Preparation of Reduced Iron Powders from Mill Scale with Microwave Heating: Optimization Using Response Surface Methodol
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ACCORDING to the different production methods and history, iron powders are classified into four types: reduced iron powder,[1] atomized iron powder,[2,3] electrolytic iron powder,[4] and carbonyl iron powder,[5] depending on the production method. These powders are used in various applications, taking advantage of their respective properties. Reduced iron powders are one of the most essential materials in modern society. They have a very wide range of applications in different industries, including powder metallurgy, magnetic material,[6–8] cutting and welding, coating,[9–13] sewage treatment,[14–16] and medicine and food.[17–20] The demand for reduced iron powder is ever increasing due to the rapid development of the car industry and overall due to betterment of living standards in developing countries. The oxidized QIANXU YE and JIAN CHEN, Master Students, HONGBO ZHU, Associate Professor, JINHUI PENG, Professor, and LINQING DAI, Doctor, are with the State Key Laboratory Breeding Base of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming, P.R. China, and also with the Key Laboratory of Unconventional Metallurgy, Ministry of Education and Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, P.R. China. Contact e-mails: [email protected]; [email protected] C. SRINIVASA KANNAN, Professor, is with the Chemical Engineering Program, The Petroleum Institute, Abu Dhabi, United Arab Emirates. PENG LIU, Assistant Engineer, is with the Changchun Gold Research Institute, Changchun 130012, P.R. China. Manuscript submitted September 24, 2012. Article published online November 2, 2013 1478—VOLUME 44B, DECEMBER 2013
mill scale[21] is formed in the process of rough machining or by further oxidizing. The output of mill scale is just 1.0 pct of rough steel consumption. China’s output of rough steel is approximately 0.68 billion tons with the proportional output of mill scale being 6.8 million tons in 2011. The global production of mill scale was reported to be about 13.5 million tons in 2008.[22] Mill scale is reported to be most suitable material for the preparation of high-value magnetic materials and reduced iron powder owing to low impurities.[23] Traditional heating methods through conventional heat-transfer modes lead to nonuniform heating, with a large variation in temperature on the surface of the material to its interior, hindering the process of gas removal and leading to long production duration and high energy consumption. Microwave heating is applied successfully in different scientific applications due to its special characteristics such as selective, uniform, and fast heating; no pollution; and low equipment cost. The mode of heat transfer is through dipole polarization, ionic conduction, and ferromagnetic resonance. When exposed to high frequency voltage, high frequency variation takes place in the direction of electromagnetic field, resulting in high frequency rotation of the polar molecule and dipole which generates he
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