Corrosion examples

Indirect Probes Some types of probes do not measure corrosion directly, but yield measurements that also are useful in detecting corrosion. Examples include ... 

There might be only a single phase within a given domain. That is typically the case for the gas phase (within the domain G in the example of Fig. 11.2). The governing equations and equations of state in the gas phase are fundamentally different than in the other domains. Two of the other volumetric domains also have only one phase each in the corrosion example (i.e., the aqueous domain A and the bulk copper domain B). However, within those phases, any number of chemical species might be present. 

In the corrosion example, we defined a layer of material containing oxidation and corrosion products. In this domain named C, for example, two phases were specified to exist, according to some particular model of the process. One of the phases is denoted CuO, and represents an oxide coating that has formed. The second phase, is designated CuS2, and contains products of an atmospheric sulfidation process. Within each phase, different chemical species may reside, for example, Cu+ ions, elemental Cu, holes, and electrons. The list of species depends on the particular reaction mechanism. 

Biocorrosion in well-oxygenated cooling systems can also involve other types of bacteria, such as nitrifying bacteria, which are commonly found where ammonia is present (say from refinery or fertilizer plant leaks). They are principally aerobic and oxidize ammonia to nitrate, causing serious local falls in pH that result in nitric acid corrosion. Examples are Nitrosomonas sp. and Nitrobacter sp. 

For reasons of ease of manufacture, the majority of solid electrodes have a circular or rectangular form. External links are through a conducting epoxy resin either to a wire or to a solid rod of a metal such as brass, and the whole assembly is introduced by mechanical pressure into an insulating plastic sheath (Kel-F, Teflon, Delrin, perspex, etc.) or covered with epoxy resin. It is very important to ensure that there are no crevices between electrode and sheath where solution can enter and cause corrosion. Examples of electrodes constructed by this process will be shown in Chapter 8. 

Failure of weapons due to corrosion. Examples can be torpedo or missile (generally made of lightweight alloys). An example is failure of ammunition... 

Metals that readily corrode can often be protected by the application of a thin coating of a metal that resists corrosion. Examples are tin cans, which are actually steel cans with a thin coating of tin, and chrome-plated steel bumpers for automobiles. 

The result of this corrosion is the formation of a porous and usually brittle shadow of the original component. Other alloy systems are susceptible to this form of corrosion. Examples include the selective loss of aluminum in aluminum-copper alloys, and the loss of iron in cast iron-carbon steels. 

A problem of particularly large economic significance is corrosion on buried pipelines, and there are special reasons to worry about the external corrosion. Examples from some communities show that a major part of the water in the public fresh water pipeline system gets lost due to leakage, mainly because of corrosion. 

In our examples of the electrolysis of NaCl, the electrodes are inert they do not react but merely serve as the surface where oxidation and reduction occur. Several practical applications of electrochemistry, however, are based on active electrodes—electrodes that participate in the electrolysis process. Electroplating, for example, uses electrolysis to deposit a thin layer of one metal on another metal to improve beauty or resistance to corrosion. Examples include electroplating nickel or chromium onto steel and electroplating a precious metal like silver onto a less expensive one. 

Our kinetic treatment of CVD will be very similar to our treatment of active gas corrosion (except, of course, material is being deposited rather than removed). There will be one key difference, however. In our treatment of active gas corrosion, we made the implicit assumption that the reaction process went to completion. In the Ti corrosion example, as long as ANY HCl(g) was available to react, we assumed that it would do so completely. As you may recall from Chapter 3, the assumption that a reaction goes all the way to completion is valid in many cases. However, there are many other reactions that do not go all the way to completion. This is particularly tme for many CVD reactions, whose thermodynamics are purposely tuned so that the driving forces for reaction are relatively small (and thus homogeneous nucleation is avoided). 

Based on this understanding of the incomplete nature of the CVD reaction, the kinetic behavior of this system under surface reaction, diffusion, and mixed control can now be developed. The results will be very similar to the active gas corrosion example with only minor changes due to the incomplete nature of the reaction and the different reaction stoichiometry of this example. 

As in the active gas corrosion example, the flux of Si can be transformed into a deposition rate (i.e., the increase in the thickness of the Si film per unit time, dx/dt) via some simple algebraic transformations using the density and molecular weight of... 

Mixed Control In the mixed-control regime, the surface reaction and diffusion rates are comparable, and thus both influence the overall rate of deposition. Analogous to the active gas corrosion example, the growth rate under mixed control for this... 

Example Accurate prediction of corrosion Example Silicon-carbide ceramic matrix... 

Fig. 5.5 specific threshold concentration of corrosive, example of hydrochloric acid... 

In principle, an improvement of rust corrosion rates in low-alloyed steels is possible as well in the tidal and immersion zone, but expectations should not be too high. The significant improvements frequently cited in the literature and patent registrations are usually based on tests in the laboratory and cannot be confirmed in practical applications or only in reduced form. It must also be noted that in the low-alloyed steels shallow pit corrosion or pitting corrosion is frequently observed in addition to uniform surface corrosion. Examples can be cited in which certain alloying elements reduce the uniform surface corrosion, only to cause increased pitting at the same time. 

Irritants. Irritants cause inflammation of the moist mucous surfaces of the body. Irritants are corrosive, but inflammation of tissues may result from concentrations well below those needed to produce corrosion. Examples of irritant materials include aldehydes, alkaline and acid mists, and ammonia. Materials that affect both the upper respiratory tract and lung tissues are chlorine and ozone. Irritants that affect primarily the terminal respiratory passages are nitrogen dioxide and phosgene. 

In certain corrosive environments, a protective siuface layer may be formed that will prevent excessive corrosion. Examples include concentrated sulfuric acid where a ferrous sulfate film protects the steel, and concentrated hydrofluoric acid that forms a fluoride film. Extreme care must be taken, however, to prevent conditions that may damage the film and lead to extremely high corrosion rates. These conditions include high velocities, condensing water (hmnidity from the air), and hydrogen bubbles floating across a surface. 

Industrial chemical cleaning involves the use of reactive chemicals to remove unwanted deposits from the surfaces of various pieces of process equipment. Included are components of power-generating units such as boilers and condensers, heat exchangers in refineries and petrochemical plants, and other industrial equipment such as digesters in paper mills. The chemical removal of unwanted surface deposits is conducted for many reasons. The first reason is to eliminate scales that contribute to increased corrosion. Examples of these types of deposits include iron oxides and copper found on the watersides of many types of process equipment. The second reason is to increase heat transfer. While steel may have a thermal conductivity of... 

By considering all systems as a single one while estimating the model parameters it is assumed that the degradation process model is the same for all systems. In most cases, the degradation process depends also on operating conditions that may be partially unknown. In the pipe corrosion example, the evolution of the pipe thickness depends on the used metal but it also depends on the characteristics of the fluid carried by the pipe (liquid/gaz, temperature, pressure. ..) and on the location (air/ground/underwater. ..) and on the environmental conditions of the pipe (temperature, humidity. ..). 

Copper Conductors Although precautions are taken to protect the copper conducting lines in printed wiring boards from enviromnental exposure, defects exist and corrosion does occur under many atmospheric conditions. For most environments that are encountered, copper is not thermodynamically stable. However, its native cuprous oxide surfece film does offer some limited protection. Atmospheric corrosion of copper is briefly described in the chapter on atmospheric corrosion. Examples of typical industrial atmospheric pollutants that are harmful to copper include SO2, H S, COS, NO, CI2, and CO2... 

Make the eroding surface resistant to corrosion. Examples include the use of cobalt-base hardfacing alloys to resist liquid erosion, cavitation, and slurry erosion aluminum bronze hardfacing alloys to prevent cavitation damage on marine propellers or to repair props that have... 

Most metals and alloys are susceptible to erosion-corrosion damage. Many depend upon the development of a surface film of some sort (passivity), for resistance to corrosion. Examples are aluminum, lead, and stainless steels. Erosion-corrosion results when these protective surfaces are damaged or... 

Applications Involving Wear and Corrosion Examples of these applications are seals, valves, pump parts, bearings, thread guides, papermaking equipment, and liners. 

Corrosive Example Sulfuric Acid. Because of its widespread usage, sulfuric acid has been called the workhorse of the industrial world. Its popularity suggests that sulfuric acid is likely to be encountered more frequently than other corrosive materials in the workplace and during hazardous materials incidents. 

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