Influence of pH, temperature and sample size on natural and enforced syneresis of precipitated silica

Precipitated silica is an amorphous solid and has a wide range of industrial applications. It may be used not only as adsorbens in liquids and gases or as pigment in paintings, but it is also added to polymeric and pharmaceutical products as an inexpensive and inert filling material. In industrial production, monomeric silicic acid is produced by mixing an inorganic, silicate-based precursor and an acid in a stirred semi-batch process. During this process, the monomeric silicic acid polymerizes to amorphous silica particles. Finally, further polymerization and agglomeration of the particles lead to a colloidal gel network. This colloidal gel network shows syneresis behavior resulting in shrinkage and expulsion of liquid which was enclosed within the gel due to the continuing polymerization reaction. Thus, the product properties (e.g., agglomerate size, porosity or internal surface) are strongly influenced by syneresis. Understanding the dependency between the process parameters and the polymerization and syneresis respectively will give the opportunity to control the precipitation process of silica in order to produce a product with properties specially designed for any specific application purpose. Please click Additional Files below to see the full abstract