Transparent Fine-Grained Oxide Ceramics

The optical quality of fine-grained MgAl2O4 and Al2O3 ceramics has been determined and related to microstructure. Optimised MgAl2O4 was found to possess exceptional transparency (75% through 1.05 mm) and a low total scattering coefficient. The transparency of fine-grained (0.45 mm) alumina was significantly less (39% through 0.62 mm) due to a combination of grain boundary scattering and residual porosity. A clear trend of increased transparency with decreases in grain size was observed for Al2O3, which is consistent with a change in scattering mechanism as the grain size approaches the wavelength of the light. A definitive measure of the optical quality of an optimum fine-grained Al2O3 is provided by expressing the total scattering coefficient as a function of wavelength.