Highly Transparent AlON Pressurelessly Sintered from Powder Synthesized by a Novel Carbothermal Nitridation Method

Transparent AlON was pressurelessly sintered from powders synthesized by a two‐step carbothermal nitridation method, using core‐shell structured Al 2 O 3 / C mixture derived from the pyrolysis of an Al 2 O 3 /ureaformaldehyde‐resin nanocomposite precursor as the starting material. It was found that the amorphous carbon layer on the Al 2 O 3 particle surface could strongly retard the coalescence and growth of Al 2 O 3 particles during the carbothermal nitridation process. As a result, the formation temperature and particle size of the AlON powder were significantly reduced. The AlON powder synthesized showed a bimodal particle size distribution at 0.2 and 0.7 μm and was well dispersed; its maximum particle size was below 0.9 μm. Under the aid of proper sintering additive, transparent AlON ceramics with an average in‐line transmittance above 80% at visible to infrared range were obtained through pressureless sintering.