CHEMICAL VAPOR INFILTRATION OF ZIRCONIA WITHIN THE PORE NETWORK OF FIBROUS CERAMIC MATERIALS FROM ZRCL4-H2-CO2 GAS-MIXTURES

On the basis of an experimental approach, new ceramic-ceramic composites have been prepared by the CVI of ZrO2 within the pore network of various fibrous preforms. The optimization of the CVI parameters has been carried out on the basis of: (i) a kinetic study (overall mass of deposited zirconia), (ii) mercury porosimetry (actual infiltration ratio, τi) and (iii) microprobe analysis (ZrO2 distribution profiles) utilizing mainly transition alumina fiber based substrates. SEM observations of failure surfaces provide evidence of a strong adhesion between alumina and zirconia in alumina fiber composites, and of weak adhesion with delaminations between pyrocarbon and zirconia in two-dimensional carbon-carbon/zirconia composites. From a kinetic point of view, the variation of residual porosity with densification time follows an exponential law. The behavior of different preforms towards the same CVI conditions has been shown to be strongly dependent on the features of the pore network. A low porosity and a low mean pore size are unfavorable to good densification. © 1989.