Theoretical and experimental investigation of the precipitation kinetics of B2-phase KCl from the solution under high pressure

Abstract

The kinetics of phase separation under hydrostatic pressure is investigated in the alkali halide system using the diamond anvil cell technique and an image processing system. The precipitation of the high pressure B2-phase from the solution is governed by a nucleation and growth process. The time dependencies of the transition rates, nucleation frequencies and the microstructure of the developing high pressure phase are measured. The in situ measurement of pressure shows a significant time dependence of the pressure in the sample chamber during the transition. Standard theories fail to explain the measured kinetic quantities. For the interpretation of the experimental data we propose a new approach using the determined transformation and nucleation rates for a numerical simulation of the transition. This procedure yields a deeper insight into the basic growth mechanisms. Based on this model a qualitatively good description of the precipitation kinetics in the diamond anvil cell is realized.

Key Words:

• High pressure
• phase transition—kinetics.