窒化ケイ素のマイクロ波焼結時の緻密化及び相転移挙動に及ぼす断熱方法の効果

概要

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Silicon nitride ceramics, with Y_2O_3, Al_2O_3 and MgO as sintering aids, have been sintered in a 28 GHz microwave applicator using a number of sample insulation techniques. The sintering characteristics in terms of densification, α→β transformation, microstructural development and power requirement were studied and compared to identical samples sintered conventionally. All of the microwave sintered materials could be sintered to near theoretical density and a full α→β transformation obtained at temperatures around 200℃ lower than the materials sintered conventionally. In addition, the microstructural development showed important differences, with the selective development of elongated β-grains being observed from the very early stage of transformation. Samples sintered using a powder bed insulation technique, achieved full α→β transformation at the lowest temperature, but a tendency to thermal runaway using this method of insulation meant the samples were susceptible to cracking. Samples sintered using silicon carbide plates as a low temperature microwave absorber reached full density and onset of transformation earlier than the other materials. In addition, the maximum power requirement for these samples was around 1/3 of that required for other insulation techniques, ans more uniform heating meant that these samples were free from cracking.
社団法人日本セラミックス協会の論文
2001-09-01