Recent Structure and Physical Properties Studies of Silicate Melts in a Large Volume Press Utilizing Synchrotron X-ray at GSECARS

Physical properties and the molecular structure of silicate melts under high pressure and high temperature are crucial in understanding the dynamic processes and evolution of the Earth's interior. Due to the difficulties in carrying out experiments with liquid samples, glasses or so-called supercooled liquids have often been used as analogs for silicate melts. However, recent studies show that the glass structure strongly depends on its thermal history(Wilding et al., 2008) and cannot represent the real liquid structure. Furthermore, Xu et al. (2018) showed that sound velocities measured for silicate liquids and glasses are significantly different, demonstrating that silicate glasses cannot serve as a proper analog for its liquid counterpart. It is therefore important to be able to directly measure physical properties and structure of silicate liquids. Here we present cases of recent in-situ high pressure high temperature synchrotron X-ray experimental results on silicate melts up to about 5 GPa and 2000 K including (1) Liquid density measurement of jadeite (NaAlSi2O6) melts using the "pink beam" high pressure X-ray tomography setup. (2) Sound velocity measurement of diopside (MgCaSi2O6) melts in the Walker-type T25 module. (3) Structure measurement of sodium silicate (Na2O·nSiO2; n=1,2) melts by X-ray total scattering and pair distribution function in our VX5 Paris-Edinburgh press + Soller slits setup. (4) Local molecular structure measurement of wollastonite (CaCaSi2O6), diopside (MgCaSi2O6), and enstatite (MgMgSi2O6) glasses using both X-ray diffraction in a Paris-Edinburgh press and Raman spectroscopy in a diamond anvil cell. These studies provide us with fresh new insights into both physical properties and molecular structures of silicate melts under extreme conditions to help us better understand their roles in Earth's interior. They also serve as the main driving force in large volume techniques developed for high-pressure liquid studies at GSECARS beamlines.