Publications

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2018
Pommier, A, Leinenweber KD.  2018.  Electrical cell assembly for reproducible conductivity experiments in the multi-anvil. American Mineralogist. 103:1298-1305.   10.2138/am-2018-6448   AbstractWebsite

Electrical conductivity experiments under pressure and temperature conditions relevant to planetary interiors are a powerful tool to probe the transport properties of Earth and planetary materials as well as to interpret field-based electrical data. To promote repeatability and reproducibility of electrical experiments among multi-anvil facilities that use this technique, we designed and developed an electrical conductivity cell for multi-anvil experiments based on the 14/8 assembly that was developed to allow access to high temperatures. Here we present the details of design and parts developed for this cell that is available via the Consortium for Material Properties Research in Earth Sciences (COMPRES). The electrical cell has been tested up to 10 GPa and about 2000 degrees C on different materials (silicates and metals, both in the solid and liquid state).

Pommier, A, Kohlstedt DL, Hansen LN, Mackwell S, Tasaka M, Heidelbach F, Leinenweber K.  2018.  Transport properties of olivine grain boundaries from electrical conductivity experiments. Contributions to Mineralogy and Petrology. 173   10.1007/s00410-018-1468-z   AbstractWebsite

Grain boundary processes contribute significantly to electronic and ionic transports in materials within Earth's interior. We report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties. We performed electrical conductivity measurements of melt-free polycrystalline olivine (Fo(90)) samples that had been previously deformed at 1200 degrees C and 0.3 GPa to shear strains up to gamma = 7.3. The electrical conductivity and anisotropy were measured at 2.8 GPa over the temperature range 700-1400 degrees C. We observed that (1) the electrical conductivity of samples with a small grain size (3-6 mu m) and strong crystallographic preferred orientation produced by dynamic recrystallization during large-strain shear deformation is a factor of 10 or more larger than that measured on coarse-grained samples, (2) the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size, and (3) conductivity is up to a factor of similar to 4 larger in the direction of shear than normal to the shear plane. Based on these results combined with electrical conductivity data for coarse-grained, polycrystalline olivine and for single crystals, we propose that the electrical conductivity of our fine-grained samples is dominated by grain boundary paths. In addition, the electrical anisotropy results from preferential alignment of higher-conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains.

2015
Pommier, A, Leinenweber K, Tasaka M.  2015.  Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle. Earth and Planetary Science Letters. 425:242-255.   10.1016/j.epsl.2015.05.052   AbstractWebsite

Electrical conductivity measurements were performed during melting experiments of olivine compacts (dry and hydrous Fo(77) and Fo(90)) at 4 and 6 GPa in order to investigate melt transport properties and quantify the effect of partial melting on electrical properties. Experiments were performed in the multi-anvil apparatus and electrical measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Changes in impedance spectra were used to identify the transition from an electrical response controlled by the solid matrix to an electrical response controlled by the melt phase. This transition occurs slightly above the solidus temperature and lasts until T-solidus + 75 degrees C (+/- 25). At higher temperature, a significant increase in conductivity (corresponding to an increase in conductivity values by a factor ranging from similar to 30 to 100) is observed, consistent with the transition from a tube-dominated network to a structure in which melt films and pools become prominent features. This increase in conductivity corresponds to an abrupt jump for all dry samples and to a smoother increase for the hydrous sample. It is followed by a plateau at higher temperature, suggesting that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of partial melting. Electron microprobe analyses on quenched products indicated an increase in Mg# (molar Mg/(Mg + Fe)) of olivine during experiments (similar to 77-93 in the quenched samples with an initial Fo(77) composition and similar to 92-97 in the quenched samples with an initial Fo(90) composition) due to the partitioning of iron to the melt phase. Assuming a respective melt fraction of 0.10 and 0.20 before and after the phase of significant increase in conductivity, in agreement with previous electrical and permeability studies, our results can be reproduced satisfactorily by two-phase electrical models (the Hashin and Shtrikman bounds and the modified brick layer model), and provide a melt conductivity value of 78 (+/- 8) S/m for all Fo(77) samples and 45 (+/- 5) S/m for the Fo(90) sample. Comparison of our results with electromagnetic sounding data of the deep interior of the Moon supports the hypothesis of the presence of interconnected melt at the base of the lunar mantle. Our results underline that electrical conductivity can be used to investigate in situ melt nucleation and migration in the interior of terrestrial planets. (C) 2015 Elsevier B.V. All rights reserved.