Silicon carbide, silicon nitride and aluminium nitride ceramics were immersed in potassium sulphate-potassium carbonate metls in air or in a nitrogen atmosphere at 1013-1200°C to examine their corrosion behaviour. Aluminium nitride ceramics exhibited great resistance to corrosive attack from potassium salts under these conditions, exhibiting only a slight weight loss. Silicon carbide ceramics dissolved slowly in molten potassium carbonate (K2CO3), but rapidly dissolved in both potassium sulphate (K2SO4) and 50 mol% K2SO4-50 mol% K2CO3 melts. The weight loss of silicon carbide in these potassium salt melts was larger in air than in nitrogen. Silicon carbide ceramics reacted with K2SO4 melt quantitatively and the stoichiometry of K2SO4/SiC was 0·8. On the other hand, the weight loss of silicon nitride ceramics was appreciable in all potassium salt metls. The reaction between Si3N4 and K2SO4 or K2CO3 proceeded quantitatively and the stoichiometry of K2SO4/Si3N4 and K2CO3/SI3N4 was 1·6 and 3·5, respectively. The presence of oxygen accelerated the reaction between Si3N4 and K2CO3, but greatly retarded the reaction between Si3N4 and K2SO4, due to the formation of a protective film. The oxidation mechanisms of Si3N4 and SiC with K2SO4 and K2CO3 melts are discussed on the basis of the experimental results.
ASJC Scopus subject areas