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Title: Kinetics of crystallisation
Author: Morris, Peter John
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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It is found that at low supercoolings, many low melting point organic materials grow from their melts in capillaries at ever-decreasing rates and often eventually stop growing altogether. Certain inorganic salts when growing from aqueous solution at low supersaturations also display this phenomenon but not to such a marked degree. The rate of retardation is greatest in smaller diameter capillaries and at low supercoolings. If a face growing at a reduced rate in a capillary is allowed to grow out of the end of that capillary into an unbounded region then the growth rate suddenly increases to the free growth rate value and thereafter growth continues at a constant rate. In an attempt to explain this retardation effect, salol crystals have been etched with a dilute alcohol etchant and whereas the etch pit density of freely grown or unretarded crystals is approximately 64,000/cm.2, the corresponding value for crystals which have apparently stopped growing is only 180/cm.2 Crystals growing at reduced rates but without having stopped growing completely have etch pit densities intermediate between these two values. Experiment shows that these etch pits are probably formed at dislocations so that it appears as though the growth rate of salol at low supercoolings is to some extent dependent upon the dislocation density. Similar, but not so pronounced, results are obtained by etching potash alum crystals. Kinetically, this can be interpreted as implying that the rate of the surface reaction step of the growth process is a function of dislocation density as well as various other possible factors. Accordingly, the retardation effect is seen to be due to a decrease in the dislocation density of the growing face and one means whereby this could occur is possibly by the growing out of dislocations to the capillary walls.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available