Noncontact modulation calorimetry of metallic liquids in low Earth orbit

Abstract

Noncontact modulation calorimetry using electromagnetic heating and radiative heat loss under ultrahighvacuum conditions has been applied to levitated solid, liquid, and metastable liquid samples. This experiment requires a reduced gravity environment over an extended period of time and allows the measurement of several thermophysical properties, such as the enthalpy of fusion and crystallization, specific heat, total hemispherical emissivity, and effective thermal conductivity with high precision as a function of temperature. From the results on eutectic glass forming Zr-based alloys thermodynamic functions are obtained which describe the glass-forming ability of these alloys. ͓S0163-1829͑97͒02302-3͔Precision measurements of the specific heat of stable and undercooled melts are of fundamental interest regarding the ultimate thermodynamic stability of undercooled melts and nonequilibrium crystals against vitrification and amorphization, 1 formation of associate structures in the melt, 2 the thermodynamic contribution to nucleation kinetics, 3 and thus the glass-forming ability of a material. In particular, Zr-based alloys have attracted considerable attention due to their glass-forming ability on rapid cooling, 4 solid-state amorphization reactions, 5 and, as base alloys of the recently discovered bulk glass formers. 6,7 However, investigations of the thermophysical properties of the chemically reactive liquid metallic specimen at elevated temperatures are usually hampered using conventional techniques due to exothermic reactions with the container walls. Therefore, a containerless method has been developed which allows one to alleviate these problems. 8,9 Due to insufficient temperature and positioning control of the samples of interest in an earth laboratory under UHV conditions the experiments have been performed in the space shuttle Columbia during the recent International Microgravity Laboratory 2 ͑IML-2͒ mission using the containerless electromagnetic processing ͑TEMPUS͒ device.10 The absence of excessive heating and fluid flow associated with levitation under 1 g conditions assures quiescent sample conditions in an ultraclean environment ͑Ͻ10 Ϫ8 Torr base pressure͒ and precise modeling of the thermal balance.Here, a metallic 8 mm diameter specimen ͑as an example Zr 64 Ni 36 ͒ is heated by a 400 kHz radio frequency dipole field and positioned in the center of the heating coil by a 200 kHz quadrupole field. Temperature is measured by a high precision, Ͻ0.1 K, well calibrated two-color InAs pyrometer.The different frequency and geometry of the heating and positioning fields allows separation of the total power input into additive components from heater and positioner, P tot ϭ P H ϩ P P Pos . The specimen equilibrium temperature T 0 , is given by P tot ϭAT 0 4 with total hemispherical emissivity,A surface area and Stefan-Bolzmann constant. Induction heating of the levitated specimen can be discussed by analytical 11,12 and numerical methods including the induced force and fluid-flow fields. 13 The rate of Jou...

Non-Contact Measurement of Thermophysical Properties of Fe, Fe–C, and Fe–C–Mn Alloys in Solid, Supercooled, and Stable Liquid Phases

“…Electromagnetic levitator (EML) enabled to measure heat capacity, thermal conductivity, and hemispherical total emissivity of Fe and Fe alloy liquids. [9][10][11][12] Surface tension and density of Fe liquid were also obtained by an aerodynamic levitator (ADL). 13) However, those measurements require elaborate analysis to account for contamination, inhomogeneous temperature, and distorted shape of samples due to gas-environment and inhomogeneous external forces.…”

Fundamentals of Liquid Processing in Low Earth Orbit: From Thermophysical Properties to Microstructure Formation in Metallic Alloys

“…However, high-precision measurements on chemically highly reactive metallic melts, such as Fe-, Ni-, Ti-, Zr-alloys, etc., require the application of containerless processing techniques and the use of high-precision non-contact diagnostic tools. 7 For highly reactive metallic melts, electromagnetic levitation (EML) is a well-developed containerless technique which offers several advantages over alternative levitation methods (electrostatic levitation, gas-phase levitation),due to the direct coupling of the high-intensity radio-frequency (rf) electromagnetic field with a metallic sample having an optimum diameter between 6 mm and 8 mm.…”

Noncontact Modulated Laser Calorimetry for Liquid Austenitic Stainless Steel in dc Magnetic Field

“…Fecht and co-workers [2][3][4][5] have developed the modulation calorimetry for electromagnetically levitated metallic melts to measure the heat capacity, thermal conductivity and hemispherical total emissivity. However, the thermal conductivity can not be measured because the convection still remained in the melt.…”

“…The oscillation and convections of the droplet were effectively suppressed by the Lorenz force in a dc magnetic field. Based on the studies described above, [2][3][4][5][6] the present authors have newly developed a noncontact modulated laser calorimetry for metallic melts in a dc magnetic field. [7][8][9] An electromagnetic levitator is equipped in a superconducting magnet to hold a droplet statically.…”