The acceleration of high temperature corrosive attack on heat-resistance alloys caused by the presence of vanadium compounds is well established. The progressive addition of sodium sulfate to the vanadium contaminant indicates that the most corrosive mixture is approximately 20 percent sodium sulfate—80 percent vanadium pentoxide. The survey of the melting temperatures of various vanadium pentoxide— sodium sulfate mixtures shows no direct correlation to corrosive behavior. There appears to be a strong indication, however, that unusually high oxygen solubility in the molten contaminant containing 20 percent sodium sulfate may be responsible for its unusually high corrosiveness. This makes it possible to postulate a more satisfactory theory of the mechanism of corrosive attack which need not involve a solid phase at the reaction interface.
Additions of calcium oxide, strontium oxide, and carbon were particularly effective in reducing the intensity of attack. The effectiveness of carbon is restricted to short time intervals during which it became oxidized. 3.5.9
