Precipitated silica is produced by mixing sodium silicate and sulfuric acid in water, resulting in pure silica pellets. The physical properties of the silica can be altered by manipulating the conditions of the reaction and the washing and drying process. It is used in various industries, including food, pharmaceuticals, and manufacturing, as an anti-caking agent, abrasive, thickener, and additive to improve characteristics of rubber and plastics.
Precipitated silica is a relatively pure form of the mineral silica, produced by the chemical process known as precipitation. In chemical precipitation, a solid forms from a liquid due to a chemical reaction. Precipitated silica is formed by mixing solutions of sodium silicate with sulfuric acid in water. A chemical reaction occurs and pure silica pellets are formed.
Sodium silicate and sulfuric acid are the raw materials used to produce precipitated silica. Large quantities of these materials are mixed with water simultaneously in measured quantities while in constant agitation. The two chemicals react with each other since sodium silicate is alkaline and sulfuric acid is a strong oxidant, being a very strong acid. The overall pH of the mixture is kept alkaline, as the precipitation reaction is not as vigorous under neutral or acidic conditions. While other acids would also work to create the conditions needed to precipitate silica, sulfuric acid is used almost exclusively.
The physical properties of the resulting silica can vary slightly depending on the exact conditions under which the precipitation reaction takes place. Variations in temperature, the concentration of the solutions used and the ratio of the ingredients in the mixture can alter the physical properties of the silica particles. Manufacturers manipulate these conditions to change the size and porosity of the silica grains.
After the silica has formed, it is separated from the solution, cleaned and dried. This involves washing the silica to remove all traces of chemical salts and by-products of the precipitation process. The washing and drying process can also influence the character of the particles. Particle size, porosity and density can be manipulated in this way to some extent. Manufacturers can prepare precipitated silica in a number of ways depending on the customer’s intended use.
Precipitated silica products are used in a variety of applications, including food, pharmaceutical, manufacturing and other industries. Pure silica is used as an anti-caking agent in some food and pharmaceutical applications, as an abrasive in toothpastes, and as a thickener in some liquids. Industrial uses for precipitated silica also abound. It is used as an additive to some types of rubber and plastics to improve characteristics such as durability and flexibility. Among its many other uses, precipitated silica is sometimes used for sandblasting.
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