The reaction between Si//3N//4 powder and H//2O has been studied at 200 degree -800 degree C under 10 and 100 MPa. Si//3N//4 reacted with H//2O to yield amorphous SiO//2 and NH//3 by oxidation above 200 degree C. Cristobalite and keatite crystallied from the amorphous SiO//2 after the almost complete oxidation of Si//2N//4 above 400 degree C. The oxidation rate calculated from the weight gain, suggested that the reaction is controlled by diffusion process. An arrhenius plot of the rate constants gives apparent activation energies of 70-80 and 130 kJ/mol for the oxidation by N//2O liquid and H//2O vapor respectively. Since the former value is similar to the activation energy reported for the H//2O diffusion in silica phases, the oxidation of Si//3N//4 by H//2O seems to be controlled by the H//2O diffusion in amorphous SiO//2 layer. Si//3N//4 was oxidized much more slowly in H//2O vapor than in the liquid after the particle surface was covered uniformly with amorphous SiO//2.
|Number of pages||6|
|Journal||Yogyo Kyokai Shi/Journal of the Ceramic Society of Japan|
|Publication status||Published - 1986 Jan 1|
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