EQUATION OF STATE FOR AQUEOUS SILICA SPECIES AT PRESSURES FROM 1 BAR TO 20 KBAR AND TEMPERATURES FROM 25O TO 900°C BASED ON SIMULATED VALUES OF THE DIELECTRIC CONSTANT

Abstract

We have used modified Born theory to extend the Shock-Helgeson-Sverjensky equation of state of aqueous silica to 20 kbar and 900°C. An important requirement of this equation of state is the dielectric constant of the solvent (ε), which has been experimentally measured only to 5 kbar and 550°C. Our extension of the Shock-Helgeson-Sverjensky equation relies, therefore, on molecular dynamics simulations which we have previously shown to reproduce the experimental data at densities between 0.25 and 1.0 g cm-3 and temperatures up to 1000°C (pressure ranging from 0.5 to 20 kbar). A combination of recent solubility measurements and of simulated values of ε provide the basis for a quantitative description of the thermodynamic properties of aqueous silica over most of the range of geologic interest from 1 bar to 20 kbar and 25-900°C.