铝电解质中碱金属阳离子对Al—O—F复合离子结构和稳定性的影响  

Effect of alkali cations on structure and stability of aluminum-oxygen-fluorine complex ions in aluminum electrolytes

作　　者：韩泽勋 蒿鹏程 陈长科 陈润东 张林威 吕晓军 HAN Ze-xun;HAO Peng-cheng;CHEN Chang-ke;CHEN Run-dong;ZHANG Lin-wei;LYU Xiao-jun(School of Metallurgy and Environment,Central South University,Changsha 410083,China;Xinjiang Joinworld Co.,Ltd,Urumchi 830000,China)

机构地区：[1]School of Metallurgy and Environment,Central South University,Changsha 410083,China [2]Xinjiang Joinworld Co.,Ltd,Urumchi 830000,China

出　　处：《Journal of Central South University》2023年第3期707-720,共14页中南大学学报（英文版）

基　　金：Project(2016CX019) supported by the Innovation-Driven Project of Central South University,China;Project(51674302) supported by the National Natural Science Foundation of China。

摘　　要：铝电解质中复杂复合离子的结构和稳定性直接影响熔体的性质,进而影响铝电解过程及其技术经济指标。为此,本文采用密度泛函理论研究了碱金属阳离子对Al—O—F复合离子([Al_(2)OF_(6)]^(2-)和[Al_(2)O_(2)F_(4)]^(2-))的结构和稳定性的影响,分析其结构特征、电荷布居、拉曼光谱、阳离子结合自由能和态密度。研究表明,对于孤立的Al—O—F复合离子体系,[Al_(2)OF_(6)]^(2-)复合离子的稳定性大于[Al_(2)O_(2)F_(4)]^(2-)复合离子;当加入碱金属阳离子后,较大尺寸的碱金属阳离子会增强[Al_(2)OF_(6)]^(2-)和[Al_(2)O_(2)F_(4)]^(2-)复合离子的稳定性,这说明Al—O—F复合离子容易生成并长期存在于冰晶石熔盐电解质中,并遵循K_(3)AlF_(6)>Na_(3)AlF_(6)>Li_(3)AlF_(6)的顺序。从电子密度差图中可以直观地看到Al原子和碱金属阳离子的部分电荷消失后聚集到O和F原子周围。本文计算的Al—O—F复合离子的拉曼频率和文献值较为一致。In the aluminium electrolytes,the structure and stability of different complex ions directly determine the properties of the melts,and further affect the process and technical-economic indicator for aluminum electrolysis.Herein,we investigate the effect of alkali cations on structure and stability of aluminum-oxygen-fluorine complex ions([Al_(2)OF_(6)]^(2−)and[Al_(2)O_(2)F_(4)]^(2−))using structural characteristics,charge population analysis,Raman spectrum,cationic binding free energy,density of state based on density functional theory calculation.The research indicates the[Al_(2)OF_(6)]^(2−)ion is more stable than[Al_(2)O_(2)F_(4)]^(2−)ion for isolated Al—O—F ions.When adding the alkali cations,the cations with larger sizes enhance the stability of[Al_(2)OF_(6)]^(2−)and[Al_(2)O_(2)F_(4)]^(2−)ions,implying the Al—O—F ions are easier to form and exist in cryolite electrolytes with a sequence of K_(3)AlF_(6)>Na_(3)AlF_(6)>Li_(3)AlF_(6).We can observe intuitively the part of electrons of Al atoms and cation disappear and then gather around O and F atoms from electron density difference diagrams.The calculated Raman frequencies of the Al—O—F ions are greatly consistent with the published literature value.

关 键 词：Al—O—F复合离子 密度泛函理论 碱金属阳离子 铝电解质 结构和稳定性 

分 类 号：TF821[冶金工程—有色金属冶金]