Synthesis, Structures, and Properties of Bulk Si(O)C Ceramics from Polycarbosilane

Bulk Si(O)C ceramics are fabricated from polycarbosilane (PCS) by bulk pyrolysis along the route of cross linking, warm‐pressing, and pyrolysis. The PCS was thermally oxidized for cross linking at various temperatures as a critical step toward the bulk transformation of PCS into bulk Si(O)C ceramics. The degree of cross linking of PSC affects the densities and bonding qualities of the warm‐pressed powder compacts and, hence, the resultant ceramics. Under optimized processing conditions, crack‐free bulk Si(O)C ceramics are obtained with a bulk density attaining 2.2 g/cm 3 . Despite the existence of a considerable amount of oxygen in the ceramics (16.08 wt%), resulting from the thermal oxidation processing, the ceramics show the characteristics of structures and properties of SiC‐based ceramics. 29 Si‐solid state nuclear magnetic resonance spectra (NMR) reveal that the as‐pyrolyzed X‐ray amorphous Si(O)C phase consists mainly of SiC 4 coordination units in the ceramic network, with the remainder being silicon‐coordinated carbon and oxygen. Microhardness tests show that the as‐pyrolyzed amorphous Si(O)C ceramics have a high hardness, attaining 24.91 GPa at a load of 2 N, and 19.82 GPa at a load of 10 N. Upon annealing at 1300°C in argon, the amorphous ceramics crystallized into nanophase β‐SiC ceramics, and the ceramics kept the bulk nature of the amorphous ceramics with an increased density. The 29 Si‐solid state NMR spectrum indicates that the nanophase β‐SiC ceramics consist of SiC 4 units together with some mixed coordination units, namely SiO 2 C 2 and SiOC 3 . The hardness of the crystallized nanophase Si(O)C ceramics attains 23.20 GPa at a load of 10 N. The present study demonstrates the possibility of fabricating bulk Si(O)C ceramics via the polymer‐processing route, resulting in ceramics with promising structural and mechanical properties.