CHEMICAL-VAPOR INFILTRATION OF TIB2 AND TIN IN POROUS AL2O3

The mechanical strength of a porous material can be improved by deposition of a thin layer at the internal surface of the preform by chemical vapour infiltration (CVI). The influence of a CVI modification on the permeability and mechanical strength of porous alumina supports for porous alumina membranes for liquid filtration have been investigated. Numerical solutions of a mathematical description of a CVI process in an open cylinder are used to evaluate the influence of some process parameters on the infiltration kinetics. These results are used to explain the observed changes in permeability and mechanical properties. Porous alumina substrates can effectively be modified with titanium nitride (TiN) or titanium diboride (TiB2) by CVI. The amount of deposited material in the substrate is determined by a combination of process parameters. Mathematical CVI model predictions indicate that a low growth rate constant and a high diffusion are beneficial for the infiltration of the deposit into the substrate, and that the surface growth rate kinetics of the deposit has an influence on the infiltration kinetics.