Vaporization of WO₃ from 3Y₂O₃⋅WO₃ Compound in Various Atmospheres

Abstract

Vaporization experiments for 3Y₂O₃⋅WO₃ were carried out by using the Langmuir and the Knudsen methods from 1630° to 1755°C, and also effects of oxygen partial pressure on the vaporization rate were determined at 1660°C. WO₃ component only vaporized selectively with a zero-order reaction in an initial stage and then with control by diffusion through remained Y₂O₃ layer in a later stage.
The vaporization rate of 3Y₂O₃⋅WO₃ exhibited a dependence of -0.079 on the oxygen partial pressure. Therefore, the vaporization reaction is assumed as follows:
3Y₂O₃⋅WO₃(s)→3Y₂O₃(s)+9/64W₃O₉(g)+6/64W₄O₁₂(g)+2/64W₂O₆(g)+3/64W₃O₈(g)+3/128O₂(g)
The standard enthalpy and the entropy changes of the reaction were 28±4kcal/mol and 3.1±1e.u., respectively, from the Knudsen vaporization.