HETEROPOLY ANIONS AS CORROSION-INHIBITORS FOR ALUMINUM IN HIGH-TEMPERATURE WATER

Corrosion of aluminium and its alloys in high temperature water (90-300-degrees-C) has been studied with and without addition of various oxotungstates by a number of methods. Substantial decrease (in some cases by 10 times) of the corrosion rate in the presence of polyoxotungstates was observed. The pitting potential was shown to shift to positive values depending on the heteropolytungstate added. According to XPS tungsten is incorporated into the surface oxide film formed during the treatment. SEM cross-sections reveal a marked decrease of the oxide film thickness in the presence of polytungstate. It is assumed that the heteropolytungstate on active site in the aluminium oxide film is preventing the recrystallization and growth protective alumina layer. Pretreatment of aluminium in solutions of heteropoly tungstates is also effective in preventing corrosion at high temperature.