Kinetics measurement of the phase transformation in Ni2SiO4 under high pressure and temperature (abstract)

Abstract

The kinetics of the pressure-induced phase transformations in minerals are of considerable importance in affecting the dynamics of convection in the Earth. Because of the long exposure time of the high pressure in situ x-ray observations, however, it was very difficult to study the kinetics of such transformations. Combination of the synchrotron radiation and a large-volume high-pressure and high-temperature apparatus made it possible to perform such a study. The kinetics of the olivine-spinel transformation in Ni2SiO4 have been studied at conditions of 3.6–4.8 GPa and 765–980 °C. X-ray diffraction experiments were carried out using the MAX-80 high-pressure, high-temperature cubic-anvil apparatus at the National Laboratory for High Energy Physics, Japan. Synchrotron radiation was supplied by an accumulator ring operating at 6.5 GeV and between 15 and 5 mA. Ni2SiO4 olivine powder was hot pressed in the olivine stability field and then the pressure-temperature conditions were changed to initiate the transformation to spinel. Reaction progress was monitored by collecting x-ray diffraction patterns at intervals of either 30 or 100 s. The extent of transformation was estimated as a function of time and the data were analyzed on the basis of a nucleation and growth model. Pressure and temperature dependence of the transformation rate were determined from the present study.