Interfacial tension between immiscible liquids in the system [K.sub.2]O-FeO-[Fe.sub.2][O.sub.3]- [Al.sub.2][O.sub.3]-Si[O.sub.2] and implications for the kinetics of silicate melt unmixing

Interfacial tension between immiscible liquids is an important thermodynamic parameter of silicate melt unmixing and a property that determines the kinetics of phase separation. In this study, we present experimental measurements of interfacial tension between immiscible Fe-rich and silica-rich melts in the system [K.sub.2]O-FeO-[Fe.sub.2][O.sub.3]-[A1.sub.2][O.sub.3]-Si[O.sub.2]. We have also measured densities and surface tensions of the individual immiscible liquid phases. The measurements were carried out in air at 1500-1550[degrees]C by the maximum detachment force method employing vertical cylinder geometry and using a gravimetric balance system. We have chosen the most oxidized and contrasting liquid compositions containing 73 and 17 wt% Si[O.sub.2] and 14 and 80 wt% FeOt, respectively, that have been shown to coexist in air at and above 1465[degrees]C. Interracial tension between the synthetic immiscible liquids decreases with increasing temperature from 16.4 [+ or -] 3.1 mN/m at 1500[degrees]C to 7.8 [+ or -] 1.1 mN/m at 1550[degrees]C. Interfacial tension between natural, less compositionally contrasting ferrobasaltic and rhyolitic melts should be even lower by a factor of 2 or 3. Very low interracial tension implies easy nucleation of immiscible liquid droplets and very slow coarsening of resulting silicate emulsions. Keywords: Immiscibility, interface, tensiometry, nucleation DOI: 10.2138/am.2010.3456