THERMAL-DEGRADATION MECHANISMS OF NICALON FIBER - A THERMODYNAMIC SIMULATION

Thermodynamic calculations for the thermal degradation of the Nicalon fibre in inert gas flow at atmospheric pressure have been performed, b ased on minimization of the Gibbs energy of the Si-C-O-H chemical syst em. 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 co mpared with recently reported TEM studies of as-received and heat-trea ted material, which illustrate the sequential morphologies of its stru cture 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 degra dation of the fibre.