Synthesis of yttrium aluminum garnet (YAG) powder by homogeneous precipitation combined with supercritical carbon dioxide or ethanol fluid drying

YAG precursors were synthesized by the urea method in aqueous solution using supercritical carbon dioxide and ethanol fluid drying technique, respectively. The composition of the precursors, the phase formation process and the properties of the calcined powders were investigated by means of XRD, IR, TG/DSC, BET, TEM and SEM. Compared with the classically prepared powders at room temperature in air, the amorphous precursor dried by supercritical CO2 fluid was loosely agglomerated and directly converted to pure YAG at about 900 °C. The resultant YAG powders showed good dispersity with an average crystallite size about 20 nm and specific surface area of 52 m2 g−1. However, the precursor dried by supercritical ethanol fluid was crystalline. Extensive phase segregation occurred during the drying process and resulted in the formation of separate phases such as monoclinic Y(OH)3 and pseudoboehmite. YAM and YAP phases appeared in the calcination process and phase pure were not detected until 1200 °C.