Thermodynamic approach to the oxidation of Hi-Nicalon (TM) fiber

A thermodynamic investigation of the oxidation of Hi-Nicalon(TM) fiber in a ir has been performed, based on the minimization of the Gibbs energy of the silicon-carbon-oxygen chemical system. The results illustrate the expected stable phases, as a function of temperature and the molar ratio of air ove r the fiber, which permits simulation of the diffusion-controlled radial ox idation of the fiber. In agreement with literature information, the model h as shown that (i) during oxidation, the external portion of the fiber is tr ansformed to silica while the core remains unaffected, (ii) in certain cond itions, a free carbon interphase is produced between the external portion a nd the core of the fiber, and (iii) low oxygen partial pressure may lead to consumption of the fiber, which illustrates an active oxidation.