THE ELECTRICAL CONDUCTIVITY OF SOME HYDROUS AND ANHYDROUS MOLTEN SILICATES AS A FUNCTION OF TEMPERATURE AND PRESSURE

Abstract

Electrical conductivity of the following molten silicate systems (in mol%): 60SiO2-40Na2O; 65SiO2-35Na2O; 75SiO2-25Na2O; 78SiO2-22Na2O; 72SiO2-24Na2O-4CaO; 66SiO2-19Na2O-15H2O; and an anhydrous and hydrous (4 wt% H2O) Mt. Erebus lava, have been measured as a function of temperature (to 1000°C) and pressure (to 1.3 kbar). The anhydrous soda-rich melts have a positive pressure coefficient of conductivity to ~200 bars and beyond this pressure the pressure coefficient is small and negative. Addition of water lowers the conductivity and gives rise to a negative pressure coefficient at the highest temperatures. The conductivity of hydrous Mt. Erebus lava passed through a maximum with increasing temperature at constant pressure. These phenomena are interpreted in terms of explanations of similar phenomena found in molten salt and aqueous electrolyte solutions.