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Platinum Metals Rev., 1964, 8, (4), 133

Effect of Rhodium on the Gold-Platinum System

  • A.S.D.
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Those gold-platinum alloys used for the manufacture of spinning jets in the production of viscose rayon have for many years been modified by small additions of rhodium, which appeared to broaden the miscibility gap and assist age-hardening. A recent X-ray study by Raub and Falkenburg (1) has shown that approximately 2 atomic per cent of rhodium completely eliminates the gold rich solid solution which normally contains 20 per cent or more of platinum. Although rhodium also reduces the solubility of gold in platinum, the effect is not so pronounced, and platinum rich solid solutions extend right across to the rhodium corner of the diagram.

Although Raub had earlier predicted the basic instability of the rhodium-platinum solid solutions it was found that heat treatments extending up to four years at 600°C failed to produce any evidence of separation. The binary gold-rhodium system was also examined. At the peritectic temperature of 1068°C saturation concentrations of the terminal solid solutions were found to be 1.5 atomic per cent of rhodium and 0.3 atomic per cent of gold.

In 1951,Grube, Schneider and Esch (2) attributed some additional lines on the diffraction pattern of a gold rich gold-platinum solid solution to an ordering reaction based on the Au-Pt composition. No other workers have hitherto detected these lines. Raub and Falkenburg, however, developed similar “sideband” structures simply by annealing the alloys for 1,000 hours in the solid solution region. The lattice parameter of this additional face-centred cubic phase increased rapidly with platinum content. This behaviour cannot easily be explained by an ordering reaction and will require further investigation.

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References

  1. 1
    E. Raub, Z. Günter Falkenburg, “ Raub and Gtinter Falkenburg ”, Z. Metallkunde, 1964, 392 – 397 55 ( 7 )
  2. 2
    G. Grube, and A. Schneider and M. Esch, Heraeus Festschrift, 1951, 20
 

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