Article ID Journal Published Year Pages File Type
4742230 Physics of the Earth and Planetary Interiors 2009 9 Pages PDF
Abstract

Trivalent cations in periclase are attracted to cation vacancies and these defects tend to associate on adjacent sites to form mobile pairs. A theory has been developed to describe the concentration-dependent diffusion of Al in the presence of Al-vacancy pairs, and has been applied to experiments conducted at 1577–2273 K and 1 atm to 25 GPa. In all but one experiment, the Gibbs free energy of binding, inferred from the diffusion profiles, is between −44 and −60 kJ/mol, with an average value of −50 kJ/mol. The absolute value of the entropy of binding is constrained to be less than 50 J mol−1 K−1, and the volume of binding is constrained to be between −1.8 and 0 cm3/mol. The diffusion coefficient of the Al-vacancy pair can be described by the equation D2 = D2,0 exp(−(E + PV)/RT), with E = 213 ± 32 kJ/mol, V = 3.22 ± 0.25 cm3/mol, and log10D2,0 = −6.17 ± 0.99 (in m2/s; all uncertainties 2σ). Calculations are presented for the diffusion of Al and Mg as functions of Al concentration, temperature and pressure.

Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Geophysics
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