Thermal Conductivity of Molten Silicate of Al 2 O 3 -CaO-Na 2 O-SiO 2 Measured by Means of a Front Heating-Front Detecti
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NTRODUCTION
HEAT transfer properties of metallurgical slags are of importance in the control and design of the solidification and refining processes of metals, as shown in the review on thermal conductivity and conductivity data by Mills and Susa.[1] Mills[2] has also suggested that NBO/T (Non-Bridging Oxygen ions per Tetrahedrally coordinated cation) representing the degree of polymerization of the network structure is related to the thermal conductivity of slags. Several reports are available on the thermal conductivity of silicates Al2O3-CaO-SiO2 at high temperature.[3–7] The derived values are different for each experiment technique because of the difficulty of the measurement at high temperature. The values of NBO/T for most measured samples are limited in the range between 0.4 and 0.9 because of the narrow liquid region of the ternary Al2O3-CaO-SiO2 system. The effect of the polymerization of the silicate network structure on thermal conductivity has been ambiguous due to the insufficient reliability of the thermal conductivity values of silicates at high temperature and limited measured range for NBO/T.
The laser flash method is recognized as a versatile technique to measure the thermal diffusivity of various materials such as metals and silicates in a wide temperature range, even above melting temperature.[8,9] The front heating-front detection laser flash method is not affected by electrical properties of the samples. This method is also recognized as a promising tool not significantly affected by radiative heat transfer.[10] This is particularly true when focusing on the initial short time region of measured temperature decay in the area irradiated by a laser pulse, where conductive heat transfer is dominant and radiative heat transfer is minor, because the resultant temperature gradient by laser is steep in the liquid state. The main purpose of this work is to obtain the thermal conductivity values of molten Al2O3-CaONa2O-SiO2 silicates by the front heating-front detection laser flash method. The chemical compositions of samples are chosen systematically in order to consider thermal conductivity in relation to network structure of silicate melts in a wide range of NBO/T values.
II. HIROKI HASEGAWA, Doctoral Student, TAKAYA KOWATARI, MSc Student, and YASUHIRO SHIROKI, MSc Student, are with the Graduate School of Science and Engineering, Ibaraki University, Ibaraki 316-8511, Japan. HIROYUKI SHIBATA, Associate Professor, and YOSHIO WASEDA, Professor Emeritus, are with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan. HIROMICHI OHTA, Professor, is with the Department of Materials Engineering, Ibaraki University, Ibaraki 3168511, Japan. Contact e-mail: 12nd108s@hcs. ibaraki.ac.jp Manuscript submitted August 31, 2012. Article published online October 18, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
EXPERIMENTAL
A. Measurement of Thermal Conductivity Measurement of thermal conductivity was carried out by a laser flash apparatus for high temperature liquid samp
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