Fumed silica, also known as pyrogenic silica, is a highly porous form of silica produced by hydrolysis of silicon tetrachloride vapors at high temperatures. It has a massive surface area ranging from 50m2/g to 400m2/g, which gives it distinctive reinforcing and rheological properties. Due to its unique characteristics, fumed silica finds widespread application in numerous industries from chemicals to food, cosmetics and more.

Morphology and Production

Its particles are typically Fumed Silica with a average size ranging from 0.1 μm to 0.3 μm. The production process involves heating silicon tetrachloride gas to 1100–1300°C in an oxygen-hydrogen flame, resulting in rapid hydrolysis and oxidation. This produces clusters of silica spheres fused together in branched, chain-like, three-dimensional secondary particles. The high surface area is attributed to the tiny primary particles and their fusing into even smaller pores during production.

Several parameters like flame velocity, reactor design and temperature control the morphology, surface area and flow behavior of fumed silica. Higher temperature favors smaller primary particle size. The production is usually carried out as a continuous, one-step process and requires strict quality control to maintain product consistency.

Properties

The characteristic that makes it unique is its extremely high specific surface area. This leads to excellent reinforcing abilities, thixotropy and rheological behavior. Fumed silica also has a neutral pH, low density and is thermally stable up to 1100°C.

It imparts thixotropic properties to liquids, allowing easy application and flow but preventing sagging and settling once applied. This makes it popular as a thickening agent and reinforcer in various applications. Fumed silica dispersions also exhibit shear thinning behavior - viscosity decreases with increasing shear rate.

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