THERMAL STABILITIES OF TUNGSTEN OXYIODIDES

A mass spectrometric and Knudsen effusion investigation of the W-O-I system at high temperatures has been conducted. Vaporization of solid WO2I2 has been observed to involve its partial dissociation to molecular iodine. Iodine pressures over solid WO2I2 in a Knudsen cell exhibit strong effusion orifice dependence. The enthalpy of WO2I2 vaporization = 45.2 ± 1.0 kcal/mol at 298°K has been derived. A decomposition reaction assumed as WO2I2(s) = WO2I(s) + 1/2I2(g) has given -136 ± 5 kcal/mol as ΔHf° of solid WO2I at 550°K. WOI3 has been observed as a minor gaseous species over solid WO2I2 in an effusion cell. From our extensive study of the WO2-I2 reaction, -102.8 ± 2.0 kcal/mol and 90.1 ± 2.0 eu have been evaluated as ΔHf° and S°, respectively, of WO2I2(g) at 298°K.