Acquisition of a Laser-Flash Apparatus for Measurement of Thermal Diffusivity to 2000C

Washington University, Saint Louis MO

Investigators

Abstract

0132275 Hofmeister Heat transport pertains to problems on all scales in Earth science, e.g., laboratory experiments, crystallization and texture of igneous rocks, ductile faulting, mantle plumes, Earth's convection patterns, and planetary formation and evolution. Understanding such processes requires knowledge of either the thermal diffusivity (D) or the thermal conductivity (k = DrCV ). The physical property k describes the rate at which heat flows from the hot to the cold end of a rigid material, and thus pertains to conductive processes. When the material flows as well (convective processes), D applies. Because density (r) and heat capacity (CV) at temperature are well-constrained or readily predicted, measurements of D provide the data needed to understand heat transport. However, the temperature dependence of D is generally unknown for geological and planetary materials and the available data are inconsistent. Disparities exist in the previous methods because heat is transported as light over the short scales of the experiments in a manner that is specific to a given experiment. The results are thus not a material property. This complex situation exists because planetary materials are transparent at some wavelengths of light (and light is heat). Technological advances in materials science have led to a device which overcomes this problem. Funds from this grant will support acquisition of such a laser-flash apparatus to measure thermal diffusivity (D) from room temperature to 2000oC. No comparable instrument exists in Earth Science research facilities in the U.S. The apparatus not only doubles the 1000oC range typical for the scant existing data, most of which are 30 years old, but is easy and rapid to use, and provides D(T) on melts. The data generated by the laser flash apparatus provide the needed tests for the T dependence for phenomenological models for k. Combining theory and experiment not only allows extrapolation of measured D and k to all conditions of interest to Earth science, but will further our understanding of the microscopic basis of transport properties. ***