Aluminum oxynitride (AlON) ceramic is an attractive material to replace magnesium fluoride on next generation missile domes. An original process has been developed to manufacture and sinter transparent AlON ceramic. First AlON was synthesized by carbothermal reduction of aluminum oxide in nitrogen. The process consists in a two step thermal treatment of an homogeneous mixture of fine alumina and carbon powders under nitrogen. The crushed powder was thus nearly full densified by hot pressing at 1700-1750°C. Significant visible and infrared transparency was achieved by an appropriate grain growth annealing at 1940°C for several hours. Yttria-doped AlON powder could also be sintered close to theoretical density under normal pressure. However translucent but not transparent samples could be obtained. This result could be related to the sample microstructure.
"Synthesis And Hot Pressing Of Transparent Aluminum Oxynitride", Proc. SPIE 1112, Window and Dome Technologies and Materials, (11 September 1989); doi: 10.1117/12.960759; https://doi.org/10.1117/12.960759