A dynamic technique for measurements of thermophysical properties at high temperatures

A technique is described for the dynamic measurement of selected thermophysical properties of electrically conducting solids in the range 1500 K to the melting temperature of the specimen. The technique is based on rapid resistive selfheating of the specimen from room temperature to any desired high temperature in less than 1 s by the passage of an electrical current pulse through it and on measuring the pertinent quantities, such as current, voltage, and temperature, with millisecond resolution. The technique was applied to the measurement of heat capacity, electrical resistivity, hemispherical total emissivity, normal spectral emissivity, thermal expansion, temperature and energy of solid-solid phase transformations, melting temperature, and heat of fusion. Two possible options for the extension of the technique to measurements above the melting temperature of the specimen are briefly discussed. These options are: (1) submillisecond heating of the specimen and performance of the measurements with microsecond resolution, and (2) performance of the experiments in a near-zero-gravity environment with millisecond resolution.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Measurement of high temperature phase stability and thermophysical properties of alloy 740

In the present study, the characterisation of phase stability and measurement of different thermophysical properties of alloy 740 has been carried out. The transformation temperatures including liquidus/solidus and corresponding enthalpy of transformation have been measured for different phase changes up to melting using dynamic calorimetry. Further, the enthalpy increment data have been measured in the temperature range of 473–1473?K to obtain the heat capacity using static calorimetry. The present calorimetric data have been analysed in corroboration with the results obtained using JMatPro and Thermo-Calc simulation. In addition, the temperature dependence of other thermophysical properties such as thermal expansivity, density, thermal diffusivity and thermal conductivity are also measured in the range of 300–1473?K using thermomechanical analyser and laser flash method.     

Fast transient thermophysical measurements at Livermore

The development of the Isobaric Expansion Experiment at Lawrence Livermore National Laboratory is described. Rod samples are self-heated by current from a capacitor bank while current and sample voltage, sample cross section, and temperature are measured continuously as functions of time. The system allows nearly complete thermodynamic characterization of a material along an isobar in a single shot. The pressure of the isobar is determined by containing the sample in argon gas at a predetermined ambient pressure. Correlation of the measured quantities allows elimination of time as a common parameter. Quantities corresponding to a given time are taken to refer to a single equilibrium state. Temperature stagnation and volume and resistivity changes during phase transitions may be seen and allow the heat of transformation and the slope of the phase line in theP, T plane to be determined. Other derived quantities are specific heatc _p, volume-corrected electrical resistivity, and bulk thermal expansion coefficient. A special advantage of the technique is that all quantities are measured on the same sample in a single experiment. The short time duration of the measurements allows access to a temperature range beyond that available to slower methods.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

A dynamic technique for thermophysical measurements at high temperatures in a microgravity environment

Millisecond-resolution dynamic techniques for thermophysical measurements, when utilized in the laboratory, are limited to the study of materials in their solid phase because the specimen becomes geometrically unstable during melting and collapses, due (at least in part) to the influence of gravity. Therefore, a millisecond-resolution dynamic technique is being developed for use in a microgravity environment in order to extend accurate measurements of selected thermophysical properties of electrically conducting refractory materials to temperatures above their melting point. The basic method involves heating the specimen resistively from ambient temperature to temperatures above its melting point in about 1 s by passing an electrical current pulse through it, while simultaneously recording the pertinent experimental quantities. A compact pulse-heating system, suitable for microgravity simulations with NASA's KC-135 aircraft, has been constructed and initial experiments have been performed to study the geometrical stability of rapidly melting specimens. Preliminary results show that rod-shaped specimens can be successfully pulseheated into their liquid phase.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.Formerly National Bureau of Standards     

Determination of thermophysical properties of solids at high temperatures by measuring phase characteristics of a plane temperature wave at two frequencies

The authors propose and substantiate a procedure to determine thermal diffusivity and the ratio of integral emissive power to thermal conductivity of solids by measuring the phase delay of a plane temperature wave at two frequencies. The method is applicable for a wide range of heat loss parameters and does not need calorimetric measurements. Errors are calculated and the domains of applicability of the given procedure are pointed out.Academic Scientific Complex A. V. Lykov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 430–435, October, 1992.     

Microsecond-resolution measurements of the thermophysical properties of liquid gold

New experimental results obtained using an accurate technique for electrical and optical measurements on pulse-heated gold samples are given. An almost-constant current pulse is used for resistive self-heating of the sample over a time interval of 50 s. Because of the high heating rate, the sample maintains its cylindrical shape in the liquid phase. High pressures are used to extend the investigated range of the liquid phase by suppressing boiling. The stability of the liquid sample is demonstrated by short-time photographs, obtained with a kerrcell camera. Measurements of current through the sample, voltage drop across the sample, surface radiation, and volume expansion allow the determination of the selected thermophysical properties. Specific enthalpy, electrical resistivity, temperature, density, and their mutual dependencies are obtained. In addition, the enthalpy of melting, as well as the specific heat capacity at constant pressure, is determined.     

Combined short-time measurements of the thermophysical properties of organic liquids

A short-time heated-wire method is used to measure the thermal conductivity, thermal diffusivity, and thermal activity of organic liquids.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 2, pp. 289–295, August, 1991.     

Fe-Cr合金钢高温性能研究

本文试验研制了四种Fe-Cr合金材料,其在900 ℃时的热膨胀率在10～11×10-3范围内,其中FeCr-4合金的热膨胀率为10.27×10-3,与钇稳定氧化锆(YSZ)相比,热膨胀率逐渐接近;与传统合金材料相比,热膨胀率之差均有了明显下降,因而降低了界面热应力,有效改善层间的热失配现象.随着温度的升高,各合金试样的电阻率呈平缓增大的趋势.在850℃时,四种合金试样的电阻率在0.95～1.17×10-3 Ω·cm范围内,其中Fe-Cr-4试样的电阻率较低,为1.17×10-3 Ω·cm,满足用作SOFC连接体材料导电性能的要求.Fe-Cr -1、4两种合金试样的抗氧化性能较好,随着氧化时间的延长,试样表面形成稳定的3Cr2 O3 Fe2 O3氧化层,氧化增重逐渐趋于稳定.累计氧化455 h后,Fe-Cr-1、4两种试样对应的氧化增重在0.0002 g/g左右;而Fe-Cr-2、3两种试样仍在0.0004 g/g以上.     

Some ways of measuring thermophysical properties by temperature wave methods

The possibility is considered of using two-dimensional temperature waves for determining the thermal diffusivity and thermal conductivity of solid and free flowing bodies from a single experiment without introducing heat sinks into the sample. Conditions are found for the reliable achievement of the boundary conditions.     

A submicrosecond pulse heating system for the investigation of thermophysical properties of metals at high temperatures

A submicrosecond ohmic pulse heating technique is described for measurements of thermal properties of cylindrical metallic samples at high temperatures. Electrical and optical measurements for determination of thermophysical data such as enthalpy, specific heat, and electrical resistivity are presented. Effects that can falsify the results are discussed.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Top loading cryogen-free apparatus for low temperature thermophysical properties measurement

The thermophysical properties of matter, especially properties at low temperature, are extremely important for engineering and materials science. Traditional liquid helium based cryostats are in many cases no longer affordable to operate due to the high liquid helium cost. This paper describes the design and test results of a cryogen-free cryostat, based on a GM cryocooler, with 50 mm diameter top loading sample facilities for thermophysical properties measurement at low temperature. The sample temperature range is tuned between 2.6 K and 300 K and it can be continuously controlled with a high resolution. Moreover, the modular sample holder can be adapted to multiple properties measurement.     

A study on the high temperature reaction of niobium pentoxide with niobium carbide and titanium carbide

The high temperature reaction of niobium pentoxide with niobium carbide and titanium carbide has been studied to investigate the feasibility of direct preparation of NbTi alloys and the titanium deoxidation tendency of niobium. Starting with oxide-carbide charges with o:c mole ratio varying from 1.01 to 1.10 and titanium content varying from 4 to 56 wt. pct., the reaction was carried out at 1900°C under high vacuum in a vacuum induction furnace followed by treatment in the electron beam melting furnace to obtain the final alloys. The material balance of the charge indicates that substantial amount of oxygen is removed as TiO(g) besides as CO during the reaction. This results in low titanium and oxygen contents and high residual carbon content in the alloy, particularly when the initial titanium content in the charge exceeds 4 wt. pct. The results obtained in the present investigation have been explained from the available/estimated thermodynamic data for the NbTiCO system.     

Recent development and applications of an optical method for measurements of thermophysical properties

The experimental determination of thermophysical properties has been greatly improved by the introduction of laser technology. The laser beam is used for sensing and also for heating (or exciting) the specimen. The advantage of using a laser beam is most strongly felt in the measurement of the thermal conductivity or the thermal diffusivity, which are some of the most difficult properties to measure. Interesting features of new techniques for investigating various aspects of thermal conductivity in fluids and solids are reviewed. An optical method, the so-called forced Rayleigh scattering method, or the laser-induced optical-grating method, has been developed and used extensively by the present author's group. The method is a high-speed remote-sensing method which can also quantitatively detect anisotropy, namely, direction dependence of heat conduction in the material. It was used for determination of the thermal diffusivity and its anisotropic behavior for high-temperature materials such as molten salts, liquid crystals, extended polymer samples, and flowing polymer melts under shear. Interesting applications of the method were demonstrated also for thermal diffusivity mapping and microscale measurement.Invited paper presented at the Twelfth symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Evaluating the measurement error of thermophysical properties of liquids at high pressures by the periodic-heating compensation method

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 39–40, June, 1992.     

Thermal contact resistance in thermophysical measurements

The author describes the basis for an experimental correction to the thermal contact resistance (TCR) in investigation of thermal conductivity and thermal diffusivity of solids, using specimens in the form of plates. Relations are obtained for thermal deformation of specimens and the contact pressure to compensate for thermal deflection.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 4, pp. 615–622, April, 1982.     

Mechanical properties of austenitic stainless steel with high niobium contents

To better understand the influence of the microstructural characteristics on the mechanical properties of Fe-Cr₂₂-Ni₂₅-Nb_x austenitic stainless steel (ASS-Nb_x), the mechanical properties were investigated. Nb addition was conducted with four different amounts: 0, 0.29, 0.58 and 0.86%. With the increasing Nb content, the mean grain size for the Fe-Cr-Ni-based alloys decreased, while the size of Nb precipitate increased. Owing to the different microstructural characteristics, their mechanical properties were altered. The highest tensile strength was obtained for ASS-Nb_0.29 alloy. However, with the increasing Nb content in ASS-Nb_0.29–0.86 alloys, the tensile strength decreases despite the grain refinement. The mechanical properties of the ASS-Nb alloys were influenced by the Nb precipitation hardening and the grain boundary cohesive strength, arising from the size of Nb precipitations.