Okabe Toru H, Hamanaka Yuki, Taninouchi Yu-Ki
International Research Center for Sustainable Materials, Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
Faraday Discuss. 2016 Aug 15;190:109-26. doi: 10.1039/c5fd00229j.
Deoxidation of Ti, or direct removal of O dissolved in metallic Ti, is known to be extremely difficult when Mg is used as the deoxidizing agent. This difficulty arises because the chemical potential of O2, pO2, under Mg/MgO equilibrium is high (approximately 10(-41) atm at 1200 K) and is equivalent to that of Ti containing ∼2 mass% O at 1200 K. Therefore, when deoxidizing Ti to the commercial level of high-grade pure Ti (below 0.05 mass% O) using an Mg reductant at 1200 K, the activity of the reaction product MgO (aMgO) must be decreased to below ∼0.025, which is difficult in practice. In this study, the removal of O in Ti in molten MgCl2 salt using an electrochemical technique was examined at ∼1173 K with the objective of obtaining Ti containing less than 0.05 mass% O. Ti samples and graphite electrodes immersed in molten MgCl2 served as the cathode and anode, respectively. A constant voltage was applied between the electrodes using an external DC source. Molten MgCl2 was employed to produce the deoxidizing agent Mg and to facilitate deoxidation of Ti by decreasing the activity of the reaction product MgO. By applying a voltage of approximately 3.1 V between the electrodes, the chemical potential of Mg in the molten MgCl2 was increased at the surface of the Ti cathode, and the Ti samples were deoxidized. The resulting O species, mainly formed O(2-) dissolved in the molten MgCl2, was removed from the molten salt by reacting with the C anode to form CO (or CO2) gas. Ti wires containing 0.12 mass% O were deoxidized to less than 0.02 mass% O. In some cases, the O concentration in the Ti samples was reduced to the level of 0.01 mass%, which cannot be accomplished using the conventional Kroll process. The possible application of this deoxidation technique to practical industrial recycling processes is discussed.
已知当使用镁作为脱氧剂时，钛的脱氧，即直接去除溶解在金属钛中的氧极其困难。出现这种困难的原因是，在镁/氧化镁平衡状态下，O₂的化学势pO₂很高（在1200K时约为10⁻⁴¹大气压），并且与1200K时含氧量约为2质量%的钛的化学势相当。因此，当在1200K下使用镁还原剂将钛脱氧至高纯度商业级钛（氧含量低于0.05质量%）时，反应产物氧化镁（aMgO）的活度必须降低至约0.025以下，而这在实际中很难做到。在本研究中，在约1173K下，采用电化学技术研究了在熔融氯化镁盐中去除钛中的氧，目标是获得氧含量低于0.05质量%的钛。浸入熔融氯化镁中的钛样品和石墨电极分别用作阴极和阳极。使用外部直流电源在电极之间施加恒定电压。采用熔融氯化镁来生成脱氧剂镁，并通过降低反应产物氧化镁的活度来促进钛的脱氧。通过在电极之间施加约3.1V的电压，熔融氯化镁中镁的化学势在钛阴极表面升高，钛样品被脱氧。生成的氧物种，主要是溶解在熔融氯化镁中的O²⁻，通过与碳阳极反应形成CO（或CO₂）气体而从熔盐中去除。含0.12质量%氧的钛丝被脱氧至低于0.02质量%。在某些情况下，钛样品中的氧浓度降低至0.01质量%的水平，这是传统克劳尔法无法实现的。讨论了这种脱氧技术在实际工业回收过程中的可能应用。
