Levitation calorimetry

Figure 6.3. Levitation of a molten metal in a radio-frequency field. The coil consists of water-cooled copper tubes. The counter winding above the sample stabilizes levitation. The same coils (and possibly additional ones) act as the induction heater. This technique has been applied to container-less melting and zone refining of metals and for drop calorimetry of liquid metals. It can be also used to decarburize and degas in ultrahigh vacuum mono-crystalline spheres of highly refractory metals (adapted from Brandt (1989)). The arrows indicate the instantaneous current flow directions in the inductors.

Enthalpy measurements via levitation calorimetry by Treverton and Hargrave (3) were over a sufficient range of temperature,... 

Bererzin et al (2) have measured the enthalpy of crystal and liquid molybdenum by levitation calorimetry in the range 1962-2869 K and 2890-2925 K, respectively. They reported Aj gH 8.741 0.314 kcal mol" at an assumed melting temperature of 2890... 

Treverton and Margrave (3) also used levitation calorimetry to measure the liquid phase enthalpy of molybdenum in the range... 

Nb(cr) and Nb(t) obtained from levitation calorimetry techniques. In the vicinity of the adopted enthalpy vlaues for Nb(cr)... 

Schaefers, K. Qin, J. Rosner-Kuhn, M. Frohberg, M.G. Mixing enthalpies of liquid Ni-V, Ni-Nb and Ni-Ta alloys measured by levitation alloying calorimetry. Can. Metall. Quart. 1996, 35 (1), 47. 

Bonell [72BON] used levitation calorimetry to measure the heat content of liquid zirconium in the temperature range 2233 to 3048 K, referring to a reference temperature of 2128 K (the melting point of zirconium see Section V. 1.1.1). The data obtained were linear with respect to temperature (Figure V-6) indicating that the heat capacity of the liquid phase is a constant. The value of the heat capacity determined for liquid zirconium from the data of [72BON] is ... 

In this study, the thermal properties of a number of metals were determined in their liquid state using levitation calorimetry. Liquid zirconium was studied from 2233 to 3048 K, with a reference temperature of 2128 K (the melting point of zirconium). The change in the enthalpy increment over this temperature range was found to be linear indicating that the heat capacity was constant and equal to (40.7 0.7) J-K -mof. From the measurements, the heat of fusion was found to be (14.7 0.3) kJ-mof. These values are accepted by this review. 

BON] Bonnell, D. W., Property measurements at high temperatures -levitation calorimetry studies of liquid metals, Ph. D. Thesis, Univ. of Rice, (1972). Cited on pages 93, 94, 294. 

Thermophysical properties are defined, in Chapter 9 by Cagran and Pottlacher, as a selection of mechanical, electrical, optical, and thermal material properties of metals and alloys (and their temperature dependencies) that are relevant to industrial, scientific, and metallurgical applications, and this covers a wide range of different material properties obtained by numerous different measurement techniques. The focus in Chapter 9 is, however, on thermophysical properties that are accessible through dynamic pulse calorimetry Other non-calorimetric techniques have been developed but, with the exception of levitation (needed to measure technologically important properties like viscosity and surface tension) have been excluded from consideration. 

Chekhovskoi, V.Ya. (1984) Levitation calorimetry, in Compendium of Thermophysical Property Measurement Methods. Vol. 1. Surrey of Measurement Techniques (eds K.D. Maglic, A. Cezairliyan, and V.E. Peletsky), Plenum Press, New York, pp. 555-589. 

Stretz, L.A. and Bautista, R.G. (1974) The high temperature heat content of liquid yttriiun by levitation calorimetry. MetaU. Trans., 5, 921-928. 

Example Levitation Calorimetry on Nickel, Iron, Vanadium, and Niobium... 

Frohberg, M.G. (1999) Thirtyyears of levitation melting calorimetry—a balance. Thermochim. Acta, 337, 7-17. 

Schaefers, K., Rdsner-Kuhn, M., and Frohberg, M.G. (1995) Enthalpy measurements of undercooled melts by levitation calorimetry the pure metals nickel, iron, vanadium and niobium. Mater. Sci. Eng. A, 197,83-90. 

Application of noncontact AC calorimetry using electromagnetic levitation under a strong DC magnetic field enables direct measurement of thermal conductivity melt fiow is suppressed and heat transfer is controlled only by conduction within a droplet, so that a droplet behaves as if it were solid [35, 36]. Furthermore, measurements are free from the sensor insulation coating. The thermal conductivity can be obtained from the ( )-co relation simultaneously with total hemispherical emissivity st, as described in Section 4.3. 

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