【作者】 马大剑；

【导师】 刘玉芹；

【作者基本信息】 中国地质大学(北京) ， 材料工程， 2012， 硕士

【摘要】 镁及其合金具有密度低、比强度和比刚度高、阻尼减震性和电磁屏蔽效果好等优点，是目前最轻的金属结构材料。开发金属镁冶炼新工艺，实现原镁的清洁生产和节约发展是我国金属镁工业亟待解决的问题。本论文是白云岩清洁生产金属镁的一部分，探讨在真空条件下，以金属铝为还原剂还原氧化镁制备金属镁，同时副产镁铝尖晶石和氧化铝的可行性。本论文首先对氧化镁铝热还原制备金属镁过程进行了热力学分析，计算了反应温度和压力对氧化镁铝热还原过程可能发生的化学反应的Gibbs自由能的影响，并据此设计了反应温度和物料配比。在此基础上，研究了物料配比、反应温度、反应时间、成型压力对氧化镁铝热还原过程的影响，用等离子体质谱分析、X射线衍射、扫描电镜、透射电镜等手段对结晶镁和固相还原产物的成分、物相、形貌进行了分析。X射线能谱表明：氧化镁铝热还原过程是一个涉及气相－液相－固相的多相化学反应过程，物料配比、反应温度、反应时间和成型压力对氧化镁的还原率和固相还原产物的物相和形貌均产生重要的影响。增加物料配比中金属铝粉的用量，提高反应温度，延长反应时间，增大成型压力，均有助与提高氧化镁的还原率。当氧化镁和金属铝的摩尔比3:2，压片的成型压力200MPa，1200℃反应5h后，氧化镁的还原率达96%。氧化镁真空铝热还原过程分两步进行，第一步是氧化镁和金属铝反应生成镁铝尖晶石；第二步镁铝尖晶石和金属铝进一步反应生成α-氧化铝。在反应温度为1200°C的部分样品中，检测到少量的θ-氧化铝，其形成原因有待进一步的研究。采用氧化镁真空铝热还原法制得的结晶镁纯度高，满足国标GB/T3499-2003中Mg9990的要求。更多还原

【Abstract】 Magnesium and its alloys offer advantages of low density, high specific strengthand toughness, shielding against electromagnetic radiation and high dampingcharacteristrics. Magnesium and its alloys are considered the lowest constructionmetals. To meet the resources concerns as well as environmental considerations in thecurrent China, it is important to develop a new method to produce primarymagnesium. Recently, a new process was developed to produce primary magnesiumusing dolomite ores as the raw materials. The magnesia and calcia are firstly seperatedfrom the calcined dolomite. Then the magnesia is used to produce primary magnesiumby thermal reduction method and calcia was used to make light weight calciumcarbonate as a coproduct. This work is focused on the production of magnesium bythermal reduction of magnesia using aluminium as a reducing agent.In this dissertation, the thermodynamic analysis for the aluminothermic reductionof magnesia was carried out. The Gibbs free energy change for the possible chemicalreactions was calculated and plotted as a function of temperature and pressure. Basedon the thermodynamic analysis, the reduction temperature and magnesia to Al molarratio for the aluminothermic reduction experiments was designed. The effects of MgOto Al molar ratio, reduction temperature, reduction time and the briquettes preparationpressure on the aluminothermic reduction of magnesia were studied experimentally.The chemical composition, phase constitution and morphology of the condensedmagnesium and the briquettes after thermal reduction were investigated byinductively coupled plasma mass spectroscopy, x-ray diffraction, scanning electronmicroscopy equipped with energy dispersive spectrometry and transmission electronmicroscopy.The aluminothermic reduction of magnesia is a heterogeneous chemical reactioninvolving gas species. The magnesia to Al molar ratio, reduction temperature,reduction time as well as briquettes preparation pressure play important roles in thealuminothermic reduction of magnesia. The reduction ratio of magnesia increaseswith the decrease in MgO to Al molar ratio, the increase in reduction temperature, the prolongation of reaction time and the increase in the briquettes preparation pressure.When the magnesia to Al molar ratio is3:2and the briquettes preparation pressure is200MPa, after5hrs aluminothermic reduction at1200°C, the reduction ratio ofmagnesia reaches up to96%.The reduction of magnesia by aluminum is probably taken place in two stages.At the first stage, the MgO react with aluminium to form magnesium vapor and spinelMgAl2O4. At the second stage, the spinel MgAl2O4reacts with aluminium to formmagnesium vapor and Al2O3. Trace amount of θ-Al2O3was detected in samplesreacted at1200°C and the mechanism for the formation of θ-Al2O3is still underinvestigation.The obtained condensed magnesium is well crystallized and its purity meets therequirement of the China national standard GB/T3499-2003Mg9990.更多还原