Title: On Ostwald’s supersaturation theory of rhythmic precipitation (Liesegang’s rings)
Abstract:Liesegang’s rings are thin precipitation bands formed when two components in solution diffuse into each other and react to form an insoluble precipitate. Ostwald’s supersaturation theory, in the quant...Liesegang’s rings are thin precipitation bands formed when two components in solution diffuse into each other and react to form an insoluble precipitate. Ostwald’s supersaturation theory, in the quantitative form given by Prager and Zeldovitch et al., correctly predicts many features of the process of ring formation in some systems. Anomalous systems not conforming to Ostwald’s theory have been known for some time, and the recent work of Ross and co-workers has demonstrated that an alternative mechanism involving autocatalytic growth of colloidal particles operates at low concentrations. They have also shown that a uniform colloidal precipitate is laid down prior to ring formation in more concentrated systems, which apparently contradicts Ostwald’s assumption that the spaces between rings remain clear of nuclei. The purpose of this paper is to suggest an interpretation of Ostwald’s mechanism which is compatible with the known facts, and to extend the analysis of Prager and Zeldovitch in various ways. Our analysis shows that each ring grows to a finite thickness which, for dilute solutions, is much less than the ring spacing. A quantitative description of ring formation is given for arbitrary values of the ratio of the component concentrations, and is used to derive the form of the phase boundary between metaphases showing Liesegang rings and showing continuous precipitation. The modifications expected to this phase diagram when the Ostwald model is replaced by a more realistic model are also discussed.Read More
Publication Year: 1984
Publication Date: 1984-10-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 67
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