Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Chemical and Biological Engineering


Contact nucleation in the citric acid monohydrate-water system was studied using a photomicroscopic technique. The (100) face of a parent crystal of citric acid monohydrate was contacted by sliding along a glass plate. When the parent crystal was contacted while in saturated solution, no nuclei were formed; however, nuclei were formed when the parent crystal was contacted in supersaturated solution. These results suggest that a growing crystal surface is necessary for formation of the nuclei and that breakage of the parent is not the source of the nuclei;The growth rates and size distribution of the nuclei formed were determined from photographs taken at timed intervals. The growth rate of any individual crystal was found to be invariant with time, but the growth rate from crystal to crystal varied indicating growth rate dispersion. The growth rates of the nuclei were found to be correlated to initial size and to supercooling; however, the dependence on initial size was not strong;Estimates for the parameters of gamma distributions were determined from the initial size and growth rate data. The distributions described with these parameters were used in a model which predicts the presence of large numbers of crystals at small sizes that cause curvature in the semilogarithmic population density-size plot from a MSMPR crystallizer. This curvature had been generally attributed to size dependent growth rates, but the present work indicates that growth rate dispersion is the primary source of the curvature. The inclusion of growth rate dependence on initial size had little effect on the results, indicating that this dependence can be neglected. Finally, the width of the initial size distribution had a negligible effect on the product crystal size distribution (CSD), while the width of the growth rate distribution had a profound effect. The semilogarithmic population density-size plot was found to curve more for wider growth rate distributions, further demonstrating the significance of growth rate dispersion on the product CSD.



Digital Repository @ Iowa State University,

Copyright Owner

Kris Arvid Berglund



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158 pages