LIBR CRYSTALLIZATION INHIBITION IN THE PRESENCE OF SOLUBLE ADDITIVES

摘要

Experiments have been performed to measure the effect of additives on the crystallization temperature of concentrated LiBr solutions. The measured crystallization temperatures do not correspond to the temperatures of equilibrium solubility but to the critical temperature for heterogeneous nucleation of the hydrated LiBr salt on the glass wall of the test tube containing the sample solution. Various additives at a concentration around 500 ppm have been measured. Some soluble additives further decreased the experimental crystallization temperature by up to 13 °C, corresponding to 22 °C below the equilibrium solubility. Large decreases in the crystallization temperature can be correlated with large complexation constants between the additive and the Li+ ion in solution. Solution complexation, however, is not sufficient to explain the magnitude of the decrease in the crystallization temperature. The only phenomenon capable of quantitatively explain the magnitude of the decrease in the crystallization temperature is the change in the crystal/solution interfacial energy due to adsorption of the additive on the surface of the pre-nucleation embryos. This different crystal/solution interfacial energy due to adsorption plays a critical role in the free energy of cluster formation and the rate of nucleation.