Transparent alumina by vacuum sintering

Alumina windows transparent in IR range and translucent in UV range were obtained by high vacuum sintering (∼10–6 mbar). To determine the influence of the atmosphere on grain growth, a sintering kinetics and intragranular porosity studies have been performed for samples sintered in air and in high vacuum atmospheres. It has been established that by using high vacuum sintering instead of the conventional one in air, alumina compacts with lower grain size, less impurities in grain boundaries and less quantity of intragranular pores were obtained. It has been proven that high vacuum sintering allows to reach high densities (>99%th) without exaggerated grain growth (d50 < 1 μm). Finally, strong correlation between microstructure and light transparency has been found and consequently it can be concluded that vacuum sintering clearly enhances the optical properties of alumina.