Thermal Conductivity of the Molten CaO-SiO 2 -FeO x System
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INTRODUCTION
MOLTEN slag produced during the ironmaking and steelmaking processes has been a major environmental issue for many years. In recent times, the enormous effort aimed at the effective recycling and utilization has allowed almost full recycling of blast furnace slag into Portland blast-furnace slag cement material, roadbed material, and concrete aggregate. However, steelmaking slag has not been intensively utilized owing to its high basicity and the existence of problematic elements. Another consideration of environmental importance is the large amount of sensible heat contained in molten slag. Generally, molten steelmaking slag from the converter or hot metal pretreatment is discharged into the slag yard and slowly cooled. Although the huge amount of sensible heat emitted during the cooling process can be highly valuable for heat recovery, the process for heat has not been satisfactorily established compared to the heat recovery of blast furnace slag. Recently, efforts devoted to the improvement of the recycling processes have focused on investigating the characteristics of crystallization and the stabilization of hazardous elements.[1–3] In addition, the optimization of the aging process, during which free-CaO is hydrated, has been attracting more attention than ever before.[4,5] On the other hand, for the development of the technology YOUNGJO KANG, formerly Research Associate, with the Institute of Industrial Science, The University of Tokyo, Tokyo 1538505, Japan, is now Senior Researcher, Technical Research Laboratories, POSCO, Pohang, Gyeongbuk 790-300, Korea. Contact e-mail: [email protected] KIYOSHI NOMURA, Associate Professor, is with the Graduate School of Engineering, The University of Tokyo, Tokyo 113-0033, Japan. KAZUTO TOKUMITSU, Research Associate, and KAZUKI MORITA, Professor, are with the Institute of Industrial Science, The University of Tokyo. HIROYUKI TOBO, Senior Researcher, is with the Steel Research Laboratory, JFE Steel Corporation, Chiba 260-0835, Japan. Manuscript submitted November 28, 2011. Article published online August 21, 2012. 1420—VOLUME 43B, DECEMBER 2012
for the heat recovery and the slag utilization, the characteristics of heat transfer in molten as well as solidified slag are certainly one of the most important factors to be clearly understood. However, the systematic study of the thermophysical properties of the steelmaking slag has been limited due to experimental difficulties, which may be caused by high temperature or experimental errors. In particular, appropriate measurements for thermal conductivity of molten steelmaking slag in the presence of the oxides of transition metals are expected to be very challenging. The transition metals usually have multivalences in the molten state, which may be of significance in considering the thermophysical properties of the melts. Hence, a clear understanding of their impact is essential. Very few examples of the measurement of the thermal conductivity of iron oxide containing slag have been found in the literature. A pionee
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