Specific Heat,Electrical Resistivity,and Linear Thermal Expansion of the Magnesium Alloy AE42 Measured by Subsecond Pulse Heating

Magnesium alloy AE42 (Mg with 4% Al and 2% rare earths) is used for the production of high-temperature creep-resistant castings. Its thermophysical properties are used as input parameters for the numerical simulation of the casting process by finite methods. Measurements of specific heat capacity, electrical resistivity, and linear thermal expansion of the magnesium alloy AE42 in the temperature range from 550 to 840 K by a transient technique are presented and discussed. Tubular specimens were Joule-heated from room temperature up to melting within 500 ms by a large current pulse. The current and the voltage drop along a defined portion of the specimen were measured by a fast precision data acquisition system. Temperature measurements were made with a high-speed broad-band infrared pyrometer. Thermal expansion was measured by a polarized-beam Michelson-type interferometer. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans France.     

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.     

Specific Heat and Electrical Resistivity of 53%Niobium-47%Titanium Alloy Measured by Subsecond Calorimetric Technique

This paper presents results of measurements of the specific heat and electrical resistivity of a 53%Ni-47%Ti superconducting alloy. Both properties were measured by a contact variant of the millisecond-resolution pulse calorimeter. W5%Re/W25%Re thermocouple thermometry enabled study from ambient temperature to 2000 K. Results are discussed, and their uncertainty is estimated.     

The Role of National Measurement Institutes in Subsecond Current-Heating Methods

The historical role of three national measurement institutes (NMIs), namely, the NBS-NIST (USA), the IMGC (Italy), and the NRLM-NMIJ (Japan), in the development of different pulse-heating methods is reviewed. In relation to their institutional interests, the indicated NMIs were mainly interested in the development and application of new measurement techniques, in the accurate measurement of thermophysical properties at high temperatures, and in the characterization of possible reference materials. An informal intercomparison of published experimental results obtained via pulse-heating techniques over 30 years on the electrical resistivity and heat capacity of niobium, molybdenum, and tungsten is presented, comparing these results with recommended curves from the literature. Good agreement is found among the pulse-heating results from the indicated NMIs, always within the combined uncertainties. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Measurement of thermophysical properties by a pulse-heating method: Niobium in the range 1000–2500 K

Data for the heat capacity, electrical resistivity, hemispherical total emittance, and normal spectral emittance (at 898 nm) of niobium are reported for the temperature range 1000–2500 K. Measurements were based on a subsecond pulseheating technique. The results are discussed and compared with the literature values. Reported uncertainties for the properties are 3% for heat capacity, 1% for electrical resistivity, 5% for hemispherical total emittance, and 4% for normal spectral emittance.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Issues and future directions in subsecond thermophysics research

The key issues and anticipated future directions in subsecond thermophysics research are presented and discussed. The main emphasis is placed on experimental techniques for measurements of selected thermophysical properties utilizing rapid volume heating (resistive self-heating) and rapid surface heating (laser pulse-heating) methods. The time regime covered is from 1 to 10^–12s. Specific research topics and key research areas are identified and discussed.Paper based on the Panel Discussion at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.Formerly National Bureau of Standards     

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 thermophysical properties of lead by a submicrosecond pulse-heating method in the range 2000–5000 K

A submicrosecond ohmic pulse-heating technique with heating rates of more than 10⁹K· s^–1 allows the determination of such thermophysical properties as heat capacity and the mutual dependences among enthalpy, electrical resistivity, temperature, and volume up to superheated liquid states for lead. Also, an estimation of the critical point data is given from investigations at elevated static pressures.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

Uniaxial pressure dependence of the Debye temperature in metals

The electrical resistance and its temperature coefficient have been measured for a platinum foil as a function of uniaxial pressure over the pressure range 0 to 60 MPa. The measurements were performed at room temperature using the transient hot-strip method. The data are analyzed using the electrical resistivity formula within the Block-Grüneisen approximation. The pressure dependence of the Debye temperature was directly obtained from an expansion of this formula and using the basic definition of the temperature resistivity coefficient. The reliability of the experimental data was then verified using the basic definition of Grüneisen constant. Within the investigated pressure range, the analysis supports the interpretation that the change in resistance of platinum under pressure is mainly due to the change in the amplitude of the atomic vibrations that are directly related to the change in Debye temperature. The pressure dependence of resistance and the Debye temperature of the platinum were reasonably good in spite of the approximations involved.     

Thermophysical Properties of W–Re Alloys Above the Melting Region

In earlier experiments we have studied pure elements with a fast pulse heating technique to obtain thermophysical properties of the liquid state. We report here results for thermophysical properties such as specific heat and dependences among enthalpy, electrical resistivity, and temperature, for four W–Re alloys (3.95, 21.03, 23.84, and 30.82 at % of Re) in a wide temperature range covering solid and liquid states. Thermal conductivity is calculated using the Wiedemann–Franz law for the liquid alloy, as.well as data for thermal diffusivity for the beginning of the liquid phase. Additionally, data for the entire temperature range studied have been analyzed in comparison with those of the constituent elements, tungsten and rhenium, since both metals have been studied previously with the same experimental technique. Such information is of interest in the field of metallurgy since W–Re alloys of low Re content in the region of mutual component solubility in the solid state are widely used as thermocouple materials for the purposes of high-temperature thermometry.     

Thermophysical properties of liquid iron

Wire-shaped iron samples are resistively volume heated as part of a fast capacitor discharge apparatus. Measurements of current through the specimen, voltage across the specimen, radiance temperature, and thermal expansion of the specimen as functions of time allow the determination of specific heat and various dependencies among enthalpy, electrical resistivity, temperature, and density for liquid iron up to 5000 K. High pressures. up to 3800 bar, are used to obtain the liquid state far above the normal boiling point. An estimate of critical-point data for iron is given by using experimental data of the vapor pressure of liquid iron.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Measurement of thermophysical properties by a pulse-heating method: Thoriated tungsten in the range 1200 to 3600 K

Thoriated tungsten (tungsten, 98%: thorium oxide. 2 % ) is a widely used electrode material for inert-gas arc-welding. Data for the heat capacity, electrical resistivity. and hemispherical total emissivity of this material are reported for the temperature range 1200–3600 K. A subsecond pulse-heating technique was applied to rod specimens: radiance temperature was measured by high-speed pyrometry. Literature values of the temperature dependence of the normal spectral emissivity of tungsten were used to obtain true temperatures, using the melting point of thoriated tungsten as a calibration point. Reported uncertainties for the properties are 4 % for heat capacity, 1.5 % for electrical resistivity, and 7 % for hemispherical total emissivity.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Thermophysical measurements on solid and liquid rhenium

A fast resistive heating technique was used to measure such thermophysical data of solid and liquid rhenium as enthalpy, specific heat, thermal volume expansion, and electrical resistivity. The measurements are performed with heating rates of slightly more than 10⁹ K · s ^–1 up to states of superheated liquid rhenium (7500 K).Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Investigation of the Heating Dynamics and Properties of Liquid Tungsten

The dynamics of electrical explosion of tungsten wires under water in microsecond times was studied. A new optical method for temperature measurement has been developed. For tungsten, uniform heating took place at 10¹¹<j(A·m^–2)<10¹², therefore one can use these regimes for the investigation of properties in the liquid phase. Temperature dependences of enthalpy, electrical resistivity, and specific heat for liquid tungsten are given and compared with literature values.     

Improved thermophysical measurements on solid and liquid tantalum

Wire-shaped tantalum samples are resistively pulse heated as part of a coaxially constructed capacitor discharge circuit. With heating rates of more than 10⁹ K · s^–1, temperatures up to about 10,000 K are reached. The tantalum wire is contained, with water as the surrounding medium, in a high-pressure vessel with sapphire windows and a maximum pressure capability of 5 kbar. Time correlated measurements of the current through the wire and the voltage drop across it, as well as surface radiation and wire expansion, were performed to permit the determination of thermophysical properties of the solid and liquid tantalum.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Thermophysical properties of rhenium

Experimental investigations of the thermophysical properties of rhenium at high temperatures (above 2000 K) are scarce and quite recent. Using an isobaric expansion technique, we performed new measurements up to 7000 K under 0.12GPa argon pressure and report here enthalpy, density, temperature, and electrical resistivity data for both solid and liquid states. Agreement is good with other pulse heating results obtained on this refractory metal (T _m =3453 K), except in the volume increase at melting.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Relaxation phenomena caused by equilibration of point defects

Relaxation phenomena due to equilibration of point defects in metals are reviewed. The relaxation effect in specific heat observed in tungsten and platinum confirms that in both cases the nonlinear increase in the high-temperature specific heat has to be attributed to point-defect formation. Relaxation phenomena observed by measurements of electrical resistivity and positron annihilation are also considered. The comparison of the data seems to be favorable for the conclusion that all the phenomena are of one origin.     

Thermal Conductivity and Thermal Diffusivity of Pulse-Heated W–Re Alloys

Results are reported for the thermal conductivity and thermal diffusivity as a function of temperature for four W–Re alloys (4.0, 21.24, 24.07, and 31.09 mass% of Re) over a wide temperature range covering the solid and liquid states. The measurements allow the determination of specific heat and dependences among electrical resistivity, temperature, and density of the alloys into the liquid phase. The thermal conductivity is calculated using the Wiedeman–Franz law. Additionally, data for thermal conductivity and thermal diffusivity of the constituent elements, tungsten and rhenium, are presented for the first time. Both metals have been previously studied with the same experimental technique.     

Thermal and Electrical Properties of Titanium Between 300 and 1900 K

The specific heat capacity and electrical resistivity of titanium were measured by a subsecond pulse-heating method. Specimens were in the form of a 1.6-mm-diameter-wire. Experiments covered the range between 300 and 1900K; thermometry was provided by Pt10%Rh/Pt and W5%Re/W25%Re thermocouples. The maximum uncertainties in the specific heat capacity and electrical resistivity determinations were less than 3 and 1%, respectively. Results are reported and discussed for both the bcc and hcp structures and the transformation between the two phases.