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Published July 15, 1968 | Published
Journal Article Open

Thermal diffusivity of Mg_2SiO_4, Fe_2SiO_4, and NaCl at high pressures and temperatures

Abstract

The pressure and temperature variations of thermal diffusivity of poly crystalline Mg_2SiO_4 have been measured for the range 24 to 50 kb and 400° to 1300°K. Effect of the olivine‐spinel phase transition on thermal diffusivity of Fe_2SiO_4 was studied at 48.5 kb for the temperature range 350° to 650°K. Synthetic samples with grain size 1 to 5 microns were used. For the pressure range studied, the reciprocal of thermal diffusivity 1/κ of Mg_2SiO_4 increases almost linearly with temperature up to about 1200°K, as expected from the theory of phonon conduction, but is nearly constant above that temperature. The 1/κ versus temperature curve of Fe_2SiO_4 (olivine) is nearly straight up to 700°K, where it becomes slightly convex. The thermal diffusivity of NaCl is measured under similar conditions for comparison with Bridgman's data. The agreement is reasonably good. The pressure derivative ∂κ/∂P, at P = 40 kb is 1.8 × 10^)−4) cm^2/sec kb (at 700°K) and 0.8 × 10^(−4) cm^2/sec kb (at 1100°K) for Mg_2SiO_4, and 4.7 × 10^(−4) cm^2/sec kb (at 700°K) for NaCl. This pressure dependence can be explained by the theory of phonon conduction. The thermal diffusivity of Fe_2SiO_4 (spinel) is about 1.5 times that of Fe_2SiO_4 (olivine) over the range 350° to 650°K. The effect of radiative heat transfer in Mg_2SiO_4 is discussed. The photon mean free path is estimated to be 0.3 mm at 1400°K.

Additional Information

© 1968 American Geophysical Union. (Received March 25, 1968.) A part of the present study was performed with the aid of the tetrahedral press of the Government Industrial Research Institute, Nagoya. We would like to thank the members of the high-pressure laboratory of the institute for their courtesy.

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Created:
August 24, 2023
Modified:
October 19, 2023