Thermal conductivity of Earth materials at high temperatures

TLDR

The authors measured the total thermal conductivity of key Earth materials from 500 K to 1900 K by generating a low‑frequency temperature wave with a CO₂ laser, recording the phase of the transmitted infrared radiation at several frequencies, and using the data to compute thermal diffusivity, extinction coefficient, and lattice, radiative, and total conductivities. They found that radiative conductivity in forsterite‑rich olivines and enstatite increases only modestly with temperature, and the maximum total conductivity at 400 km depth in an olivine mantle is 0.020 cal cm⁻¹ s⁻¹ °C, less than twice the surface value.

Abstract

The total thermal conductivity (lattice plus radiative) of several important earth materials is measured in the temperature range 500°–1900°K. A new technique is used in which a CO2 laser generates a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. Phase data at several frequencies yield the simultaneous determination of the thermal diffusivity and the mean extinction coefficient of the material. The lattice, radiative, and total thermal conductivities are then calculated. Results for single-crystal and polycrystalline forsterite-rich olivines and an enstatite indicate that, even in relatively pure large-grained material, the radiative conductivity does not increase rapidly with temperature. The predicted maximum total thermal conductivity at a depth of 400 km in an olivine mantle is 0.020 cal/cm sec °C, which is less than twice the surface value.