OPTIMAL PRESSURES AND TEMPERATURES FOR ISOBARIC, ISOTHERMAL CHEMICAL-VAPOR INFILTRATION

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