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Materials science

Percolation frustrated

Nature volume 389, pages 121–122 (1997)Cite this article

In the gold-mining industry, the ‘richness’ of gold ore extracted from a mine is assayed by cupellation, that is, reduction to metal in a heated carbon crucible using an appropriate flux, followed by weighing. This has been done for centuries. The button of gold generated by cupellation contains some silver, because the flux will not dissolve this away. To get a reliable value of richness, the less noble silver is removed by nitric acid to leave pure gold — the Au-Ag mix becomes de-alloyed. If, however, the silver content is too low, the silver cannot be leached out; there is a ‘parting limit’ of about 65% silver. The solution to this problem has long been to re-melt the gold button, add more silver, freeze and then attack with acid. If the initial silver content is high enough, then all the silver can be removed1.

The science of de-alloying has been studied for the past 130 years. One eminent physicist (A. J. Forty) has devoted much of his research career to a deep study of parting in Ag-Au alloys2. Special interest has also attached to the dezincification of brass (a copper-zinc alloy) because this can happen in sea water, where brass is used in large quantities. But trace amounts of arsenic, antimony or boron can reduce dezincification, and a new study by Wang et al., published in one of the journals of the Chinese Academy of Sciences3, may explain why. These elements appear to block the diffusion of vacancies in zinc channels.

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Figure 1: Percolation channels in brass, an alloy of copper (red) and zinc (grey).

References

  1. Adamson, R. J. (ed.) in Gold Metallurgy in South Africa 191 (Cape Town, Chamber of Mines S. Africa, 1972).

  2. Forty, A. J. in Sir Charles Frank, OBE, FRS: An Eightieth Birthday Tribute (eds Chambers, R. G. et al.) 164-187 (Hilger, Bristol, 1991).

  3. Wang, J., Jiang, X. & Li, S. Chinese Sci. Bull. 42, 1135–1139 (1997).

    Google Scholar 

  4. Bocquet, J. L., Brébec, G. & Limoge, Y. in Physical Metallurgy4th edn (eds Cahn, R. W. & Haasen, P.) 537-668 (Elsevier, Amsterdam, 1996).

  5. Ramstetter, R., Lampert, G., Seeger, A. & Schüle, W. Phys. Status Solidi 8, 863 (1965).

    Google Scholar 

  6. Pickering, H. W. & Wagner, C. J. Electrochem. Soc. 114, 698–706 (1967).

    Google Scholar 

  7. Review, R. W. & Uhlig, H. H. Corrosion Sci. 12, 669–671 (1972).

    Google Scholar 

  8. Broadbent, S. R. & Hammersley, J. M. Proc. Camb. Phil. Soc. 53, 629–641 (1957).

    Google Scholar 

  9. Sieradzki, K. & Newman, R. C. J. Electrochem. Soc. 133, 1979–1980 (1986).

    Google Scholar 

  10. Sieradzki, K., Kim, J. S., Cole, A. T. & Newman, R. C. J. Electrochem. Soc. 134, 1635–1639 (1987).

    Google Scholar 

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  1. the Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, CB2 3QZ, Cambridge, UK

    Robert W. Cahn

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Cahn, R. Percolation frustrated. Nature 389, 121–122 (1997). https://doi.org/10.1038/38113

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