SULFIDE CORROSION OF HEAT-RESISTANT NICKEL-BASE ALLOYS

The corrosion of nickel alloys in molten sodium sulfate, sulfate-chlor ide mixtures, chromate, molybdate, tungstate at 700-1000-degrees-C, 30 h is in agreement with the model of basic and acid fluxing of protect ive oxides in sulfide corrosion. Sulfidizing of an alloy exerts a subs tantially lesser effect on the corrosion rate. In molten sodium molybd ate, tungstate, and sulfate aluminum and nickel oxides have weak prote ctive properties, and chromium oxide has moderate ones. In sodium chro mate all alloys corrode moderately, most slowly those that have a prot ective film of Al2O3. In sodium sulfate the corrosion rate is highest at 750-degrees-C and lowest at 850-degrees-C. The former is connected with the mechanisms of sulfidizing of nickel, the latter with the form ation of chromium sulfides.