Molecular dynamics investigation of viscosity, chemical diffusivities and partial molar volumes of liquids along the MgO-SiO2 join as functions of pressure

摘要

Molecular dynamics simulations are carried out to systematically address the effects of composition and pressure on melts, along the MgO-SiO2 join and elucidate the role of structural modifier content on silicate melt properties. The MgO-SiO2 System shows non-ideal mixing with a negative excess volume of mixing at low pressures, but the mixing becomes closer to ideal at higher pressures. At atmospheric pressure, the viscosities and diffusivities vary by more than 3 orders of magnitude as the composition is varied along this join, with the low SiO2 melts characterized by lower viscosities and higher diffusivities these results are in quantitative agreement with experimental results for the dependence of viscosity and diffusivity on structural modifier content in a wide range of silicate systems. The transport properties of melts in this system converge at higher pressures; at pressures greater than similar to 15 GPa the viscosity and diffusivities vary by less than an order of magnitude across the entire range of compositions. The relevance of equations that relate the viscosity and diffusivity is also addressed. (c) 2006 Elsevier Inc. All rights reserved.