FABRICATION OF SILICON CARBIDE CERAMICS FROM RICE HUSKS

Abstract

Silicon carbide ceramics were prepared by 2 paths; first, carbothermal reduction in powder form preparation before sintering and secondly, carbothermal reduction plus in situ reaction bonding. The carbothermal reductions of silicon carbide powders were prepared from rice husks which were carbonized in an incineration furnace. The carbonized rice husks were ground under variousconditions. The ground powders were placed in alumina crucibles, closed with graphite lids, and pyrolized at different temperatures and soaking times in argon and nitrogen atmospheres. Pyrolized samples were characterized. The beta silicon carbide phase was present in all samples that were pyrolized in the argon atmosphere. Samples pyrolized in the nitrogen atmosphere consisted of beta-silicon carbide and silicon oxynitride. The main phase in the synthesized sample is beta-silicon carbide in particle form with a small amount number of whiskers. The beta-silicon carbide particles were increased when the soaking time was increased. On the other hand, the silicon carbide whiskers decreased when the soaking time was increased. The sample which was pyrolized in the argon atmosphere at 1600oC was selected to be pressed and sintered at different temperatures and compared with a commercial powder. With an increased sintering temperature, the density of the sintered sample was increased. The density of the sintered sample is closed to samples prepared from the commercial powder when the sintering temperature was increased upto 1850oC. For the carbothermal reduction plus in situ reaction bonding, carbonized rice husks were treated with HCl solution, mixed with Si metal powder and pyrolized in argon at various temperatures. The silicon carbide quantity and porosity increased when the pyrolysis temperature was increaseddue to the reaction and gas phase in the system.