H. Jäger

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.

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 μs, 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.

Thermophysical properties of POCO AXF-5Q graphite up to melting

Abstract Measurements of the thermophysical properties of a particular POCO graphite (AXF-5Q) have been made up to melting. Results were obtained in two different laboratories using two heating rates. Data for temperature, volume, enthalpy, and electrical resistivity are shown. The measured melting point was found to be 4900 K ± 200 K.

Determination of the critical point of gold

Wire-shaped gold specimens are placed in a new, improved high-pressure vessel, which is part of a fast capacitor-discharge circuit and in which static pressures above 600 MPa can be reached with distilled water as the pressure-transmitting medium. The specimens are self-heated resistively by a current pulse. The current through the specimen, the voltage drop across it, and its temperature are recorded as a function of time with submicrosecond resolution. The radial expansion of the specimen is determined with a CCD camera, Experiments are performed at different pressures. When the critical pressure is exceeded, there is no liquid–gas phase transition; hence, no sudden change in the thermal expansion rate is observed. The results for temperature, pressure, and specific volume at the critical point of gold are as follows: Tc =7400±1100 K, pc=530±20 MPa, and vc=0.13±0.03 × 10−3m3·kg−1.

Investigations of thermophysical properties of liquid metals with a rapid resistive heating technique

Abstract Wire-shaped metal samples are resistively pulse heated as part of a capacitor discharge circuit. With heating rates between 10 8 and 10 9 K/s, temperatures up to about 12000 K can be achieved. The measurements allow the determination of heat capacity and the mutual dependencies between enthalpy, electrical resistivity, temperature and volume. They are performed from room temperature up to superheated liquid states far above the normal boiling point. A summary of data of the following elements is given: W, Re, Ta, Mo, Nb, Fe, Co, Ni, Cu, Pb, and In.

High-temperature, high-pressure thermophysical measurements on liquid zinc

Wire-shaped zinc samples were resistively volume heated as part of a fast-capacitor discharge circuit. Time-resolved measurements with submicrosecond resolution of the current through the specimen, the voltage drop across it, and the thermal expansion of the specimen as a function of time allow determination of the enthalpy, electrical resistivity, and density at different temperatures up to superheated liquid states of zinc far above the normal boiling point. High static pressures, up to 3800 bar of the ambient medium water, were used. An estimate of the critical pressure for zinc is given by investigations of the stability of the sample with a framing CCD camera, taking pictures of different samples varying the ambient static pressure. The critical volume and the critical temperature are obtained by means of an extrapolation of measured data at different pressures.

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.

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 μs. 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.

A review of determinations of critical point data of metals using subsecond pulse heating techniques

Abstract One of the main steps in establishing a phase diagram is finding the critical point data. Static steady state techniques for measuring of thermophysical properties of metals are limited to temperatures below about 2000 K. Fast dynamic resistive pulse heating experiments have been developed to permit the extension of the measurements to higher temperatures up to about 10000 K. Different experimental techniques are reviewed, which lead to a determination of critical point data for the metals lead, indium, zinc, iron and cobalt, using fast resistive pulse heating.

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.