Wu Shiyu, Wu Daoyong, Huang Youfen
College of Resources and Environmental Engineering, Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 50025, China.
ACS Omega. 2021 Jul 1;6(27):17680-17689. doi: 10.1021/acsomega.1c02251. eCollection 2021 Jul 13.
We observed the growth of salt crystals in sulfate saline soil solution during evaporation at constant relative humidity and temperature and studied the formation mechanism of soil deformation induced by salt crystallization. The growth of salt crystals is recorded by images using a CCD camera under an optical microscope, and the solution supersaturation and crystallization pressure are calculated taking advantage of digital image processing. The growth of sodium sulfate multilayer crystals is observed conforming to the Kossel model. Moreover, it is estimated that the maximum growth rate in the longitudinal direction is almost ten times that in the lateral direction in large pore contribution to the nucleation barrier during crystal formation. The crystals act on the liquid film pushing away soil particles, achieving the "self-cleaning" effect finally. The liquid film shows elastic deformation property in a short time during crystal growth, demonstrating that crystallization pressure is exerted by the liquid film. During mirabilite crystal growth, the crystallization pressure values fluctuate within 0-12.57 MPa because the supersaturation of the film is consumed, destroying pores in sulfate saline soil and eventually expressed by salt expansion.
我们观察了在恒定相对湿度和温度下蒸发过程中硫酸盐盐渍土溶液中盐晶体的生长，并研究了盐结晶引起的土壤变形形成机制。利用光学显微镜通过电荷耦合器件（CCD）相机拍摄图像记录盐晶体的生长情况，并借助数字图像处理计算溶液过饱和度和结晶压力。观察到硫酸钠多层晶体的生长符合科塞尔模型。此外，据估计，在晶体形成过程中，大孔隙对成核势垒有贡献，纵向最大生长速率几乎是横向的十倍。晶体作用于液膜，推开土壤颗粒，最终实现“自清洁”效果。在晶体生长过程中，液膜在短时间内表现出弹性变形特性，表明结晶压力是由液膜施加的。在芒硝晶体生长过程中，由于液膜过饱和度被消耗，破坏了硫酸盐盐渍土中的孔隙，最终表现为盐胀，结晶压力值在0 - 12.57兆帕之间波动。
