PURITY DROP OF SODIUM CHLORIDE CRYSTALS BY LIQUID INCLUSION FORMATION DURING GROWTH IN A SUSPENSION CRYSTALLIZER

摘要

Sodium chloride was spontaneously crystallized batch-wise in 1 and 2 liter glass vessels, and the product crystals, after classified by sieving, were examined under an optical microscope. In every crystal, many liquid inclusions were found to be distributed spatially but non-uniformly. Total volume V of the liquid inclusions per crystal is successfully correlated with crystal size d in a form of V = 4.0×10~(-6)×d~4 for agitation crystallization. In case of non-agitation crystallization, the total volume decreased drastically to one tenth ～ one hundredth of that for agitation crystallization and it was correlated as V = 9.1×10~(-5)×d~3. Liquid inclusions were considered to be induced in three ways by mechanical impacts given to a crystal, by small crystal adhesions and large crystal agglomerations. Mechanical impacts and small crystal adhesions were confirmed to induce liquid inclusions by in-situ observation experiments.