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

✍ Scribed by E. V. Kiryanova

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 186 KB
• Volume: 45
• Category: Article
• ISSN: 0232-1300
• DOI: 10.1002/crat.201000168

✦ Synopsis

Detailed precision investigation of aqueous solutions of NaBr . 2Н 2 О, KBr, RbNO 3 , and K 2 SO 4 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 NaNO 3 , KNO 3 and K 2 CrO 4 solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na + →K + , Rb + , NH 4 + (nitrate systems), CrO 4 2-→SO 4 2-and Br -→NO 3 -(potassium systems), and NO 3 -→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.