Journal of Materials Science

, Volume 20, Issue 4, pp 1291–1300 | Cite as

The hydrogen reduction of cobalt-tungsten mixed oxides

  • G. J. French
  • F. R. Sale
Papers

Abstract

The hydrogen reduction of two non-stoichiometric samples of cobalt tungstate (one cobalt-rich, the other heavily tungsten-rich) has been studied over the temperature range 600 to 1100° C using thermogravimetry, X-ray diffraction analysis and scanning electron microscopy. The products are shown to be non-equilibrium at most reduction temperatures. In order to explain the experimentally observed X-ray diffraction data it is postulated that the reduction process occurs via the formation of an amorphous phase which contains cobalt, tungsten and oxygen. The amorphous phase becomes unstable at low oxygen potentials and precipitates either, or both, Co3W and Co7W6 depending upon the degree of cobalt enrichment of the amorphous phase. These are the only two cobalt-containing crystalline phases in the products of reduction and are not detected before at least 53% reduction has occurred. During the early stages of reduction either tungsten (for near stoichiometric, cobalt-rich oxide) or WO2 (for tungsten-rich oxide-CoWO4 plus WO3) are the only crystalline products of reduction.

Keywords

Cobalt Tungsten Thermogravimetry Crystalline Phasis Amorphous Phase 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    F. Gortsema andP. Kotval,Plansee. Pulvermet. 24 (1976) 254.Google Scholar
  2. 2.
    S. Takatsu,Powder Met. Int. 10 (1978) 13.Google Scholar
  3. 3.
    K. Ushijima,ibid. 11 (1979) 158.Google Scholar
  4. 4.
    T. D. Halliday, F. H. Hayes andF. R. Sale in “Industrial Uses of Thermochemical Data”, edited by T. I. Barry, Special Publication No. 34 (Chemical Society, London, 1980) p. 291.Google Scholar
  5. 5.
    G. J. French, PhD thesis, University of Manchester (1983).Google Scholar
  6. 6.
    J. Guerassimov, Proceedings 16th IUPAC International Congreess of Pure and Applied Chemistry, Paris (Butterworth, London, 1957) p. 227.Google Scholar
  7. 7.
    A. K. Basu andF. R. Sale,J. Mater. Sci. 12 (1977) 1115.Google Scholar
  8. 8.
    Idem, ibid. 13 (1978) 2703.Google Scholar
  9. 9.
    P. Walkden andF. R. Sale, “Proceedings 2nd European Symposium on Thermal Analysis (ESTA-2)”, Aberdeen (1981), edited by D. Dollimore (Heyden, London 1981) p. 531.Google Scholar
  10. 10.
    Idem, in “Electrical Contacts 1982”, Proceedings 28th Annual Holm Conference on Electrical Contacts, Illinois Institute of Technology, Chicago (1982) p. 101.Google Scholar
  11. 11.
    P. Bracconi andL. Dufour,Met. Trans. B 7B (1976) 321.Google Scholar
  12. 12.
    Idem, ibid. 7B (1976) 329.Google Scholar
  13. 13.
    T. Ekstrom andR. J. D. Tilley,J. Solid State Chem. 22 (1977) 331.Google Scholar
  14. 14.
    N. Schonberg,Acta Chem. Scand. 8 (1954) 630.Google Scholar
  15. 15.
    W. Morcom, W. Worrell, H. Sell andH. Kaplan,Met. Trans. 5 (1974) 155.Google Scholar
  16. 16.
    A. K. Basu andF. R. Sale, in “Modern Developments in Powder Metallurgy”, Vol. 9, edited by H. H. Hausner and P. V. Taubenblat, (Metal Powder Industries Federation and American Powder Metallurgy Institute, New Jersey, 1977), p. 171.Google Scholar
  17. 17.
    T. Wilken, C. Wert, J. Woodhouse andW. Morcom,ibid.in, p. 161.Google Scholar

Copyright information

© Chapman and Hall Ltd. 1985

Authors and Affiliations

  • G. J. French
    • 1
  • F. R. Sale
    • 1
  1. 1.Department of Metallurgy and Materials ScienceUniversity of ManchesterUK

Personalised recommendations