Thermodynamics of the Si-N-O system and kinetic modeling of oxidation of Si3N4

Thermodynamic calculations were performed on the Si-N-O system, and the results are discussed in relation to the thermal oxidation of crystalline Si3N4. Based on previous oxidation results at temperatures in the range of 1200-1400 C and oxygen partial pressures of 0.05-1.0 atm in oxygen-argon or oxygen-nitrogen-argon gas mixtures, a kinetic model describing the growth of the oxidation scale on Si3N4 developed. Good agreement between the experimental results and the model supports the hypothesis that the oxidation of pure and dense Si3N4 under the above conditions is probably rate-limited by molecular oxygen diffusion through the structurally dense Si2N2O intermediate phase. 19 refs.