Mechanism of Ball Milling Effect on Carbothermic Reduction of Industrial Magnesia by Coke
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CARBOTHERMIC reduction of magnesia to produce raw magnesium, compared with the Pigeon process or the molten salt electrolysis process, is an attractive process for magnesium metallurgy because of its environmentally friendly advantages of lower energy consumption, less environmental pollution, and less difficulty in continuous production.[1–6] Many researchers have studied different aspects of the magnesium metallurgy process to increase reaction rate, to improve product purity, to reduce risk of explosion, and to find the possible reaction mechanism. Adding addictive, increasing reductant’s proportion, and milling raw materials are common methods to reach a higher chemical reaction rate at a not-too-high temperature and for a not-too-long time.[7–15] YUN JIANG and YA-FANG WANG are with the School of Science, China University of Geosciences (Beijing), No. 29, Xueyuan Road, Haidian District, Beijing 156, China. Contact email: [email protected] YU-QIN LIU and ZI-MENG ZHAO are with the School of Materials Science and Technology, China University of Geosciences (Beijing), No. 29, Xueyuan Road, Haidian District, Beijing 156, China. ZHI-YU YAN is with the School of Materials Science and Technology, China University of Geosciences (Beijing), and also with the Beijing BOE Display Technology Co., Ltd., No. 118, 1st Jinghai Road, Beijing 156, China. WEI-GONG ZHOU is with the School of Great Wall, China University of Geosciences (Beijing), No. 1689, Nanerhuan Road, Baoding 156, China. Manuscript submitted October 16, 2018. Article published online May 15, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
Mechanical milling is used in almost every carbothermic reduction process because carbon reductants are always fragile during milling. In preparing rutile by carbothermic reduction of ilmenite, ball milling ilmenite and graphite led to a higher reaction rate and a lower onset reaction temperature[16,17] and helped to complete gradual deoxidizing of titanium oxides.[18] To obtain Mn3O4 or MnO using reduction of manganese ore by graphite, milling enhanced its reduction rate at a lower temperature.[19] In carbothermic reduction of hematite by graphite, increasing milling time of mixture made the peaks of each reaction curve move toward the low-temperature range.[20,21] Dry milling mixture of celestite and coke in a planetary ball mill promoted partial amorphization of solids along with structural distortions in celestite, so carbothermic reduction of celestite was improved.[22] Aiming at the effect of ball milling on carbothermic reduction of magnesia by graphite, this work pointed out that refinement of magnesia crystallites and formation of amorphous graphite phase led to a larger interfacial area of particles, and then resulted in an enhancement of the reduction rate.[13] The effect of ball milling on carbothermic reduction is obvious, but the evolution process that materials experience is still not clear. In this work, we studied the ball milling contribution to raw materials and then to the reaction at a similar condit
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