Abstract
It had been experimentally found that the rate constant (K) of the coarsening cubic-law for Y2BaCuO5 (Y211) particles in Ba-Cu-O melts has been classified into two groups for the volume fraction (Vf), under 15% and over 20%, of Y211 particles, in which the drastic reduction of K existed from the low Vf to the high Vf groups. In the present study, coarsening kinetics for the Y211 particles was simulated using a two dimensional phase field model (PFM) that was proposed for the interface movement of Y211 particles to be tracked. The coarsening simulation of Y211 particles as a stoichiometric compound was performed by solving the diffusion equation, in which the deviation of the solute concentration in the solid phase was restricted to be a negligibly small value. The present PFM calculation indicated that this significant reduction of K appeared between 15% and 20% of the area fraction (Af) of Y211. It was implied that the rate constant reduction was caused by the transition of the coarsening mechanism from the mean field model to the communicating neighbor one, which was quantitatively confirmed by the observation of the different shapes of solute concentration contour lines around disappearing particles and the radical shape transformation of the particles size distribution from Af15% to Af20%.
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