Synthesis of silicon nitride/silicon carbide nanocomposite powders throughpartial reduction of silicon nitride by pyrolyzed carbon

An alternative method to incorporate nanometer-sized silicon carbide (SiC) particles into silicon nitride (Si3N4) powder was proposed and investigated experimentally. Novolac-type phenolic resin was dissolved in ethanol and m ixed with Si3N4 powder. After drying and curing, the resin was converted to reactive carbon via pyrolysis, Si3N4 powder was partially reduced carbothe rmally using the pyrolyzed carbon, and nanometer-sized SIC particles were p roduced in situ at 1530 degrees-1610 degrees C in atmospheric nitrogen. At temperatures <1550 degrees C, the reduction rate was low and the SIC partic les were very small; no SiC whiskers or barlike SIC was observed. At 1600 d egrees C, the reduction rate was high and the reaction was close to complet ion after only 10 min, with the appearance of SiC whiskers as well as curve d, barlike, and equiaxial SiC, all of which were dozens of nanometers in di ameter; this size is greater than that at observed temperatures <1550 degre es C. A longer soaking time at 1600 degrees C led to agglomerates. SiC part icles were close to the surface of the Si3N4 particles. The SiC content cou ld be adjusted by changing the carbon content before reduction and the redu ction temperature. A reaction mechanism that involved the decomposition of Si3N4 has been proposed.