In situ Observation of Growing NaCl Crystals

Abstract

In the field of industrial crystallization, the control of crystal size distribution and purity is the most essential aspect, and has been investigated extensively. However, most of the previous studies were carried out on the final products, in other words, they were in a sense indirect results. It is therefore appropriate to observe the processes of crystallization so that how differently treated crystals grow can be determined under given solution conditions. It is the purpose of this study to investigate the crystallization process of NaCl on differently treated crystals by the in situ observation method under the optical microscope. From the observation results, it was found that the crystal surfaces were observed to have a large number of tiny rectangular columns originating from detached pieces which adhered to the crystal surface, with many inclusions and cracks, and these surface conditions always changed during growth under different solution conditions. Also we obtained the linear crystal growth rate and the crystal growth step velocity as follows, respectively, G_L=7.1ΔC^1.47, G_S=3.4×10²ΔC^2.32.