Synthesis of yttrium aluminum garnet powder by a citrate gel method

Abstract

Yttrium aluminum garnet (YAG) powder was synthesized by a citrate gel method using nitrates and citric acid. The citrate gel almost decomposed at similar to600degreesC and began to crystallize into YAG at 800degreesC with concurrent formation of a very small amount of an intermediate hexagonal YAlO3 (YAH) phase, which completely transformed to YAG after prolonged heating (greater than or equal to2 h) or at higher temperatures (greater than or equal to1000degreesC). Well-crystallized, phase-pure YAG powder could be obtained after calcination at 900degreesC for 6 h. Attrition milling of the powder for 2 h resulted in an average particle size of 0.55 mum. However, during the milling process, ZrO2 (652 ppm Zr) was introduced into the powder containing SiO2 (131 ppm Si) as a sintering aid and found to retard densification of YAG. Despite the presence of ZrO2, sintering the powder compacts for 6 h in air exhibited a considerable densification at temperatures above 1400degreesC, resulting in a relative density of 95.2% at 1600degreesC.