SOL-GEL PROCESSING AND SINTERING OF YTTRIUM-ALUMINUM-GARNET (YAG) POWDERS

Gels of yttrium aluminum garnet (YAG) with the stoichiometric composit ion 3Y(2)O(3) . 5Al(2)O(3), were prepared by a sol-gel technique and d ried by supercritical extraction with CO2. Powders were produced by li ghtly grinding the dried gels. Crystallization of the powder occurred at approximate to 900 degrees C and within the limits of detection, th e X-ray diffraction pattern of the crystallized material was identical to that of the stoichiometric composition. Powder compacts with a gre en density of approximate to 0.50 of the theoretical were sintered to nearly full density in O-2 during constant heating rate sintering at 5 degrees C min(-1) to 1600 degrees C. This is better than the density obtained with powders from a similar gel dried conventionally (by evap oration of the liquid) and considerably better than that obtained with powders prepared by solid state reaction. The room temperature flexur al strength and fracture toughness of the material fabricated from the supercritically dried gels were 190 MPa and 2.2 MPa.m(1/2), respectiv ely. These strength and fracture toughness values are higher than thos e reported in other studies for YAG produced by the sintering route.