Density of Bi₂O₃-B₂O₃ binary melts

The densities of xBi₂O₃·(100-x B₂O₃ binary melts (x = 0-100 mol%) have been measured systematically in the temperature range of 973 to 1373 K using the Archimedean double-bob method. In addition, the molar volume and coefficient of volume expansion have been determined from these density measurements. The density of melts in the Bi₂O₃-B₂O₃ binary system decreased with increasing temperature for all compositions, and increased with increasing Bi₂O₃ content. The molar volume calculated at 1273 K showed a minimum at around 20-30 mol% Bi₂O₃. The deviation of molar volume from ideality and the partial molar volumes of B₂O₃ and Bi₂O₃ single-component melts were calculated, and the relationships between these properties and Bi₂O₃ content were investigated. The Δ(MV) (deviation of molar volume from ideality) was negative in the Bi₂O₃-B₂O₃ binary melts and showed a minimum of -7.5 cm³ (-17.3%) at 40 mol% Bi₂O₃ and 1273 K. The PMV (partial molar volume) of the B₂O₃ melt decreased with increasing Bi₂O₃ content, up to 70 mol% Bi₂O₃, and was constant above 70 mol% Bi₂O₃. The PMV of the Bi₂O₃ melt was constant up to 30 mol% B₂O₃ (considered from the viewpoint of Bi₂O₃), and then decreased sharply with further addition of B₂O₃. The coefficient of volume expansion increased sharply up to 20 mol% Bi₂O₃ and decreased with further addition of Bi₂O₃ at 1273 K. From this result, it can be inferred that the temperature-induced structural changes taking place in the melts are greatest at 20 mol% Bi₂O₃.