In Situ Observation of NaCl Crystal Growth by the Vapor Diffusion Method with a Mach–Zehnder Interferometer

Vapor diffusion experiments with different thicknesses of oil barriers are observed by a real-time optical diagnostic system consisting of a Mach–Zehnder interferometer, a microscope and an image processor. Spatiotemporal analysis is first employed to extract the absolute concentration evolution and supersaturation during the entire crystallization process. The nucleation and crystal growth processes are then analyzed. It is found that the crystallization process can be easily classified into four stages in our experiments, according to the analysis of interferograms and the absolute concentration curve. This can help us understand the details of crystal growth. The rule of quality change of crystals with increasing thickness of oil barriers is also analyzed, and could be interpreted by the absolute concentration variation and crystallization phase diagram.