The viscosity of CaMgSi₂O₆ liquid at pressures up to 13 GPa

The viscosity of CaMgSi₂O₆ (diopside) liquid has been determined up to 13 GPa and 2200 °C using in situ falling sphere viscometry with X-ray radiography. The experiments were carried out in a 1500 t multianvil apparatus at the SPring-8 synchrotron (Japan). A new, high-pressure sample assembly was developed with LaCrO₃ replacing the traditionally used graphite furnace material, allowing experiments within the diamond stability field to be carried out. The viscosity of CaMgSi₂O₆ liquid increases slightly from 3.5 to 10 GPa and then decreases slightly at higher pressures. However, over the entire ranges of temperature (2030-2473 K) and pressure (3.5-13 GPa) investigated, variation in viscosity does not exceed ±0.5 log units. The viscosity results from this study are consistent with those calculated from the pressure dependence of oxygen self-diffusion in CaMgSi₂O₆ liquid using the Eyring equation with a translation distance (λ ) of 0.45 nm providing the best correlation. Both sets of results indicate a change in pressure dependence at approximately 10 GPa, where viscosity results show a maximum with pressure and silicon and oxygen self-diffusivity results show a minimum.