Optimal pressures and temperatures for isobaric, isothermal chemical vapor infiltration



This study addresses the possibility identifying optimal pressure and temperature pairs that can be used to give the least processing time during isobaric isothermal chemical-vapor infiltration (CVI) within a window of operating conditions. Optimal pressure—temperature pairs are determined as the solution of an optimization problem that seeks to minimize the processing time predicted by a CVI model under the constraint that the maximum density difference in the preform at the end of the densification does not exceed a preset limit. Results are presented on the dependence of the optimum processing time on the type of structure of the preform, the specifications that the final product has to conform to, and the kinetics of the chemical reaction. The results show that operation at low pressure affects adversely the processing time and that a dramatic reduction in the processing time can be achieved by operating in the vicinity of the optimal pressure.