以Si-Cu合金为还原剂的热还原制镁新方法及其热力学分析

Preparation of Mg Using Si-Cu Reduction and Its Thermodynamics

结合Si-Fe相图,分析了硅铁热还原制镁(皮江法)反应过程中Si-Fe中形态,结果显示:初始含Si量75%的Si-Fe在1200℃基本处于固态,硅铁热还原制镁还原反应主要为固-固反应,反应过程中,物料间的热量及质量传输较困难,反应难于快速、彻底进行。介绍了采用Si-Cu合金还原剂实现固-液还原的Si-Cu热还原制镁新思路、新方法,结合Si-Cu相图,分析了Si-Cu热还原制镁中Si-Cu的形态,结果显示:Si-Cu热还原制镁时,初始含Si量低于35%的Si-Cu在1200℃几乎全过程保持液态,还原反应基本为固-液反应,反应较易快速、彻底进行。采用热力学分析方法,推演出了Si-Cu热还原制镁的主要反应式、吉布斯自由能估算式,临界反应温度估算式,分析了影响吉布斯自由能、临界反应温度及还原反应热力学可行性的因素,结果显示:Si-Cu热还原制镁反应的热力学临界温度随系统气压降低及Si-Cu中Si含量增加而减小;对应于常规真空硅热还原制镁(皮江法)温度(1473 K)和系统气压(13.3 Pa),Si-Cu合金中的Si含量只需高于0.034%,Si-Cu热还原制镁即具备热力学可行性。

The characteristic of Si-Fe alloy,which was used as reductant for the preparation of Mg using vacuum Si-Fe thermal reduction,was analyzed with Si-Fe phase diagram.The results showed that the reduction reaction was roughly solid-solid reaction when reaction temperature was about 1200 ℃ and initial Si content ratio in Si-Fe was 75%.Heat and mass transferring among the reaction materials was difficult.The reaction speed and rate were lowered.Preparation of Mg using Si-Cu reduction was introduced.The characteristic of Si-Cu alloy reductant was analyzed with Si-Cu phase diagram.The results indicated that almost the whole process of the reduction reaction could be solid-liquid reaction when temperature was about 1200 ℃ and the initial Si content in Si-Cu alloy was less than 35% and the reduction reaction tends to be fast and completely.The reduction reaction equation,the Gibbs free energy and critical reaction temperature were induced.The factors influencing the Gibbs free energy,critical reaction temperature and thermodynamics feasibility were analyzed.The results showed the thermodynamic critical temperature of Si-Cu reduction reaction decreased with reducing of system gas pressure and increasing of Si content in Si-Cu.At corresponding temperature（1473 K） and system gas pressure（13.3 Pa） of Pidgeon process,the thermodynamics feasibility of Si-Cu reduction reaction was favorable with Si content in Si-Cu alloy to be more than 0.034%.