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What is silica fume?

Silica fume, also known as condensed silica fume or microsilica, is a spherical sub-micron amorphous silicon dioxide used in many applications.

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 to 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 specific 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:

  • The nano-sized spherical non-porous particles create an efficient “filler effect”
    • Primary particles have an average diameter of about 0.15 μm (150 nanometers)
  • Microsilica is a highly reactive form of silica producing a “chemical effect”
    • Thanks to its amorphous nature and high specific surface area.

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 ELKEM MICROSILICA®.

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

ELKEM MICROSILICA® for high performance concrete

Speciality products include (this list is not limited to the following, you can find all our microsilica products for construction in our market pages above)


The ELKEM MICROSILICA® 940 product, a dry silica fume powder that improves the properties and characteristics of high-performance concrete and specialist mortar formulations, acting physically to optimize particle packing and chemically as a highly reactive pozzolan. It is available in undensified (U) and densified (D) forms.
Product data sheet fibre cement applications
Product data sheet gypsum board applications
Product data sheet concrete applications


The ELKEM MICROSILICA® 920 product, a dry silica fume powder that serves as a key ingredient in a wide range of construction materials, acting physically as a filler and chemically as a highly reactive pozzolan. It is used in fiber cement applications as a process aid, to improve ingredient dispersion and to increase hardening and overall durability. It is available in undensified (U) and densified (D) forms.
Product data sheet concrete applications
Product data sheet fibre cement applications
Product data sheet gypsum board applications

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.

Speciality products include:


The ELKEM MICROSILICA® 971 product, a high quality, purpose-made, low-impurity grade, for versatile applications in refractories, available in densified (D) or undensified (U) form, to be used in advanced refractory products such as self-flowing, low, ultra-low and no-cement castables.
Product data sheet


The ELKEM MICROSILICA® 968 product, a cost-effective alternative for low cement castables, featuring a controlled and stable chemical composition.
Product data sheet


The ELKEM MICROSILICA® HQ product is a cost-effective alternative for low cement castables, with controlled and stable chemical composition, based on low alkalis and higher reactivity.
Product Data Sheet


The ELKEM MICROSILICA® 955 product, a medium-quality grade silica fume with tight specification limits based on in-process control, resulting in higher silica content and reduced impurities.
Product data sheet

For oilfield cementing operations, ELKEM MICROSILICA® products offer the following advantages:

The Elkem Oilfield drilling, cementing and completion portfolio includes numerous microsilica additives to ensure essential bonding and mechanical properties.

Speciality products include:


The MICROBLOCK® product, a slurrified multifunctional microsilica additive with a high surface area, processed with quality-controlled particle size distribution that limits gas migration and natural fluid-loss, and improves cement bonding and mechanical properties.
Product data sheet


The MICROLITE® P product, a dry microsilica that creates extra binder phases resulting in lower set-cement permeability and cement slurry density, while maintaining required compressive strength, fluid loss and corrosion resistance in lightweight cement systems.
Product data sheet


The MICROLITE® L product, a pozzolanic slurry with high surface area, which like its powder version enhances compressive strength, lowers permeability, fluid loss and viscosity, resulting in early strength development, strong bonding, and corrosion resistance.
Product data sheet

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.

What makes 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. The highly competent Elkem staff provides full customer services, technical assistance, product development advice and support.

Sustainability at Elkem

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


Elkem Materials Mixture Analyser

Elkem Materials Mixture Analyser

Get the best out of Elkem's Silica fume / Microsilica material by leveraging upon our world reknown software to optimize your mixture.

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