Thermodynamic Analysis of the Chemical Vapor Deposition of Composite 〈Si 3 N 4 〉‐〈BN〉 Coatings

A thermodynamic analysis of the chemical vapor deposition of the composite ceramic (Si 3 N 4 (BN) was performed using a general computer program for the calculation of heterogeneous equilibria. Reactants assumed were (H 2 SiCl 2 ), (BCI 3 ), and (NH 3 ). The equilibrium conditions for the deposition of condensed phases in the B‐Si‐N system wire determined as a function of the variables temperature, total system pressure, and gram‐atomic reactant gas fractions B/(Si + B) and N/(CI + N). The phase assemblage (Si 3 N 4 )‐〈BN〉 was found to be stable over a large region. Predominant gaseous species at equilibrium were (HCI), (N 2 ), (H 2 ), and the silicon chlorides. Deposition efficiencies at equilibrium for (Si 3 N 4 ) and (BN) were high, particularly in the presence of excess (NH 3 ) and at temperatures below 1600 K.