Processing of large and complex-shaped fine-grained alumina bodies with high transparency

The paper presents the development of unique processing methods for large alumina windows, domes, and thin sheets with a fine-grained structure and high optical transmission. Gelcasting combined with post-hot isostatic pressing proved to be a suitable processing method for windows and domes. This method provided alumina ceramics with a real in-line transmission of up to 72 % at a wavelength of 633 nm and with a theoretical in-line transmission in the infrared region between 1500 and 4000 nm for 0.8 mm thick bodies. Complex-shaped bodies, domes, were prepared with minimum warping during sintering. Thin transparent alumina sheets were prepared by gel-tape casting. This novel tape casting method utilized the advantages of the gelcasting method. The real in line transmission of the tapes was lower compared with the windows. Nevertheless, the thin tapes with a thickness below 350 mu m exhibited reasonable transparency even after pressureless sintering and without a polishing of sintered samples.