Formation of SiC whiskers from silicon nitride
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Attempts have been made to produce SiC whiskers through vacuum pyrolysis of Si3N4 without any addition of extraneous carbon. Vacuum pyrolysis of Si3N4 granules and powder compacts, has been carried out at 1550 and 1700°C using a graphite resistance furnace. The products of pyrolysis have been identified through XRD and SEM as SiC whiskers and particles. Small amounts of elemental silicon at 1550°C and free carbon at 1700°C have been detected through X-ray diffraction. Detection of elemental silicon through X-ray diffraction and solidified silicon droplets at the whisker tips in the SEM provide important clues regarding the mechanism of SiCw formation, as the one involving the reaction 2Si(l) + CO(g) → SiC(s) + SiO(g) Silicon carbide whiskers, 3–4 mm long, have been grown from Si3N4 compacts at 1550°C over a short period of 0.5 h. It has been shown in the present study that Si3N4 can be completely converted to SiCw, when a loose bed of Si3N4 in the form of granules is pyrolysed in the presence of CO at about 1550°C.
KeywordsCarbide Pyrolysis Nitride Powder Compact Silicon Carbide
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