铝电解槽阴极电化学侵蚀机理研究

The most attractive problem in the aluminum reduction industry is to reduce the energy consumption. One of the effective way is applying the graphitized cathode blocks to the aluminum reduction cells. However, the erosion of the graphitized cathode is much faster than the traditional cathode, which limits the lifetime of the aluminum reduction cells. Therefore, it is significant to clarify the mechanism of cathode erosion, which would advance the cathode design, improve the life time of aluminum reduction cells and reduce the energy consumption. The previous studies have approved that the electrochemical formation of porous aluminum carbide is the primary cause of the cathode erosion; the formation rate of aluminum carbide is proportional to the local current density on cathode surface; the diffusion of ions in the electrolyte controls the formation rate of aluminum carbide. Currently, there is almost no research work on the electrochemical erosion of the cathode in China. Most research works on cathode life time focus on the physical damage caused by sodium penetration. In this study, the diffusion coupled experiments of Al-C will be carried out to systematically investigate the impacts of electrical current, properties of graphite material and the amount of electrolyte between the aluminum pad and carbon cathode on the micro-structure of the aluminum carbide formed on the cathode surface. The structure and composition of ions in the electrolyte will be analyzed based on the molecular dynamics. The diffusion mechanisms of the ions in the porous aluminum carbide would be clarified and the kinetic of the aluminum carbide formation will be revealed clearly. The established CFD model of cathode dynamic erosion in aluminum reduction cells would be improved.

降低能耗是国内外铝电解工业的热点，石墨化阴极是铝电解槽节能降耗的有效途径。然石墨化阴极炭块较高的侵蚀速率是制约铝电解槽寿命的关键问题。因此，阐明石墨化阴极的侵蚀机理，对改进阴极设计，提高铝电解槽寿命和进一步节能降耗具有重要意义。研究表明，阴极表面由电化学反应生成多孔状碳化铝是其侵蚀的根本原因，碳化铝的生成速率与阴极电流密度成正比，电解质在碳化铝层中的扩散是炭阴极表面生成碳化铝的控速环节。目前，国内对铝电解槽阴极侵蚀的研究主要集中在纳渗透引起阴极材料膨胀而造成的物理破坏，尚未在阴极电化学侵蚀方面有较多的研究。本项目拟通过Al-C扩散偶实验,系统研究电流密度、石墨材料特性以及阴极与铝液间电解质层厚度对生成的碳化铝微观结构的影响规律；基于分子动力学原理探讨电解质中的离子结构和组成，阐明电解质离子在碳化铝层孔隙中的传质机制，揭示碳化铝生成的动力学规律；进一步完善铝电解槽阴极侵蚀的动态CFD模型。

降低能耗是国内外铝电解工业的热点，石墨化阴极是铝电解槽节能降耗的有效途径。然而石墨化阴极炭块较高的侵蚀速率是制约铝电解槽寿命的关键问题。因此，阐明石墨化阴极的侵蚀机理，对于改进阴极设计，提高铝电解槽寿命和进一步节能降耗具有重要意义。本项目通过Al-C扩散偶实验，系统研究了电流密度、电解时间、石墨材料特性以及阴极与铝液间电解质层等因素对阴极表面生成碳化铝层微观结构的影响规律。采用热力学计算、量子化学计算、高温原位拉曼研究了NaF-AlF3，NaF-AlF3-Al2O3，NaF-AlF3-Al4C3三种熔盐体系的离子结构与组成，阐明了不同熔盐组成下电解质离子的相互转换与传质特性。获得了熔盐中可能存在的化合物的特征结构和拉曼、红外光谱等基础数据，并提出一种新方法用于模拟熔盐拉曼光谱，基于该方法确认了Al4C3在NaF-AlF3熔盐体系中的主要溶解产物为Na3Al3CF8。进一步完善了铝电解槽阴极侵蚀的动态CFD模型，充分研究了非均匀电流密度分布、碳化铝生长与溶解、石墨与铝液间熔盐层离子传质等因素对阴极腐蚀速率的影响，为工业生产中预测铝电解槽使用寿命提供参考依据。