UBC Undergraduate Research

A model for the viscosity of melts within the Phlegraen Fields, Italy Matysek, Nikolas

Abstract

The viscosity of silicate melts is perhaps the most important factor in volcanic processes. Presented here is a model that predicts the non-Arrhenian Newtonian viscosity of 25 anhydrous and hydrous naturally-occurring silicate melts as a function of temperature. This model was created from 437 measurements of viscosity on 16 real-world samples, of which 9 were enriched with water content ranging from 0.30 to 6.32 Wt%. The VFT equation [log η = A + B/(T(K)-C)] was used to describes the non-Arrhenian temperature dependence of viscosity. A hightemperature viscosity limit (A) was assumed and the optimal value was calculated to be -4.74 (e.g. η = 10ˉ⁴·⁷ Pa s). The parameters B and C account for the compositional dependence but a method to calculate them from chemical data was not determined. The model predicts viscosity continuously across 14 orders of magnitude (10³ – 10¹⁶ Pa s) and can calculate the glass transition temperature (Tg) and melt fragility (m). Model parameters B and C are compared against each other and show a strong negative correlation. Anhydrous parameters show noticeable trends when compared against all measures but is clearest against SiO₂. The affect of water is complex and seems to have little systemic influence expect for when B is compared against NBO/T. These cases provide the best avenues of investigation for determining the compositional dependence.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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