High Pressure Electrolyte Conductivity of the Homogeneous, Fluid Water-Sodium Hydroxide System to 400℃ and 3000 bar

摘要

Above the melting temperature of 319℃ 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℃ 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℃ 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 at nearly constant molar concentration of 50 mol·dm~(-3). At 350℃ and 400℃ 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-Hueckel addition and with two realistic adjustable parameters for viscosity and interionic approach.