Non-Arrhenian multicomponent melt viscosity: A model

Newtonian viscosities of 19 natural multicomponent melts ranging in composition from basanite through phonolite and trachyte, to dacite have been analysed in the range of 10⁰-10¹² Pa s. These data, together with the results of previous investigations obtained using concentric-cylinder, parallel-plate and micropenetration methods, form the basis of an analysis of multicomponent non-Arrhenian Newtonian viscosity. Regressions of the combined (high and low temperature) viscosities (ca 350 data points) were performed using the three-parameter Tammann-Vogel-Fulcher (TVF) equation: log₁₀ η= A _TVF+B_TVF/T-T₀ The resulting TVF parameters were used to compose the first non-Arrhenian model for multicomponent silicate melt viscosity. The model accommodates the effects of composition via an empirical parameter, here termed the structure modifier content (SM). SM is the mol% summation of molar oxides of Ca, Mg, Mn, Fe_tot/2, Na and K. The approach is validated by the predictive capability of the viscosity model. The model reproduces the entire original dataset to within <10% on a logarithmic scale, over 10 orders of magnitude of viscosity, 1000°C and the entire range of composition. Comparison with other empirical parameters and the Shaw model [Shaw, Am. J. Sci. 272 (1972) 870-893] is also provided.