Production of Al_2TiO_5 sintered body with ultrafine microstructure.

(1)在Al_2 (SO_4) _3溶液中悬浮粒径为20 ~ 40 nm的TiO_2细颗粒，采用均匀沉淀法合成了Al_2O_3水合物包覆TiO_2颗粒，并对其烧结性能进行了研究。在1500℃的温度下烧结4h，得到了96%理论密度和100% Al_2TiO_5相的烧结体。烧结体由10 μ m以上的颗粒组成。除Y_2O_3外，在1400℃的温度下烧结可获得t.d为92%的烧结体，但晶粒长大到8 μ m左右。(2)采用硫酸盐（Al_2 (SO_4) _3, TiOSO_4）溶液共沉淀法制备了Al_2TiO_5粉末，并研究了添加剂对烧结体显微组织的影响。添加BaO、ZrO_2或ZrSiO_4对抑制晶粒生长均有较好的效果。在不添加添加剂的情况下，在1300℃下烧结的Al_2TiO_5由约10 μ m的晶粒组成，晶界处存在较大的裂纹。在添加10mol%BaO或5mol%ZrO_2的情况下，可以得到致密的烧结体（90%以上），晶粒大小约为1 μ m，烧结体中不存在裂纹。烧结体中形成的BaAl_2O_4相或ZrTiO_4相抑制了Al_2TiO_5的晶粒长大。添加了BaO或ZrO_2的烧结体热膨胀系数略大，其迟滞比未添加的烧结体小。BaO和ZrO_2抑制了Al_2TiO_5分解为α - al_2o_3和TiO_2（金红石）。在Al_2TiO_5-ZrSiO_4体系中，在1400℃的温度下，以Al_2TiO_580mol%-ZrSiO_420mol%的组分烧结，可以得到具有微观结构的复合烧结体。试样的热膨胀系数与未添加添加剂的试样基本相同。1100℃加热8h，试样未发生分解。

(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.