Properties of rare earth oxide doped translucent polycrystalline alumina

This paper presents the results of an investigation into the properties of rare earth oxide doped translucent polycrystalline alumina (PCA). Materials containing very high concentrations of dopant with 50% translucency have been fabricated in less than 30 min. Fully dense translucent aluminas have a number of applications such as in electric discharge tubes for lighting applications, dental brackets and electrical insulators. The sintering of translucent PCA traditionally requires prolonged high temperatures and a hydrogen atmosphere to encourage grain growth and reduce porosity. Using a liquid-doping technique involving the introduction of the rare earth metal nitrate into the partially sintered powder compact, the dopant is located at the grain boundaries. Also, with the introduction of relatively large amounts of rare earth oxide dopant the sintering behaviour is modified, both to increase the required firing temperatures and to affect porosity and its distribution. The effects of two rare earth oxides are reported in terms of sintering behaviour, density, grain size and component translucency.