Zum Verständnis der Flüchtigkeit von GeO2 in Gegenwart von WO2

On the Understanding of the Volatility of GeO₂ in the Presence of WO₂ The equilibria composition of the gaseous and the solid phase in the system GeO₂/WO₂ is calculated with an improved thermodynamical program for temperatures 1100 < T < 1400 K and constant volume. By means of the results the experimental observed migration of GeO₂ in the presence of WO₂ in a temperature gradient T₂ → T₁ (1200 → 1100 K) in sealed evacuated silica tubes is dued to a chemical transport with H₂ as the transporting agent. The H₂ is formed by H₂O which is desorbed by the quartz glass of the ampoules. The also observed volatility of WO₂ and its deposition in form of Ge_0.75 W₃O₉ at the “cold” end (T₁) of the tubes is performed by gaseous GeWO₄. The calculated and experimental transport rates are compared and discussed.