Greatly reducing cost in CVI fabrication of C/C composites

There exist many fast CVI (chemical vapor infiltration) equipments for fabricating C/C (carbon/carbon) composites sample, one at a time. We aim to reduce the fabrication cost greatly while retaining the advantage of conventional CVI equipment to fabricate several C/C composites samples at the same time; furthermore we aim to make these samples much more oxidation resistant. In this study, a new densification process of C/C composites is investigated by what we call catalytic chemical vapor infiltration (CCVI). Ni/Al₂O₃ catalysts with different weight percentages of nickel are added in the carbon fiber cloth substrate. Propylene, which is carried in flowing hydrogen, deposits on the substrate as source under catalysis of Ni/Al₂O₃ at 750-900°C. Being deposited for 100 h, the density of C/C composites can reach 1.68 g/cm³, and its rate of depositing is at least three times faster than that of the case in which catalyst is not used; thus, the fabrication cost is greatly reduced. After high temperature heat treatment, the weight loss of C/C composites prepared by CCVI is small, and, more importantly, the sample's initial oxidation temperature is 155°C higher than that of the case in which catalyst is not used. The surface morphology of pyrolytic carbon is characterized by scanning electronic microscopy (SEM) and polarized light microscopy (PLM) respectively. The mechanism of the catalytic deposition and increase of resistance against oxidation is studied preliminarily.