PREPARATION OF SILICON CARBONITRIDES FROM AN ORGANOSILICON POLYMER .2. THERMAL-BEHAVIOR AT HIGH-TEMPERATURES UNDER ARGON

The preparation and the conversion in ceramics of the precursor cross- linked copolysilazane (CPSZ) of formula (ViSiHNH)x(MeSiHNH)y have been summarized in Part I. Part II will examine the evolution and the ther mal behavior of CPSZ at high temperatures under argon atmosphere. Gase ous phase, graphite or alumina crucible environments, and the activity of free carbon in ceramic residues have shown decisive effects on rea ction products. The changes in crystallinity, powder morphology, XRD s pectra, SEM observations, and oxidation behavior for samples annealed from 1200-degrees to 1450-degrees-C are consistent with an amorphous-t o-crystalline transformation. The influence of nitrogen atmosphere on the structural rearrangement will be shown in Part III.