Vaporization of Iridium and Rhodium

The vaporization of iridium and rhodium have been studied by Knudsen effusion and Langmuir evaporation techniques. The vapor pressure of iridium over the temperature range of from 2100° to 2600°K is represented by the equation: logpmm=10.46— (33980/T), and the vapor pressure of rhodium over the temperature range of from 2050° to 2200°K by the equation: logpmm=10.28— (28300/T). Third-law analyses of the data yield the following heats of vaporization:iridium, ΔH298=158.4±0.5 kcal/mole; rhodium, ΔH298=132.8±0.3 kcal/mole. Estimated boiling points for iridium and rhodium are 4800° and 3980°K, respectively.