SYNTHESIS OF SILICON-CARBIDE WHISKERS USING THE VAPOR-LIQUID-SOLID MECHANISM IN A SILICON-RICH DROPLET

SiC whiskers can be produced from 1350-1500 degrees C by carbothermal reduction of the silica in a fixed bed percolated by a hydrogen flow. At 1450 degrees C and above, the addition of iron to the silica-carbon mixture leads to the formation of submicrometre whiskers in the bed, ending with a silicon-rich droplet. The iron has evaporated and conden sed at a lower temperature, a few centimetres downstream from the bed, allowing the formation of silicon carbide whiskers ending with an iro n droplet according to the vapour-liquid-solid (VLS) mechanism. Submic rometre whiskers are also obtained without iron over a broader range o f temperatures. Silicon carbide whisker production in a fixed bed is t hen possible using a (VLS) mechanism in a silicon-rich droplet and may be controlled without the addition of transition metals, thus improvi ng the purity.