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 posthot isostatic pressing proved to be a suitable processing method for windows and domes. This method provided alumina ceramics with a real inline 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 could be 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 mm exhibited reasonable transparency even after pressureless sintering and without a polishing of sintered samples.