The Physical Properties Of Molten XBi₂O₃-(1-x)GeO₂ System

The densities and surface tensions of xBi₂O₃-(1-x)GeO₂ melts have been measured systematically and precisely within the range of 0.25≤x≤0.86 from their respective melting point temperatures up to about 1480K. Based on the results mesured and published, some physical properties, such as density, surface tension, temperature coefficient and volume expansion coefficient, have been studied. Furthermore, the abnormal behaviors observed in the melts of this system have also been discussed.In the work, an improved Archimedean method and a ring method were used respectively to measure the densities and surface tensions of xBi₂O₃-(1-x)GeO₂ melts. The following are the experimental results.1. Within the range of 0.25≤x≤0.86, the density decreases linearly and monotonously with the increase of temperature during both heating and cooling. And at fixed temperatures, the densities of melts increase with the addition of Bi₂O₃.2. Based on the density data, the volume expansion coefficient (β) and the temperature coefficient of density (dρ/dT) were caculated. It is found thatβincreased and dρ/dT decreased with the increase of molar concentration of Bi₂O₃.3. The surface tension versus the temperature during both heating and cooling processes is the same and corresponds to a quadratic polynomial function within the range of 0.25≤x≤0.86.4. At fixed temperatures, the surface tension increases slowly with the increase of molar concentration of Bi₂O₃, and then decreases rapidly with further increasing the molar ratio of Bi₂O₃ after reaching a maximum peak at x=0.50. However, the temperature coefficient of surface tension (dγ/dT) decreases slowly with the addition of Bi₂O₃, when passing a critical value x=0.40 where dγ/dT changes sign from positive to negative. In addition, in order to discuss the influence of Bi₂O₃ to the structure of melts, the partial molar volume (P.M.V) and the deviation of molar volume (â–³Mv) of bismuth germanate (BGO) and bismuth borate (BBO) system have also been calculated based on the measured density data. After comparison, a fact has been pointed out that whether the germanate anormaly is exist or not should depend on both the short-range order structure and the medium-range order structure of Ge atom. At the same time, a conclusion may be drawn that it is insufficient to discuss the abnormal positive dγ/dT of some oxides melts with network structures only based on Gibbs absorption rule.