Synthesis of yttrium aluminum garnet powder by 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 ~600ºC and began to crystallize into YAG at 800ºC with concurrent formation of a very small amount of an intermediate hexagonal YAlO3 (YAH) phase, which completely transformed to YAG after prolonged heating (≥2 h) or at higher temperatures (≥1000ºC). Well-crystallized, phase-pure YAG powder could be obtained after calcination at 900ºC for 6 h. Attrition milling of the powder for 2 h resulted in an average particle size of 0.55 μm. 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 1400ºC, resulting in a relative density of 95.2% at 1600ºC.