Physical properties of Elkem Microsilica®
Elkem Microsilica® is an amorphous silicon dioxide (silica) consisting of sub-micron spherical primary particles and agglomerates of these. The material is highly reactive in cementitious and ceramic bond systems.
The average diameter of a microsilica sphere is about 0.15 micron. Although some of the spheres exist as single entities, most of them form primary agglomerates. The size of these may vary between 0.1 and 1 micron. This rather wide particle size distribution contributes to high packing efficiency.
Microsilica will also contain secondary agglomerates (typically 5 - 50 microns), often generated during filtration and collection. These are - unlike the primary agglomerates - easily broken down when the powder is dispersed in a liquid.
Microsilica has no internal porosity, and the specific gravity of microsilica is about 2.3 g/cm3. The specific surface area may vary between 15 and 30 m2/g.
Areas of application
- Steel and foundry: Blast furnace troughs and runners, ladle linings, sliding gates, etc.
- Cement: Preheater linings, lining in the chain system and lining of in- and outlet zones of rotary kilns
- Glass and ceramics: Kiln furniture
Grades recommended for refractories
The different grades are available in an undensified version (called U) and a densified version (D), depending on the applications. They are listed here from the purest to the lowest grade
The different qualities are detailed under the product data sheets section. Both grades are delivered in both small bags and big bags.
Microsilica is slightly hygroscopic. A slight increase in moisture content is to be expected from production through shipment and during storage. Normally an equilibrium value in the range of 0.8-1.2% is attained depending on the ambient conditions.
Specific limit values for moisture content is restricted to material condition at the time of delivery, unless otherwise specified, and tested according to Elkem Standard Test Methods for Microsilica, Test M-1; Water Content.
In order to give best results, Elkem Microsilica should be used in quantities of 3-8 wt% of the total dry mix. When optimum particle packing is applied, the water demand is normally 4 - 5 % of the total dry weight, depending on the microsilica quantity.
For microsilica to have the desired flow enhancing properties, it is vital that it is well-dispersed. It is generally advised to use a deflocculant. Among a variety of different additives available, we highly recommend to use SioxX in microsilica containing castables.
For hints and problem-solving concerning handling of microsilica, please contact our business unit: Furnace, Filtration and Powder Technology.