Vapor pressures of platinum, iridium, and rhodium

Abstract

The vapor pressures of platinum, iridium, and rhodium h ave been measured using a microbalance t echnique based on the Langmuir method. Heats of sublimation at 298 oK were calculated with the aid of free energy functions. The least square lines for the vapor pressure data, the heats of sublimation, and the normal boiling points obtained were as follows: (1) Platinum: 27 ,575 Log P. tm = 6.761-T-(1,916 t o 2,042 OK) ~H~ (298) = 134.9 ± 1.0 kcaI /mole bp = 4,100 ± 100 oK (2) Iridium: 33,337 Log P. tm = 7.139-T-(1,986 to 2,260 OK) ~H~ (298) = 159.9 ± 2.0 kcaI /mole bp = 4,800 ± 100 oK (3) Rhodium: 27,276 Log P. tm = 6.894-T-(1,709 t o 2,075 OK) MI~ (298) = 132.5 ± 2.0 kcaI/ moIe bp = 4,000 ± 100 oK. The indicated uncertainties ar e estimates of the overall limits of error. The value of t he gas constant R u sed in the calculation of ~H~ is 1.98726 caI/d egree mole .