Constraints on oxygen fugacity within metal capsules
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Author(s)
Berry, Andrew
Jackson, Ian
Garapić, Gordana
Cline II, Christopher J.
Faul, Ulrich
Date Issued
December 2017
Journal
Physics and Chemistry of Minerals
Publisher
Springer Berlin Heidelberg
Citation
Faul, Ulrich H., et al. “Constraints on Oxygen Fugacity within Metal Capsules.” Physics and Chemistry of Minerals, vol. 45, no. 6, June 2018, pp. 497–509.
Version
Author's final manuscript
Abstract
Experiments were conducted with olivine encapsulated or wrapped in five different metals (Pt, Ni, Ni[subscript 70]Fe[subscript 30], Fe, and Re) to determine the oxygen fugacity in the interior of large capsules used for deformation and seismic property experiments. Temperature (1200°C ), pressure (300 MPa), and duration (24 h) were chosen to represent the most common conditions in these experiments. The oxygen fugacity was determined by analysing the Fe content of initially pure Pt particles that were mixed with the olivine powder prior to the experiments. Oxygen fugacities in the more oxidizing metal containers are substantially below their respective metal-oxide buffers, with the fO[subscript 2] of sol–gel olivine in Ni about 2.5 orders of magnitude below Ni–NiO. Analysis of olivine and metal blebs reveals three different length-, and hence diffusive time scales: (1) Fe loss to the capsule over ∼ 100 μm, (2) fO[subscript 2] gradients at the sample–capsule interface up to 2 mm into the sample, and (3) constant interior fO[subscript 2] values with an ordering corresponding to the capsule material. The inferred diffusive processes are: Fe diffusion in olivine with a diffusivity ∼10[superscript −14]m[superscript 2]/s, diffusion possibly of oxygen along grain boundaries with a diffusivity ∼10[superscript −12]m[superscript 2]/s , and diffusion possibly involving pre-existing defects with a diffusivity ∼10[superscript −10]m[superscript 2]/s. The latter, fast adjustment to changing fO[subscript 2] may consist of a rearrangement of pre-existing defects, representing a metastable equilibrium, analogous to decoration of pre-existing defects by hydrogen. Full adjustment to the external fO[subscript 2] requires atomic diffusion. Keywords: Oxygen fugacity, Olivine defects, Diffusion, Upper mantle
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
https://doi.org/10.1007/s00269-017-0937-7
