Further lowering of temperature for sol-gel processing of ceramic powders

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Sol-gel preparation of α-alumina powders and silica glass at temperature as low as possible was aimed. Following results have been obtained.(1) Alumina gel powders prepared from the aluminum butoxide through the sol-gel reaction at 0 ℃, in the presence of HCI were partially (40 to 50 %) transformed to α-alumina around 500 ℃, when they were seeded with corundum particles to a level of 1 wt %.(2) The CL^- were forun to have an important role in the low temperature α-formation of alumina gels, and were considered to make chemical bridges between aluminoxane oligomers.(3) AlCl_3 and / or Al metal powders could replace aluminum alkoxide for low temperature formation of α-alumina.(4) The HNO_3-catalyzed alumina gel were completely transformed to α-alumina at 800 ℃.(5) The atomic scale structure of amorphous bio-silica, which was analyzed by X-ray diffraction technique, was very similar to fused silica (glass), suggesting the possibility of the room-temperature formation of silica glass even through sol-gel reaction of TEOS.(6) The silica prepared from TEOS by the sol-gel method in the presence of organic substances such as tartaric acid was revealed to have a structure similar to fused silica.