Characterization of nearly stoichiometric SiC ceramic fibres

A comparative study of the chemical composition and microstructure of Hi-Ni calon, Hi-Nicalon type S, Tyranno SA, Sylramic and Carborundum fibres has b een conducted. This analysis has confirmed results already published but ha s also evidenced some original features. The Hi-Nicalon type S fibre has a near stoichiometric composition but it still contains some oxygen (approxim ate to1 at. %) and free carbon (approximate to2 at. %). The expected near s toichiometric composition of both the Tyranno SA and the Sylramic fibres is only effective near the edge region, while the core of the fibres contains some amount of free carbon (e.g., up to approximate to 14 at. % and approx imate to6 at. % respectively in large diameter fibres) as well as some resi dual oxygen (approximate to0.5 at. %). The composition of the Carborundum f ibre is very close to stoichiometric SiC except rare and localised free car bon or B4C inclusions. The properties of the different fibres, some of them still beeing at a development stage, are discussed from a chemical and a p hase composition point of view, on the basis of what is known about their r espective preparation process.