NdFeB表面纳米结构Al膜的离子液体电沉积机理及耐蚀性尺寸效应

Magnetic material NdFeB is apt to be corroded in hot and humid environment, then the structure and magnetic performance are destroyed. Nowadays, it is an urgent problem to be resolved. Nanocrystalline aluminum(Al) film with the character of good physical properties, similar potential with NdFeB (value difference is 0.06V) and dense oxide film formed on the surface in the natural atmospheric environment, has a broad application prospects in the field of magnet protection. In this project, the crystallization and corrosion mechanism of nanocrystalline Al film electrodeposited in imidazole ionic liquid on NdFeB will be researched. Experimental techniques such as electrodeposition electrochemical noise (EES), quartz crystal microbalance (QCM), etc. are adopted to study the effects of solution composition, additives, current densities, etc. on the “nucleation/growth” mechanism of Al film, as well as, the important parameters and key steps of nanocrystalline size control. Moreover, theoretical model will be set up to clarify the mechanism of nanocrystalline Al film on NdFeB. On the base of the above study, the corrosion mechanism of nanocrystalline Al film in service environments will be researched using electrochemical corrosion noise (ECN) and electrochemical impedance spectroscopy (EIS) techniques. Finally, the relationship between microstructure and performance (corrosion resistance mainly) of nanocrystalline Al film will be discussed to reveal the size effect of its corrosion resistance. The implementation of this project has an important practical significance and theoretical value in the industrial development and application of nanocrystalline Al film electrodeposited on NdFeB.

钕铁硼(NdFeB)在高温、潮湿环境易腐蚀进而导致磁性能下降的问题亟待解决。纳米结构Al膜具有物理性能好、与NdFeB电位差小(0.06V)、表面易形成致密氧化膜等特点，在磁性材料防腐领域具有广阔应用前景。项目拟在咪唑类离子液体中实现NdFeB表面纳米结构Al膜的电沉积；联用电沉积电化学噪声(EEN)、石英晶体微天平等技术，探讨溶液组成、添加剂、电流密度等对Al膜“成核/生长”机制的影响，查明调控Al膜晶粒尺寸的重要参数和关键步骤，建立相关理论模型，阐明NdFeB表面纳米结构Al膜的电沉积机理；在上述研究基础上，采用电化学腐蚀噪声(ECN)、EIS等技术，研究晶粒尺寸变化对纳米结构Al膜在服役环境中腐蚀电化学机制的影响，探讨Al膜“微结构-性能（主要是耐蚀性）”关系，揭示其耐蚀性尺寸效应。本项目的开展可为NdFeB表面纳米结构Al膜的工业开发和应用提供坚实基础，具有重要实际意义和理论价值。

钕铁硼具有较高饱和磁通量、矫顽力、磁能积以及良好的机械加工特性，在声学、航空、电子、自动化、生物、通讯等众多领域得到广泛应用。然而NdFeB磁体在服役环境中易发生腐蚀（主要形态为晶间腐蚀），导致其性能下降。改善NdFeB磁体在实际应用环境中的耐腐蚀性能，是亟待解决的问题。项目以咪唑类离子液体（EMIC）为研究体系，以烧结型NdFeB为基体，联合电沉积电化学噪声（EEN）、电化学阻抗（EIS）、扫描电化学显微镜（SECM）、石英晶体微天平（QCM）等实验技术，探讨了溶液组成、温度、电流密度、沉积电压、添加剂（2-氯烟酰氯）等对“离子液体/电极”界面Al还原过程、Al膜的三维瞬时成核机制。Al在NdFeB磁体上的沉积电位为-0.615V，电极反应速度受扩散控制。恒电位方式沉积时，沉积电压为-0.6V，有利于在NdFeB上沉积出致密均匀的Al膜，且耐蚀性最佳。Al膜上晶粒主要为Al面心立方结构，在(200)、(220)和(311)择优取向；采用脉冲电沉积Al膜时，在沉积电流密度12.5mA/cm2，脉冲频率5Hz，占空比0.5条件下制备的NdFeB/Al样品耐腐蚀性能最佳；添加剂（2-氯烟酰氯）含量的增加，可降低阴极的沉积速率，促进Al晶粒尺寸减小，获得细致光亮耐蚀性好的镀层。NdFeB/Al样品的耐蚀性能随着表面Al膜晶粒尺寸的减小而增强。为了进一步提高NdFeB/Al样品的耐蚀性，通过溶胶旋涂法在NdFeB表面获得了Al/TiO2复合膜。热处理温度为450℃，添加剂（聚乙二醇）含量10mg/L时，NdFeB/Al/TiO2在紫外氙灯（365nm）光照下3.5%NaCl溶液中的自腐蚀电位负移50mV（VS. NdFeB/Al），产生的光电流密度为112µA/cm2，自腐蚀电流密度降低明显。本项目研究成果可为NdFeB表面防护性纳米结构Al膜的工业开发和应用提供基础，为NdFeB在复杂环境（湿热、冷热交替等）微型机械中的应用提供技术支持，具有重要的实际意义和理论价值。