Journal Archive

Platinum Metals Rev., 1996, 40, (2), 62

Thermodynamic Properties of the Platinum Metals on ITS-90

  • By J. W. Arblaster
  • Rotech Laboratories, Wednesbury, West Midlands, England

Selected properties taken from recent reviews written by the present author of the thermodynamic properties on the International Temperature Scale, ITS-90, are listed in the Tables below (1, 2). Values in these reviews correspond to a standard state pressure of one bar and have been corrected to the 1993 atomic weights (3): ruthenium 101.07, rhodium 102.90550, palladium 106.42, osmium 190.23, iridium 192.217 and platinum 195.08 (revised to 195.078 in 1995) (4).

Selected values for solid rhodium and iridium at 298.15 K and below are based on the assessments of Furukawa, Reilly and Gallagher (5).

Table I

Low Temperature Properties

  Ru Rh Pd Os Ir Pt
Superconducting temperature (Tc), K 0.48 0.000325 - 0.64 0.1125 -
Electronic specific heat coefficient (γ). mJ/mol K2 3.00 4.65 9.42 2.05 3.20 6.54
Debye temperature (θD), K 550 512 272 467 420 236
Table II

Properties at 298.15 K (solid)

  Ru Rh Pd Os Ir Pt
Specific heat (C°p), J/mol K 24.05 24.90 25.85 24.69 25.09 25.65
Enthalpy (H°298.15 - H°0), J/mol 4577 4914 5444 4992 5266 5694
Entropy (S°), J/mol K 28.50 31.56 37.64 32.56 35.49 41.53
Heat of sublimation (ΔH°298.15), kJ/mol 649 558 377 788 670 565
Table III

Properties at 298.15 K (gas)

  Ru Rh Pd Os Ir Pt
Specific heat (C°p), J/mol K 21.524 21.014 20.786 20.788 20.788 25.531
Enthalpy (H°298.15 - H°0), J/mol 6235.2 6206.6 6197.4 6197.4 6197.4 6576.6
Entropy (S°), J/mol K 186.509 185.827 167.066 192.579 193.584 192.409
Table IV

Melting Point Properties

  Ru Rh Pd Os Ir Pt
Melting point, K * 2606 2236 1828.0 3400 2719 2041.3
Heat of fusion (ΔH°s, l), kJ/mol 39.0 27.3 16.1 70.0 41.3 21.3
Entropy of fusion (ΔS°s, l), J/mol K 15.0 12.2 8.8 20.6 15.2 10.4
Vapour pressure, bar 1.05 × 10-5 5.05 × 10-6 4.23 × 10-5 7.75 × 10-5 9.84 × 10-6 1.90 × 10-7

* The melting points of all but Os are proposed secondary fixed points on ITS-90 (6)

Table V

Vapour Pressures

Pressure, bar Temperature, K
Ru Rh Pd Os Ir Pt
1 ×10-12 1684 1468 1060 2048 1751 1489
1 ×10-11 1772 1546 1122 2156 1844 1569
1 ×10-10 1871 1634 1191 2277 1949 1659
1 ×10-9 1982 1733 1269 2411 2065 1759
1 ×10-8 2107 1845 1359 2563 2197 1872
1 ×10-7 2249 1972 1462 2736 2347 2002
1 ×10-6 2412 2119 1582 2934 2520 2156
1 ×10-5 2602 2293 1725 3163 2721 2339
1 ×10-4 2842 2508 1899 3435 2976 2556
1 ×10-3 3134 2772 2120 3793 3288 2821
1 ×10-2 3498 3102 2400 4239 3681 3149
1 ×10-1 3965 3530 2765 4810 4193 3567
1 4588 4110 3259 5571 4894 4122
NBP 4592 4114 3263 5576 4898 4125

NBP: Normal boiling point at one atmosphere pressure (1.01325 bar)

References

  1. 1
    J. W. Arblaster, Platinum Metals Rev., 1994, 38, (3), 119 (Pt)
  2. 2
    J. W. Arblaster, Calphad, 1995, 19, 327 (Pd), 339 (Ru), 349 (Os), 357 (Rh), 365 (Ir)
  3. 3
    Commission on Atomic Weights and Isotopic Abundances, Pure & Appl. Chem., 1994, 66, 2423
  4. 4
    Commission on Atomic Weights and Isotopic Abundances, Pure & Appl. Chem., to be published
  5. 5
    G. T. Furukawa, M. L. Reilly and J. S. Gallagher, J. Phys.Chem. Ref. Data, 1974, 3, 163
  6. 6
    R. E. Bedford, G. Bonnier, A. Maas and F. Pavese, Metrologia, to be published
 
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