Kinetic studies of the crystallisation of coesite using synchrotron radiation

Abstract

For energy-dispersive X-ray powder diffraction under high pressure and high temperature a multi-anvil-X-ray apparatus (MAX 80) has been installed at HASYLAB. This instrument allows to measure diffraction data at very short intervals and thus study time dependent phenomena. As an example we have investigated the kinetics of the α-quartz-coesite phase transformation. The kinetics was determined by in situ experiments between temperatures of 870 and 1170 K and in a pressure range of 30–50 kbar. The structural changes were directly imaged using synchrotron radiation. The experimental results yield the rate constant Kc for the growth of coesite from quartz as a starting material under dry conditions. For the transition three Kc values from 6.0 × 104to 2.2 × 104 s−1 for different p/t-ranges were determined.