Kinetics and mechanism of cluster growth in mixtures of calcia and magnesia

Abstract

The growth of CaO and MgO clusters in dense hot-pressed mixtures of calcia and magnesia was studied. The kinetics observed obeyed a fifth-power law which was expressed in the form CS 5− CS 0 5 = Kt (where CS is the average cluster size at a time t, CS 0 is the average cluster size at zero time and K is a constant); the mechanism proposed for cluster growth was coalescence by atom diffusion along dislocations. Microstructural evidence showing the presence of dislocations was provided, and a dislocation pipe diffusion coefficient of 6.22 × 10 −12m 2s −1 was estimated. Also a dislocation density of 5.2 × 10 6 cm −2 agrees well with the value of 10 7 cm −2 observed for asfired polycrystalline MgO.