Sucrose Dissolution Studies Leading to a Generic Shrinking Object Model for Batch Dissolution of Regular-Shaped Particles |
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| Authors: | Victor W Truesdale |
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| Institution: | (1) School of Life Sciences, Oxford Brookes University, Gipsy lane, Headington, Oxford, OX3 0BP, UK |
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| Abstract: | The dissolution of sieved sucrose crystals has been studied spectrophotometrically by observing the increase in dissolved
sucrose concentration with time. Equations recently derived from the shrinking sphere model for the batch dissolution of a
solid in under-saturated conditions tested successfully on both single crystal-size and mixtures of two sizes of sucrose crystals.
Single-sized crystals provided a straight line for the plot of the fraction of un-dissolved solid to the power one-third,
versus time ( vs. t). The dissolution of mixtures of two crystal sizes fitted the non-linear equation tested earlier on sodium chloride in water-propanone
mixtures. Together, these two sets of tests on ionic and covalent substances verify that many simple dissolutions will be
easily modelled using this physical model based on shrinkage, where the chemical composition of the solids is very much of
secondary importance. Consequently, there is an increased chance that the equations will describe the dissolution of biogenic
silica in seawater, the problem which originally inspired this study. More than this, though, the equations are discovered
to be mathematically generic; very many geometries other than the sphere satisfy the same equations, and the “shrinking object
dissolution model” is thereby defined. The approach should also apply even to non-aqueous dissolutions. A prototype plot of
shrinking object rate constant (obtained from numerical fitting of the model to sucrose) versus particle size is presented,
and it is shown how analogous treatments for other substances will be central to collection and use of much dissolution data
in the future. The study is placed in context with much earlier solid phase decomposition studies, concluding that the key
characteristic of the simplest of all dissolutions is that the interface between solid and liquid should advance at a uniform
linear rate. It is shown how this approach leads to equations of the same mathematical forms already discussed above. |
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| Keywords: | Dissolution Dissolution kinetics Shrinking object model Sucrose Diatom frustules Silica cycling Mixed particles |
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