DIRECT PYROLYSIS OF RAW RICE HUSKS FOR MAXIMIZATION OF SILICON-CARBIDE WHISKER FORMATION

A new alternate route for the production of SiC from rice husks has been described. The proposed single-stage process has the advantage of reduced time of production and a much higher yield of SiC whiskers than the conventional two-stage process. Direct pyrolysis of raw rice husks was carried out in a graphite furnace under vacuum and the reaction products were analyzed through macroscopic examination, XRD, SEM, and chemical analysis. Effects of time and temperature on the relative yields of the various reaction products have been determined over a wide range. The pyrolysis of raw rice husks has been found to be accompanied by four different competitive processes, viz., formation of SiC whiskers, formation of SiC polycrystals, crystallization of amorphous silica, and graphitization of amorphous carbon. Crystallization of silica and formation of SiC(w) are dominant processes at 1150-degrees to 1310-degrees-C. At higher temperatures formation of SiC polycrystals and graphitization of carbon are more favored. A multistep pyrolysis to 1310-degrees-C was found to yield a still higher amount of SiC(w) than direct pyrolysis.