THERMAL-BEHAVIOR OF (ORGANOSILICON) POLYMER-DERIVED CERAMICS .5. MAINFACTS AND TRENDS

Extensive investigations of polymer-based ceramic materials taken with in the Si-C-N-O-(H) system have been performed and previously publishe d as parts I - IV. This paper reports the main results, facts, trends and conclusions which can be drawn from them, regarding the physical a nd chemical behavior of these materials submitted to an increasing the rmal treatment. Both similarities and discrepancies are described and explained, whatever the chemical composition of the ceramic, (i.e. con taining Si-C or Si-C-N, Si-C-O, Si-C-N-O). Emphasis is made on the mec hanisms, and the role of various parameters, either intrinsic (e.g. th e role of compositional C, O, or N) or extrinsic (e.g. influence of th e atmosphere), is examined. The overall results indicate, among others , that excess carbon (relative to the SiC stoichiometry) is always ben eficial both to the structural stability of the ceramic and the mechan ical properties (when measurable), while heteroatoms (O, N) are always finally detrimental. They thus sustain the current efforts to develop ceramic fibers from chemical systems as simple as possible, using oxy gen-free curing processes. More generally, they provide guidelines for understanding, and somewhat predicting, the thermochemical behavior o f any related materials.