Thermophysical properties of thoriated tungsten above 3600 K by a pulse-heating method

Thoriated tungsten (tungsten, 98% thorium oxide, 2%) is a widely used electrode material for inert-gas arc-welding. 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, with the melting point of thoriated tungsten as a calibration point. Experimental results obtained in the temperature range from 3600 K to the melting point (3693 K) are presented and discussed, along with data obtained during the initial part of the free cooling period. The electrical resistivity results show a regular behavior up to the melting point, indicating that thoria remains an insulator up to 3680 K. During heating, a heat capacity anomaly is found near 3666 K, interpreted as the melting point of thoria. During cooling, two anomalies are found, the first one with a peak near 3660 K and a second one (possibly a Frenkel disorder) with a peak near 3148 K.Visiting scientist from Institute of Physics, Slovak Academy of Sciences,Bratislava SlovakiaPaper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln Germany.     

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.     

Thermophysical Properties by a Pulse-Heating Reflectometric Technique: Niobium, 1100 to 2700 K

Pulse-heating experiments were performed on niobium strips, taking the specimens from room temperature to the melting point is less than one second. The normal spectral emissivity of the strips was measured by integrating sphere reflectometry, and, simultaneously, experimental data (radiance temperature, current, voltage drop) for thermophysical properties were collected with sub-millisecond time resolution. The normal spectral emissivity results were used to compute the true temperature of the niobium strips; the heat capacity, electrical resistivity, and hemispherical total emissivity were evaluated in the temperature range 1100 to 2700 K. The results are compared with literature data obtained in pulse-heating experiments. It is concluded that combined measurements of normal spectral emissivity and of thermophysical properties on strip specimens provide results of the same quality as obtained using tubular specimens with a blackbody. The thermophysical property results on niobium also validate the normal spectral emissivity measurements by integrating sphere reflectometry.     

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.     

Thermophysical properties of tungsten electrodes by subsecond pulse calorimetry

Prediction of the behavior of tungsten electrode material in high-temperature plasma generators requires knowledge of its thermophysical properties over a wide temperature range. For determination of its relevant thermophysical properties, the direct pulse heating calorimetry technique was chosen as the most appropriate, as it meets requirements of both high-speed measurements and the widest temperature range. As a high-temperature sensor, the method used simultaneously a fine-gauge thermocouple and an optical pyrometer. Such a combination enables coverage of a few thousand degrees within a second, with a time resolution of less than 1 ms. The measurement technique and details of the apparatus as well as experimental results for specific heat, electrical resistivity, normal spectral, and hemispherical total emittance in the temperature range from 300 to 2500 K are presented.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Measurements of specific heat and electrical resistivity of austenitic stainless steel (St. 1.4970) in the range 300–1500 K by pulse calorimetry

A direct heating pulse calorimetric technique has been applied for the measurements of specific heat, electrical resistivity, and hemispherical total emissivity of austenitic stainless steel (St. 1.4970), a candidate for thermal conductivity standard reference material. The specific heat and electrical resistivity were measured in the range 300 to 1500 K, and the hemispherical total emissivity was measured in the range 1300 to 1500 K. The maximum measurement uncertainties were estimated to be 3% for specific heat, 1% for electrical resistivity, and 5% for emissivity.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Thermophysical and Thermal Optical Properties of Vanadium by Millisecond Calorimetry Between 300 and 1900 K

A variant of millisecond-resolution pulse calorimetry in use at the Institute of Nuclear Sciences Vina since 1983 involves measuring the specific heat and electrical resistivity of electrical conductors from room temperature to 2500 K and the hemispherical total emissivity and normal spectral emissivity from about 1300 K to the same maximum operating temperature. The method was applied successfully to different materials: pure metals, ferrous and nickel-base alloys, reactor materials, and refractory metals in thermal characterization of candidates for thermophysical property standard reference materials. This paper presents and discusses new data obtained in the study of thermophysical and thermal optical properties of vanadium.     

Thermal Properties of Tantalum Between 300 and 2300 K

A subsecond pulse heating method was applied to measure the specific heat capacity, electrical resistivity, total hemispherical emissivity, and normal spectral emissivity of 99.9% pure tantalum in the form of 2-mm-diameter wire. W/Re thermocouple thermometry was applied from 300 to 2300 K, with emissivity measurements above 1300 K involving pyrometric measurements. The maximum uncertainties in the specific heat capacity and electrical resistivity were less than 3 and 1 % respectively. The uncertainty of emissivity measurements was estimated as ±5%. The results are compared with literature values.     

Measurements of thermophysical properties of molten silicon by a high-temperature electrostatic levitator

Several thermophysical properties of molten silicon measured by the high-temperature electrostatic levitator at JPL are presented. They are density, constant-pressure specific heat capacity, hemispherical total emissivity, and surface tension. Over the temperature range investigated (1350<T _m<1825 K), the measured liquid density (in g·cm⁻³) can be expressed by a quadratic function,p(T)=p _m−1.69×10⁻⁴(T−T _m)−1.75×10⁻⁷(T−T _m)² withT _m andp _m being 1687 K and 2.56 g·cm⁻³, respectively. The hemispherical total emissivity of molten silicon at the melting temperature was determined to be 0.18, and the constant-pressure specific heat was evaluated as a function of temperature. The surface tension (in 10⁻³ N·m⁻¹) of molten silicon over a similar temperature range can be expressed by σ(T)=875–0.22(T−T _m). Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

A new microsecond pulse-heating system to investigate thermophysical properties of solid and liquid metals

A new discharge system for resistive self-heating has been constructed for the measurement of accurate thermophysical properties. A constant-current pulse is used to heat metals over a time interval of 50 to 100 s, reaching temperatures up to the boiling point. New techniques have been developed to obtain sound speeds in the pulse-heated sample, emissivities, and vapor pressure. A new pyrometer allows the extension of the measured temperature range down to the melting point of copper.     

Measurement of the heat of fusion of tungsten by a microsecond-resolution transient technique

A microsecond-resolution pulse-heating technique was used for the measurement of the heat of fusion of tungsten. The method is based on rapid (100 to 125s) resistive self-heating of a specimen by a high-current pulse from a capacitor discharge system and measuring current through the specimen and voltage across the specimen as functions of time. Melting of a specimen is manifested by changes in the slope of the electrical resistance versus time function. The time integral of the power absorbed by a specimen during melting yields the heat of fusion. Measurements gave a value of 48.7 kJ · mol^–1 for the heat of fusion of tungsten with an estimated maximum uncertainty of ±6%. The electrical resistivity of solid and liquid tungsten at its melting temperature was also measured.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

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.     

Evaluation of the thermodynamic properties of tungsten

A new evaluation of the thermodynamic properties of tungsten has been made. A set of parameters describing the Gibbs energy of each individual phase as a function of temperature and pressure is given. The experimental information on the P, T phase diagram and the thermodynamic data are compared with calculations made using the presented set of parameters.     

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.     

Hemispherical Total Emissivity of Niobium, Molybdenum, and Tungsten at High Temperatures Using a Combined Transient and Brief Steady-State Technique

The hemispherical total emissivity of three refractory metals, niobium, molybdenum, and tungsten, was measured with a new method using a combined transient and brief steady-state technique. The technique is based on rapid resistive self-heating of a solid cylindrical specimen in vacuum up to a preset high temperature in a short time (about 200 ms) and then keeping the specimen at that temperature under steady-state conditions for a brief period (about 500ms) before switching off the current through the specimen. Hemispherical total emissivity is determined at the temperature plateau from the data on current through the specimen, the voltage drop across the middle portion of the specimen, and the specimen temperature using the steady-state heat balance equation based on the Stefan–Boltzmann law. Temperature of the specimen is determined from the measured surface radiance temperature and the normal spectral emissivity; the latter is obtained from laser polarimetric measurements. Experimental results on the hemispherical total emissivity of niobium (2000 to 2600 K), molybdenum (2000 to 2700 K), and tungsten (2000 to 3400 K) are reported.     

Measurements of thermophysical properties of nickel with a new highly sensitive pyrometer

A new, sensitive, and fast (response time, 100 ns) pyrometer used for the measurement of temperature in pulse heating experiments is described. The monochromatic instrument may use two detectors, namely, a Si diode and an InGaAs diode. Since monochromatic pyrometers usually are self-calibrated with the plateau of the melting transition of the investigated metal, a high sensitivity is desirable. The pyrometer is sensitive down to 1000 K and may be used at the melting plateau of copper, a reference point on the International Temperature Scale of 1990. A wide temperature range in a single measurement is possible with the use of a fast operational amplifier with linear and logarithmic outputs. Electrical resistivity, heat capacity, and enthalpy of nickel were measured in the temperature range 1500 to 2200 K using a fast pulse heating technique.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Thermophysical properties of solid and liquid tungsten

The thermophysical properties of solid and liquid tungsten have been measured up to an enthalpy ofH = 1.4 MJ · kg^–1 using an isobaric expansion technique. These measurements give the pressure, temperature, volume, enthalpy, electrical resistivity, and sound velocity as fundamental quantities. From these, other properties may be calculated, such as specific heat at constant volume and pressure, heat of fusion, isothermal and adiabatic bulk moduli and compressibilities, and thermodynamic. Results of these calculations are presented for liquid tungsten and compared with literature values where such data exist. These data will help in understanding liquid-metal phenomenology theoretically and in the design and modeling of exploding wires, foils, and fuses.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

Thermophysical Properties of Solid Phase Hafnium at High Temperatures

The thermophysical properties of several hafnium samples with a content of zirconium below 1% were experimentally studied over a wide temperature range. The specific heat capacity and specific electrical resistivity were measured from 300 to 2340 K, the hemispherical total emissivity from 1000 to 2130 K, while the thermal diffusivity was measured in the range from 300 to 1470 K. The thermal conductivity and Lorentz number were computed from measured properties for the range from 300 to 1470 K. The specific heat capacity, specific electrical resistivity, and hemispherical total emissivity were measured by subsecond pulse calorimetry, and the thermal diffusivity using the laser flash method. Samples in the form of a thin rod or wire, and in the form of a thin disk were used in the first and second methods, respectively. For data reduction and computation of relevant parameters, recent literature values of the linear thermal expansion were used. The results are compared with literature data and discussed.     

Measurement of thermophysical properties of metals and ceramics by the laser-flash method

Several recent advances made in the author's laboratory in the experimental apparatus and measuring procedures for precise measurements of thermophysical properties by the laser-flash method are reviewed. Heat-capacity measurement has been done on metals and ceramics within an accuracy of ±0.5% in the range from 80 to 800 K, and within ±2% from 800 to 1100 K. Thermal diffusivity has been also measured from 80 to 1300 K with reasonable corrections for heat leak and finite pulse width. As an example of the experimental results by the method, the data of heat capacity, thermal diffusivity, and thermal conductivity of vanadium-oxygen alloys containing 1.07 and 3.46 at.% of oxygen from 80 to 800 K are presented and compared with those of pure vanadium metal.Presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.