熔融态氯化镁直接热解制备氧化镁粉体及表征

Preparation and characterization of magnesia powder by direct pyrolysis process of molten magnesium chloride

利用Kroll法冶炼钛过程中还原蒸馏产生的熔融氯化镁,在通氧条件下,直接热解制备出超细的氧化镁粉体。考察热解温度、热解时间、氧气分压对熔融氯化镁热解效率的影响。通过单因素实验确定的最佳工艺条件如下：热解温度1 000℃,输入氧分压0.08 MPa,热解时间50 min。优化条件下氯化镁的热解率达93.5%。实验制备的样品氧化镁经X射线衍射和扫描电镜分析：其平均粒径为80~100 nm,粒度分布均匀,分散性好,纯度很高,获得的氧化镁颗粒为不规则六面体形。热解反应的动力学研究表明：氯化镁热解过程的初始阶段受化学反应控制,表观活化能为93.7 kJ/mol;反应后期受扩散与化学反应混合控制,表观活化能为26.3 kJ/mol。

The molten magnesium chloride, from reduction-distillation process in Kroll method of titanium metallurgy, was used to produce ultra fine magnesia powder under the condition of oxygen by direct pyrolysis. The effects of pyrolysis temperature, pyrolysis time and oxygen pressure on the pyrolysis efficiency of molten MgC12 were investigated. The single factor experiments show that the optimum reaction conditions are as follows： pyrolysis temperature 1 000 ~C, pyrolysis oxygen partial pressure 0.08 MPa and pyrolysis time 50 min. The pyrolysis rate of molten MgC12 can reach 93.5% under the optimum conditions. The obtained MgO powder was analyzed by XRD and SEM. These MgO powders, showing an irregular hexahedral shape, have an average diameter of 80-100 nm with uniform size distribution, good dispersity and high purity. The dynamic study of pyrolysis reaction show that this reaction is controlled by chemical reaction at the initial stage of reaction, with the apparent activation energy Ea=93.7 kJ/mol. At the later reaction stage, both diffusion and chemical reaction become the restricting factors with the apparent activation energy Ea=26.3 kJ/mol.