Thermal behavior of (organosilicon) polymer-derived ceramics .5. Main facts and trends

Extensive investigations of polymer-based ceramic materials taken within the Si-C-N-O-(H) system have been performed and previously published as parts I - IV. This paper reports the main results, facts, trends and conclusions which can be drawn from them, regarding the physical and chemical behavior of these materials submitted to an increasing thermal treatment. Both similarities and discrepancies are described and explained, whatever the chemical composition of the ceramic, (i.e. containing Si-C or Si-C-N, Si-C-O, Si-C-N-O). Emphasis is made on the mechanisms, and the role of various parameters, either intrinsic (e.g. the role of compositional C, O, or N) or extrinsic (e.g. influence of the atmosphere), is examined. The overall results indicate, among others, that excess carbon (relative to the SiC stoichiometry) is always beneficial both to the structural stability of the ceramic and the mechanical 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 oxygen-free curing processes. More generally, they provide guidelines for understanding, and somewhat predicting, the thermochemical behavior of any related materials.