Frequency-dependent electrical conductivities of solutions of aqueous sodium chloride have been measured from T = 298 K to T = 623 K at p = 20 MPa, over a very wide range of ionic strength (2·10 −5 to 0.17 mol·kg −1 ) using a unique highprecision flow-through alternating current (AC) electrical conductance instrument. Experimental values for the equivalent conductivity, Λ, were used to calculate molar conductivities at infinite dilution, Λ°, using the Fuoss−Hsia−Fernandez−Prini (FHFP) and Turq−Blum−Bernard−Kunz (TBBK) ionic conductivity models. The resulting values for the limiting conductivity Λ°and the ion association constant of NaCl, from this work and critically evaluated literature data above 277 K, were represented to within the combined experimental uncertainties, as functions of viscosity and solvent density, respectively. New values and new correlations are reported for the limiting equivalent conductivities of the sodium ion, λ°(Na + ), and the chloride ion, λ°(Cl − ) from 277 K and 100 kPa to 1073 K and 500 MPa.

The apparent molar volumes V φ of aqueous R-alanine, β-alanine, and proline have been determined with platinum vibrating tube densitometers at temperatures from 298 to 523 K and at pressures in excess of steam saturation. Values of the standard partial molar volumes V°for the aqueous amino acids increase with temperature then deviate toward negative values at temperatures above 398 K, consistent with a lowering of the critical temperature in the solutions relative to water. This is opposite to the behavior predicted by the correlations developed by Shock and Helgeson (Geochim.

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Temperature-dependent Raman studies of the aqueous speciation of boric acid and sodium borate have been carried out at 25 and 80 °C. Normalized solvent-corrected reduced isotropic Raman spectra were obtained from perpendicular and parallel polarization measurements using perchlorate anion, [ClO4]−, as an internal standard. The intensity variations of these bands with concentration and temperature provided strong evidence that these arise from boric acid B­(OH)3, borate [B­(OH)4]−, and the polyborate species [B3O3(OH)4]−, [B4O5(OH)4]2–, and [B5O6(OH)4]−. A very weak high frequency shoulder on the borate band may indicate the presence of the diborate species [B2O­(OH)5]−. Temperature- and concentration-independent quantitative Raman molar scattering coefficients (S) for the symmetric vibrational bands of boron-containing species were calculated, consistent with the mixed solvent electrolyte model reported by Wang et al. (Pure Appl. Chem. 2013, 85, 2117–2144) up to approximately 100 °C. The band assignments and scattering parameters reported here provide a framework for using reduced isotropic Raman spectroscopy as a research tool for measuring quantitative speciation of boric acid/polyborate solutions under conditions relevant to nuclear reactor primary coolant circuits and spent fuel bays, among other applications.

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