Effects of the two-step sintering process on the optical transmittance and mechanical strength of polycrystalline alumina ceramics

The effects of a two-step sintering (TSS) process on the optical transmittance and mechanical strength of polycrystalline alumina ceramics were analyzed. High-purity alumina with a ppm impurity level was fabricated using a ceramic injection molding process by applying a TSS process in a high temperature vacuum atmosphere. A temperature of 1780 °C was effective for the first step sintering, which represents the highest densification rate, and a second isothermal sintering condition of 1300-1600 °C was applied for a different length of time to prevent surface diffusions and the secondary phases. An increasing sintering temperature and hold time in the TSS process proportionally increased the grain size and growth in the sintering bodies.