烧结NdFeB永磁体的腐蚀行为研究

Corrosion behavior of sintered Nd-Fe-B magnets

摘要:

通过静态腐蚀实验,研究了烧结钕铁硼磁体在3.5 wt.% NaCl溶液中浸泡不同时间段的腐蚀特征。采用扫描电镜、拉曼光谱分析各个阶段的腐蚀形貌和腐蚀产物组成,通过动电位极化曲线、电化学阻抗谱研究不同腐蚀阶段磁体表面结构的变化及腐蚀机理,采用等效电路模型模拟各阶段的腐蚀行为。研究结果表明,烧结NdFeB磁体在3.5 wt.% NaCl溶液中依次发生点蚀、选择性晶间腐蚀、全面腐蚀行为,形成的腐蚀产物层结构疏松,只能产生短时减缓腐蚀速率的效果,而富钕相优先溶解会造成主相颗粒脱落,导致磁体粉化、破坏。腐蚀产物类型随腐蚀时间延长而有所变化,主要为铁和钕的氧化物或氢氧化物。

Abstract:

The corrosion behavior of Nd-Fe-B magnets was studied through immersion test in 3.5 wt.% NaCl solution. The morphology and composition of corrosion product were characterized by scanning electron microscope (SEM) and Raman spectroscopy. The corrosion behavior of the specimens were investigated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electrochemical equivalent circuits were used for fitting the EIS data. Results are as follows: Pitting corrosion, intergranularScorrosion and StotalScorrosion occurred in sequence during the immersion period. However, the corrosion product layer ofSlooseSstructure could only temporarily slow down the corrosion rate. At the initial stage, the Nd-rich phase atStheSgrain boundary preferentially dissolved into the media. Later the main phase particles were exposed to the corrosive solution and quicklyScorroded, causing a damage to the magnets. The corrosion products were mainly iron and neodymium oxides or hydroxides which was evolving with the immersion period.