Gernot Pottlacher

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.

Thermophysical properties of a Ti–44%Al–8%Nb–1%B alloy in the solid and molten states

Abstract The families of titanium aluminide intermetallic alloys have attractive high temperature mechanical properties which make them potential candidate materials for a wide range of applications, particularly in the aeronautic and automobile sectors. The development of appropriate manufacturing techniques is an essential stage in the engineering exploitation of these materials, e.g., Induction Skull Melting is one of the techniques which needs to be optimised for the casting of titanium aluminides. Research is underway to develop a computer model of this process but data are required for the key thermophysical properties. Pulse-heating techniques have been used to measure properties for the Ti–44Al–8Nb–1B system. Rectangular samples have been prepared and are resistively heated as part of a fast capacitor discharge circuit. Time-resolved measurements with sub-μs resolution of currents through the specimen were made with a Pearson probe current monitor using the induction principle. Voltages across the specimen were determined with knife-edge contacts and voltage dividers, and radiance temperatures of the sample were measured with a pyrometer. These measurements allow the calculation of specific heat and dependencies between enthalpy, electrical resistivity and temperature of the alloy up into the liquid phase. Data for thermal diffusivity have been obtained by using the Wiedeman–Franz relation. The results are compared with those obtained using DSC and the four-probe method to measure the temperature dependence of the resistivity.

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.

Microsecond Laser Polarimetry for Emissivity Measurements on Liquid Metals at High Temperatures—Application to Tantalum

The aim of this work was to determine accurate and reliable thermophysical properties of liquid tantalum from melting up to temperatures of 5000 K. Temperature measurements on pulse-heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity over the whole liquid range because of the lack of data for liquid metals. The uncertainty in temperature measurement is reduced in this work by the direct measurement of emissivity during the experiments. The emissivity measurements are performed by linking a laser polarimetry technique with the established method for performing high speed measurements on liquid tantalum samples at high temperatures during microsecond pulse-heating experiments. A set of improved thermophysical properties for liquid tantalum, such as temperature dependences of normal spectral emissivity at 684.5 nm, heat capacity, enthalpy, electrical resistivity, thermal diffusivity, and thermal conductivity, was obtained.

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.

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.

Thermal conductivity of pulse-heated liquid metals at melting and in the liquid phase

Thermal conductivities as a function of temperature of the elements W, Re, Ta, Mo, Nb, Fe, Co, Ni, Au and Cu are here reported for the first time in a temperature range, covering the melting point and the liquid state.

A Fast Laser Polarimeter Improving a Microsecond Pulse Heating System

The microsecond pulse heating system has been used for more than 15 years to investigate thermophysical properties of solid and liquid metals and alloys. The only way to measure temperature in the time and temperature range of these experiments (duration of a few tens of microseconds, temperatures up to 7000 K) is optical pyrometry. The radiance temperature can be measured very accurately. However, to obtain true temperature from radiance temperature the normal spectral emissivity at the wavelength of interest of the material under investigation has to be known. Because normal spectral emissivity measurements on pulse heated liquid metals were not possible in the past, an assumption about the behavior of the emissivity in the liquid phase had to be made, which increased the uncertainty of the temperature determination. To overcome this limitation in temperature measurement, a microsecond division of amplitude polarimeter (µ-DOAP) was added to the pulse heating system. The normal spectral emissivity at 684.5 nm is derived from the measured change in the state of polarization of laser light that is reflected off the sample surface. The working principle of this polarimeter system is presented, and experimental results of the normal spectral emissivity at 684.5 nm as a function of radiance temperature at 650 nm are discussed.

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.