In aqueous solutions all electrolytes tend to associate at high temperatures (low dielectric constants). Ion association results in the formation of uncharged substrates, which are substantially more volatile than their precursor ions. Thus knowledge of the association constants is important in interpreting the thermodynamics of the partitioning of electrolytes to the vapor phase in a fully speciated approach. Electrical conductance measurements provide a unique window into ionic interactions of solutions at high temperatures and pressures.
In this study, the electrical conductivities of dilute (<0.1 molal) aqueous solutions of NaCl (100-600°C to 300 MPa ) and sodium and potasium hydroxides (0-600 and 100-600°C, respectively, and to 300 MPa) were measured. The results show that the extent of association of Na+ and Cl- is similar to those for Na+ and K+ with OH- in solution from subcritical to supercritical conditions.