The benefits of fumed silica and silica fume in the manufacturing and construction industries are well known. While the two terms seem similar, the products have clear differences. Unfortunately, most people use the terms interchangeably. Here is everything you need to know about fumed silica and silica fume.
Fumed silica or pyrogenic silica is a multi-purpose silica-based additive commonly used to manipulate viscosity, rheology and enhance functionality of existing polymer matrices. It has a low particle size and low bulk density, meaning the surface area is very high. It is known for its film and cured adhesives strengthening, sag resistance and anti-settling properties.
When silicon tetrachloride is heated in an aerobic environment at temperatures above 1500°, silicon dioxide is formed. With increasing heat and pressure, this silicon dioxide combines and combines with itself, forming aggregates and then fumed silica agglomerates.
The three-dimensional structure of fumed silica increases viscosity. Fumed silica also exhibits a thixotropic behaviour, particularly when used as a reinforcing filler or thickener. It is typically classified into treated and untreated categories (hydrophilic and hydrophobic). Generally, hydrophobic fumed silica is cheaper than hydrophilic.
Fumed silica commonly exhibits a particle size of around 5-50 nm, bulk density of 160 – 190 kg /m3, and a surface area of 50 – 600 m2/g. It is commercially used as:
- Adhesives and sealants strengtheners
- Anti-caking and thickening agents in powders
- Viscosity adjustment in coatings and paint
- Cosmetics for its light- diffusing properties
Bisley supplies both hydrophilic and hydrophobic fumed silica under the name Bi-Sil.
Silica fume is another silica-based additive used in cementitious applications. It is classified as ultrafine, with the size of spherical particles being less than 1 µm in diameter, 100 – 150 times smaller than an average cement particle. When it is used in cementitious applications like concrete, repair products, and shotcrete, it acts as a pozzolan and filler. A pozzolan is a siliceous material with little or no cementitious composition.
Silica fume is a byproduct of the reaction between quartz and coal, coke or wood-chips and also forms in the production of silicon and ferrosilicon alloys.
Silica fume can be supplied with different levels of densification, generally being classified as undensified (with a density of 130 kg/m3) to densified (600 kg/m3). The specific surface area of silica fume can be measured with the BET or nitrogen adsorption method, and typically ranges from 15 – 30 m2/g.
When silica fume is added to Portland cement, its compressive strength, bond strength and abrasion resistance are improved, as a result of the very fine powder filling in cement gaps, and the pozzolanic reaction between the silica fume and the free calcium hydroxide. It also reduces the concrete permeability to chloride ions, which protects steel reinforced concrete from moisture and corrosion. With the addition of silica fume, workability, segregation and bleeding in concrete are all improved.
Some of the benefits of silica fume include:
- Increased compressive and bond strength
- Increased workability
- Enhanced abrasion and corrosion resistance
- Reduced permeability and porosity
- Is economically and environmentally viable because it is reused instead of being discarded into landfill
When mixed with concrete, silica fume transforms the cement paste’s structure. The result is high-strength calcium silicate hydrates and weaker, soluble, and fewer calcium hydroxides. The particles are small, making it easy to disperse and separate cement particles. This provides a uniform matrix offering flexural, higher compressive, and bond strength. Bisley offers both densified and undensified silica fume.
Find Quality Fumed Silica & Silica Fume and Today at Bisley & Company
Whether you’re a paints and coatings or concrete manufacturer, at Bisley & Company, we supply both high-quality fumed silica and silica fume to help you meet local standards and industry specifications. Before shipping our products, we ensure that they are thoroughly inspected so you can be sure to achieve the desired results. Get in touch with us today to get specifications or a quote and discover how we can help you meet your upcoming projects’ needs.