Temperature‐concentration oscillations as a result of nanoheterophase structure of concentrated aqueous solutions of salts

Abstract

AbstractDetailed precision investigation of aqueous solutions of NaBr·2H2O, KBr, RbNO3, and K2SO4 salts showed oscillations of crystal‐solution phase equilibria in the temperature range of 15–45 °C. The maximum deviations from the smooth correlation between the saturation temperature and the salt concentration (up to 4% of concentration and up to 10 °C) were found to correspond to simplest salt‐water ratios. Recently, similar trends were observed for NaNO3, KNO3 and K2CrO4 solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na+→K+, Rb+, NH4+ (nitrate systems), CrO42–→SO42– and Br–→NO3– (potassium systems), and NO3–→Br– (sodium systems). Increase in total content of impurities (2‐4‐fold) in solution results in 1.5‐2‐fold elevation of the oscillation amplitudes. A concept of nanoheterophase solution was suggested to account for the observed temperature‐concentration oscillations. The concept is based on the original experimental data on interrelated variation of different properties of aqueous salt solutions depending on their concentrations. Characteristic features of the phase diagrams are discussed and influence of the oscillations on crystal growth is elucidated. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)