Thermodynamische analyse des einflusses von sauerstoff auf die reaktionsgleichgewichte im hochtemperaturbereich des systems wolfram-fluor

The gas-phase composition in the heterogenous system W/F₂/O₂ has been calculated using a digital computer on the basis that thermodynamic equilibrium is attained at the gas/solid interface and that the rate of reaction is not kinetically controlled.The partial pressures of the various components, i.e. WF, WF₂, WF₄, WF₅, WF₆, WO₂F₂, WOF₄, F₂, F, O₂, O and WO, WO₂, WO₃, W₂O₆, W₃O₈, W₃O₉ and W₄O₁₂ have been evaluated as a function of the temperature and the relative concentrations of fluorine and oxygen in the input gas.From the temperature dependence of the mass balance of tungsten, the direction of the chemical transport reactions may be predicted. The transport reactions are very much influenced by the presence of oxygen. Due to the formation of WO₂F₂ the maximum which occurs in the mass balance at moderate temperatures (as found in the pure W/F₂ system) is lowered and transport down the temperature gradient at low temperatures is very much reduced. In the high temperature region, oxygen only has a limited effect on the transport properties.The calculations have been confirmed by some experimental observations on halogen incandescent lamps.