利用X射线衍射和拉曼光谱法对KCl和NaCl混合溶液微观结构的研究

利用X射线衍射法和拉曼光谱法系统研究了25 ℃下, 0-26%质量分数浓度范围内KCl和NaCl混合溶液的结构。通过分析X射线衍射法所得的混合溶液的差值结构函数F(Q)以及差值对分布函数G(r)发现,混合溶液组分中的K⁺的水化层半径及其水化数均大于Na⁺,从而揭示出常温下NaCl在水中的溶解度大于KCl的原因。在拉曼光谱的研究中,观察到溶液中水分子的四面体氢键受破坏程度随KCl浓度的增加和NaCl浓度的减少,先增大后减小,并结合X射线衍射法的结果,推断混合溶液中Na⁺对水溶液中氢键结构的破坏程度比K⁺严重,且加入适量的K⁺会使Na⁺由结构缔造者转变为打破结构者,对水溶液结构的破坏增强。

Study of the Hydrated Structure of KCl and NaCl Mixed Solutions Using X-ray Diffraction and Raman Spectroscopy

Research on the hydrated structure of KCl and NaCl mixed solutions with a concentration range between 0 and 26% was conducted using X-ray diffraction and Raman spectroscopy at 25 ℃. Their reduced structure functions, F(Q), and reduced pair distribution functions, G(r), obtained from X-ray diffraction indicate that compared with Na⁺, the hydration numbers and shell radii of the hydrated K⁺ ions are larger. This explains why the solubility of NaCl is higher than that of KCl at 25 ℃. According to the Raman spectroscopy, the tetrahedral hydrogen bonds of water molecules will be destroyed with the increase in KCl concentration and the decrease in NaCl concentration. The extent of the bond destruction has systematic variations; for example, increasing at first and then decreasing. These results show that the destruction of the hydrogen bond structure resulting from Na⁺ is more serious than from K⁺. Also, with the appropriate K⁺ content in the NaCl solution, Na⁺ will behave as a structure breaker instead of a structure maker, which enhances the destructiveness of the solution structure.