Surface Tension and Density of Bismuth Germanate Melts as a Function of Composition and Temperature

The surface tension and density of x Bi₂O₃–(1− x )GeO₂ (BGO) melts have been measured systematically from their respective melting points up to around 1480 K within 0.25≤ x ≤0.86. With the addition of Bi₂O₃, the density of this system increased smoothly with a positive curvature. Deviation of molar volume from ideality of this system melts decreased firstly, past a minimum at about x =0.4, and then increased. Partial molar volumes of Bi₂O₃ and GeO₂ have also been calculated based on the measured density data and compared with those of a binary bismuth borate system. On increasing the content of Bi₂O₃, the surface tension of BGO melts increased slowly when x <∼0.40, past a maximum at about x =0.50, and then decreased rapidly. In addition, the temperature coefficient of surface tension remained positive within the lower content range of Bi₂O₃, changed sign from positive to negative at about x =0.38, and then was almost independent of the composition within the measured temperature range when the Bi₂O₃ content was increased further.