Vapour pressure of the binary system I2–Ag7I4PO4

Previous solubility studies of absorbed gaseous iodine by Ag7PO4I4 (API) in a wet atmosphere showed that API absorbs a great quantity of iodine (up to 1.8 mol of iodine per mol of API). The absorption rate law depends on the square root of iodine fugacity plus a constant term that represents a threshold fugacity (image) for the iodine absorption process. In this work, thermodynamic measurements carried out on the system {API + I2}, by using solid-state galvanic cells, gives a value (pI2=(1.2±0.7)×10−2 Pa at 298 K) consistent with the one previously obtained with kinetic measurements. The API compound is stable for activity values lower than the mentioned fugacity.