Corrosion types bimetallic

The corrosion problems associated with mechanical fixtures are often one of two types, i.e. crevice corrosion or bimetallic corrosion ", which have been dealt with in some detail in Sections 1.6 and 1.7, respectively. 

The classification given in Table 1.2 is based on the various forms that corrosion may take, but the terminology used in describing corrosion phenomena frequently places emphasis on the environment or cause of attack rather than the form of attack. Thus the broad classification of corrosion reactions into wet or dry is now generally accepted, and the nature of the process is frequently made more specific by the use of an adjective that indicates type or environment, e.g. concentration—cell corrosion, crevice corrosion, bimetallic corrosion and atmospheric corrosion. 

There are many special factors controlling atmospheric bimetallic corrosion that entitle it to separate treatment. The electrolyte in atmospheric corrosion consists of a thin condensed film of moisture containing any soluble contaminants in the atmosphere such as acid fumes from industrial atmospheres and chlorides from marine atmospheres. This type of electrolyte has two characteristics which are summarised in a paper by Rosenfel d . 

Many other types of corrosion can occur. An important example is bimetallic corrosion which occurs at the junction between two different... 

Provide written observations of specific corrosion phenomena for individual coupons, including ease of removal (ease of separation of crevice/bimetallic coupons), amount and type of loose deposits, staining, discoloration, pitting, tenacious or loose oxides, raised embedded particles felt with a gloved finger, etc. 

The last three chapters are dedicated to improving the durability of the catalyst/ electrode. Chapter 22 reports the development and evaluation of bimetallic Pt-Ru (Ir) oxygen evolution catalysts on 3M s nanostructured thin film (NSTF). This type of catalyst may significantly reduce carbon corrosion and Pt dissolution during transient conditions of fuel cells. Chapter 23 discusses the unique properties of carbide-modified carbon as the support for fuel cell catalysts. The final chapter gives a comprehensive review of novel materials other than carbon black as catalyst support. The interactions between the supports and catalysts are intensively discussed in the last two chapters. 

In the previous case, it was a question of a type of bimetallic corrosion without electrical contact between the metals involved. The process initially is difficult to understand it is, however, easy to understand if one considers it as a battery with an external short circuit caused by an electrolyte behaving in the same way. The results of measurements on a model and the action of cathodic protection are described in Ref. 23. 

The corrosion-like electrochemical process of material removal refers to spatially uniform general corrosion of the metal surface. However, the wet CMP environment can also support certain other types of undesirable electrochemical corrosions, such as localized pitting, and bimetallic/galvanic decomposition that contribute to surface defects. The considerations for mitigating these defects constitute a major aspect of slurry (additive) selection, which in turn can be facilitated by the use of electrochemical techniques. 

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