Inorganic chemicals, corrosion effects

Where crevices cannot be avoided, precautions should be taken to prevent ingress of corrosion by improving the geometry, fit, or surface texture. Where possible, laps and crevices should be avoided or sealed effectively, especially in areas of heat transfer, between metal and a porous material, or where an aqueous environment contains inorganic chemicals or dissolved oxygen. 

Corrosion takes many forms but is always an electrochemical process, whereas deposition and fouling are often combinations of both chemical and physical processes, involving inorganic and organic contaminants, the effective control of which tends to be much more of an art than a science. 

The most popular inorganic treatments are those with silica [4], phosphates [5], molybdate [6], and chromate [7], all of which serve mainly to reduce the chemical reactivity of the metallic pigments (Fig. 14.13). This includes corrosion inhibition of the pigment and inhibition of its often catalytic effect as well as a change in the physical surface characteristics, for example, where chargeability is important. 

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