Oxidation of titanium carbide-graphite hetero-modulus ceramics with low carbon content. I. Phenomenological modeling of the ridge effect

Abstract

Hetero-modulus ceramic composite materials (HMC) present an opportunity to combine a ceramic matrix having high Young's modulus with inclusions of a material having a considerably lower value of Young's modulus, resulting in a material with significantly improved properties. The isobaric-isothermal oxidation of 93 vol.% TiC-7 vol.% C (graphite) hot-pressed HMC was studied at temperatures of 400-1000 °C and pressures of 0.13-65 kPa in oxygen flow using a microbalance. The TGA data and carbon content analysis of oxidised samples were applied in the kinetics phenomenological modeling for both carbon burn-off and oxygen consumption processes. The activation energies Q and orders of reaction m were determined for all oxidation parameters and stages of the process, described using a linear-paralinear model. The oxidation behaviour of the material is characterised by the presence of a so-called "ridge effect". The ridge temperature and ridge oxygen pressure serve as boundaries between regions defined by higher or lower values of oxidation parameters and mark a change in the prevailing oxidation mechanism, as while traversing the ridge parameter the values of Q and m change their sign. © 2008 Elsevier Ltd. All rights reserved.