Equilibria between Bi2O3 and Bi5O7I in aqueous solutions at 10-60 degrees C, and in oxygen atmospheres at 550-800 degrees C

Equilibria between Bi5O7I and Bi2O3 have been measured with the solids in contact with aqueous solutions at 10-60 degrees Celsius, and with low-pressure oxygen (0.2-10 kPa) at 550-800 degrees Celsius. In the aqueous systems, iodide activites were measured as function of pH and temperature. In the dry system, iodine partial pressures were measured spectrophotometrically while varying the temperature and oxygen partial pressure. The standard enthalpy of formation and entropy of α-Bi5O7I were derived from these measurements, and values for BiOI were also estimated. The results combine to give a self-consistent account of phase relations between Bi5O7I and Bi2O3 up to 800 degrees Celsius. Some equilibria involving BiOI are discussed briefly