Phase Relations in the System Bi ₂ O ₃ ‐WO ₃

Abstract

Phase relations in the system Bi 2 O 3 ‐WO 3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi 2 O 3 · WO 3 , 7Bi 2 O 3 · 2WO 3 , Bi 2 O 3 · WO 3 , and Bi 2 O 3 · 2WO 3 , were found. The 7B 2 O · WO 3 phase is tetragonal with a 0 = 5.52 Å and c 0 = 17.39 Å and transforms to the fcc structure at 784°C; 7Bi 2 O 3 · 2WO 3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi 2 O 3 · WO 3 and Bi 2 O 3 · 2WO 3 are orthorhombic with (in Å) a 0 = 5.45, b 0 =5.46, c 0 = 16.42 and a 0 = 5.42, b 0 = 5.41, c 0 = 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO 3 , 907°± 3°C and 70 mol% WO 3 , and 965°± 5°C and 10 mol% WO 3 .