The effect of density on the corrosion of NdFeB magnets
1999; Elsevier BV; Volume: 292; Issue: 1-2 Linguagem: Inglês
10.1016/s0925-8388(99)00443-0
ISSN1873-4669
AutoresGaolin Yan, A. Williams, J.P.G. Farr, I.R. Harris,
Tópico(s)Superconducting Materials and Applications
ResumoThe corrosion and degradation of Nd–Fe–B magnets by hydrogen from moisture in the environment has been termed the Negative Harris Effect. In order to provide more information on this phenomenon, different density Nd–Fe–B magnets have been subjected to vacuum desorption, XRD and electrochemical corrosion examination. During the normal vacuum sintering procedure used in producing the magnets, the residual hydrogen coming from the hydrogen decrepitation process is desorbed completely. However, the Nd–Fe–B magnets can absorb hydrogen readily from moisture in the environment. In these studies it has been found that the higher the density of the magnets the less is the hydrogen absorbed. The combined effects of the lattice expansion due to the formation of Nd2Fe14B–H solutions and NdH2+x phases as a result of hydrogen absorption and the volume expansion on formation of Nd(OH)3, lead to the eventual disintegration of the magnets. Thus hydrogen plays a vital role in the corrosion of Nd–Fe–B type magnets when they are exposed to a humid environment.
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