Solute clustering in supersaturated solutions

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1992
Authors
Lumba, Deepak
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The phenomenon of solute clustering in aqueous solutions of ammonium paramolybdate has been characterized using the following experimental techniques: laser Raman spectroscopy, concentration gradient studies, and multi-angle light scattering. Additionally, light scattering techniques have been developed to investigate the occurrence of solute clustering in concentrated and supersaturated solutions;The results of these experimental techniques indicate that solute clustering occurs in undersaturated, saturated, and supersaturated solutions of ammonium paramolybdate. The age of the solutions does not affect the degree of clustering in these solutions. The size of solute clusters increases with supersaturation and the degree of clustering increases at the saturation temperature. The clusters are not expected to have a crystalline structure. Clusters of size 12 nm (from concentration gradient experiments) and 142 nm (from light scattering experiments) were estimated in molybdate solutions. However, until the amount of solute existing as clusters can be clearly defined, a definitive measurement of cluster-size cannot be achieved;A model explaining the state of the solute in concentrated and supersaturated solutions is proposed. This model considers the phenomenon of nucleation from solution as a two-step process. In the first step, large solute clusters in solution would nucleate in their interior. This would be followed by the rapid crystallization of the whole cluster because of its high supersaturation relative to the molten state (the second step);Light scattering techniques have been successfully developed to investigate the phenomenon of solute clustering in concentrated and supersaturated solutions. A unique light scattering work station was designed and acquired and special light scattering sample cells constructed. Experimental techniques have also been developed to conduct in situ light scattering experiments with vertical columns of concentrated and supersaturated solutions.

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Chemical engineering
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