Abstract
The oxidation kinetics in air of a commercial NdFeB magnet have been investigated over the temperature range 335–500°C. The oxide microstructure has been characterized by SEM, XRD and cross-sectional TEM. The results show that the external scale formed consists of an outer layer of Fe2O3 and an inner layer of Fe3O4 but that the principal degradation process is the formation of an extensive zone of internal oxidation. HREM has been used to show that this zone contains NdO particles embedded in an α-Fe matrix. These particles are discrete and very small, approximately 2 nm in diameter, and have an amorphous structure. The α-Fe matrix has a columnar grain structure with a grain width of approximately 100 nm. It is argued that the high rates of internal oxidation arise because the external-oxide layers are not protective at the oxidation temperature, and oxygen penetrates to the zone front by fast diffusion along the columnar α-Fe grain boundaries.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
R. Blank and E. Adler, Proc. 9th Int. Workshop on Rare Earth Magnets and their Applications (Badsoden, Germany, 1987), p. 537.
A. S. Kim and J. M. Jacobson, IEEE Trans. Magn. Magn. 23, 2509(1987).
J. Jacobson and A. Kim, J. Appl. Phys. 61, 3763(1987).
J. M. Le Breton and J. Teillet, IEEE Trans. Magn. Magn. 26, 2652(1990).
J. M. Le Breton and J. Teillet, J. Magn. Magn. Mater. 101, 347(1991).
J. M. Le Breton, J. Teillet, P. J. McGuiness, D. S. Edgley, and I. R. Harris, IEEE Trans. Magn. 28, 2157(1992).
D. S. Edgley, J. M. Le Breton, S. Stayaert, F. M. Ahmed, I. R. Harris, and J. Teillet, J. Magn. Magn. Mater. 128, L1(1993).
D. S. Edgley, J. M. Le Breton, S. Stayaert, F. M. Ahmed, I. R. Harris, and J. Teillet, J. Magn. Magn. Mater. 173, 29(1997).
C. Wagner, Z. Elektrochem. 63, 772(1959).
S. Steyaert, J. M. Le Breton, and J. Teillet, J. Phys. D: Appl. Phys. 31, 1534(1998).
I. Barin, Thermochemical Data of Pure Substances, Federal Republic of Germany, 1993.
B. Hallemans, P. Wollants, and J. R. Roose, J. Phase Diag. Equil. 16, 137(1995).
D. J. Young and O. Ahmed, Mater. Sci. Forum, in press.
F. Gesmundo, F. Viani, and Y. Niu, Oxid. Met. 47, 355(1997).
F. Maak, Z Metallkunde 52, 538(1961).
J. H. Swisher and E. T. Turkdogan, Trans AIME 239, 426(1997).
D. P. Whittle, Y. Shida, G. C. Wood, F. H. Stott, and B. D. Bastow, Phil. Mag. A. 46, 931(1982).
N. Belen, P. Tomaszewicz, and D. J. Young, Oxid. Met. 22, 227(1984).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Li, Y., Evans, H., Harris, I. et al. The Oxidation of NdFeB Magnets. Oxidation of Metals 59, 167–182 (2003). https://doi.org/10.1023/A:1023078218047
Issue Date:
DOI: https://doi.org/10.1023/A:1023078218047