CORROSION OF SiC, Si//3N//4 AND AlN IN MOLTEN K//2SO//4 AND K//2CO//3 SALTS.

SiC, Si//3N//4 and AlN ceramics were immersed in K//2SO//4 or K//2CO//3 melts exposed to air and nitrogen gas atmosphere at 900 degree -1200 degree C to examine the corrosion behavior. Since oxide films of AlON and alpha -Al//2O//3 were formed on the surface of AlN, AlN ceramics exhibited high resistance to corrosive attack with potassium salts under the present experimental conditions. SiC ceramics dissolved slowly in K//2CO//3 melt, but the reaction between SiC and K//2SO//4 melts proceeded quantitatively with the stoichiometry of K//2SO//4/SiC equals 0. 8. Si//3N//4 ceramics reacted with both K//2SO//4 and K//2CO//3 melts quantitatively and the stoichiometries of K//2SO//4/Si//3N//4 and K//2CO//3/Si//3N//4 were 1. 6 and 3. 5, respectively. The presence of oxygen prevented the successive reaction between Si//3N//4 and K//2SO//4 due to the formation of a protective film. The rate of oxidation of Si//3N//4 in both K//2SO//4 and K//2CO//3 melts was controlled by the surface chemical reactions, and the apparent activation energies were 724 and 126 kJ/mol, respectively.