Particle size effects on yttrium aluminum garnet (YAG) phase formation by solid-state reaction

The solid-state reaction of yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) during the heat treatment of Y 2 O 3 and Al 2 O 3 powder mixtures, differing in particle size and size ratio, was quantified using in situ high-temperature x-ray analysis and Rietveld refinement. Y 2 O 3 particle size has the most profound effect on YAG formation. When the Y 2 O 3 particle size was decreased from 5000 to 30 nm (on reaction with 270 nm Al 2 O 3 ), the YAG formation rate increased from 20 to 48 vol% min −1 over the temperature range of 1350–1450 °C. In this case, the final YAG content increased from 75 to 91 vol%. A simple model that includes the reactant particle coordination number, and thus particle size ratio, shows that when the size ratio ( d A / d Y ) is >1 diffusion through the alumina powder is rate controlling whereas when the ratio is