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Noncontact laser modulation calorimetry for high purity liquid iron


K. Sugie1, H. Kobatake1, H. Fukuyama1, M. Uchikoshi1, M. Isshiki1, K. Sugioka2 and T. Tsukada2

1Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
2Department of Chemical Engineering, Tohoku University, Sendai, Japan

Keywords: laser calorimetry, electromagnetic levitation
property: heat capacity, thermal conductivity
material: liquid iron

Recently, a numerical simulation has been developed for modeling of heat and mass transfer in refining, casting and welding processes of steel. Accurate thermophysical properties such as heat capacity and thermal conductivity of liquid iron are necessary as input parameters for the simulation. However, the thermophysical properties of liquid iron are not well established because of the high chemical reactivity and fluidity of liquid iron. To overcome the difficulties, we have developed the noncontact laser modulation calorimetry using an electromagnetic levitator (EML) in a dc magnetic field [1]. An iron sample was electromagnetically levitated and melted in a dc magnetic field. The top surface of the liquid iron droplet was sinusoidally heated by a semiconductor laser irradiation. The temperature of the bottom surface was measured using a single-color pyrometer. A dc magnetic field was applied up to 10 T to the sample to suppress the convection in the sample. The heat capacity and thermal conductivity of the liquid iron can be measured by analyzing the temperature response over a wide temperature range. In this study, the high purity iron sample (purity: 99.997 mass %), which was prepared by an ion exchange method, was also used for this measurement. The molar heat capacity at constant pressure of liquid iron was successfully measured at lower dc magnetic fields (3, 4 and 5 T). This can be explained by the accomplishment of the semi-adiabatic condition caused by the higher thermal conductance of the convection in liquid iron droplet [2]. The values of heat capacity had negligible temperature dependence, and the average value was determined as, cP / J×kg-1×K-1 = 45.4 +- 3.2 [1816 - 1992 K] This value showed a good agreement with the recommended values by NIST-JANAF [3]. On the other hand, as increasing a dc magnetic field, the apparent thermal conductivity of liquid iron decreased, and finally the value was converged at 9 T. This result indicates that convection was suppressed enough to measure the thermal conductivity at 9 T or larger. The values of thermal conductivity obtained at 9 T or larger was independent on a temperature, and the average value was expressed as, k / W×m-1×K-1 = 39.1 +- 2.5 [1794 - 2050 K] The present results were distributed between the recommended value by Touloukian [4] and data obtained by Zinovyev [5].

References
  1. H. Fukuyama, H. Kobatake, K. Takahashi, I. Minato, T. Tsukada, S. Awaji, Meas. Sci. Technol., 18 (2007), p.2059-2066.

  2. K. Sugie, H. kobatake, H. Fukuyama, Y. Baba, K. Sugioka, T. Tsukada, Tetsu-to-hagane, 12 (2010), p.673-682.

  3. NIST-JANAF Thermochemical Tables, Fourth Edition, PartⅡ, p.1224-1225.

  4. Touloukian, Y.S., The TPRC data series volume 1, Plenum, New York, (1970), p.169.

  5. V. Y. Zinovyev, V. F. Polev, S. G.. Taluts, G. P. Zinovyeya, S. A. Ilinykh, Phys. Met. Metallog., 61 (1986), p.85-92.

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