Sinterability and Hydration Resistance of Magnesia and Calcia Coated with TiO_2

摘要

With the purpose to improve sinterability and hydration resistance of magnesia and calcia sintered bodies, titania coating was applied on the surface of magnesia and calcia powders by means of a Ti chelate compound, and sintered bodies were prepared by firing at 1400-1700 deg C. As the results of investigations on sinterability and hydration resistance of these sintered bodies, the following conclusions were obtained.1) For uncoated magnesia and calcia powders, although sintering progressed to some extent, almost no improvement of hydration resistance was obtained. For example, increasing the firing temperature of magnesia from 1400 deg C to 1600 deg C, increased the bulk density by 18 percent, but the improvement of hydration rate was limited only to 3 percent at 24 hours hydration time indicating an almost complete 95 percent hydration.2) By applying titania coating on heavy quality magnesia, sintering was enhanced. A titania coating of 0.3 mass percent and firing at 1500 deg C produced a sintered body with bulk density 3.2 g/cm~3. The hydration resistance of this sintered body was excellent, showing hydration rate of 0.7 percent after the 24 hours hydration test.3) As for calcia, applying a titania coating at 0.3 mass percent and firing at more than 1700 deg C, produced a sintered calcia body of with excellent sinterability and hydration resistance. A bulk density was 3.1 g/cm~3 and the hydration was 4 percent after the 8 hours hydration test.4) As for the improvement of sinterability and hydration resistance of magnesia and calcia by means of titania coating, as mentioned in items 2) and 3) above, titania was effective in both materials, but more effective with magnesia.The effectiveness of coating, was revealed more at the latter stage of sintering than at the initial stage, (particle growth of magnesia, etc.)