Alpha alumina transformation in seeded boehmite gels

The kinetics and surface area changes during the γ to α-Al₂O₃ transformation sequence of an α-Al₂O₃ seeded boehmite sol-gel are compared to an unseeded boehmite sol gel. The seeded gels exhibited increased kinetics, however the activation energy for the γ to α-Al₃O₃ transformation was lowered only 17% indicating the α-Al₂O₃ transformation is growth controlled. Transmission electron microscopy showed that each α-Al₂O₃ seed acts as a multiple nucleation site for the θ to α-Al₂O₃ transformation. The higher surface area of the seeded boehmite results from the prevention of vermicular microstructure development. Thus, by seeding boehmite sol gels with α-Al₂O₃ the growth process during transformation to α-Al₂O₃ is controlled resulting in a fine, uniform microstructure which sinters at significantly lower temperatures.