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:log10η=ATVF+BTVFT−T0 sulting 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, Fetot/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.