Abstract
The kinetics of the θ → α A12O3 transformation were studied in the range 1080 to 1180 °C. Conversion was determined using quantitative X-ray diffraction analysis on quenched samples. Also, the particles were studied by transmission electron microscopy. The theta alumina was prepared by calcination of an electrochemically precipitated hydrate. The transformation-kinetic data were successfully treated by a two-stage, diffusional/synchro-shear model, according to which the rate is controlled by slow diffusional crystallite size increase, or crystallite perfection, of the theta phase to a critical degree, followed by rapid martensitic type transformation to alpha. Good agreement between model and experiment is indicated when a Gaussian distribution of theta crystallite size is assumed.
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