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Journal of Materials Science

, Volume 26, Issue 5, pp 1401–1408 | Cite as

Oxidation sizing of iron and iron-neodymium-boron powders

  • M. Stewart
  • B. Roebuck
  • M. G. Gee
Papers

Abstract

A powder sizing test developed for use on WC powders has been extended for use on iron and iron-neodymium-boron powders. In this test the particle size is derived from the rate of oxidation, because finer powders oxidize quicker. The rate of oxidation is monitored in a thermogravimetric analyser, where the powders are subjected to a controlled heating rate from room temperature to 1100 °C. If the constants from the Arrhenius law are known the powder size can be determined by comparing experimental oxidation plots with theoretical curves. For the sizing of a commercial spherical iron powder, the oxidation technique compared favourably with direct sizing using scanning electron microscopy and image analysis. The values for the activation energy of 125 kJ mol−1 determined in this study agree with previous studies. Validation of the sizing technique on a hydrogen-decrepitated stoichiometric Nd2Fe14B powder proved difficult because it was not possible to determine a definitive size distribution independently. Metallography of partially oxidized samples showed that the process is two-stage, at low temperatures the neodymium oxidizes, and above 400 °C the powder behaves as pure iron. Theoretical curves based on one oxidation process with an activation energy of 100 kJ mol−1 gave the best fit to the experimental curves.

Keywords

Iron Activation Energy Neodymium Pure Iron Iron Powder 
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.

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References

  1. 1.
    B. Roebuck, E. G. Bennett, E. A. Almond and M. G. Gee, J. Mater. Sci. 21 (1986) 2033.CrossRefGoogle Scholar
  2. 2.
    B. Roebuck, E. A. Almond and J. L. F. Kellie, in “Horizons of Powder Metallurgy, PM86”, Part 1, European Powder Metallurgy Federation, Dusseldorf, July 1986, edited by W. A. Kaysser and W. J. Huppmann (Verlag Schmid, Freiburg, Germany, 1986) pp. 123–6.Google Scholar
  3. 3.
    B. E. Higgins and H. Oesterreicher, IEEE Trans. Magn. 23(1) (1987) 92.CrossRefGoogle Scholar
  4. 4.
    R. Blank and E. Adler, in “Proceedings of the 9th International Workshop on Rare Earth Magnets and their Applications”, Bad Soden, FRG, September 1987, edited by C. Herget and R. Poerschke (University of Daytona, School of Engineering, 1987) pp. 537–44.Google Scholar
  5. 5.
    M. Stewart, M. G. Gee and B. Roebuck, in “Concerted European Action on Magnets (CEAM)”, edited by I. V. Mitchell, J. M. D. Coey, D. Givord, I. R. Harris and R. Hanitsch (Elsevier Applied Science, London, 1989) pp. 532–42.CrossRefGoogle Scholar
  6. 6.
    E. E. Underwood, “Quantitative Stereology” (Addison Wesley, Reading, Massachusetts, 1970) pp. 117–33.Google Scholar
  7. 7.
    O. Kubachewski and B. E. Hopkins, “Oxidation of Metals and Alloys” (Butterworths, London, 1962) pp. 108–14.Google Scholar
  8. 8.
    P. Schrey, IEEE Trans. Magn. 22(5) (1986) 913.CrossRefGoogle Scholar

Copyright information

© Chapman and Hall Ltd. 1991

Authors and Affiliations

  • M. Stewart
    • 1
  • B. Roebuck
    • 1
  • M. G. Gee
    • 1
  1. 1.Division of Materials MetrologyNational Physical LaboratoryTeddingtonUK

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