Alkali chlorides are well known to cause accelerated corrosion. At elevated temperatures, the presence of alkali chlorides as vapors or molten deposits can cause accelerated attack of either high temperature metal alloys or ceramics. The mechanism of attack is different in the two cases, however, with the chlorine (component being most aggressive for corrosion of metals and the alkali being most aggressive for corrosion of ceramics. The reaction of the alkali chloride with the oxide scale on metals releases chlorine which causes accelerated corrosion. The corrosion rate can be reduced by absorbing this chlorine. For ceramics, the alkali oxide species produced by such reactions is most damaging and the rate of corrosion can be reduced by adding chlorine to the system.
Alkali chloride salts are major components of sea salt, and can also be encountered in other environments associated with industrial heating processes and waste incinerators. They are known to accelerate corrosion of metals when present either as soluble contaminants in aqueous solutions at room temperature or when present in high temperature environments either as molten salts or as vapors. They can also produce accelerated attack of ceramic materials, but the mechanism of attack differs substantially from that produced on metals. This paper discusses the mechanism of accelerated corrosion of these two classes of materials in high temperature environments containing alkali chlorides.