Preheated shock experiments in the molten CaAl₂Si₂O₈‐CaFeSi₂O₆‐CaMgSi₂O₆ ternary: A test for linear mixing of liquid volumes at high pressure and temperature

Abstract

(EOS). Ambient pressure density measurements on these and other Fe-bearing silicate liquids indicate that FeO has a partial molar volume that is highly dependent on composition, which leads to large errors in estimates of the densities of Fe-bearing liquids at ambient pressure based on an ideal mixing of any fixed set of end-member liquids. We formulated a series of mixing tests using the EOS determined in this study to examine whether ideal mixing of volumes might nevertheless suffice to describe the ternary system CaAl 2 Si 2 O 8 -CaFeSi 2 O 6 -CaMgSi 2 O 6 at high temperature and pressure. The ideal mixing null hypothesis is rejected; compositional variations in partial molar volume of FeO appear to extend to high pressure. Only densities of Fe-bearing liquid mixtures with oxide mole fraction of FeO less than 0.06 can be adequately approximated using an ideal solution.

Structure and Density of H2O‐Rich Mg2SiO4 Melts at High Pressure From Ab Initio Simulations

“…Using a Vegard‐type mixing model in which the molar V of a silicate melt is given by a linear combination of partial molar V of MgO and FeO oxide components using the ratio from Lange and Carmichael (1987) and appropriate molar weights, we estimate ρ 0 for (Mg 0.71 Fe 0.29 ) 2 SiO 4 melt at 1,800 K (Table S3). While ideal mixing of volumes has proven to be a reliable method of determining ρ 0 of silicate melts (Lange & Carmichael, 1987), there is evidence that the partial molar volume FeO ( ) varies with composition (e.g., Guo et al, 2014; Thomas & Asimow, 2013), with negligible effect on ρ 0 for the melt composition considered here. For consistency with previous work (Jing & Karato, 2008), we use the linear mixing approach.…”

Density of NaAlSi2O6 Melt at High Pressure and Temperature Measured by In-Situ X-ray Microtomography

“…However, the density of jadeite melt, as well as the effect of alkali components on the density of silicate melts at high pressures more generally, is poorly determined, due to experimental difficulties. The high viscosity, high reactivity, and low density of alkali-rich melts hinder the application of some of the most widely used melt density measuring techniques, such as the sink-float [1,[26][27][28][29] and shock-wave [30][31][32] techniques. Until now, the only experimental data on the density of jadeite melt at high pressures were obtained by Sakamaki [33] using the X-ray absorption method [34][35][36][37], in which the density was calculated from the X-ray absorption contrast between the sample and diamond lid using the Beer-Lambert law and the mass absorption coefficients, but his results are not in agreement with a recent first-principles molecular dynamics (FPMD) study on jadeite melt [38].…”