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Kinetic analysis of the processing of porous biomorphic titanium carbide ceramics by chemical vapor infiltration

Abstract:

Porous biomorphic TiC ceramics derived from three different wood types-beech, pine, and rattan-were produced by chemical vapor infiltration (CVI). First, the wood samples were carbonized at 850°C in an inert atmosphere, yielding carbon biotemplates (Cb-template) which were subsequently converted into TiC by CVI with TiCl4 in an excess of hydrogen. In order to estimate the infiltration depth in the pores of the C b-template, an infiltration model was developed, considering the rate of the chemical reaction and the effective diffusion coefficient, as well as the geometry of the pores. The parameters of the formal kinetics, based on a power law rate equation, were determined experimentally using non-porous substrates. The depth of infiltration into the pores of the C b-template, expressed as the infiltration factor (η), varies depending on the pore size of the wood samples. Thiele modulus (Φ) values in the range 0.2-2.0 were calculated, corresponding to a η value between 56 % and 99 %. The calculated infiltration depths were compared with the experimental results from scanning electron microscopy (SEM) images. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.