Modification And Sintering Properties Of Alumina Powder

As a fine chemical material, high purity alumina powder that Al2O3 content exceeds 99.99% are rapidly developed and widely used in all of the industries. The quality of high performance alumina powder means high purity, superfine, homogeneous particle size distribution and without hard agglomeration. Up to now, high purity alumina powder for high quality transparent alumina ceramics were monopolized by foreign producer such France Baikowski, Japan Sumitomo Chemical et al. Though there are many domestic producers of alumina powder, their capabilities of mass producing high purity alumina powders are so absence that they can not hold the market share. Recently, there is a breakthrough in controlling the minim impurities of high purity alumina powder. There are still two problems to be solved. One is the instability among different batches. The other is wide particle size distribution and agglomeration. Therefore, the quality of transparent alumina ceramics can not be guaranteed using domestic alumina powders.Facing this situtation, we developed the treatment technologies including purifying the powder, modifying the particle size distribution and improving dispersive property. Moreover, transparent alumina ceramic tube for ceramics metal halide lamps and dome for infrared windows were prepared using different forming process with the modified alumina powders. The conclusions are following.In high temperature, the Fe, Na, K, Mg and Ca impurities in alumina powder could be decreased with the HC1 gas which was produced by H2 and Cl2 gases.Three domestic high purity alumina powders were milled with a deionized water as media and adding some dispersants. The agglomeration of alumina powder was improved and the powder showed good dispersive, ball-shaped, homogenous particle size distribution. Particle size of D50 was 1μm.Alumina ceramics with fine grain and high strength was successfully prepared by sintering Xinxiang alumina powder adding with MgO additive at a low temperature of 1500℃. The grain size was just 2～3μm and the three-point flexural strength arrived at 545MPa. Alumina ceramics adding with 15wt% ZrO2 has higher three-point flexural strength arrived at 797MPa sintered at 1450℃. It was increased 46% than alumina ceramics without ZrO2. High quality transparent alumina ceramics was successfully prepared used Xinxiang alumina powder doped with MgO, ZrO2 and La2O3, respectively. Three sintering additives were helpful to decrease sintering temperature and improve in-line transmittance of alumina ceramics. MgO and ZrO2 had no effect on the alumina grain growth. But reversely, La2O3 obviously restrained the grain growth and the microstructure of ceramics was homogenous.High optical quality monolithic transparent alumina ceramic tube for ceramic metal halide lamps and domes for infrared windows were successful prepared using slip casting forming process and vacuum sintering.