【作者】 李志华；

【导师】 戴永年；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2004， 博士

【摘要】 本文综合评述了国内外镁行业的发展情况和金属镁及镁合金的性质、用途及各种生产方法。通过对比，作者认为无论是电解法还是硅热还原法都存在严重缺陷：电解法工艺复杂，投资大，生产过程中会产生有毒气体—氯气，其废气、废水、废渣处理的任务重，费用大，生产设备和厂房腐蚀严重，维修费用大。硅热法炼镁主要存在三大弊端：①、它所广泛使用的还原剂为含硅75％的硅铁，价格比较高，这就提高了生产成本。②、皮江法所使用的还原罐是山特殊的合金钢制成，不但价格昂贵，使用寿命也不长。③、由于罐内抽真空、罐外常压加热，还原罐的尺寸小，单罐装料量低，还原罐产能低，热效率不高，而且是间断生产，生产能力和劳动生产力低。 把真空冶金技术用于金属镁的制取，利用廉价的煤碳代替昂贵的硅铁，用自行研制的内热式真空炉代替还原罐，真空炉的规模可以突破罐子容量的限制，提高热效率和单台设备的产能，有可能降低生产成本，改善劳动条件。由于所有的冶金过程都在密闭的真空系统中进行，对环境污染小。 经国际联机检索，国内无此相关文章发表，国外也很少，根据其中最具代表性的R.Winand于1990年发表的文章来看，他也只做到了如何在真空中用碳还原氧化镁产出镁蒸气，而并没有解决如何使还原出来的镁蒸气冷凝成为液态或固态结晶镁，后因管道发生堵塞问题而停止。 热力学计算结果表明，在真空中用碳还原氧化镁提炼金属镁可行，与常压碳热还原反应相比，真空作业可以降低反应温度300～400℃，还原出的金属镁也不易被氧化。得到块状冷凝镁的条件是：还原温度不应低于1352℃，对应的露点温度在651℃(镁熔点)以上，冷凝温度不应太低。 小型实验结果证明：还原温度升高，还原时间延长，氧化镁还原率增大，添加适量的氟化物对还原反应有促进作用；还原过程中真空度随时间的变化具有规律性，由此可以判断还原反应进行的速度与程度；真空中煤还原氧化镁的条件是：配料时保证C：MgO(摩尔比)＝3∶1，并加入占总料重10％的氟化钙作为催化剂，尽可能的提高反应温度至1500℃以上，保温30～40分钟 小型实验成功的得到了结晶状态较好、呈粗纤维状垂直生长在冷凝面上的固态块状冷凝镁，冷凝镁的生长方式属于层生长型，冷凝物中金属镁的纯度最高可达99％以上，优于前人只能得到镁粉的研究。昆明理T人学博卜学位论文摘要 小型实验设计、制造了新型真空炉，与从前实验初期用的炉型相比，新炉型具有自动化水平高;易操作，安全性较好等优点，一个设备就能完成真空焦结、真空热还原和镁蒸气冷凝作业，整个过程未加入其它气体，控制适当的冷凝条件，就可以直接产出纯度很高的冷凝金属镁块而不是镁粉，从而勿需后续镁粉蒸馏工艺，工艺流程较短，提高了人员操作的安全性。 为解决真空炉内喷料问题，本研究将煤化学、炼焦学与真空冶金学相结合，提出了真空焦结工艺，并采用SEM(扫描电镜)、EPMA(电子探针)和XRD(X一射线衍射)等现代化的分析测试手段，详细研究了不同比例的氧化镁与焦煤混合物在真空条件下焦结后得到类似于半焦的焦结产物的变化规律，确定了真空条件下煤炭还原氧化镁工艺中真空焦结作业的最佳条件是，600℃左右焦结30分钟，较好的解决了还原过程中发生的喷料现象，从而解决了管道堵塞问题。同时，真空焦结工艺还可用于真空条件下，煤炭还原其它粉状金属化合物的过程，丰富了真空冶金的相关理论。 动力学研究表明，与大多数金属氧化物的碳还原机理不同，氧化镁碳热还原反应中，C比CO更容易还原Mgo;差热一差重的结果显示，在N，保护下，C一MgO体系在1200℃附近发生强吸热反应，此反应很可能是C还原MgO的反应;通过平衡常数的比较，在温度区间(1400一2000K)内，MgO离解出O原子的反应是整个还原反应中的限制环节:作者认为，由于C一O键比Mg一O键稳定，高温下，因为C的存在而破坏了Mg一O键，形成更稳定的C一O键，从而促进了还原反应的发生:加入氟盐后，F一能够破坏MgO表面晶格，使MgO晶体产生畸变，促进Mg一O键的断裂，形成更稳定的C一O键，氟盐可以降低C一MgO体系的熔点，促进C还原MgO反应的发生，降低还原反应的活化能，从而达到加快总还原速率的目的;经过计算机拟合，C一Mgo还原反应符合界面化学反应模型，动力学方程为l一(l一。){二0 .1 92。一221400 衬了’t，表观活化能E=22 1 .4kJ/mol。更多还原

【Abstract】 The development of the domestic magnesium industry, properties, applications and preparation methods of primary magnesium and magnesium alloy are overviewed in the thesis. It’s the opinion of the author that there are grave defects in traditional methods: moltensalt electrolysis and silicothermic reduction of oxides. The former process is complex, needs vast investment, and emits toxic gases like chlorine gas; treatment of production wastes is overburden costly; erosion of the production equipments and plant buildings is badly, and maintenance cost overwhelming. The flaws in the process of magnesium extraction by silicothermic reduction of oxides are: ?high production cost with the higher cost of major reductant, ferrosilicon (75%);(2) short service life, but high price of reduction retort, which is made of high Ni-Cr alloy; (3) Since the retort is vacuumed inside and heated under the normal pressure outside, small-size retort, low forced filling rate, low production capacity and thermal efficiency, batch production and low productivity are lead to.Introduction of vacuum technology in magnesium extraction, high Ni-Cr alloy is substituted by cheaper carbon and reduction retort by internal heating vacuum furnace; scale of vacuum furnace is free of the limit of retort cubic capacity;thermal efficiency and production of single equipment are raised, cost decreased andworking conditions improved. Since all reactions take place in the closed vacuum furnace, there is less influence upon environment.Through inter-link retrieve, relevant papers are absent domestic; and abroad are scarce. R.Winand, the most epitomized, solved only how to produce magnesium vapor through magnesia reduction by carbon, conditions and devise of condenser used to condense the vapor into liquid or solid critical magnesium was not touched upon. Extended test ended deplorably due to clogging.Thermodynamic calculation gives that: the process, magnesia reduced by carbon in vacuum, is feasible, that by comparison with atmosphere carbothermic reduction, vacuum method decreases reaction temperature by 300~400癈,and that reaction efficiency is enhanced under the situation of reduction temperature higher than or equal to 1352癈,homologous dew point higher than 651癈( melting point of magnesium).Laboratory test results in improver reduction rate by enhancing reduction temperature and elongating reduction time, additionally by adding appropriate fluoride. During reducing process, vacuum degree changes with time and by which decides the reduction rate and completeness. The condition, of magnesia reduction by coal in the vacuum, is: C:MgO (molar ratio) is 3:1, calcium fluoride, which is 10% of total weight, is added as catalyst, the reaction temperature is raised above 1500癈 and holding-time is 30-40min.The better crystalline state and heavy fibrous structure solid magnesium lump condensates, growing vertically on condensation face, are succeeded to acquire in laboratory tests. The condensed magnesium have a layered growth and the purity of condensed magnesium is up to 99%, which are superior to former researches only getting magnesium powers.The novel vacuum furnace is employed in laboratory study. Compared with atmosphere magnesium carbothermic reduction furnace, this new one has the merits of high automation, easy manipulation and fine safety. Vacuum coking, vacuum carbothermic reduction process and magnesium vapory condensation process can be carried out in a furnace. And the whole reduction process, without gas H2 or N2, can directly yield very high purity magnesium lump condensates, then omits the following process of distilling magnesium powders, shortens the whole flow sheet-IV-Abstractand improves the operation security.The dissertation integrates coal chemistry and coking with vacuum metallurgy to bring up vacuum coking procedure. Updated analysis and test procedure such as SEM, EPMA, XRD, are exploited to explore the law behind coking varied ratio of magnesia and coal in vacuum to get semi-coking material. The doctoral t更多还原