Production of Al_2TiO_5 sintered body with ultrafine microstructure.

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(1)Al_2O_3 hydrate-coated TiO_2 particles were synthesized by homogeneous precipitation technique from Al_2 (SO_4) _3 solution in which TiO_2 fine particles in 20-40 nm diameter were suspended and their sinterability was studied. The composite powder gave a sintered body with 96% of theoretical density and 100% Al_2TiO_5 phase by sintering at 1500ﾟC for 4h. The sintered body consisted of grains above 10 mum. In addition of Y_2O_3, a sintered body with 92% T.D.could be obtained by sintering at 1400ﾟC,but, the grains grew into the large size of about 8 mum.(2)Al_2TiO_5 powder prepared by coprecipitation from sulfate (Al_2 (SO_4) _3, TiOSO_4) solution was sintered and the effect of additives on the microstructure of the sintered body was investigated. The addition of BaO,ZrO_2 or ZrSiO_4 was very effective for suppression of grain growth.In the case of no additive, Al_2TiO_5 sintered at 1300ﾟC consisted of grains of about 10 mum, and large cracks existed at the grain boundaries. In addition of 10mol%BaO or 5mol%ZrO_2, the dense sintered body (above 90%) having a microstructure consisted of grains of about 1 mum could be obtained, and no crack existed in a sintered body. BaAl_2O_4 phase or ZrTiO_4 phase formed in the sintered body is thought to suppress grain growth of Al_2TiO_5. Thermal expansion coefficients of sintered bodies added with BaO or ZrO_2 were larger a little, and their hysteresis became smaller than no additive. BaO and ZrO_2 suppressed a decomposition of Al_2TiO_5 to alpha-Al_2O_3 and TiO_2 (rutile).In Al_2TiO_5-ZrSiO_4 system, a composite sintered body having a microstructure could be obtained by sintering at 1400ﾟC in the component of Al_2TiO_580mol%-ZrSiO_420mol%. A thermal expansion coefficient of the specimen was almost the same as that of no additive. The specimen did not decompose by heating at 1100ﾟC for 8h.