1987 Volume 13 Issue 2 Pages 216-222
Needle crystals of calcium sulfate dihydrate were grown in a supersaturated solution in a DTB type semi-batch crystallizer. After adding the seed crystals, whose mass, number and size distribution were measured before, the mass was weighed every one or two hours, and number and size distribution were measured using microscopic photograph techniques. These operations were continued for 8 to 25 hours in the range of averaged-supersaturated concentrations, i.e. 0.0036 to 0.0088 mol·l-1. Growth rates of needle crystals in longitudinal and latitudinal directions were measured. The mean values of ratio of longitudinal to latitudinal length were evaluated from the size distribution. The ratio increased with increasing mean latitudinal length for 10 to 20 μm, and was almost constant for 20 to 40 μm. The ratio decreased for more than 40 μm. It was found that the observed longitudinal growth rate began to decrease at the point (θc) where the total number of the crystals began to increase, though the latitudinal growth rate was constant. No breakage occurred until the mean latitudinal length reached the critical value of Lbc at θc. Beyond that point, the crystals grew with longitudinal breakage.
