JOURNAL OF RESEARCH of the National Bureau of Standards -A. Physics and Chemistry Thermal Conductivity, Electrical Resistivity, and Thermopower of Aerospace Alloys from 4 to 300 K* J. G. Hust, ** D. H. Weitzel,** and R. L. Powell** Institute for Basic Standards, National Bureau of Standards, Boulder, Colorado 80302 (March 10, 1971) Thermal conductivity, electrical resistivity, and thermopower have been measured for several aerospace alloys: titanium alloy A110-AT, aluminum alloy 7039, Inconel 718, and Hastelloy X. Tables and graphs of the measured properties and Lorenz ratio are presented over the range 4 to 300 K. Comparisons to other measurements and theoretical analysis of the data are included. The uncertainties of the property data are estimated as (1) 0.7 to 2.5 percent for thermal conductivity, (2) 0.25 percent in electrical resistivity, and (3) about 0.1μ V/K in thermopower. Key words: Aluminum alloy; cryogenics; electrical resistivity; Lorenz ratio; nickel alloys; Seebeck 1. Introduction The development of new structural materials and renewed interest in existing materials by the aerospace industry is creating a demand for thermal and electrical property measurements on these materials. Such data are needed for the selection of suitable construction materials and the prediction of operating characteristics of low temperature systems. To help satisfy the immediate needs for these data, an apparatus has been built to measure the thermal conductivity, electrical resistivity, and thermopower of solids. This apparatus is designed to measure samples with thermal conductivities varying from 0.1 to 5,000 W m-1 K-1 at temperatures from 4 to 300 K. Thermal conductivity data of technically important solids accurate to 5 percent satisfy current demands. However, future demands will likely be more stringent. For this reason this program is directed toward the acquisition of thermal conductivity data accurate to within 1 percent; this is difficult to do especially for poor conductors and temperatures above about 120 K, because of the difficulty of maintaining thermal losses at a sufficiently low level. This paper contains results of measurements on titanium A-110 AT, Iconel 718, Hastelloy X, and aluminum 7039. 2. Apparatus The present apparatus is similar to that described by Powell, et al. [1].2 A detailed description of the present *This work was carried out at the National Bureau of Standards under the sponsorship of the NASA (SNPO-C) Contract R-45. **Cryogenics Division, National Bureau of Standards. Boulder, Colorado 80302. The use in this paper of trade names of specific products is essential to a proper understanding of the work presented. Their use in no way implies any approval, endorsement, or recommendation by NBS. (See reference [8]). * Figures in brackets indicate the literature references at the end of this paper. The apparatus used is based on the axial one-dimensional heat flow method. The specimen is a cylindrical rod with a heater at one end and temperature controlled heat sink at the other. The heat sink is controlled to any temperature from 4 to 300 K by means of several cryogenic baths and an automatic electronic temperature controller. The temperature distribution along the specimen is measured with respect to a constant temperature reference block with eight Chromel [8] versus Au-Fe (Au-0.07 at. % Fe) thermocouples. The reference block temperature is determined with a platinum resistance thermometer at temperatures above 10 K and from the vapor pressure of liquid helium near 4 K. The thermocouple calibrations are based on standard reference tables by Sparks, et al. (NBS Monograph-in review) and small corrections to these tables based on spool calibrations at 4 K, 20 K, 78 K, and 273 K and in-place calibrations from 4 to 30 K. The platinum resistance thermometer was calibrated by NBS, Washington. Details of these calibrations are given by Hust et al. [2]. The sample assembly is surrounded by a cylindrical temperaturecontrolled shield to reduce heat losses by conduction and radiation. To further reduce losses by radiation, the space between the shield and the specimen is filled with high-density glass fibers. The entire sampleshield assembly is enclosed in a container and evacuated to less than 10-5 torr (1.3 x 10-3 N/m2). 3. Specimen Preparation and Measurement Techniques The specimens are machined and ground to specified nominal dimensions, after which they are accurately measured in a temperature-controlled measurement lab. Without further undue mechanical or thermal abuse, each specimen is fitted with thermocouple holders and heater. The specimen assembly is installed in the cryostat, the space between the shell and specimen is packed with glass fiber, and the vecuum can is soldered into place. The cryostat is evacuated to better than 10-5 torr and is subsequently cooled with the desired cryogenic liquid. The specimen is brought into equilibrium with the bath temperature and the emf of each thermocouple at zero temperature gradient is read. These zero corrections, caused by various inhomogenities in the circuit, are considered to be constant for all runs with each cryogenic bath. Data on a given run are taken only after thermal steady state has been established with a vacuum of better than 10-5 torr. Thermal steady state is considered established after systematic drift of the indicated thermocouple temperatures are below the detection or control limit of approximately 1 millidegree per hour. Isothermal electrical resistivity data are taken at the same time that the zero emfs are recorded. Also, to obtain further isothermal resistivity data and information regarding the differences between the eight measuring thermocouples, data are taken with the floating sink above the temperature of the surrounding bath but with no heat input to the specimen. The thermocouples thus indicate the temperature difference from the specimen to the reference block. If the specimen is in equilibrium with the floating sink, then all eight thermocouples should produce the same emf. The scatter in these recorded emfs is an indication of the validity of using a single calibration table for all eight thermocouples. No significant deviations between thermocouples have been detected by this procedure. significant figures retained in these parameters is dictated by the number of terms in eqs (1), (2), and (3), and only indirectly by the accuracy of the data. Values of thermal conductivity, electrical resistivity, absolute thermopower, and Lorenz ratio as computed from eqs (1), (2), and (3) are tabulated in tables 6 through 9 and illustrated in figures 2 through 7. The raw experimental data have been tabulated in an informal report for future reference. A detailed error analysis for these measurements has been presented previously by Hust et al. [2]. Based on this analysis of systematic and random |