Degree Type

Dissertation

Date of Award

1988

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Maurice A. Larson

Second Advisor

Glenn L. Schrader

Abstract

Three experimental studies, consisting of a laser Raman spectroscopic study, a vertical column experiment, and a microscopic observation, were carried out to evaluate the structures and characteristics of solute clustering in NaNO[subscript]3 solution systems and the relations between solute clustering and crystallization from solution;The results of these experimental studies suggest that solute clustering occurs in NaNO[subscript]3 solution systems. These solute clusters are apparently solvated clusters that have no solid-phase structure, and they may exist in saturated and supersaturated, as well as in undersaturated, solutions. The relative number of the solute clusters and the degree of clustering increase with solution concentration. The results also suggest that with an observation field of about 20 microns, there is no significant difference between the solution structures at and near the crystal-solution interface of a growing crystal and that in the bulk solution;For a given solution concentration, as the solution becomes supersaturated, a dynamic rearrangement occurs between lower-ordered ionic species and clusters. The present study explains this rearrangement process in terms of the coalescence of some of the clusters at the expense of other clusters and the dilution of the lower-ordered species;Thermodynamic considerations and analyses of this solute clustering are described in terms of relationship of free energy versus the solute mole fraction. Models for the nucleation and the crystal growth mechanisms are proposed. These models are based on the fluctuations and changes in structures and properties of solvated solute clusters;The proposed nucleation models consider two types of mechanisms: the mechanism that occurs under metastable conditions, and the mechanism that occurs under unstable conditions. The latter mechanism is associated with the spinodal-type decomposition. The proposed crystal growth model suggests a dynamic arrangement between the lower-ordered species and the clusters at and near the crystal-solution interface of a growing crystal. The model also suggests a depletion of the clusters as the solution concentration decreases during the growth process.

DOI

https://doi.org/10.31274/rtd-180813-12732

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Irwan Tjahjadi Rusli

Language

en

Proquest ID

AAI8825444

File Format

application/pdf

File Size

139 pages

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