What is silica fume?

Silica fume: Basic chemistry and multiple advantages

Silica fume is a co-product of silicon or ferrosilicon production, consisting of ultrafine (sub-micron), amorphous, non-porous, perfectly spherical silicon dioxide (SiO₂) particles, with purity levels of 85–99%.

The main effect of these ultra-fine particles is to greatly improve particle packing and produce a highly pozzolanic reaction in concrete and other cementitious bond systems where the silicon dioxide reacts with calcium hydroxide, heightening performance levels and the strength and durability of these materials.

Additionally, silica fume, because of its amorphous (non-crystalline) structure and its high specific surface area, provides other useful features to various applications, including improved sintering capabilities and enhanced high-temperature performance of refractory castables, resulting in reactions between microsilica and other components of the refractory mix.

To summarize, silica fume has two key features which alone or in combination are the basis for its high performance:

• An efficient 'filler effect', resulting from the size of the spherical, non-porous primary particles of about 0.15 μm (150 nm)
• The 'chemical effect', resulting from the fact that its amorphous nature and high specific surface area make it highly reactive.

A review of some leading products and applications in different industries

Applications are very numerous, including uses in construction, well drilling & cementing, refractories, polymers, etc. This versatility also explains why silica fume is referred to by different names in different industries, such as condensed silica fume or microsilica, the latter used, for example, in high-performance materials (HPM) in the construction and refractory industries.

Elkem markets its wide range of silica fume products under the brand name of MICROSILICA^®.

In construction, the Elkem MICROSILICA^® line of products improves the performance of a wide range of materials in a variety of applications:

• High-performance concrete with microsilica reduces construction time and provides structural advantages and durability for buildings, bridges, transport tunnels, roadways, etc.

• Fiber cement with microsilica is used in roofing materials, such as flat and corrugated sheets, tiles, pipes and moldings for new structures or to efficiently help replace asbestos.

• Gypsum board with microsilica improves fire resistance and core strength.

For refractory materials, Elkem MICROSILICA^® products offer the following advantages:

• Improved strength and service life in high-temperature applications
• Compatible with the making of complex structures, such as castables and shaped parts, thanks to good placement characteristics and low porosity, combined with excellent heat resistance properties.

For oilfield cementing operations, Elkem MICROSILICA^® products offer essential bonding and mechanical properties.

Elkem also offers complementary materials such as specialty weighting agents, free-flow products designed for easy mixing, and excellent dispersion, flexible components or fibers customized to deal with well stresses etc. The choice between these closely related products is based on specific applications.

Elkem MICROSILICA^® – The best-in-class choice

Elkem MICROSILICA^® products are carefully and accurately processed to ensure key quality parameters, with a careful choice of raw materials (low alkalis, low volatiles), constant quality control, thanks to the application of our rigorous Statistical Process Control System (SPC). This ongoing quality assurance program includes continuous in-process monitoring and analysis of our production, stable charges and adjustments in furnace conditions and post-control of finished products.

This results, among other things, in:

• A higher percentage of silicon recovery and a lower level of impurities
• Consistent quality and good workability in flow and setting and hardening properties achieved through chemical consistency.

At the application stage, customers are then fully supported by experienced Elkem industry specialists to get the results they require in their very competitive businesses. Our highly competent staff provide full customer services, technical assistance, product development advice and support.

Sustainability at Elkem

To learn more about our sustainability initiatives, check our webpage.

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