Fumed silica or pyrogenic silica is a fine powder material comprising amorphous silica spheres in branching chains of different lengths. It commonly has a particle size of about 5-50 nm, a bulk density of 160 – 190 kg /m2, and a high surface area of about 50 – 600 m2/g. Fumed silica is commonly used to improve rheology and viscosity and enhance the efficiency of polymer matrices.
It is also known for its film and cured adhesive-strengthening, anti-settling, and sag-resistance properties. These properties make it fit for use as an adhesive and sealant strengthener, anti-caking and thickening agent, and a viscosity adjustment agent in coatings and paint.
How is Fumed Silica Formed?
Fumed silica is produced through a vapor-phase hydrolysis procedure, where silicon tetrachloride (SiCl4) is mixed with a flame of hydrogen and oxygen and heated at temperatures above 1500°.
The heat causes the silicon tetrachloride to decompose into silicon dioxide and hydrogen chloride (HCl). With increasing heat and pressure, the silicon dioxide reacts with water vapor in the air to form amorphous silica. Amorphous silica is collected as a fine, white, colloidal powder.
The resulting fumed silica has a highly porous and sponge-like structure. It also has a larger surface area than other forms of silica, such as ground silica and precipitated silica. The surface area makes fumed silica highly reactive and capable of absorbing water. The amorphous nature of fumed silica gives it a wide range of physical and chemical properties that make it useful in various applications.
How Does Fumed Silica Absorb Water
Fumed silica has a high affinity for moisture and is famous for its ability to absorb water vapor from the atmosphere. It can absorb up to 40% of its weight in water, depending on the temperature and humidity conditions. The large surface area of the fumed silica allows it to have many sites where moisture can be absorbed.
It absorbs water through a process known as capillary condensation. Water molecules are typically attracted to the silica particles’ surface and drawn into its pores. The highly porous structure creates a large surface area for vapor to condense. The van der Waals force between the water molecules and the silica surface causes the water to be drawn into the material’s pores.
Besides its ability to absorb water, fumed silica is highly reactive and has several active sites on its surface. This makes it a suitable catalyst, absorbent, and thickening agent in various commercial and industrial applications.
Generally, fumed silica has a high capacity for absorbing moisture. This makes it widely preferred in various applications.
Shop Quality Fumed Silica From Bisley International
Fumed silica is generally grouped into treated and untreated categories (hydrophilic and hydrophobic). At Bisley International, we supply hydrophilic and hydrophobic fumed silica with a variety of physical properties under the name Bi-SiL. Contact us today for more information about fumed silica and how you can place an order.
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