Interfacial tension between immiscible liquids in alkaline earth - boron oxide binary systems

Liquid immiscibility is common in glass-forming oxide melts, and interfacial tension between the conjugate liquid phases is an important property that determines the kinetics of phase separation. Here we present, to the best of our knowledge, the first experimental measurements of interfacial tension between immiscible melts in the alkaline earth - boron oxide binary systems; MgO-B₂O₃, CaO-B₂O₃ and BaO-B₂O₃. We have also measured surface tension for the conjugate borate liquids. The measurements were carried out at 1100-1250 °C by the maximum detachment force method employing a vertical cylinder geometry and using a gravimetric balance system. The values of interfacial tension between immiscible melts of the binary systems are 28 ± 3.5, 12 ± 2.8 and 2.1 ± 0.5 mN/m, for the Mg-, Ca- and Ba-bearing systems respectively. These results yield a positive, linear correlation with the width of miscibility gap expressed in molar units. We recognise no direct, simple relationship between the liquid-liquid interfacial tensions and the individual surface tensions of the conjugate liquids in air.