Thermal plasma synthesis of SiC from rice hull (husk)
Recently the synthesis of ultrafine powders has drawn considerable attention because these powders can have physical and chemical properties superior to those of bulk specimens. In particular, emphasis is on the preparation of ultrafine ceramic powders for their applications in the development of sintered products having higher density and lower sintering temperature. One such industrially important ceramic material is SiC. In many cases ultrafine SiC has been prepared by thermal plasma processes [1]. However, these processes require one or more reactive/corrosive gases. This letter describes a new method to overcome such problems. For this purpose thermally pretreated rice hull was used as the solid precursor. Rice hull, an agricultural waste product, was first used by Cutler [2] as a starting material for the production of silicon carbide. Since the rice hull route promises to be most economical, much attention has recently been paid to it [3-6]. Rice hull consists of silica in hydrated amorphous form, and cellulose which yields carbon when thermally decomposed. The relative abundance of silica with very high surface area in close proximity to active carbon in rice hull makes it amenable for SiC formation during the pyrolysis process. The possible reaction was given by Lee and Cutler [7] as
High-vacuum synthesis of SiC from rice husk: a novel method
A new technique for the production of SiC from rice husk is reported in this paper. The high-purity β-SiC is synthesized in a short time of 5 min. The samples are characterized by x-ray diffraction and scanning electron microscopy analysis. The results are compared with the previously reported result that was obtained by conventional process.
Growth of SiC whiskers in the system SiO2-C-H2nucleated by iron
Abstract A study has been made of the nucleation, growth and morphology of α- and β-SiC whiskers obtained from silica and carbon in hydrogen between 1200 and 1300°C by a VLS process with iron as agent. On polycrystalline substrates - the solid starting materials or an inert third material - β-whiskers are obtained mainly grown in the [111] direction; on basal {0001} and prismatic {10 1 0} faces of α-SiC single crystals in addition α-[0001] and α-[1 1 0] whiskers respectively grow epitaxially. The growth rate is in the order of 1 mm/hr, irrespective of polytype and growth direction. The rate depends on the relative position of C, SiO2 and substrate; in a given arrangement the rate increases with increasing temperature with an activation energy of about 85 kcal/mole. As to be expected for a VLS process in which the supply of vapour is rate-limiting, the rate is higher for whiskers grown from relatively larger droplets. The β-[111] whiskers often show a fluctuation in diameter, whereas the α-whiskers are always smooth. For smooth whiskers the ratio of the diameter of the Fe-Si-C alloy droplet at the tip and the diameter of the whiskers is about 2, and for knotted whiskers generally larger. These ratios are associated with minima in the Gibbs free surface energy at the vapour-liquid-solid interface. It is discussed how instabilities in the liquid can give rise to knottiness of β-[111] whiskers in a system where solid SiC grows from a gas phase with Si/C ⪡ 1 via a liquid phase with Si/C ⪢ 1.