用透射电镜、Auger能谱,X射线和Mossbauer等方法研究了烧结NdFeB永磁材料在90℃潮湿空气中的氧化行为。结果表明,黑色氧化组织先在富Nd晶界相处形成。沿晶界深入和扩展进入基体相Nd_2Fe_(14)B晶粒,形成表面氧化层。黑色组织内富O和Nd而贫Fe。经500h氧化后,粉末组成仍以Nd_2Fe_(14)B粒子为主,余为Fe_3O_4,Nd_2O_3和少量a-Fe_2O_3,立方Fe_2O_3。经氧化的Nd_2Fe_(14)B相四方晶格内Fe原子分布发生变化,c晶位Fe原子大部分逸失,这是氧化导致材料磁化强度降低的重要原因。
The oxidation of sintered NdFeB magnets in humid atmosphere at90℃ has been studied by TEM, AES, X-ray and Mossbauer spectroscopy. The blackoxidized structure, enriched with Nd and oxygen and depleted of Fe, was found inthe surface layer by the selective corrosion of the Nd-rich boundary phase and thenpenetrated along grain boundary and spreaded into Nd_2Fe_(14)B matrix phase. Thebrown rust powder, consisting of residual Nd_2Fe_(14)B particles and oxides, e. g., Fe_3O_4,Nd_2O_3, α-Fe_2O_3 and cubic Fe_2O_3, was found after 500 h oxidation. The changes indistribution of Fe atoms at six crystalline sites, especially the loss of Fe atoms atc-site, in oxidized Nd_2Fe_(14)B lattice was measured. The decreaslng in magnetizationof oxidized NdFeB magnets was reported.
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