Cobalt oxides, coatings containing

Calorised Coatings The nickel- and cobalt-base superalloys of gas turbine blades, which operate at high temperatures, have been protected by coatings produced by cementation. Without such protection, the presence of sulphur and vanadium from the fuel and chloride from flying over the sea promotes conditions that remove the protective oxides from these superalloys. Pack cementation with powdered aluminium produces nickel or cobalt aluminides on the surfaces of the blade aerofoils. The need for overlay coatings containing yttrium have been necessary in recent times to deal with more aggressive hot corrosion conditions. 

Fig. 7. Current voltage curves of the anodic oxygen evolution at different temperatures in 30 wt% KOH at nickel anodes with coatings containing cobalt oxides (a) La0 5Co -.EaC), (b) Nin2, CouxLaO , (c) Co,04, and, for comparison, (d) RuO..

A typical coating contains iron oxides (sometimes doped with cobalt or chromium), a polymer system that acts as a binder, various additives (including up to 1.5% lecithin on a dry solids basis), and solvents such as methyl ethyl ketone and cyclohexanone (454 58). This material is milled into a dispersion and deposited onto the tape and dried. 

Black cobalt oxide Co O is used as a coating on high-temperature solar collectors and for this purpose is superior to black chromium coatings, often used. CO3O, can be applied by plating, by pyrolysis of cobalt salts or simply by use of paints containing cobalt oxide. More sophisticated methods are also used, e.g. vacuum deposition. 

Porcelain enamels on metal are similar to glazes, in that they are basically a silicate glass coating, but they are fired for shorter periods and at lower temperatures. During firing, a ground coat containing nickel or cobalt oxide, or a nickel dip (of the metal in a nickel sulfate solution), is frequently used to... 

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