Theoretical Analysis of Chemical Vapor Deposition of Ceramics in an Impinging Jet Reactor

Abstract

A mathematical model for chemical vapor deposition in an impinging jet reactor is extended to consider growth of materials that are nonstoichiometric or that contain multiple solid phases. The model treats the fluid flow of the reactant gas mixture, multicomponent heat and mass transfer, and simultaneous gas‐phase and surface reactions. For a given system, insight into the rate‐limiting steps can be obtained by identifying a set of reaction rate constants that gives a match between theoretical results and experimental data. The calculations also provide quantitative information on the relationships between operating conditions, deposition rate, and deposit composition. Results for production of boron carbide from BCI 3 , CH 4 , and H 2 are presented as an example. Under typical processing conditions, deposition of B y C is found to be controlled primarily by the rate of CH 4 decomposition and the extent of surface coverage by CH 4 Theoretical calculations are presented for different sets of operating conditions to illustrate the predictive capability of the model. Also, the sensitivity of results to various reaction mechanisms and to values for solid‐phase activities is evaluated. Analogies are drawn between the boron carbide process and deposition of other ceramics in which a carbon‐containing reactant is used.