Composition and Structure of Ceramic Fibers Prepared from Polymer Precursors

Abstract

Ceramics fibers in the system Si-C-N-O prepared by pyrolysis of melt-spun, cured, amorphous organosilicon polymers have a predominantly amorphous chemical structure, consisting of carbon, nitrogen, and oxygen bonds to silicon. These amorphous silicon oxycarbonitrides have chemical bonding approach a random distribution: i.e. individual silicon atoms are simultaneously bonded to C, N, and O in a random fashion. Such structures have not been characterized previously. Excess C, present in all compositions studied, appears to be present as very small polyaromatic crystallites ({approx} 4 nm domain size in the aromatic plane) resembling pyrolytic carbon in structure. This carbon is highly resistant to oxidation. The amorphous, random structure of these ceramics is a consequence of small-scale elemental homogeneity in the amorphous polymer precursor and of insufficient thermal energy during pyrolysis to promote crystallization.