Preparation of polymer-derived Si-B-C-N monoliths by spark plasma sintering technique

The present paper reports the preparation of sintering additive-free Si-B-C-N monoliths by spark plasma sintering (SPS) under nitrogen of polymer-derived Si-B-C-N powders. Powders are synthesized in nitrogen or ammonia atmosphere to modify their carbon content. The nitrogen-treated powders sintered in the temperature range 1500-1900 degrees C lead to monoliths with a density increasing from 2.4 to 2.6 g/cm(3), Vickers harness and Young's modulus ranging from 0.7 to 5.4 GPa and 48 to 102 GPa, respectively. SiC was the first phase to nucleate around 1700 degrees C, whereas Si3N4 grew at 1800 degrees C. At this temperature, monoliths are pure electrical conductor nanocomposites mainly composed of Si3N4 and SiC nanophases embedded in a turbostratic BN(C) matrix. Above 1800 degrees C, Si3N4 was not identified. In comparison, ammonia-treated powders sintered at 1800 degrees C represent dense insulator composites mainly composed of Si3N4 and BN with a Vickers hardness as high as 15 GPa and an excellent stability in air. (C) 2014 Elsevier Ltd. All rights reserved.