Being hydrophobic, fumed silica does not absorb water. While fumed silica itself does not absorb water, it can absorb moisture from the air, particularly in humid conditions. Fumed silica, sometimes called pyrogenic silica, is a type of amorphous silicon dioxide produced by burning silicone-rich material in a high-temperature flame. The resulting material is a very fine, highly porous, and lightweight powder.

Properties of Fumed Silica

  • High surface area: Fumed silica is a highly absorbent, non-porous, and finely divided amorphous material with a large surface area of 50-600 m2/g. The large surface area gives fumed silica excellent absorbent, thickening, gelling, and suspending properties.
  • Thermal conductivity: Fumed silica has low thermal conductivity, low refractive index, and a low bulk density of 160 to 190 kg/m3.
  • Safety : Fumed silica is a non-toxic, odorless, and chemically inert material.
  • Filler: Fumed silica is a filler that boosts the viscosity of a product and can serve as a thermal insulator.
  • Fumed silica also shows thixotropic properties, especially when used as a reinforcing thickener.
  • Insoluble: Fumed silica is insoluble in most organic solvents, acids, and bases. This makes it a stable and inert additive in a variety of formulations

Types of Fumed Silica

Fumed silica is typically classified into two categories: hydrophilic fumed silica and hydrophobic fumed silica (also known as treated and untreated).

Hydrophilic Fumed Silica

This is a type of fumed silica used to thicken and stabilise suspensions, improve the surface area, and increase the shelf life of products. Sometimes it is used as an anti-caking and thickening agent in powders.
Hydrophilic fumed silica consists of spherical particles with an average particle size of five to fifty nanometers and a surface area of 50 – 600 m2/g. This type of fumed silica is highly versatile and is used in a variety of applications, such as sealants, coatings, and adhesives. It can also increase the viscosity of oils and greases.

Hydrophobic Fumed Silica

Hydrophobic silica is a type of fumed silica that has been treated with an organosilane or silane coupling agent to make it water-resistant. This material is a fine white powder with a large surface area, making it suitable for use as an anti-caking and thickening agent. It is also used as an absorbent in a wide range of industries and applications.

Functions and Application of Fumed Silica

Fumed silica has a wide variety of applications; it is commercially used as:

  • A thickener – Fumed silica helps increase the viscosity of various products, such as adhesives, sealants, paint, and coatings.
  • A reinforcement agent – Fumed silica is used as a reinforcement agent in different materials, including plastic and rubber compounds. It helps improve the durability and strength of the material.
  • An absorbent – Fumed silica is used as an absorbent in products like diapers to help in absorbing moisture and odors.
  • Filler – Fumed silica is used as filler in various products to help reduce costs by replacing more expensive ingredients.
  • An anti-caking agent – Fumed silica is used as an anti-caking agent in powdered products, such as sugars, salts, and spices.

Buy Fumed Silica from Bisley International

Bisley & Company is proud to provide you with high quality fumed silica. We supply both hydrophobic and hydrophilic fumed silica under the name Bi-Sil. Contact us today online or call 02 8905 4200, and our team will help you find the fumed silica grade you need.