FURTHER-STUDIES OF THE STABILITY OF PCS-BASED CERAMIC FIBERS AT HIGH-TEMPERATURES .1. OXIDATION BEHAVIOR

A polycarbosilane based fibre (Nicalon(R)) was heat treated under vari ous oxidising conditions covering passive and active oxidation regimes . Samples were investigated with scanning electron microscopy, high re solution transmission electron microscopy, and chemical microanalysis. In addition to the usual observations (occurrence of a silica layer a nd maintenance of the fibre stability beyond the degradation temperatu re in passive conditions), new features are described regarding, for e xample, the development of SIC grains and the chemical composition of the silica/fibre interface. Relevant mechanisms are proposed which emp hasise the role of both the local thermodynamic conditions and some ph ysical parameters such as grain size.