Conductance of Dilute LiCl, NaCl, NaBr, and CsBr Solutions in Supercritical Water Using a Flow Conductance Cell

Abstract

Conductivities of LiCl(aq), NaCl(aq), NaBr(aq), and CsBr(aq) solutions have been measured in the range of concentrations from 0.013 to 4 × 10-8 mol·dm-3 using a flow conductance cell at temperatures between 603 K and 674 K and pressures between 15 MPa and 28 MPa (water densities from 650 to 200 kg·m-3). Limiting equivalent conductances and ionization equilibrium constants calculated from the concentration dependence of the equivalent conductance are reported. Previous measurements of equilibrium constants in the low-density supercritical region, although of lesser accuracy, agree well with the present results. Even at the critical density and 2.5 K above the critical temperature there is no evidence for the critical effects which make the Debye−Hückel limiting law invalid at the critical isotherm−isobar. No critical scaling of Λ0 is observed. Walden's rule is not obeyed and the Stokes radius increases by 70% near the critical region as the density goes from 700 to 200 kg·m-3, suggesting an increase in the number of water molecules carried along with the ion. The differences in mobility between different ions are rather small when compared to the differences in crystallographic ionic radii. The association constants are in the order CsBr < NaBr < NaCl ≈ LiCl.

Extrapolation Methods for AC Impedance Measurements Made with a Concentric Cylinder Cell on Solutions of High Ionic Strength

“…a m NaCl = 0.001100 molÁkg -1 , b m NaCl = 0.009412 molÁkg -1 , c m NaCl = 0.05320 molÁkg -1 , d m NaCl = 0.1057 molÁkg -1 , and e m NaCl = 0.4938 molÁkg -1 and 10 kHz were used. This is the range that has been used in the past for cells with concentric cylindrical geometry albeit with larger cell constants [5,14,30,31].…”

Electrical Conductivity in Hydrothermal Binary and Ternary Systems

“…The electrical conductivity of this system involves fl uxes of ionic solute species in the solvent due to the electrical potential gradient or electric fi eld, E. In a system formed by solute particles (concentration c i ) moving with velocity v i in a solvent which moves with a convective velocity v C , the molar fl ux J i (the number of moles transported per unit area per time relative to fi xed coordinates) is given by Sat. 1-2 Quist and Marshall (1968b) el-HBr-1.1 <0.1-1 Gruszkiewicz and Wood (1997) el-NaBr-4.1 Sat.…”

“…In order to overcome the above-mentioned problems and to perform measurements on aqueous solutions near the critical point of water a fl ow-through conductance cell was developed by Wood and co-workers (Zimmerman et al, 1995;Gruszkiewicz and Wood, 1997;Sharygin et al, 2001).…”

“…(4.19) requires very precise conductivity data, as those measured in hydrothermal systems with the fl ow-through cells (Zimmerman et al, 1995;Gruszkiewicz and Wood, 1997;Ho et al, 2000a;2000b;. Wood and co-workers (Sharygin et al, 2001) have compared the FHFP and TBBK equations for associated electrolytes using conductivity data for aqueous NaCl at high temperature and pressure (623.9 K, 19.79 MPa and r = 0.596 g·cm −3 ).…”

“…A linear increase of Λ 0 with decreasing solvent density is suggested by the experimental data from the ORNL group (Ho et al, 1994(Ho et al, , 1997(Ho et al, , 1998 in good agreement with the Marshall model. However, from the precise measurements on very dilute solutions by Wood and co-workers (Zimmerman et al, 1995;Gruszkiewicz and Wood, 1997) it is observed that Λ 0 reaches a plateau or even goes through a maximum and then decreases as the solvent density decreases.…”