Normal pressure sintering and high pressure sintering of superfine Al_2O_3 powder with high purity
Microcrystalline Al2O3 ceramic with high purity was prepared by normal pressure sintering and high pressure sintering using superfine alumina powder.The experimental results indicated that high-speed ball milling in ethanol could reduce the average size of Al2O3 particles remarkably,and increase the specific surface area and sintering activity of Al2O3 powder.Pure Al2O3 ceramic with a relative density of 98.71% was fabricated under sintering pressure of 4.5 GPa and at a temperature as low as 1230℃ in 30 min.As compared with normal pressure sintering,the sintering temperature was decreased remarkably in the high pressure sintering process,the velocity of mass transfer was increased and the sintering time was shortened.High pressure sintering could achieve the effect of fast and low-temperature sintering.Because of a relatively low sintering temperature in the high pressure sintering process,liquid phase did not exist in MgO-doped Al2O3 ceramic and MgO had no effect on densification and restraint of Al2O3 grain growth.