High-temperature oxidation of CVD silicon-based ceramics

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:518587

Goto, Takashi; Hirai, Toshio; Iguchi, Yasutaka ^[1]

---

1. Tohoku Univ., Sendai (Japan); and others

Oxidation behavior of CVD SiC and CVD Si{sub 3}N{sub 4} was studied at 1773 to 2023 K in Ar-O{sub 2}, N{sub 2}-O{sub 2} and CO-CO{sub 2} atmospheres. In Ar-O{sub 2} and N{sub 2}-O{sub 2} atmospheres, the active oxidation rates for CVD SiC and CVD Si{sub 3}N{sub 4} were dominated by oxygen diffusion through a gas boundary layer. The active-to-passive transition oxygen partial pressures for CVD SiC were slightly greater than those for CVD Si{sub 3}N{sub 4}. In CO-CO{sub 2} atmospheres, at PCO{sub 2}/PCO < 10{sup -3} inward diffusion of CO{sub 2} gas controlled the active oxidation rates for CVD SiC; however, a chemical reaction controlled the rates for CVD Si{sub 3}N{sub 4}. At PCO{sub 2}/PCO > 10 {sup -2}, SiO{sub 2} particles or layers formed during the active oxidation; the decomposition of SiO{sub 2} could control the active oxidation rates. The Wagner model can be used to explain the active-to-passive transition in these atmospheres for both CVD SiC and CVD Si{sub 3}N{sub 4}. The volatility diagram and thermodynamic calculation, including mass balance relationship, were also useful to understand the transition behavior.

• OSTI ID: 518587
• Report Number(s): CONF-960367--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHEMICAL VAPOR DEPOSITION
DIFFUSION
LAYERS
MASS BALANCE
MASS TRANSFER
MORPHOLOGY
OXIDATION
PRESSURE DEPENDENCE
SILICA
SILICON CARBIDES
SILICON NITRIDES