Electrical Conductivity of Solid/Liquid Coexisting Systems: Dependence of Electrical Conductivity on Surface Hydrophilicity

Electrical conductivities were measured for α-SiC or α-quartz powder impregnating CaCl2 aqueous solution systems by an ac impedance method. The influence of the surface hydrophilicity of each powder on the electrical conductivity of the electrolyte solution near the surface of the solid phase is discussed. The activation energy, ΔEa, for the electrical conductivity was determined from a temperature dependence of the electrical conductivity. The "apparent average thickness" parameter was introduced in order to estimate the influence of the solid phase. This parameter was calculated from the following formula: (total volume of liquid phase)/(total surface area of solid phase). For the system consisting of α-quartz powder and CaCl2 aqueous solution, the value of ΔEa increased with a decrease in the apparent average thickness. However, for the system consisting of α-SiC powder and CaCl2 aqueous solution, the value of ΔEa was nearly constant with the apparent average thickness, though the values were larger than that of the parent solution. It is suggested that the electrical conduction of the ionic species on the surface was influenced by the hydrophilicity of the solid surface. For the system containing α-SiC powder and CaCl2 · 6H2O, an abrupt change in electrical conductivity corresponding to the melting of the hydrate was observed. However, as this temperature was constant with the liquid content, an influence of the solid phase was not observed in this system.