真空碳热法制备金属镁过程中可逆反应对镁蒸气冷凝的影响

Negative Influence of Reverse Reactions on Magnesium Condensation in Vacuum Carbothermic Reduction

对真空碳热法制备金属Mg过程中可能发生的逆反应进行了热力学分析,结果表明,系统压力为60 Pa,且温度低于900 K的条件下,冷凝过程中会有逆反应发生。实验研究表明,冷凝温度越接近镁的露点温度,直收率越高。通过对还原产物和蒸馏产物的X射线衍射、扫描电镜及X射线光电子能谱仪的对比分析可以发现,还原产物在受到逆反应的影响的条件下,所形成的镁粉晶粒排列不规则且尺寸较小:而没有逆反应影响所形成的金属Mg晶粒排列规则致密且尺寸较大,因此有效控制逆反应的发生成为收集到结晶较好金属Mg的关键。

The possiblereverse reactions in vacuum carbothermic reduction of Mg O was mathematically modeled,theoretically analyzed in thermodynamics and experimentally evaluated. The influence of the reverse reaction and condensation temperature on the recovery and morphology of the Mg condensate was investigated with X-ray diffraction,energy dispersive spectroscopy and scanning electron microscopy. The calculated results show that the reverse reactions of Mg and CO start at 60 Pa and 900 K. The experimental results reveal that depending on the condensation temperature,the reverse reactions strongly affected the Mg recovery efficiency and morphology of Mg grains. To be specific,condensation at a temperature closer to the dew-point of Mg resulted in a higher recovery-efficiency; the reverse reactions were responsible for the formation of highly porous Mg-condensate with small irregularly sized,heavily C-contaminated Mg-grains,in contrast to the compact,highly pure,long needle-shaped Mg-grains condensed with no interference of the reverse reactions.