Thermophysical Properties of Germanium for Thermal Analysis of Growth From the Melt
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THERMOPHYSICAL PROPERTIES OF GERMANIUM FOR THERMAL ANALYSIS OF GROWTH FROM THE MELT
ROGER K. CROUCH, A. L. FRIPP, W. J. DEBNAM NASA Langley Research Center, Hampton, Virginia USA R. E. TAYLOR AND H. GROOT Thermophysical Properties Research Laboratories, Purdue University, Indiana, USA
Lafayette,
ABSTRACT The thermal diffusivity of Ge has been measured over a temperature range from 3000 C to 10100 C which includes Specific heat has been measured from values for the melt. room temperature to 7270 C. Thermal conductivity has been calculated over the same temperature range as the difThese data are reported along with fusivity measurements. the best values from the literature for the other parameters which are required to calculate the temperature and convective fields for the growth of germanium by the Bridgman method. These parameters include the specific heat, the viscosity, the emissivity, and the density as a function of temperature.
INTRODUCTION In order to do a successful experiment in the space environment, it is important to be able to make theoretical predictions as to the thermal environment in the furnace as well as the distribution of temperatures in the material One of the materials of interest to the Materials which is being studied. While this is a fairly well behaved Processing in Space Program is germanium. and understood material, a search of the literature for temperature dependent values of properties which are required in order to do a thermal analysis revealed that some values are either not available or are in conflict, To resolve this conflict, especially in the vicinity of melting point (9370 C). a program was undertaken by Langley Research Center and the Thermophysical Properties Research Laboratory (TPRL) of Purdue University to measure some of the properties of germanium and to choose the best values from the literature for the remaining properties which are required to solve the heat, momentum This paper reports the results of measurements and mass conservation equations. of the thermal diffusivity over a temperature range from 3000 C to 10100 C and measurements of the specific heat over a temperature range from room temperature Thermal conductivities have been calculated from these measurements to 7270 C. In addition to this information, values from the literaand are also reported. ture have been compiled as a function of temperature for the specific heat, the viscosity, the emissivity and the density for the solid and liquid phases. MEASUREMENTS AND RESULTS Thermal diffusivity Thermal diffusivity (a) was determined using the laser flash diffusivity The flash method, in which the front face of a small disc-shaped sample method. is subjected to a short laser burst and the resulting rear face temperature rise In order to avoid the is recorded, was used for these measurements.[l]
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TABLE I Thermophysical properties of germanium Temp.
(oC)
Density* 3 (gm/cm )
5.35 200 300 5.34 5.33 400 5.32 500 5.31 600 5.30 700 5.29 800 5.28 900 5.28 915 5.28 920 5.28 925 5.28 930 5.28 935 5.
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