Precipitated and Fumed Silicas and Related Products

Abstract

Precipitated and fumed silicas are important, high-value, effect fillers mainly used in elastomers, sealants, adhesives, and surface coatings. They are amorphous materials, with primary particles in the nano-range and with high specific surface areas. The precipitated products are lower in cost and have the majority of the market in terms of volumes used. One of their most important applications is in fuel-efficient, energy, or green tires. The fumed silicas are an essential component of many silicone elastomer formulations. Both forms are excellent thixotropic agents for liquid systems such as surface coatings, sealants, and adhesives, with the fumed product being the most effective. Silica fume, a by-product from the manufacture of silicon and alloys, is a totally different product to fumed silica, although it is often confused with it and has very limited polymer applications today. Silica gels, which have much in common with precipitated silica, are used in a number of specialist polymer applications, including coatings and films. Surface treatments play a key role in many of the applications, with both functional and nonfunctional organo-silanes being widely used.