The SiO₂‐Si₃N₄ Interface, Part I: Nature of the Interphase

Abstract

Recent reports in the literature have suggested that Si2N2O forms in the oxidation of Si3N4 as a buffer suboxide below the silica crust, and that equilibrium between SiO2 and Si3N4 requires the presence of this buffer. Here we report the examination of SiO2/Si3N4 boundaries of different genesis, by a variety of techniques, all of which failed to detect Si2N2O. What was found in each case is a graded suboxide whose composition merges seamlessly with the higher oxide above and the Si3N4 below. Part I presents the results of compositional depth profiling across the suboxide. In Part II a model is proposed to explain how O2 diffusion in the graded suboxide limits Si3N4 oxidation kinetics.

A new measurement and treatment for kinetics of isothermal oxidation of Si3N4

“…6), it showed that oxidation behavior followed a parabolic rate law, indicating that the step of diffusion of oxygen through the oxide product layer to the oxide/Si 3 N 4 interface is the rate-controlling step, which is in coincident with the results in literatures [7][8][9][10][11][12][13].…”

“…Al 2 O 3 , Y 2 O 3 , etc., and found that the oxidation also followed the parabolic rate law but they reported that the oxide layer formed could not prevent Si 3 N 4 from being oxidized efficiently, implying that the rate-controlling step was not the outward diffusion of oxygen through the silicate film, but the outward diffusion of cations in the intergranular glass. Ogbuji and Bryan [9] and Ogbuji [10] also compared the oxidation rate of Si 3 N 4 (CVD) with SiC (CVD) in the temperature range from 1473 to 1773 K…”

“…However, there are wide variation in the observed reaction rates and the morphology of the reaction products. Du et al [7,8], Ogbuji and Bryan [9] and Ogbuji [10] have studied the oxidation behavior of Si 3 N 4 synthesized by chemical vapor deposition (CVD) at the temperature range from 1523 to 1673 K and found that the surface of Si 3 N 4 produced a protective oxide layer. They further verified that the oxidation process followed the parabolic rate law and the oxidation kinetic was controlled by the diffusion of oxygen.…”

“…(2) occurred at most cases and passive oxidation has been extensively studied in literatures [6][7][8][9][10][11][12][13][14]. However, there are wide variation in the observed reaction rates and the morphology of the reaction products.…”

Corrosion of Ceramic Materials

“…This assumption results in impossibly high nitrogen pressures at the Si2ON2/N2 interface (Du et al, 1989b). Other work by Ogbuji and Bryan (1995) shows an amorphous oxynitride layer with a continuous gradation in oxygen and nitrogen composition from SiO2 to Si3N4. The accompanying model (Ogbuji, 1995) proposes that oxidation proceeds by a substitution of oxygen for nitrogen across the graded SiOxNy network rather than at an interface.…”