LAUSR

The thermodynamic properties of osmium were reviewed by the author in 1995 (1) with a further review in 2005 (2) to estimate a most likely value for the melting point at 3400 ± 50 K to replace the poor quality experimental values which were being quoted in the literature. More recently Burakovsky et al. (3) have estimated a value of 3370 ± 75 K in good agreement with the above selected value. In the 1995 review the enthalpy of fusion was unknown but was estimated from a relationship between the entropy of fusion and the melting point which showed a high degree of correlation for the platinum group metals (pgms). However the derived entropy of fusion value for osmium was based on values for the other pgms available at that time but since then the values for both palladium and platinum have been revised so that the entropy of fusion value for osmium would also be revised leading to a new estimate of 68.0 ± 1.7 kJ mol–1 for the enthalpy of fusion. This would then require the thermodynamic properties of the liquid phase to also be updated. A comment is included on an independent much lower estimate of the enthalpy of fusion. Wherever possible measurements have been corrected to the International Temperature Scale (ITS-90) and to the currently accepted atomic weight of 190.23 ± 0.03 (4).