珪藻土からの窒化ケイ素ウイスカの合成における酸化物添加効果

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Two types of Si_3N_4 whisker and a Si_3N_4 powder were obtained by the reduction and nitridation of di atomaceous earth in a flowing mixture of nitrogen and ammonia at 1350℃. It is revealed that the addition of 2 wt% various metal oxides brought about remarkable effects on the shape and the yield of Si_3N_4. Addition of either vanadium, manganese, yitriuln or cobalt oxide increased the yield of inside whiskers which have a nee dle like shape and form on the Si_3N_4 powder. Addition of manganese oxide promoted the formation of outside whiskers siguificantly, which have a wool like shape and form on the wall at the lower part of the reactor tube. Most of the outside whiskers produced in the presence of metal oxide had droplets on their top, which were mainly composed of Si and Fe. These results indicate that the outside whiskers have grown by the vapor liquid solid (VLS) mechanism and that Fe is necessary for the growth of the outside whiskers. During the reaction, most of the added metal oxides seem to be reduced to the corresponding metals. The melting point of metallic manganese is the lowest among the added metals. Moreover, manganese has a strong affinity to nitrogen. Therefore, it is estimated that manganese and iron oxides in diatomaceous earth are reduced to metallic Mn and Fe. Then the metallic Mn and Fe evaporate and migrate to the position where the outside whiskers are produced, and whereupon the vapor condenses to droplets of Fe Mn alloy. mcorpora tion of nitrogen into the droplets will be augmented by the Mn contained in the droplets. This may account for the enhanced fonnation of the outside whiskers.
社団法人日本セラミックス協会の論文
1994-06-01

珪藻土からの窒化ケイ素ウイスカの合成における酸化物添加効果

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