Viscosity of liquids sulfur and selenium at high pressures and high temperatures and their correlations with liquid structure

Abstract:

Knowledge of viscosity of polymer structure liquids with varying composition and/or conditions (temperature, pressure) is important in wide range of scientific and engineering areas including Earth science. For example, strong change in viscosity of polymerized silicate melt is of interests in discussing migration of magma in the Earth’s interior and volcanic activity near surface. However, our understanding particularly for influence of pressure on viscosity and structure of polymer structure liquids remains poor. Here we show pressure and temperature dependence of viscosities of polymer structure liquids sulfur and selenium. Viscosity of liquid sulfur strongly decreases with increasing temperature, while it less depends on pressure. Similarly to viscosity, structure of liquid sulfur shows strong decrease of chain length with increasing temperature, while it is almost constant with varying pressure. This data imply that viscosity of liquid sulfur is mainly controlled by chain length. On the other hand, viscosity of liquid selenium strongly decreases with increase of both pressure and temperature. Structure measurement shows that liquid selenium forms new inter-chain bonding at high pressures and high temperatures, which may be the cause of viscosity decrease at high pressures and high temperatures. Similar structure changes such as polymer length change due to change of non-bridging oxygen and/or formation of tri-cluster have been identified in silicate melt with varying composition, pressure, and /or temperature. The viscosity-structure correlation obtained in liquid sulfur and selenium would provide important knowledge in understanding nature of silicate melt at high pressures.