Chemistry and kinetics of chemical vapor infiltration of pyrocarbon-V.: Infiltration of carbon fiber felt

The paper is concerned with the chemical vapor infiltration of a carbon fiber felt, 2 cm in thickness, exhibiting a porosity of 88%. The studies were performed at a temperature of 1100 degrees C using pure methane at a total pressure of 20 kPa (felt III) and a methane/hydrogen mixture of p(CH4)/p(H2) = 7:1 at total pressures of 20 and 30 kPa (felt I and II, respectively). The infiltrations were finished after 4 days (felt II), 5 days (felt III), and 6 days (felt Ij. After infiltration the total, open and closed porosities were determined as: 14.53/10.83/3.71% (felt I); 19.02/10.38/8.64% (felt II); 19.87/13.81/6.06% (felt III). Deposition at the external surface occurred only in the case of felt III. Thus, further infiltration of felt I and II should lead to decreased porosities, in the case of felt I to less than 10% total porosity. The results are shown to agree with earlier results obtained with a porous alumina ceramic showing an initial porosity of only 23%. (C) 1999 Elsevier Science Ltd. All rights reserved.