Transmittance enhancement of AlON transparent ceramic by aqueous gel-casting with phosphoric acid-treated powder

Aluminum oxynitride (AlON) transparent ceramics were prepared through aqueous gel-casting forming technique. To prevent hydrolysis, the homemade AlON powder was treated in 1% phosphoric acid at 70 °C for 30 min. Then the surface-treated AlON powder was dispersed in an aqueous-organic solution to prepare low viscosity slurry with 40 vol% solids loading, which was shaped by gel-casting forming technique. The hydrolysis of AlON powder was prevented effectively and the transmittance of sintered ceramics had been significantly improved by introducing hydrolysis protection of the powder. The sample sintered with the treated powder can reach an ultimate infrared transmittance of 78% with 2 mm thickness. The surface modification of AlON powder with phosphoric acid was confirmed by various techniques such as scanning electron microscopy (SEM), pH, Viscosity, X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR). The related hydrolysis protection mechanism via this available method was discussed.