Effect of heat treatment of green bodies on the sintering and optical properties of large-size and thick transparent YAG ceramics

Large-size and thick yttrium aluminum garnet (YAG) transparent ceramics with complex shapes were successfully fabricated by solid-state reaction and vacuum sintering using commercial high-purity oxide powders as starting materials. Before sintering in vacuum, green bodies were calcined at different temperatures in a muffle furnace. The effects of heat treatment temperature on the particle size of green bodies as well as the compressive strength, densification, phase transformation and optical transparency of YAG ceramics were examined. After calcination at 1000 degrees C, the compressive strength of the green bodies reached 81.7 MPa. Using this calcinating procedure, large-size and thick YAG transparent ceramic dome (120 mm diameter, 15 mm thickness) was successfully obtained by sintering at 1750 degrees C for 30 h, without any apparent defects including microcracks. The in line optical transmittance of the as-prepared ceramic was 83.1% and 76.8% at wavelengths of 1000 nm and 400 nm, respectively. Such transparent ceramic domes can be used as missile domes or transparent protective covers for submersibles, and detection equipment at full ocean depth (maximum depth of 11,000 m).