NaCl-H2O和NaCl-KCl-H2O溶液低温相变过程的原位XRD研究

应用原位X射线衍射法对盐湖卤水体系的两个子体系--NaCl-H₂O和NaCl-KCl-H₂O溶液在低温条件下进行扫描，获得了实验条件下体系的衍射图谱，得到了溶液低温相变过程的信息。图谱解析结果表明：含NaCl 26.25%的溶液在-20~-25℃范围内析出了冰、NaCl、低水合氯化钠和二水氯化钠，含NaCl 25.70%的溶液没有发生相变；对于NaCl-KCl-H₂O体系，含NaCl 20.03%和KCl 10.19%的溶液在0~-25 ℃范围内析出了氯化钾和氯化钠，含NaCl 22.40%和KCl 7.28%的溶液在-10~-25 ℃范围内只有氯化钾析出，含NaCl 21.90%和KCl 6.46%的溶液没有发生相变。实验结果显示：这两个水盐体系低温相变过程析出盐的种类与相图结果有差异，原因在于两者的状态不同；体系中二水氯化钠的析出需要经过氯化钠与水的化合过程，该过程是分步进行的；实验体系在低温条件下发生相变受结晶因素控制，温度只是其中一个因素，体系相变发生与否是结晶因素综合影响的结果。

Study on Phase Transition Process of NaCl-H2O and NaCl-KCl-H2O at Low Temperature with in Situ XRD

The diffraction patterns of two systems--NaCl-H₂O and NaCl-KCl-H₂O at low temperature were determined with in situ XRD. The details of systems’ phase transition were further obtained. The solids were analyzed according to the patterns. For NaCl-H₂O system, the phase transitions were different because of their different compositions. For the solution of 26.25% NaCl the solids included ice, NaCl, NaCl·XH₂O(X<2), NaCl·2H₂O in temperature range of -20~-25 ℃, for the solution of 25.70% NaCl the phase transition did not occur under experimental conditions. For NaCl-KCl-H₂O system, the phase transitions were different too. For the solution of 20.03% NaCl and 10.19% KCl the solids were KCl and NaCl in temperature range of 0~-25 ℃, for the solution of 22.40% NaCl and 7.28% KCl the solid was KCl only in temperature range of -10~-25 ℃, as for the solution of 21.90% NaCl and 6.46% KCl there was no phase transition under the experimental conditions. The results show that there are some differences between the experimental and theoretical results due to their different states. The combination of sodium chloride with water results in the appearance of NaCl·2H₂O. Crystallization processes as well as temperature control the occurrence of the phase transition. The phase transitions of the systems are results from comprehensive influences of several factors.