Abstract
The decomposition isotherms of Al2TiO5 powders with the narrower grain size distribution were sigmoidal at temperatures between 1000° and 1200°C. The shape of the isotherm was found to vary with temperature and grain size. Kinetic equations of decomposition were newly derived in this work, using parameters of a nucleation constant in one grain, k and a growth rate constant, G=1/τ (τ means an average of time in which the decomposion initiates and then completes on a grain), for the accelerating period (t≤τ), α=1/kτ{kt-(1-e-kt)} and for the decelerating period (t≥τ), ln (1-α)=ln{1/kτ(ekτ-1)}-kt, where α is the fraction decomposed with the decomposition time, t. These two equations were confirmed to fit well over a wide range with the data measured in the present work.
An Arrhenius plot of the two parameters calculated from the equations gave a curve for k with a maximum at about 1100°C and a straight line for G. From the slopes on k and G vs. 1/T, the activation energies for the decomposition were about 150 kcal/mol for the nucleation at lower temperature region and 57 kcal/mol for the growth of nucleus.
