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

Equilibria between Bi 5 O 7 I and Bi 2 O 3 have been measured with the solids in contact with aqueous solutions at 10–60 °C, and with low-pressure oxygen (0.2–100kPa) at 550–800 °C. In the aqueous systems, iodide activities were measured as functions 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-Bi 5 O 7 I 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 Bi 5 O 7 I and Bi 2 O 3 up to 800 °C. Some equilibria involving BiOI are discussed briefly.

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