Thermal degradation mechanisms of Nicalon fibre : a thermodynamic simulation

Thermodynamic calculations for the thermal degradation of the Nicalon fibre in inert gas flow at atmospheric pressure were performed, based on minimisation of the Gibbs energy of the Si-C-O-H chemical system. The calculations are based on a critically selected thermodynamic database of the participating compounds. The results are presented by means of diagrams illustrating the quantities of condensed and gaseous species obtained as a function of treatment temperature. These are compared with recently reported TEM studies of as-received and heat-treated material, which illustrate the sequential morphologies of its structure and nanotexture as a function of treatment temperature. The main step of the observed degradation mechanism is successfully simulated in terms of the temperature, the oxygen content and the weight loss of the material. An endogenous oxidation mechanism is proposed for degradation of the fibre. 31 refs.