Viscosity-temperature relationships of melts at 1 atm in the system diopside-albite

Ansrnlcr The viscosities of six melt compositions have been measured along the join diopsidealbite with a concentric-cylinder viscometer. Measurements were made between 1600 and I 150'C; viscosities were independent of shear rate, indicating Newtonian viscous behavior. Viscosities decreased with increasing temperature and, at constant temperature, they decreased with increasing amounts of diopside component in the mixtures. The temperature dependence ofthe viscosity above the liquidus was fitted to an Arrhenius relationship from which activation eneryies for viscous flow, ranging from 88 kcaVmol for a melt of albite composition to 38 kcal/mol for a melt of diopside composition, were derived. Viscosities over the entire range of the melt and supercooled liquid temperatures were fitted by the method of least squares to the Fulcher equation. Viscosity is strongly dependent upon the mole fractions of silica and alumina and on the number of nonbridging oxygens (NBO/T) in the melt. Addition of diopside to albite melt probably causes a reorganization of the three-dimensional network in favor of a more depolymerized structure. Furthermore, activation energies indicate significant differences in the flow properties ofdiopside versus alumina-bearing melts across the join.