A MATHEMATICAL-MODEL FOR CHEMICAL VAPOR INFILTRATION WITH VOLUME HEATING

A detailed mathematical model is presented to investigate the chemical vapor infiltration (CVI) of fiber-reinforced ceramic composites with a volume-heating source. Volume heating may be achieved by using microwave power or radio frequency (RF) induction in the case of conductive substrates. The analysis includes a set of constitutive equations describing the space and time dependence of species concentration, temperature, pressure, and porosity. The infiltration of carbon-fiber preforms with carbon resulting from methane decomposition is selected as a model system for analysis. Particular emphasis is placed on the impact of absorbed power on deposit uniformity and processing time. CVI with volume heating may lead to complete densification with considerably lower processing times when compared to conventional CVI processes. It is shown that when a constant power is used, there exists a critical power value above which accessible porosity is trapped within the composite. Several power modulation schedules are suggested to achieve rapid and complete densification without residual accessible porosity.