Publications

Export 2 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C D E F G H I J K L M N O P Q R S [T] U V W X Y Z   [Show ALL]
T
Pommier, A, Gaillard F, Pichavant M.  2010.  Time-dependent changes of the electrical conductivity of basaltic melts with redox state. Geochimica Et Cosmochimica Acta. 74:1653-1671.   10.1016/J.Gca.2009.12.005   AbstractWebsite

The electrical conductivity of basaltic melts has been measured in real-time after fO(2) step-changes in order to investigate redox kinetics. Experimental investigations were performed at 1 atm in a vertical furnace between 1200 and 1400 degrees C using air, pure CO2 or CO/CO2 gas mixtures to buffer oxygen fugacity in the range 10(-8) to 0.2 bars. Ferric/ferrous ratios were determined by wet chemical titrations. A small but detectable effect of fO(2) on the electrical conductivity is observed. The more reduced the melt, the higher the conductivity. A modified Arrhenian equation accounts for both T and fO(2) effects on the electrical conductivity. We show that time-dependent changes in electrical conductivity following fO(2) step-changes monitor the rate of Fe2+/Fe3+ changes. The conductivity change with time corresponds to a diffusion-limited process in the case of reduction in CO-CO2 gas mixtures and oxidation in air. However, a reaction at the gas-melt interface probably rate limits oxidation of the melt under pure CO2. Reduction and oxidation rates are similar and both increase with temperature. Those rates range from 10(-9) to 10(-8) m(2)/s for the temperature interval 1200-1400 degrees C and show activation energy of about 200 kJ/mol. The redox mechanism that best explains our results involves a cooperative motion of cations and oxygen, allowing such fast oxidation-reduction rates. (c) 2009 Elsevier Ltd. All rights reserved.

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.