The effect of fluorine on viscosities in the system Na2O-Al2O3-SiO2: implications for phonolites, trachytes and rhyolites
b"The effect of fluorine on melt viscosities of five compositions in the system Na2O-Al2O3-\\nSiO2h as been investigateda t one atmospherea nd 1000-1600'Cb y concentric-cylinder\\nviscometry. The compositions chosen were albite, jadeite and nepheline on the join\\nNaAlOlSiO2 and two others of the join at 75 mole percent SiO2, one peralkaline and one\\nperaluminous. All melt viscosities were independent of shear rate over two orders of\\nmagnitude, indicating Newtonian behavior. All viscosity-temperature relationships were\\nArrhenian within error. Fluorine reduces the viscosities and activation energies of all melts\\ninvestigated. The viscosity-reducing power of fluorine increases with the SiO2 content of\\nmelts on the join NaAlO2-SiO2 and is a maximum at Na/Al (molar) = I for melts containing\\n75 mole percent SiO2. Fluorine and water have similar effects on aluminosilicate melt\\nviscosities, probably due to depolymerization of these melts by replacement of Si-O-(Si,\\nAl) bridges with Si-OH and Si-F bonds, respectively. Evidence from slag systems shows\\nthat fluorine also reduces the viscosity of depolymerized silicate melts. The viscous flow of\\nphonolites, trachytes and rhyolites will be strongly afected by fluorine. It appears that\\nfluorine contents of igneous rocks may be combined with water in calculation schemes for\\ndetermining the viscosity of natural melts."