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Polymers 2015, 7(12), 2504-2521; doi:10.3390/polym7121528

Influence of pH, Temperature and Sample Size on Natural and Enforced Syneresis of Precipitated Silica

Karlsruhe Institute of Technology (KIT), Institute of Thermal Process Engineering, Kaiserstraße 12, 76131 Karlsruhe, Germany
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Academic Editor: Walter Remo Caseri
Received: 22 October 2015 / Revised: 18 November 2015 / Accepted: 25 November 2015 / Published: 1 December 2015
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Abstract

The production of silica is performed by mixing an inorganic, silicate-based precursor and an acid. Monomeric silicic acid forms and polymerizes to amorphous silica particles. Both further polymerization and agglomeration of the particles lead to a gel network. Since polymerization continues after gelation, the gel network consolidates. This rather slow process is known as “natural syneresis” and strongly influences the product properties (e.g., agglomerate size, porosity or internal surface). “Enforced syneresis” is the superposition of natural syneresis with a mechanical, external force. Enforced syneresis may be used either for analytical or preparative purposes. Hereby, two open key aspects are of particular interest. On the one hand, the question arises whether natural and enforced syneresis are analogous processes with respect to their dependence on the process parameters: pH, temperature and sample size. On the other hand, a method is desirable that allows for correlating natural and enforced syneresis behavior. We can show that the pH-, temperature- and sample size-dependency of natural and enforced syneresis are indeed analogous. It is possible to predict natural syneresis using a correlative model. We found that our model predicts maximum volume shrinkages between 19% and 30% in comparison to measured values of 20% for natural syneresis. View Full-Text
Keywords: silica; syneresis; consolidation; shrinkage; gelation; precipitation; polymerization; membrane; extrapolation silica; syneresis; consolidation; shrinkage; gelation; precipitation; polymerization; membrane; extrapolation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Wilhelm, S.; Kind, M. Influence of pH, Temperature and Sample Size on Natural and Enforced Syneresis of Precipitated Silica. Polymers 2015, 7, 2504-2521.

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