In situ observation of the dehydration of Li2SO4.H2O monocrystals

In this study the dehydration reaction of Li2SO4.H2O crystals is investigated at different temperatures with the help of optical microscopy. The nucleation and nuclei growth processes during the reaction were recorded photographically using a camera system. Based on a series of pictures the propagation of the reaction front on the crystal surface was captured and an effective speed of growth (in μm/min) was estimated. It is demonstrated, using this in situ measurement technique, that the effective speed at certain temperature and water vapor pressure is a constant for different nuclei. From the surface observations it appeared that the mode of growth of nuclei is non-isotropic with a preferential direction along the [010] axis. In order to measure the growth rate in-depth, measurements on encapsulated crystals were also carried out. It is observed that the propagation of the interface in the crystal is linear and cracks have a remarkable influence on this propagation speed because of a higher mass diffusivity in the cracks.