Abstract
The effect of impurities, such as Fe2O3, Al2O3, TiO2, MgO and CaO, contained in silica-containing natural substances on the growth of SiC whiskers were investigated, with emphasis placed on the yield and length of the whiskers. The yield of SiC whiskers synthesized from silica-containing natural substances was improved by the addition of cryolite. The-most remarkable effect appeared on volcanic ash and led to a total maximum yield of 21mass%. Fe2O3 contributed to increasing the length and yield of SiC whiskers on the graphite boat. On the other hand, Al2O3 only slightly affected the improvement of the yield on the graphite tube and the length on the graphite boat. The dominant factor in the growth of the whiskers due to transition metal component was clarified based on EDX analysis of the droplet existing at the tip of the whiskers. The content of the metal component in the droplet at the tip of SiC whiskers was related to the solubility of metal in Si, and the content of Fe in the droplet was greatest among other metal elements. The increase in the yield and the higher Fe content in the droplet in the case of using volcanic ash, containing more Fe2O3 among other natural substances, supported the belief that Fe2O3 is very effective in growth promotion of whiskers deposited on a graphite boat.
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