Synthesis of silicon nitride/silicon carbide nanocomposite powders through partial 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 mixed with Si3N4 powder. After drying and curing, the resin was converted to reactive carbon via pyrolysis, Si3N4 powder was partially reduced carbothermally using the pyrolyzed carbon, and nanometer-sized SIC particles were produced in situ at 1530 degrees-1610 degrees C in atmospheric nitrogen. At temperatures <1550 degrees C, the reduction rate was low and the SIC particles were very small; no SiC whiskers or barlike SIC was observed. At 1600 degrees C, the reduction rate was high and the reaction was close to completion after only 10 min, with the appearance of SiC whiskers as well as curved, barlike, and equiaxial SiC, all of which were dozens of nanometers in diameter; this size is greater than that at observed temperatures <1550 degrees C. A longer soaking time at 1600 degrees C led to agglomerates. SiC particles were close to the surface of the Si3N4 particles. The SiC content could be adjusted by changing the carbon content before reduction and the reduction temperature. A reaction mechanism that involved the decomposition of Si3N4 has been proposed.