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Journal of Materials Science

, Volume 43, Issue 4, pp 1324–1333 | Cite as

Oxidation of NdFeB-type magnets modified with additions of Co, Dy, Zr and V

  • I. Skulj
  • H. E. Evans
  • I. R. Harris
Article

Abstract

The oxidation characteristics of NdFeB alloys, modified by additions of Co up to 10 at.% and with minor additions of Dy, Zr and V, have been examined in this article over the temperature range 250–500 °C. The surface oxide consisted of an outer surface layer of polycrystalline haematite, regardless of Co content, and an inner layer of Co-modified magnetite. Underlying this two-layer surface oxide was an extensive internal oxidation zone (IOZ) formed as a result of preferential reaction with oxygen of the magnetic phase, Nd2(Fe, Co)14B. The IOZ consisted of a bcc solid solution of Fe and Co and contained a fine dispersion of Nd-rich oxide particles. The zone grew by inward oxygen diffusion, principally along high-angle grain boundaries within the Fe-rich matrix. The thickening of the IOZ occurred with parabolic kinetics but at a rate which decreased with increasing alloy Co content by a consistent factor of 2–3 in parabolic rate constant at all test temperatures. The activation energy for the growth of the IOZ lay in the approximate range 91–104 kJ/mol for the various alloys but there did not appear to be a systematic variation with alloy composition.

Keywords

Oxygen Permeability Oxygen Flux Surface Oxide Layer Parabolic Rate Constant Internally Oxidise Zone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The authors are grateful to the Engineering and Physical Sciences Research Council (grant GR/N64755/01) and Marie Curie Fellowships for their financial support for this work. Thanks are also given to Less Common Metals Ltd. for the provision of the material used in this study.

References

  1. 1.
    Blanc R, Adler E (1987) Proceedings of the 9th International workshop on rare earth magnets and their applications. Bad Soden, Germany, p 537Google Scholar
  2. 2.
    Li Y, Evans HE, Harris IR, Jones IP (2002) Oxid Met 59:167CrossRefGoogle Scholar
  3. 3.
    Edgley DS, Le Breton J-M, Lemarchand D, Harris IR, Teillet J (1993) J Magn Magn Mater 128:L1CrossRefGoogle Scholar
  4. 4.
    Edgley DS, Le Breton J-M, Steyaert S, Ahmed FM, Harris IR, Teillet J (1997) J Magn Magn Mater 173:29CrossRefGoogle Scholar
  5. 5.
    Higgins BE, Oesterreicher H (1987) IEEE Trans Magn 23:92CrossRefGoogle Scholar
  6. 6.
    Lemarchand D, Delamare J, Vigier P (1992) J Appl Phys 72:1996CrossRefGoogle Scholar
  7. 7.
    Osawa Z, Higuchi M, Hinohara S (1992) J Mater Sci 27:5445CrossRefGoogle Scholar
  8. 8.
    Steyaert S, Le Braton J-M, Teillet J (1996) J Phys Condens Matter 8:10721CrossRefGoogle Scholar
  9. 9.
    Skulj I (2005) PhD thesis. The oxidation behaviour of Co and Dy modified NdFeB magnets. The University of Birmingham, Birmingham, UKGoogle Scholar
  10. 10.
    Wagner C (1959) Z Elektrochem 63:772Google Scholar
  11. 11.
    Skulj I, Douvalis AP, Harris IR (2005) J Alloys Compd 407:304CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of Metallurgy and MaterialsSchool of Engineering, University of BirminghamBirminghamUK
  2. 2.Institute of Metals and TechnologyLjubljanaSlovenia

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