HIGH-PRESSURE ELECTROLYTE CONDUCTIVITY OF THE HOMOGENEOUS, FLUID WATER-SODIUM HYDROXIDE SYSTEM TO 400-DEGREES-C AND 3000 BAR

Above the melting temperature of 319 degrees C the ionic fluid sodium hydroxide is completely miscible with dense water. The electrolyte conductivity of such a fluid ''water-salt''-system has been studied from dilute aqueous solution to the ionic melt. Apparatus and procedure are described to perform conductance measurements from 25 to 400 degrees C and from 100 to 3000 bar with eight NaOH-mole fractions from 0.024 to 0.93 and with the pure NaOH-melt. At 400 degrees C and 2000 bar the specific conductance rises slightly from 2.09 ohm(-1) cm(-1) for the pure melt to 2.58 ohm(-1) at 64.0 mol% NaOH and reaches a maximum of 4.28 ohm(-1) cm(-1) at 30 mol%. Density measurements permitted the determination of molar NaOH conductivity isotherms al nearly constant molar concentration of 50 mol . dm(-3). At 350 degrees C and 400 degrees C the isotherms ascend continuously from molten hydroxide to dilute aqueous solutions. A function is presented which describes the conductance over the whole composition range with a quadratic combination of the two limiting conductances, with a Debye-Huckel addition and with two realistic adjustable parameters for viscosity and interionic approach.