Transparent sub-micrometre alumina from lanthanum oxide doped common grade alumina powder

Common grade high purity alumina (99.99%) powder doped with lanthanum oxide was slip cast, dried and pressureless sintered to sub-micrometre grain sized alumina at 1380-1410 degrees C. Samples that attained > 96% theoretical density (TD) were subsequently hot isostatically pressed to fully dense alumina having >= 99.95% TD. Sintered sub-micrometre alumina samples, ground to 2 mm thickness and polished to 0.5 mu m surface finish, displayed > 82% transmission in the 3-5 mu m wavelength range. Samples of 0.5 mm thickness also exhibited 40-60% transmission in the visible wavelength region of 400-900 nm. Lanthanum oxide addition within 0.10 wt% was shown to be favourable for improved transparency in the visible region. The alumina samples also exhibited high Vickers hardness values of 2144+45 kg/mm(2) at 5 kg indentation load. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.