Effects of colloid forming conditions on thermal stability of high-temperature-resistant alumina with high surface area

Sintering is an important factor that causes the decrease of surface area of alumina at high temperature. This paper studies the effects of colloid forming conditions, such as drip feed rate of ammonia, pH value, temperature, and concentration of Al(NO3)(3) solution, on the thermal stability of alumina prepared by the sol-gel method and using La and Ba as the additives. The sintering mechanism of alumina is also discussed. The results show that the surface area, pore volume, and pore diameter of alumina vary obviously with the colloid forming conditions. Suitable conditions may prevent alumina from sintering at high temperature, increase the surface area of alumina, and improve the pore properties of alumina. The alumina prepared under the optimum conditions remains a surface area of 92.3 m(2)/g after calcination at 1 100 degreesC for 20 h. The alumina sintering is found to be governed by two types of mechanisms, the viscous or plastic flow mechanism and the surface diffusion mechanism at the first stage and the second stage of the sintering, respectively.