always rinse the FCE sensor between standard/buffer solutions. Ensure the FCE sensor is clean and free of debris.
B. pH Calibration using pH 7, 4, and 10 Buffer Solutions.
NOTE: You should always calibrate with pH 7 first.
1. Thoroughly rinse the PT4 by submerging the sensor in pH 7 Buffer rinse solution and swirling it around.
2. Push and release the push button to turn the PT4 on.
3. Push and hold the push button. The display will alternate between “CAL”, “FAC CAL”, “ºCºF TEMP”, “ModE SEL”, “PAr SEL”, “SOL ck”, and “ESC”.
4. Release the button when “CAL” displays.
5. The display will alternate between “PUSHnHLD” and “CAL.
6. Push and hold the button, The display will alternate between “PH” and “ORP”.
7. Release the button when “PH” is displayed.
8. The display will indicate “CAL” and the LED will flash rapidly.
9. While the LED flashes rapidly, dip the PT4 in pH 7 Buffer Calibration Solution so that the sensor is completely submerged.
10. While the LED flashes slowly, the pH calibration point will display along with “CAL”.
Swirl the PT4 around to remove bubbles, keeping the sensor submerged.
11. If the pH 7 calibration is successful, the display will indicate “SAVEd”, then “PUSHCONT” will be displayed (“PUSHCONT” will NOT be displayed if only calibrated with pH 4 or 10).
12. Push and release to continue or let the unit time out to exit after a 1-point or 2-point calibration.
13. Repeat steps 9 through 12 with pH 4 and 10 Buffer Solutions. After the 3rd calibration point is successfully saved, the display will indicate “SAVEd” and power off.
14. Verify calibration by retesting the calibration solution in solution check mode “SOL ck”, see section V below.
C. ORP Calibration using 80mV Quinhydrone, 260mV Quinhydrone, or 470mV MLC Light’s ORp Standard Solution.
NOTE: The PT4 has automatic temperature compensation in ORP calibration mode (from 15ºC to 30ºC).
1. Follow pH calibration steps 1 through 6, using ORP Solutions.
2. Release the button when “ORP” is displayed.
3. The display will indicate “CAL” and the LED will flash rapidly.
4. While the LED flashes rapidly, dip the PT4 in ORP Standard Solution so that the
sensor is completelysubmerged.
5. While the LED flashes slowly, the ORP calibration point will display along with “CAL”.
Swirl the PT4 around to remove any air bubbles, keeping the sensor submerged.
6. If the ORP calibration is successful, the display will indicate “CAL SAVEd”, then time out.
7. Verify calibration by retesting the calibration solution in solution check mode.
Save 10% on the Myron L Ultrapen PT4 Free Chlorine and Temperature Pen at MyronLMeters.com.
TweetWEFTEC offers you the opportunity to learn about topics in an in-depth, hands-on workshop format. Topics for 2013 include: Collection Systems Pipeline Repair & Replacement Deamonification Decentralized Wastewater Energy Generation & Management Food and Beverage Industry Reuse Nutrient Removal Microbiology Modeling Odors Pathogens Stormwater Utility Management Visit http://www.weftec.org/workshops/ for details!
WEFTEC offers you the opportunity to learn about topics in an in-depth, hands-on workshop format.
Topics for 2013 include:
- Collection Systems Pipeline Repair & Replacement
- Decentralized Wastewater
- Energy Generation & Management
- Food and Beverage Industry Reuse
- Nutrient Removal
- Utility Management
Visit http://www.weftec.org/workshops/ for details!
TweetAbstract This paper provides a followup on the health impact of providing access to water treatment and flush toilets to region of Honduras. Significant reductions were found in the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides […]
This paper provides a followup on the health impact of providing access to water treatment and flush toilets to region of Honduras. Significant reductions were found in the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides compelling evidence that such interventions significantly reduce the disease load from waterborne pathogens within this population. Furthermore, the finding that initial results are significantly different, even in the initial round of testing, if individuals who are not followed up are eliminated from the analysis has profound methodological implications which warrant further investigation and demonstrates the need for precise definitions of community in future studies.
A key component of the United Nations Millennium Development Goal Number 7 states “halve, by 2015 the proportion of the population (global) without sustainable access to safe drinking water and basic sanitation.” Most waterborne diseases result in diarrhea which continues to be a leading cause of morbidity and mortality worldwide. According to World Health Organization data, using existing technologies approximately ten percent of the worldwide burden of disease would be removed by the water supply, sanitation, hygiene, and management of water resources, making water-related diseases arguably the most manageable set of health problems affecting humans .
A great deal of work has been done attempting to measure the impact of interventions to provide improved water sources at the household level, and less frequently at the community level. The overwhelming majority of these studies have also used either key informant or self-reporting of diarrhea (defined as three or more loose stools per day) as the measure of disease burden [2–4]. Reliance upon such nonobjective measures introduces a host of potentially confounding variables [2, 5, 6] and yet appears to have been used in all of the 2,120 published studies reviewed in a far reaching meta-analysis produced for the World Bank on diarrhea and water interventions . While some of these deficiencies may be reduced by shortening recall time to seventy-two hours or less, potentially profound observer effects remain. Estimates of disease load changes are further impeded by researchers’ concentration on known users of water systems rather than measurements on community disease levels of disease changes regardless of compliance, thus making extrapolations of disease rate changes inappropriate.
In 2006, Water Missions International (WMI) received a grant from the Pentair Foundation to provide improved water source access and toilet systems to all of the people in the district of Colon, Honduras, an area that contains approximately 340,000 people. The goal of 100% coverage utilizes a combination of solutions including home-based filtration systems (provided by a different NGO) for communities with less than 300 people, and a variety of high-capacity treatment systems for larger communities. In the initial phase of the study, all 604 water sources for the control and test communities were tested by pressure filtration methods, and all failed quality testing by being positive for coliform bacterial growth. For all households that lacked adequate sanitation facilities and agreed to assist in installation, sanitary pit latrines with pour-flush toilet (toilets with water traps and no reservoir that are flushed by pouring a bucket of water into the basin) were also provided. Water treatment systems and pour-flush toilets deployed during the present study were developed and manufactured by Water Missions International, a nonprofit organization based in Charleston, SC, that works to provide sustainable water treatment capacities and sanitation facilities for people in developing countries. The technology uses a combination of multimedia, multistage filters, and chlorination to provide treated water for drinking and cooking that meets the most stringent class of WHO drinking water standards as well as passed present US standards from the EPA—specifically, tests on treated water grew no coliform bacteria on repeated, monthly testing during the period of this study. In addition, WMI provides community development programs that include education and microenterprise strategies to assure sustainability of these interventions.
In the baseline study phase of the project, water sources for 613 communities were identified. Various water quality tests were conducted on the community water sources by standard membrane filter test. High counts of coliform bacteria indicative of fecal contamination were found in 100% of the water sources. As previously published , initial stool tests also showed that 29.3% (53 of 181) of the volunteer subjects from the twelve communities that had been randomly selected from the state of Colon carried at least one of the three tested protozoan parasites. Also as reported previously, the prevalence of positive protozoan parasite levels was significantly lower in the intervention groups as compared to the test group. Even greater reductions of disease rates (at least 52%) were noted in the medical chart reviews of visits to the local health facility for diarrhea and dysentery as well as self-reporting of the same diseases via ethnographic interviews. Ethnographic data further suggested widespread acceptance and community-wide reproduction of the awareness of health benefits derived from consuming treated water. The present paper is a followup to that report primarily looking at the development of positive parasite stool tests in the same communities twelve months after the initial round of tests with an expanded study population.
Twelve communities from three different categories were randomly selected from the Colon district. Four communities had not yet obtained a water treatment system and were used collectively as the Control Group. Four other communities where water systems (Water Only Group) had been deployed were entered into the study as were four more communities where both water systems and sanitary flush latrines had been installed (Water and Sanitation Group). For both the initial tests in 2009 and the final round of tests in 2010, volunteers were recruited by poster advertising and via community leaders. Methods of recruitment were identical in all communities. All subjects who tested positive for protozoan antigens in either study (2009 or 2010) were treated with an appropriate dose of tinidazole (500 mgs per day for three days for adults with weight adjusted dosing for children). Subjects were directly observed to take the initial dose, which in management of Giardia has been shown to be highly effective without the additional doses. No side effects of treatment were reported. One hundred and sixty-three of the 200 subjects in the final round of testing in 2010 had also participated in the prior studies conducted 12 months earlier.
The effect of previous medical treatment of subjects upon the present study is to provide a population that either tested negative or were given highly effective treatment in 2009—thus providing a subpopulation which was believed to have begun the 12-month test period free of any of the three tested protozoans. The results among the subjects tested both times, therefore, may be regarded as the rates of reinfection over the 12-month period (or a one-year incidence rate) for all three groups.
Recent advances in highly sensitive and specific rapid immunoassays for waterborne parasite diseases have made field testing of individual fecal specimens now possible [9, 10]. These devices test for species-specific antigens of common parasites known to be primarily waterborne. The device chosen for this study tested for three protozoan parasites: Giardia lamblia (now widely known as Giardia intestinalis), Entamoeba histolytica/Entamoeba dispar, and Cryptosporidium parvum antigens. Previous work has shown these tests to have both specificity and sensitivity in excess of 96% for the aforementioned pathogens.
Immunoassay of stool for these waterborne parasites was used as an indicator that the subject had been exposed to waterborne pathogens and was therefore at risk of these and other infectious waterborne illnesses. A separate subset of 163 subjects from the three groups who also gave specimens twelve months earlier was analyzed as a separate subgroup. Given the highly effective cure rates of tinidazole for Giardia and Entameba and the fact that the vast majority of non-immunocompromised subjects will clear Cryptosporidium infections spontaneously, this subset is thought to represent recolonization rates with waterborne protozoan during the year after the initial round of testing and treatment. All specimens were tested within 12 hours of collection using the Triage Micro Parasite Panel manufactured by Biosite Incorporated.
Further information regarding diarrhea and dysentery rates was obtained by reviewing medical records from a public health clinic in a community where a water treatment system had been previously installed. Ethnographic data was collected using a combination of KAP surveys and guided interviews. The medical records review and the majority of the ethnographic data have been previously reported in this journal .
3. Role of the Funding Source and Ethics Review
Water Missions International maintains a country program in Honduras whose staff provided support and significant amount of labor for this project. The study design, collection, and analysis of data and interpretation of the data were the sole responsibility of the author.
Prior to initiation of the study, the Colon Minister of Health and the Institutional Review Board of Water Missions International reviewed and gave approval and consent for the project and study. Consistent with this review, no information from medical chart reviews which could identify subjects of the study was retained outside of the local healthcare facility. Under the supervision of a licensed physician, all individuals in whom potential pathologic parasites were found were given free treatment with regimens previously approved by the Colon Minister of Health. The control communities where no water treatment or sanitation facilities existed were selected from a preexisting construction queue and intervention was not withheld as a result of this study. Verbal consent was obtained and recorded from all subjects.
Age distributions within the three groups are seen in Tables 1 and 2. Gender distribution is seen in Table 3. Parasite test results for the control group compared to the combined water only group and water and sanitation group are seen in Table 4. Giardia and Entameba accounted for all but one positive test in all categories. Giardia accounted for 46% and Entameba 48% of the positive tests while Cryptosporidium remained rare at 6% of the totals.
Table 1: Age distribution of all subjects in all groups.
Table 2: Mean age distribution by group.
Table 3: Gender by intervention group.
Table 4: 2010 data comparing control group to the combination of water only group and water and sanitation group.
Subjects living in communities that did not have access to water systems had significantly higher rates of positive tests than subjects who had either access to water or who had access to water and flush toilets both in the initial survey of 2009 and in the 2010 followup (). These finding are summarized in Figure 1.
In 2009, a comparison of the rate of positive parasite tests appeared to demonstrate that, while access to a water treatment system reduced parasite levels, communities that had both treatment systems and installed flush toilets demonstrated a higher rate of positive parasite tests. These findings show a distinct gender bias toward women and are summarized in Figure 2. Additional ethnographic witnessing suggested that this finding may possibly be explained by the fact that women exclusively cleaned the toilets, often with inadequate supplies and protection. Water Missions International responded to this suggestion with additional training and supplies. In the followup parasite survey of 2010, what had appeared to have been a negative effect of the toilet systems was no longer present, as seen in Figure 2.
A separate analysis of parasite test results including only subjects who were available in both 2009 and 2010 is summarized in Figure 3. Of interest is that the apparent negative effect of the toilets in the 2009 data (Figure 1) completely vanishes when subjects lost to follow up in 2010 are removed from the 2009 analysis.
The present paper is a followup of the research previously reported  and adds support to the conclusion that access to community-based water treatment systems and flush toilets reduced the disease load in this region of Honduras. To our knowledge, these are the first studies to combine self-reported data, medical chart review, and stool immunoassays as an indicator of exposure to potential waterborne pathogens. The triangulation of these methodologies provides powerful support to what are otherwise strongly subjective and questionable measures of disease loads from waterborne pathogens.
The previously reported ethnographic data from these communities suggests a high level of understanding of the causes and prevention of diarrhea among the communities studied. The overwhelming majority (130 of 142) of the people interviewed attributed the majority of their diarrheal diseases to water and sanitation issues and improvement of the condition to improved water sources and access to flush toilets. There were also significant signs of a shift of ideations regarding drinking untreated water toward an appreciation of the importance of purified water and prohibitions against drinking untreated water with the addition of water treatment facilities and community education.
Ethnographic data found during this study suggests that, consistent with other similar work, the availability of improved water is felt by its recipients to improve a general sense of health and well-being. High levels of knowledge related to water issues exist in this area of Honduras which could be attributed to many factors including sophisticated public health efforts, high literacy rates comparable to the region, widespread health education in public schools, and the training offered by Water Missions International and other NGOs. Local indigenous belief systems appear uncommonly (mentioned in only 6 of 46 individual interviews and in none of the four focus groups) and for no one were they the basis for a preferred method of treatment.
Immunoassay evidence of decreased prevalence of waterborne parasites strongly supports the contention that community-based water treatment facilities reduce the overall stool parasite load, at least of the three protozoan species tested. Since all subjects who tested positive for either Giardia or Entameba were treated with three doses of tinidazole adjusted for age and weight, the follow-up study of all subjects who submitted stool samples initially is felt to represent the reinfection rates, in essence eliminating concerns regarding residual colonization from exposures that occurred prior to initiation of this study. Previous treatment of subjects who tested positive for any parasite creates the potential for a Hawthorne effect; however, the elevated number of positive tests initially found within the control communities would potentially bias this group more than the test groups and would tend to lessen rather than strengthen the differences found.
Also, as previously reported , when parasite antigens were detected in stool samples of individuals who had access to improved water sources, ethnographic investigation revealed lapses of behavior in spite of the high level of understanding of the risks associated with drinking from untreated sources. Further analysis of the interviews of subjects whose stool was positive for potential waterborne parasites suggests that risk and time management decisions rather than cultural or knowledge-based differences accounted for lapses in behavior and willingness to drink untreated water. Subjects reported that the time required to obtain treated water, sometimes a difference of only a minute or less, was too great to overcome their concerns with potential health risks associated with untreated tap water.
Multiple pathogens and inflammatory conditions cause diarrhea, making monitoring this symptom alone an inexact measure of the disease load related to water quality. Worldwide, the most common causes of diarrhea are viral infections such as the rotavirus, an ubiquitous infection that may be transmitted by personal contact. Food contamination and noninfectious inflammatory diseases add to the diarrhea prevalence. Though not precisely known, the number of diarrhea cases unrelated to waterborne pathogens is likely substantial. This means that the 52% drop in diarrhea rates noted in the previously reported community chart reviews may represent an even greater majority of the cases that could possibly be related to potential water and sanitation issues. This follow-up study strongly supports this finding and suggests that the effect where water treatment systems are maintained may even increase over time.
A comparison of the 2009 parasite test data excluding those lost to follow up a year later was dramatically different from when these individual tests were included (Figure 3). This suggests that the population that was lost to follow up significantly added to the initial rate of positive tests. This phenomenon deserves future scrutiny and incorporation into discussions of the idea of community as a social construct. If community is defined as those present at a given point in time, we see a negative impact from presence of the toilets. When we define community as those who reside in the geographic area for at least one year we find the exact opposite as this apparent negative impact is not detected. As this finding demonstrates, the unit of analysis remains paramount in such studies.
This combination of qualitative data, health records reviews, and immunoassays provides compelling evidence that community-based water treatment facilities with or without providing flush toilets significantly reduced the burden of diseases in the communities of Colon, Honduras. We further validate with objective measures prior work based upon self-reporting of diarrhea rates. Finally, this data suggests that interventions to provide potable water access on a community level when combined with community development efforts and sanitation can play a significant role in the reduction of mortality and morbidity from waterborne diseases and associated comorbidities.
Providing access to water treatment or water treatment and flush toilets significantly reduced the one-year incidence of positive test results for the three protozoan species tested. This finding combined with the previously reported ethnographic and medical chart review data provides compelling evidence that such interventions significantly reduce the disease load from waterborne pathogens within this population. Furthermore, the finding that initial results are significantly different, even in the initial round of testing, if individuals who are not followed up are eliminated from the analysis has profound methodological implications which warrant further investigation.
Adding a temporal definition of community resulted in a completely different finding regarding the impact of supplying flush toilets, demonstrating the need for precise definitions of community in future studies.
The method used here where objective measurements of health effects are coupled with more traditional anthropological tools may serve as a template for future studies in medical anthropology.
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by Jeffery Deal
Health Studies at Water Missions International, 2049 Savannah Highway, Charleston, SC 29407, USA
Received 1 November 2011; Accepted 30 November 2011
Academic Editor: Kaushik Bose
Copyright © 2011 Jeffery Deal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Tweet Myron l Meters Ultrameter III 9PTKA from Myron L Meters
TweetThe PT1 is designed to be very reliable and requires only infrequent calibration. Myron L Meters recommends calibrating each measurement mode you use once monthly. However, you should check the calibration whenever measurements are not as expected. The PT1 is programmed for 2 calibration options: Wet Calibration or Factory Calibration. Wet calibration is most accurate. […]
The PT1 is designed to be very reliable and requires only infrequent calibration. Myron L Meters recommends calibrating each measurement mode you use once monthly. However, you should check the calibration whenever measurements are not as expected. The PT1 is programmed for 2 calibration options: Wet Calibration or Factory Calibration. Wet calibration is most accurate. But if a high quality standard KCl-1800 µS or 442-3000 ppm solution is not available, the PT1 can be returned to factory settings.
Use calibration solution specified for measurement mode: Use KCL- 1800 for Cond KCl; Use 442-3000 for tdS 442, SALt 442, tdS NaCl, and SALt NaCl. See Specifications table for 442 solution ppm NaCl equivalent value. Calibrating TDS simultaneously calibrates SALt for the same value and vice versa.
1. Pour calibration solution into a clean container.
2. Rinse the pen 3 times by submerging the cell in fresh calibration solution and swirling it around.
3. Remove pen from solution, then fill the container one more time.
4. Press and release the push button. The LCD will briefly display the firmware version then the current measurement mode. Ensure the PT1 is in the correct solution mode.
5. Immediately push and hold the push button. The display will scroll through “CAL”, “SOL SEL”, “FAC CAL”, “ºCºF TEMP”, and “ESC”. Release the button when “CAL” displays.
6. Grasp the pen by its case with your fingers positioned between the
display and the pen cap to avoid sample contamination.
7. While the LED flashes rapidly, dip the pen in calibration solution so that the cell is completely submerged. If you do not submerge the cell in solution before the flashing slows, allow the pen to power off and start over.
8. While the LED flashes slowly, swirl the pen around to remove bubbles, keeping the cell submerged. Keep pen at least 1 inch (2½ cm) away from sides/bottom of container.
9. When the LED light stays on solid, remove the pen from the solution. “CAL SAVED” will display indicating a successful calibration.
Note: If an incorrect solution is used or the measurement is NOT within calibration limits for any other reason, “Error” displays alternately with “CLEAn CEL/CHEC SOL”. Check to make sure you are using the correct calibration solution. If the solution is correct, clean the cell by submerging the cell in a 1:1 solution of Lime-A-Way® and water for 5 minutes. Rinse the cell and start over.
10. Small bubbles trapped in the cell can give a false calibration. Measure the calibration solution again to verify correct calibration. If the reading is not within ±1% of the calibration solution value, repeat calibration.
If you do not have the proper calibration solution or wish to restore the pen to its original factory settings for any other reason, use the FAC CAL function to calibrate the PT1.
1. Press and release the push button. The LCD will briefly display the firmware version then the current measurement mode.
2. Immediately push and hold the push button. The display will scroll
through “CAL”, “SOL SEL”, “FAC CAL”, “ºCºF TEMP”, and “ESC”. Release
the button when “FAC CAL” displays.
3. While the display scrolls through “PUSHnHLD” and “FAC CAL”, push and hold the push button until the display scrolls through “SAVEd” and “FAC CAL”, indicating the pen has been reset to its factory calibration.
4. Allow the pen to time out to turn power off.
TweetRedox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the […]
Redox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the redox potentials of six nanomaterials (either zinc oxide (ZnO) or cerium oxide (CeO2)) dispersions were measured using an oxidation-reduction potential (ORP) electrode probe. The particles under testing differed in terms of their particle size and dispersion stability in deionised water and in various ecotox media. The ORP values of the various dispersions and how they fluctuate relative to each other are discussed. Results show that the ORP values are mainly governed by the type of liquid media employed, with little contributions from the nanoparticles. Seawater was shown to have reduced the ORP value, which was attributed to an increase in the concentration of reducing agents such as sulphites or the reduction of dissolved oxygen concentration. The lack of redox potential value contribution from the particles themselves is thought to be due to insufficient interaction of the particles at the Pt electrode of the ORP probe.
The size of engineered nanomaterials makes many novel and innovative products, as evident by the increasing number of commercially available nanotechnology products. Thus, there is a huge concern surrounding the potential toxicity of these nanomaterials and there is a need to sufficiently test such materials. The goal here is to understand and control risk, and both toxicity testing and physicochemical characterisation should be conducted. Although our current understanding of risk associated with nanomaterials is limited, attempts have been made in order to assess this systematically. Recently, Aschberger et al.  have carried out a risk assessment based on several case studies. They have indicated the risk expected from metal and metal oxide nanomaterials, which was particularly relevant in the case of algae and Daphnia. They have attributed the risk from such materials their exposure to both the particles and corresponding dissolved ions.
There is a general consensus within the nanoecotoxicological community that physicochemical characterisation of nanomaterials in complex media is not a trivial matter, and so the reliability of such measurements is vital if we are to understand and control the risk imposed by nanomaterials [2, 3]. In recent years, the OECD initiative has adopted a holistic approach to this problem and that physicochemical characterisation should be carried out with as many parameters as possible, to include redox potential. The PROSPEcT (Ecotoxicology Test Protocols for Representative Nanomaterials in Support of the OECD Sponsorship Programme) project is the UK’s contribution to this OECD initiative, and the UK is responsible for two types of nanomaterials: cerium oxide (CeO2) and zinc oxide (ZnO) . Out of all seventeen OECD parameters identified, redox potential is the most ambiguous in its definition, what this parameter means and how it is measured, in a nanoecotoxicological context.
Integral to any ecotoxicological investigation is the ability to measure the redox conditions of a given system as indicated by the redox potential. In nature, redox reactions are an important part of phenomena such as mineral weathering, bacterial respiration, and degradation of pollutants . In soil chemistry, for example, the redox potential value can estimate whether the soil is aerobic or anaerobic, and whether chemical compounds such as Fe oxides or nitrate have been chemically reduced or are present in their oxidised form. In natural waters, redox reactions include the oxidation of organic matter and various reduction reactions such as the reduction of oxygen to water, nitrate to elementary nitrogen dioxide, iron (III) to Fe (II), sulphate to sulphide, and carbon dioxide to methane . In terms of nanomaterial toxicity, redox potential is a parameter that has been associated with inducing oxidative stress. Recently, Burello and Worth , in their prediction of a given nanomaterial to induce oxidative stress, have developed a theoretical framework that combines measurements of nanoparticle particle size and redox potential. The need to accurately measure redox potential is evident, in particular we need to understand the extent that nanomaterials can influence the natural redox phenomena should these materials be released into the environment.
Redox potential is a measure of a system’s affinity for electrons, and the measurement of redox potential will only have meaning when there are reduced and oxidised species, called the redox couple, in the liquid media. The redox couple undergoes a redox reaction, in which the reduction (gain of electrons) of one redox species is accompanied by the oxidation (loss of electrons) of another . The movement of electrons, governed by kinetics (e.g., transport limitations of the redox species to the electrode), creates an electric potential. The potential measured is determined by the ratio of activities of oxidised and reduced species, as defined by the Nernst equation; this is a thermodynamic property . The redox potential can be directly measured using a potentiometer (high impedance voltmeter) with an oxidation-reduction potential (ORP) electrode . This is the recommended technique under the current OECD guidelines for the testing of nanomaterials (NMs) ; essentially it is a measurement of potential difference (in mV) across a two-electrode system, that is, an inert platinum (Pt) electrode and silver-silver chloride (Ag/AgCl) reference electrode. Rogers et al. have recently adopted this approach to measure the redox potential of nanomaterial dispersions, that is, cerium oxide dispersed in synthetic freshwater algal medium .
There are theoretical and practical difficulties associated with the measurement of redox potential and these, although not well recognised, have already been discussed for many years . Firstly, redox potential is based on the concepts of equilibrium thermodynamics, and as such it can only be adequately measured at equilibrium. A reliable redox potential measurement requires that equilibrium be established not only at the electrode, but also among the various redox couples in solution. Many redox reactions are slow and often are at nonequilibrium conditions. Secondly, most redox potential measurements represent mixed potentials, and certain redox species may not contribute significantly towards the redox potential value; that is, not all will react sufficiently fast enough at the electrode and therefore will not contribute towards stable and reliable redox potential measurements . If the particles themselves act as a redox species, then there are various factors that may prevent them contributing towards the final ORP value, including sedimentation events, diffusion limitations, and the barrier of electron exchange at the Pt electrode. If this is true, then redox potentials of nanomaterial dispersions are likely to be solely dominated by dissolved redox species in the media, rather than contributions arising from the particles themselves. In this study, we aim to investigate if this is the case. Although the ORP probe has been conveniently used in the past by scientists to directly measure redox potential, it is essential that the reliability of such data should be questioned when measuring nanomaterial dispersions. There is the risk that researchers may treat such a tool as a black box and thus may not be fully aware of the inherent limitations in the use of such a tool in these measurements.
In this study, the ORP values of six nanomaterial (either ZnO or CeO2 dispersed in one of the four liquid media) dispersions will be measured using an ORP probe. Dispersions will be carried out according to the dispersion protocol as recommended under PROSPEcT. The ORP values of the nanomaterial dispersions will be compared relative to each other and to the corresponding media blank, to identify if there is any evidence of redox contributions as a result of the particles themselves. If there are redox contributions from the particles themselves, then this is likely to happen when dispersions are stable, as this would allow sufficient time for the particles to interact with the Pt electrode. Consequently as part of the investigation, the properties associated with the different nanomaterials will be characterised, parameters of interest to include particle size, zetapotential, and dispersion stability (as reported by the so-called half life values). Zeta-potential is a well-known parameter that characterizes the electric properties of solid surface in contact with liquid and is a way to probe surface charge. The magnitude of this value is related to dispersion stability, that is, the higher the value, the better the dispersion stability . The concept of “half-life” has been put forward in the OECD guidelines as the measurand to indicate dispersion stability through time that is, the larger the half-life value; the longer it takes for the concentration to reduce by half and thus the more stable the dispersion. Lastly, the corresponding scanning electron microscopy (SEM) data, that is, the primary particle size (mean Feret diameter) and the corresponding standard deviation, will also be reported.
2. Experimental Section
All experiments were performed in a temperature-controlled laboratory, and for the redox potential measurements the temperature of the dispersions were monitored using a temperature probe (reported value of ~20°C) to ensure that any change in the readings was not attributed to temperature changes in the dispersions.
The NMs supplied from the PROSPEcT programme were of two types, either CeO2 or ZnO, and are as follows:
(a) Nanograin CeO2 (from Umicore Belgium),
(b) Nanosun ZnO (from Micronisers, Australia),
(c) Micron ZnO (from Sigma Aldrich, UK),
(d) Z-COTE ZnO (from BASF, Germany),
(e) Micron CeO2 (from Sigma Aldrich, UK),
(f) Ceria dry CeO2 (from Antaria, Australia).
The particles were used as received and did not contain any added surface stabilisers.
DI water (resistivity of 18 Mohm) from a Millipore, MilliQ system was used to prepare all aqueous solutions and suspensions.
For the purpose of zetapotential measurements, DI water with 5 mM sodium chloride (Sigma Aldrich, UK) was employed in addition to deionised water; the NaCl here served as background electrolyte for the measurement of zetapotential. The “recipes” (chemical compositions) used for making up the ecotox media were obtained from the University of Exeter, one of our collaborators in the PROSPEcT project.
Three types of ecotox relevant media were prepared accordingly and for long-term storage, the ecotox solutions were autoclaved and kept refrigerated until needed.
(a) Seawater, in which 25 g per L of Tropic Marine Sea Salt (Tropical and Marine Limited) was made up, resulting in pH ~8.8.
(b) Daphnia freshwater media. This was prepared by firstly dissolving appropriate salts (196 mg CaCl2·2H2O, 82 mg MgSO4·7H2O, 65 mg NaHCO3, 0.002 mg Na2SeO3, as obtained by appropriate dilutions of a 2 mg/mL stock solution) in 1 L of DI water. Upon continued stirring, further DI water was added so that conductivity of the solution was between ~360 and 480 μS/cm. End volume ~1–1.5 L. Final pH ~7.9.
(c) Fish freshwater media. This was prepared in three separate steps. First, salts (11.76 g CaCl2·2H2O, 4.93 g MgSO4·7H2O, 2.59 g NaHCO3, 0.23 g KCl) were dissolved separately in 1 L of DI water to make four separate stock solutions. Second, 25 mL of each salt stock solution was aliquot into a clean bottle and diluted in DI water (made up to 1 L volume). Third, 200 mL of the stock solution from step 2 was aliquoted and further diluted with DI water (made up to 1 L volume). Final pH ~7.3.
Nanomaterials were dispersed using the protocol as previously reported (Tantra, Jing, Gohil 2010) (http://www.nanotechia-prospect.org/publications/basic). Briefly, this involved weighing the nanoparticle powder into small, clean vials using an analytical mass balance. Dispersion was carried out by adding the appropriate liquid media (fish, daphnia, seawater, or DI water) dropwise (5 drops from a Pasteur pipette) and mixing using a spatula so as to produce a thick paste before adding 15 mL of liquid media and stirring gently, using the same spatula. The formation of a thick paste as a first step was necessary to allow the efficient displacement of powder-air interface with the powder-liquid interface. The subsequent deagglomeration step was carried out using an ultrasonic probe (130 Watt Ultrasonic Processors); this was done by inserting the ultrasonic probe tip (6 mm Ti) half way down the 15 mL volume of dispersed nanoparticles, and sonication was carried out with 90% amplitude for 20 s. After sonication, the nanoparticle suspension was diluted using the appropriate liquid media, in order to make up to 1 L total volume. A glass rod was used to gently mix the final dispersion, to ensure homogeneity. The dispersions (in the four different media) were stored in separate precleaned 1 L media bottles and left undisturbed. Dispersion concentrations were 50 mg/L. Analyses of redox potentials, half-lives, and zetapotentials were conducted on the day immediately after the dispersions were made.
2.2. High-Resolution SEM
SEM images were obtained using a Supra 40 field emission scanning electron microscope from Carl Zeiss (Welwyn Garden City, Hertfordshire, UK), in which the optimal spatial resolution of the microscope is a few nanometres. In-lens detector images were acquired at an accelerating voltage of 15 kV, a working distance of ≈3 mm, and a tilt angle 0°. The SEM was calibrated using a SIRA grid calibration set (SIRA, Chislehurst, Kent, UK). These are metal replicas of cross-ruled gratings of area 60 mm2 with 19.7 lines/mm for low magnification and 2160 lines/mm for high magnification calibrations, accurate to 0.2%. For analysis of the “as received” nanoparticle powders, a sample of each powder was sprinkled over a SEM carbon adhesive disc; one side of the carbon disc was placed securely on a metal stub, whilst the other side was exposed to the nanoparticle powder. Excess powder was removed by gently tapping the stub on its side until a light coating of powder on the surface became apparent. An adequate magnification was chosen for image acquisition for example, for the estimation of primary particle mean diameter, the shape and limits of the primary particles should become apparent. SEM micrographs were analysed by manually tracing contours of primary particles onto a transparency sheet. The transparency sheet was scanned for further image analysis using Image J software, which automatically calculated particle diameter dimensions.
2.3. Redox Potential Measurements
Redox potentials were measured using an ORP Oakton Waterproof ORP Testr, purchased from Cole-Parmer, UK. This, in effect, measures the potential difference across two electrodes (a Pt electrode against a double junction Ag/AgCl reference electrode). The ORP instrument manufacturer has specified a resolution of ±1 mV, with an accuracy of ±2 mV.
The electrode was used in accordance with the manufacturer’s instructions. Prior to use, the electrode was preconditioned in clean tap water for 30 minutes before a final rinse with distilled water. When making measurements, the electrode was carefully placed in a vial containing the nanomaterial dispersion sample; there must be sufficient liquid sample to cover the sensing element. The electrode was carefully stirred a little and then placed in a fixed position, slightly above the bottom of the container. The signal output was allowed to settle for 5 minutes before a reading, the “field potential,” was noted. At this point, the signal was stable and there was no further change observed within the next few minutes. After measurement, the electrode was cleaned with tap water and rinsed with distilled water, after which further measurements could be made. When not in use, the electrode was stored in Oakton electrode storage solution.
The redox potential ORP electrode was calibrated against YSI Zobell ORP Calibration Solution (purchased from Cole-Palmer). This reagent was made available in dry form and was reconstituted with 125 mL of DI water prior to use, after which the solution has ~6-month expiry date. This standard solution was used to verify the performance of the electrode at the beginning and end of the study. For Ag/AgCl reference, the redox potential value for Zobell solution was quoted to be 231 ± 10 mV (depending on temperature); at ~20°C, this value was ~237 mV.
Redox potential measurements were carried out on freshly dispersed nanomaterial in the four chosen media, as detailed above. All field potential values recorded were subjected to an additive correction factor of +206 mV. This was necessary so that the final value was reported as if the reference electrode was a standard hydrogen reference electrode (SHE) instead of the Ag/AgCl, as previously documented . The conversion from Ag/AgCl to SHE is typically on the order of 200 to 220 mV, and voltage correction is temperature dependent and also varies slightly with the concentration of KCl (~3.5 M) in the electrode filling solution.
2.4. Measurement of Half-Lives through Turbidity Measurements
Turbidity was measured using an HF Scientific-Micro100 RI turbidity meter (Cole-Palmer, UK); this meter has an infrared light source that meets the international standard ISO 7027 for turbidity measurements. The meter was calibrated on standards, which are based on AMCO-AEPA-1 microspheres; these standards are traceable to standard formazin suspension. Standard values of 1000, 10 and 0.02 NTU were used to calibrate the meter. Prior to use, the meter was allowed to warm up for 30 minutes. Sample cuvettes (HF Scientific (USA)) were used to hold the samples. Note that glass thickness may vary from cuvette to cuvette and within the same cuvette. Hence, individual vials were indexed; indexing of the cuvette entails finding the point of the cuvette that light passes through that gives the lowest reading and, once indexed, the holder can be marked accordingly. Prior to their use, cuvettes were cleaned, in accordance with manufacturer’s instructions. This involved washing the interior and exterior of the cuvette with a detergent (2% Hellmanex in DI water); it was then rinsed several times in distilled water before finally rinsing in DI water. The cuvette was further rinsed with the sample two times before filling (30 mL) and analysed. The cuvette was placed into the meter and signal allowed to settle before taking readings. Turbidity readings were taken at regular time intervals. When not in use, the vials (containing the dispersions) were stored in the dark.
2.5. Zetapotential Measurements
Electrophoretic measurements were obtained using a Zetasizer Nano ZS (Malvern Instruments, UK) equipped with a 633 nm laser. The reference standard (DTS1230, zetapotential standard from Malvern) was used to qualify the performance of the instrument. Sample preparation involved filling a disposable capillary cell (DTS1060, Malvern). Prior to their use, these cells were thoroughly cleaned with ethanol and deionised water, as recommended by the instrument vendor. For analysis, the individual cell was filled with the appropriate sample and flushed before refilling; measurement was carried out on the second filling. Malvern Instrument’s Dispersion Technology software (Version 4.0) was used for data analysis, and zetapotential values were estimated from the measured electrophoretic mobility data using the Smoluchowski equation, as documented in a previous publication .
3. Results and Discussion
Results show that ORP values are dominated by the type of liquid media used for dispersions. Nanomaterial dispersions in seawater resulted in a much smaller ORP values in comparison with dispersions made in other media. In addition, this is also the case with the ORP values of the corresponding blank media, that is, blank seawater having the smallest ORP value, of 384 mV, compared to the rest of the blank liquid media (redox potential values all above 400 mV). The ORP values reported here is not specific to a single chemical species and thus represent an aggregate oxidization-reduction of all species that can react at the Pt working electrode . The fact that the type of liquid media itself seems to have some contribution to the final ORP values is not surprising, as dissolved redox species in the liquid can easily interact with the Pt electrode of the ORP probe. In fact, such ORP measurements are often employed as an accurate gauge of water quality and for the monitoring of dissolved species in the water . Seawater in particular is shown to be more reducing in nature, that is, due to higher concentration of reducing agents (such as N O2 −) in such media, if compared to the other liquid media. The presence of reducing agent has the effect of lowering the ORP value . Furthermore, we expect a much-reduced level of oxidising agent such as dissolved oxygen in such a high saline solution, as the more saline the water can be the less oxygen the water can hold. If there is a reduction in oxidising agents, then this also has an effect of lowering the ORP value .
The ORP readings reported here were taken three times with very little variation among the replicates, that is, not more than ±2 mV. However, the second and third replicates were acquired soon after acquiring the 1st replicate, by taking the ORP probe out of the dispersion and reimmersing it back into the dispersion. The variations in the replicates here thus represent variations of the instrument’s accuracy; they will not represent any variations that might be due to other factors such as differences in dispersion quality. Table 1 also shows the change in ORP values (values reported in brackets) upon addition of the nanomaterials relative to the corresponding blank media. Results show that, in most cases, there is a change of less than ~10 mV associated upon addition of the nanomaterials. There are only three cases in which the ORP value change is greater than 15 mV: Nanograin CeO2 in fish medium, Micron CeO2 in DI water, and Ceria dry CeO2 in fish media. Currently, we offer no explanation as to why there is a much larger change in ORP values in these three cases, apart from potential variations in dispersion quality, for example, due to potential redox contaminants associated with the different samples received. In addition, no real differentiation can be made between ZnO and CeO2 particles, with Z-COTE ZnO (BASF, Germany) having the same 9 mV change as the Ceria dry CeO2 (Antaria, Australia), when both are dispersed in DI water.
Results show that zetapotential values of nanomaterials when dispersed in seawater cannot be successfully measured (due to high conductivity) and thus displayed as N/A in Table 2. Such unsuccessful measurements were reported in the corresponding “quality report” at the end of the measurement. In general, results indicate high zetapotential values for nanomaterials that are dispersed either in DI water or DI water + 5 mM NaCl. Results of the DI water are similar to the corresponding DI water + NaCl case; the addition of NaCl into the DI water was carried out so as to have greater confidence in the DI water results, as the measurement of zetapotential usually involves the presence of inert background electrolyte. Overall, results show that nanomaterials are most stable when dispersed in DI water (or DI water + NaCl) and least stable when in an ecotox media. This is true apart for the case of Micron CeO2 showing that it is least stable in DI water, that is, −7 mV when compared to other ecotox media such as fish medium, that is, −22 mV. Currently, no explanation is available for this behaviour, and dispersion stability was further measured by using the concept of half-life values (as previously discussed in the introduction, the larger the half-life, the more stable the dispersion). Results in Table 3 show that, as with zetapotential measurements, results in DI water are generally more stable (with the largest associated with Z-COTE ZnO of 4038 minutes) than when in ecotox media. However, unlike the zetapotential values, Micron CeO2 also shows the same trend, that is, most stable in DI water than when in an ecotox media. The reason for this discrepancy lies in the fact that dispersion stability was measured in two different ways: through the measurement of interparticle force (zetapotential) or through analyzing the stability via sedimentation measurements (turbidity with time). The former measurement is solely governed by the electric properties of the solid surface in contact with liquid, which will subsequently contribute towards sedimentation rate; the latter measurement is not only determined by the zetapotential value but also by other factors, for example, particle size (in which the larger particles are expected to sediment at a much faster rate) . The SEM results (Table 4) show the mean (Feret) primary particle sizes and the corresponding standard deviations (to reflect on the polydispersity of the primary particle size). Results presented in Table 4 show that the mean primary particle sizes of the samples range from ~30 nm to ~890 nm, the largest being the Micron ZnO and Micron CeO2 from Sigma Aldrich. The SD values show the large degree of polydispersity associated with samples received: high polydispersity associated with Sigma Aldrich samples, less so with Nanosun ZnO, Microniser. The SEM micrographs indicated that all particles tested here were highly aggregated together into agglomerates of irregular shape.
If there is any particle contribution towards the final ORP values, then, out of the two types of nanomaterials tested, we expected CeO2 to have a bigger contribution compared to ZnO. This is on the basis that CeO2 particle can act as a redox couple of Ce(IV)/Ce(III), which is not the case for ZnO. If CeO2 particles had contributed to the final ORP value, then we expect this to occur with Nanograin CeO2 (having the smallest particle size of ~30 nm, as shown in Table 4) and when dispersed in DI water, as this resulted in a highly stable dispersion (noted by its high dispersion stability value of 2676 min and high zeta potential value of 33 mV, as shown in Tables 3 and 2, resp.). A highly stable dispersion will mean sufficient time to allow particles to diffuse to the Pt electrode, thus interacting with the Pt electrode in order to contribute towards the final ORP reading. Hence, we expected the redox potential to be affected most by the Nanograin CeO2 in DI water and clearly this was not the case. As shown in Table 2, Nanograin CeO2 in DI water only resulted in an ORP value change of 11 mV compared to a change of 21 mV when the same particles were dispersed in fish medium. Overall, results suggest that the particles have minor effects on the final ORP readings.
The study investigated the redox potential measurements, using ORP probe electrode, of different ZnO and CeO2 dispersions, in various liquid media. The variations in the ORP readings for the different dispersions could not be regarded as being highly significant and were mainly governed by the type of liquid media that the nanomaterials were dispersed in. This is not surprising, as ORP values are dominated by the amount of dissolved chemical species in the liquid media. Dispersions in seawater resulted in the lowest ORP values, suggesting that the media is reducing in nature. This was attributed to a much higher concentration of reducing agents such as sulphites or a reduction in the concentration of dissolved oxygen under a high salinity environment. The study shows that there was little contribution from the particles themselves towards the final ORP reading, with no significant differentiation between CeO2 and ZnO. As it is clear that redox potential measurements using an ORP electrode will not indicate a particle’s contribution towards the final redox potential value, the work has highlighted the need to have better tools for such measurements. There are several alternatives to using the ORP probe, including X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) and electron energy loss spectroscopy (EELS) . However, these technologies rely on the indirect measurement of redox potential and the accuracy of the values reported may come into question.
This work was conducted as part of PROSPEcT, which is a public-private partnership between DEFRA, EPSRC, and TSB and the Nanotechnology Industries Association (NIA Ltd.) and its members, and was administered by the DEFRA LINK Programme. The authors would like to thank Dr. Alex Shard for continuing support and Mr. Jordan Tompkins for the initial handling and distribution of the nanomaterials. R. Tantra gratefully acknowledges Professor Philip N. Bartlett from the University of Southampton and Dr. Andy Wain, whose expertise in electrochemistry has immensely helped in our understanding of the study.
Copyright © 2012 Ratna Tantra et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Ratna Tantra, Alex Cackett, Roger Peck, Dipak Gohil, and Jacqueline Snowden, “Measurement of Redox Potential in Nanoecotoxicological Investigations,” Journal of Toxicology, vol. 2012, Article ID 270651, 7 pages, 2012. doi:10.1155/2012/270651
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EquiPower Resources is owned by Energy Capital Partners (ECP). For more information about ECP, please visit ECP’s website at www.ecpartners.com. EquiPower Resources also manages the Empire Generating Project, a 635 MW combined cycle natural gas fired power plant located near Albany, New York, Odessa-Ector Power Partners, a 1,000 MW combined cycle natural gas fired power plant located in Odessa, Texas, and Red Oak Power Holdings, an 802 MW combined cycle natural gas fired power plant located in Sayreville, New Jersey, all of which are also owned by ECP. For more information, please visit www.empiregen.com, www.odessapower.com and www.redoakpower.com. Myron L Meters is proud to do business with EquiPower. Please visit us on the web at: Facebook: Twitter: Google +: Linkedin: YouTube: News:
EquiPower Resources is owned by Energy Capital Partners (ECP). For more information about ECP, please visit ECP’s website at www.ecpartners.com.
EquiPower Resources also manages the Empire Generating Project, a 635 MW combined cycle natural gas fired power plant located near Albany, New York, Odessa-Ector Power Partners, a 1,000 MW combined cycle natural gas fired power plant located in Odessa, Texas, and Red Oak Power Holdings, an 802 MW combined cycle natural gas fired power plant located in Sayreville, New Jersey, all of which are also owned by ECP. For more information, please visit www.empiregen.com, www.odessapower.com and www.redoakpower.com.
Myron L Meters is proud to do business with EquiPower.
Please visit us on the web at: