Automobiles controlling corrosion

Since steel is the main structural material for bridges, buildings, and automobiles, controlling its corrosion is extremely important. To do so, we must understand the corrosion mechanism. Instead of being a direct oxidation process, as we might expect, the corrosion of iron is an electrochemical reaction, as illustrated in Fig. 11.17. 

Since steel is the main structural material for bridges, buildings, and automobiles, controlling its corrosion is extremely important. To do so, we must... 

Decorative chromium plating, 0.2—0.5 ]lni deposit thickness, is widely used for automobile body parts, appHances, plumbing fixtures, and many other products. It is customarily appHed over a nonferrous base in the plating of steel plates. To obtain the necessary corrosion resistance, the nature of the undercoat and the porosity and stresses of the chromium are all carefliUy controlled. Thus microcracked, microporous, crack-free, or conventional chromium may be plated over duplex and triplex nickel undercoats. 

The Electrolytic Corrosion Test. Also developed for use on nickel—chromium and copper—nickel—chromium decorative automobile parts is the electrolytic corrosion (EC) test (44). Plated specimens or parts are made anodic in a corrosive electrolyte under controlled conditions for 2 min, and then tested for penetration to the substrate. 

Corrosion of solders used in the electronics industry is usually a function of the presence of residues from various manufacturing and assembly operations. Corrosion in heat exchangers, particularly in automobiles is a more significant problem and a test methodology has been described as well as various factors controlling the corrosion of tin-lead alloys in radiators... 

Maintenance of a correct inhibitor concentration (level) is particularly important where low-level treatments, e.g. less than 100 p.p.m. are used. Such treatments are, however, usually applied (for economic and effluent reasons) in large capacity systems, and plants of this nature will usually have skilled personnel available for control purposes. In smaller closed systems, e.g. automobile engines, higher concentrations of more than approximately 0-1% are commonly used, but in these applications there is usually a good reserve of inhibitor allowed for in the recommended concentration and routine checking is of less importance. Nevertheless, since these inhibitors are often of the dangerous type, gross depletion may lead to enhanced corrosion. 

What effect does acid rain have on the rate of corrosion of metals used in buildings, automobiles, and statues How can concentration of the acid in the rain, and thus the rate of corrosion, be controlled ... 

Alany existing applications involve small adsorption systems for home and automobile applications, eg, refrigerant drying in automobile air conditioners, dual-pane window desiccants, medical oxygen systems, and muffler corrosion protection. Such small adsorption systems will continue to be developed for new uses in indoor air pollution and odor abatement and for the enhancement of the performance of other equipment and appliances. For example, adsorption-based control of the composition of air in refrigerators can provide improvements in the storage of fruits and vegetables. 

Corrosion control technology is a mainstay of automobile coatings as well as household appliances for example, the lifetime of water heaters is extended and often governed by the presence of a magnesium sacrificial anode that represents a small fraction of the appliance price. 

Application of a top coat is the final step in the finishing process. The topcoat is applied for cosmetic reasons and has little effect on the corrosion performance of the automobile. Advances over the last 40 years have led to better overall paint system performance. The robotic processing and control equipment has led to more uniform paint coverage and superior performance. Simplified vehicle design and optimization of the painting process resulted in increased finish quality, which in turn increases corrosion resistance. 

Electrochemical tests are rapid techniques to determine mechanisms, determine the effect of various parameters on corrosion rate, and screen out a large number of materials [43]. They usually involve measurement of corrosion potentials, corrosion currents, polarization curves, and electrochemical impedance. They are used to evaluate metals and alloys and the behavior of metallic, inorganic, and oiganic coatings. The simplest test involves the measurement of the corrosion potential and its use in conjunction with other measurements. A zero resistance ammeter (ZRA) is commonly used to measure corrosion currents between dissimilar metals and alloys. Controlled potentitd tests and anodic and cathodic polarization curves using potentiostats are the most commonly used electrochemical tests. These are powerful tools for investigating the effect of various parameters on corrosion behavior. These incorporate the use of cycUc polarization and polarization resistance for localized corrosion and corrosion rate measurements. Table 4 lists electrochemical tests that can be used for corrosion tests in the automobile industry. 

Cabinet tests are the most commonly used laboratory tests in the automobile industry. These have been developed to simulate the effects of atmospheric corrosion 44. Normally, a test chamber is used and the desired environment is introduced under controlled conditions. A list of these tests is given in Table 6. The simplest of these is the humidity test whereby the temperature and relative humidity within a chamber are controlled. A condensing humidity chamber, which operates at 100 % relative humidity and 38°C, provides... 

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