Analysis of Recrystallization of Fine-Crystalline Corundum in a Supercritical Water Medium Using the Lognormal Particle Size Distribution Function

Abstract

The mechanism of synthesis of fine-crystalline corundum from aluminum hydroxide under induced nucleation conditions in a supercritical water fluid at 400°C and initial pressure of 26.4 MPa followed by exposure in the synthesis medium was studied. The crystal size distribution was analyzed by electron microscopy. The use of the lognormal function to describe the crystal size distribution of the synthesized corundum particles was substantiated. The possibility of using the lognormal particle size distribution function and the time dependence of its parameters to reveal the routes of product formation was analyzed. The dimensional spectrum of microcrystals has four components, whose appearance is associated with different routes of product formation. The number of distribution components remains unchanged during prolonged exposure, but their average characteristics have different time dependences. The mass redistribution during recrystallization, generally leading to a decrease in the average crystal size, is explained by differences in the crystal structure mobility of different components. It was concluded that the states of corundum in the newly formed crystals and in the overgrown layer on the particles of the inducing additive are different.