Diffusion in periclase by combination of analytical formulas and thermodynamic model

E. Dologlou

doi:10.5194/nhess-12-1841-2012

Abstract

Abstract. Analytical formulas for the temperature dependence of elastic constants of MgO combined with a thermodynamic model, which interconnects bulk properties to point defect parameters, can successfully reproduce the self diffusion coefficients of periclase at temperatures representative of the Earth's mantle conditions. Although the calculated diffusion coefficients are estimated from a single measurement and cover a broad range of values (i.e. five orders of magnitude), an almost excellent agreement with the experimental ones is observed. The slight discrepancy at the highest temperature lies at error margins.

Highlights

In a recent paper (Sarkar et al, 2009), the elastic constants and the bulk modulus for ionic solids of cubic structure such as NaCl, KCl, MgO, CaO have been evaluated at different temperatures by means of analytical formulas based on Murnaghan’s equation of state (Murnaghan, 1944) and Tallon’s (Tallon, 1980) models
Various equation of state for the thermal dependence of elastic properties of solids are reported in literature (Anderson, 1995) and experimental data for the variation of these properties with temperature for a large number of materials can be found in Anderson and Isaak’s book (1995)
Where “i” denotes the different process mechanism, ci is a dimensionless constant which can be considered as independent of temperature and pressure, B is the isothermal bulk modulus, is the mean atomic volume per atom. It has various successful applications in many cases such as in alkali and silver halides (Varotsos and Alexopoulos, 1978, 1979, 1986), in alkali halide mixed crystals (Varotsos and Alexopoulos, 1980b; Varotsos, 1980), and in seismic electric signals (SES) emitted prior to large earthquakes (Varotsos and Alexopoulos, 1984a, b; Varotsos et al, 1986) from crystalline materials included in Published by Copernicus Publications on behalf of the European Geosciences Union

Summary

Introduction

In a recent paper (Sarkar et al, 2009), the elastic constants and the bulk modulus for ionic solids of cubic structure such as NaCl, KCl, MgO, CaO have been evaluated at different temperatures by means of analytical formulas based on Murnaghan’s equation of state (Murnaghan, 1944) and Tallon’s (Tallon, 1980) models. Various equation of state for the thermal dependence of elastic properties of solids are reported in literature (Anderson, 1995) and experimental data for the variation of these properties with temperature for a large number of materials can be found in Anderson and Isaak’s book (1995). For a better understanding of the rheological properties of the Earth’s interior and of the kinetic mechanisms of underlying solid-state transport, the diffusion equation of MgO in the prevailing temperature conditions of the lower

The thermodynamical cB model

Dologlou

Data and analysis

Conclusions