Thermal Conductivity of Liquid Metals

Over the last decades, many experimental methods have been developed and improved to measure thermophysical properties of matter. This chapter gives an overview over the most common techniques to obtain thermal conductivity λ as a function of temperature T. These methods can be divided into steady state and transient methods. At the Institute of Experimental Physics at Graz University of Technology, an ohmic pulse-heating apparatus was installed in the 1980s, and has been further improved over the years, which allows the investigation of thermal conductivity and thermal diffusivity for the end of the solid phase and especially for the liquid phase of metals and alloys. This apparatus will be described in more detail. To determine thermal conductivity and thermal diffusivity with the ohmic pulse-heating method, the Wiedemann-Franz law is used. There are electronic as well as lattice contributions to thermal conductivity. As the materials examined at Graz University of Technology, are mostly in the liquid phase, the lattice contribution to thermal conductivity is negligibly small in most cases. Uncertainties for thermal conductivity for aluminum have been estimated ±6% in the solid phase and ±5% in the liquid phase

Inductive measurement of thermophysical properties of electromagnetically levitated metallic melts

For the containerless processing of high temperature metallic melts the electromagnetic levitation technique, which utilizes high frequency alternating magnetic fields for the contactless, inductive positioning and heating of electrically conducting samples, is well established. For the contactless measurement of surface tension and viscosity of levitated samples via the oscillating drop method optical methods are generally used. But the existence of alternating magnetic fields in electromagnetic levitation facilities suggests to use also inductive methods for non-contact measurements of liquid metal properties. Within a joint ESA project of DLR and TU Graz a measurement device was designed and constructed by DLR, which utilizes the high frequency magnetic fields of microgravity electromagnetic levitation facilities imultaneously also for an inductive determination of thermophysical properties of levitated metallic melts. Although originally planned for electrical resistivity measurements only, the device allows also the detection of surface oscillations, which can be used for a determination of surface tension and viscosity of the levitated droplets. The present paper compares the optical with the inductive measurement technique

Density of liquid Ti-6Al-4V

Ti-6Al-4V is due to its high strength-density ratio a commonly used alloy in aerospace industry applications. But liquid phase data are scarce as preventing contaminations of the reactive high temperature melt during the investigation process poses a challenge. The thermophysical quantity density is of special interest since it is necessary input parameter in modern numerical casting and solidification simulations. Liquid phase density of Ti-6Al-4V as function of temperature was determined employing a fast resistive pulse-heating technique based on the approach to avoid contaminations of the specimen by extremely reducing the experimental duration of the investigation process. Temperature dependent density of liquid Ti-6Al-4V was determined in a temperature range between 2050 K and 2590 K and is presented

High Temperatures ^ High Pressures, 2003/2007, volume 35/36, pages 667 ^ 675 DOI:10.1068/htjr138

Optical properties (at 684.5 nm) and radiance temperatures at the melting point of group VIIIb transition metals cobalt, nickel, palladium, and platinu

Thermal diffusivity and conductivity of ruthenium in the temperature range 200 to 1670 K

This work presents experimental results of thermal diffusivity and computed values of thermal conductivity of pure polycrystalline ruthenium specimens in the temperature range 200 to 1670 K for diffusivity and 250 to 1650 K for conductivity. The results of thermal diffusivity were obtained by an interlaboratory comparison using the laser flash method. A brief description of the two measuring systems applied is given. Specimens were disk shaped, 2 and 3 mm in thickness and 10 and 12.5 mm in diameter. Literature data are used to correct for thermal expansion of the specimens. All the values obtained from the individual laboratories as well as a polynomial fit to the results over the entire temperature range are presented and compared with results found in literature. By using the thermal diffusivity data and previously measured results of specific heat capacity of different pure polycrystalline ruthenium specimens, the values of ruthenium thermal conductivity are estimated and presented together with related literature data.11th International Workshops on Subsecond Thermophysics (IWSSTPs), Jun 21-24, 2016, Polan

Thermal diffusivity and conductivity of ruthenium in the temperature range 200 to 1670 K

This work presents experimental results of thermal diffusivity and computed values of thermal conductivity of pure polycrystalline ruthenium specimens in the temperature range 200 to 1670 K for diffusivity and 250 to 1650 K for conductivity. The results of thermal diffusivity were obtained by an interlaboratory comparison using the laser flash method. A brief description of the two measuring systems applied is given. Specimens were disk shaped, 2 and 3 mm in thickness and 10 and 12.5 mm in diameter. Literature data are used to correct for thermal expansion of the specimens. All the values obtained from the individual laboratories as well as a polynomial fit to the results over the entire temperature range are presented and compared with results found in literature. By using the thermal diffusivity data and previously measured results of specific heat capacity of different pure polycrystalline ruthenium specimens, the values of ruthenium thermal conductivity are estimated and presented together with related literature data.11th International Workshops on Subsecond Thermophysics (IWSSTPs), Jun 21-24, 2016, Polan

Preparation Method of Spherical and Monocrystalline Aluminum Powder

This paper presents a new production method for a spherical and monocrystalline aluminum powder. Aluminum powder of irregular particle shapes was mixed with silica nanoparticles and heated to a temperature above the melting point of aluminum. Due to its molten state, high surface tension, and poor wettability, the aluminum particles were transformed into liquid and spherical droplets separated by silica nanoparticles. The spherical shape was then retained when the aluminum particles solidified. The influence of the processing temperature on the particle shape, phase composition, and microstructure was investigated. Moreover, calorimetric, X-ray diffraction, grain size, and scanning electron microscopy with electron backscatter diffraction (SEM-EBSD) measurements of the particles’ microstructure are presented. It is proven that, by this means, a spherical and monocrystalline aluminum powder can be efficiently created directly from an air-atomized irregular powder. The observed phenomenon of particles becoming round is of great importance, especially when considering powder preparation for powder-based additive manufacturing processes