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.
A new technique of high-temperature thermal-conductivity measurement is described. A CO2 gas laser is used to generate 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. A mathematical expression is derived which enables phase data at several frequencies to be used for the simultaneous determination of thermal diffusivity and mean extinction coefficient. Lattice and radiative thermal conductivities are then calculated. Test results for sintered aluminum oxide at temperatures from 530 to 1924 °K are within the range of error of previously existing data.
Laboratory procedures and equipment have been developed to measure thermal response of rock under a simulated in situ environment of overburden stress, pore fluid pressure, and temperature. Routine tests are conducted up to 250°C, with stress levels to 100 MPa, on basalt, shale, tuff, and sandstone. High-pressure high-temperature use of the transient “needle-probe” heat source technique for the measurement of thermal conductivity is discussed. Considerations in the design of the thermal expansion apparatus, which maximize stability and minimize error, are included. Laboratory procedures used, calibration techniques, and overall accuracy of the testing are reviewed. Thermal conductivity and thermal expansion are measured on equipment calibrated by using fused quartz as a standard. Uncertainty of calibrations caused by some inconsistency in published values for fused quartz is discussed. Methodical specimen preparation, frequent calibrations and computer test control, and data reduction allow accuracy to be maximized and relatively long-term tests to be conducted with a high degree of repeatability. Where possible, results of the tests are compared with previously published values. A suite of data obtained in support of studies on a potential nuclear waste repository in tuff is examined. Comparisons of theoretical thermal conductivities and expansions, derived from the behavior of the mineral constituents of the rock, and the measured responses are made. The advantages of these systems lie in the relative ease by which specimens may be tested at elevated temperatures and pressures, and the repeatability of the results. The accuracies (which are dependent upon calibration accuracies) are well within the range of engineering investigations.
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