Oxygen diffusion in three silicate melts along the join diopside-anorthite

Abstract

The self-diffusion of oxygen has been measured for three silicate melts along the join diopsideanorthite. The experiments were done by isotope exchange between an “infinite” reservoir of oxygen gas and spheres of melt. The oxygen self-diffusion coefficients for the three melts are given as: C-1(diopside): D = 1.64 × 10 1 exp(−(63.2 ± 20)( kcal/ mole)/ RT) cm 2/ sec C-2(Di 58An 42): D = 1.35 × 10 −1 exp(−(46.8 ± 9)( kcal/ mole)/ RT) cm 2/ sec C-3(Di 40An 60): D = 1.29 × 10 −2 exp(−(44.2 ± 6)( kcal/ mole)/ RT) cm 2/ sec The self-diffusion coefficients do not agree with the Eyring equation unless mean ionic jump distances (λ) considerably larger than the diameter of oxygen anion are assumed. However, the sense of variation of the actual diffusivities is as the Eyring equation predicts. Consideration of the results of this study and the bulk of previous work shows that oxygen appears to conform to the compensation law for cationic diffusion in silicate melts and glasses. The range of oxygen diffusivities was also found to encompass the field of divalent cation diffusivities in silicate melts. Those results imply that the diffusion of oxygen in silicate melts may involve a contribution from a cation-like diffusion mechanism (discrete O 2− anions) as well as contributions from the diffusion of larger structural units.