Abstract
SiC, Si3N4 and AlN ceramics were immersed in K2SO4 or K2CO3 melts exposed to air and nitrogen gas atmosphere at 900°-1200°C to examine the corrosion behavior. Since oxide films of AlON and α-Al2O3 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 K2CO3 melt, but the reaction between SiC and K2SO4 melts proceeded quantitatively with the stoichiometry of K2SO4/SiC=0.8. Si3N4 ceramics reacted with both K2SO4 and K2CO3 melts quantitatively and the stoichiometries of K2SO4/Si3N4 and K2CO3/Si3N4 were 1.6 and 3.5, respectively. The presence of oxygen prevented the successive reaction between Si3N4 and K2SO4 due to the formation of a protective film. The rate of oxidation of Si3N4 in both K2SO4 and K2CO3 melts was controlled by the surface chemical reactions, and the apparent activation energies were 724 and 126kJ/mol, respectively.
