The specifications of microsilica can be divided into different types based on density and particle size, and different grades of microsilica have varying performance, prices, and uses. Here are the details:
Classification by SiO2 Content
- SiO2 ≥ 85%, typical value above 88%, mainly controlling the loss on ignition (≤6%), used for concrete and low-grade refractories.
- SiO2 ≥ 90%, typical value around 92%, impurities controlled according to customer requirements, used for concrete and general refractories.
- SiO2 ≥ 92%, typical value around 94%, specific requirements with emphasis on flowability, used for mid to high-grade refractories.
- SiO2 ≥ 97%, typical value above 96%, strict impurity and pH value requirements, but customer priorities may vary, used for high-grade refractories.
Classification by Density
- As-is state, 100-170 kg/m3, prone to sticking and poor conveyability.
- Slightly densified, 250-400 kg/m3, almost no particles, significantly improved conveyability, but unstable due to temperature effects.
- Semi-densified, 400-500 kg/m3, loose particles start to appear, less prone to sticking, good conveyability.
- High density, 500-700 kg/m3, primarily composed of harder particles (different products may have different particle sizes and compactness), excellent conveyability.
Classification by Particle Size or Specific Surface Area
- Median diameter around 0.3 μm, specific surface area in the range of 15-25 m2/g, almost all particles have diameters ≤1 μm, most silica powders worldwide fall into this category.
- Median diameter around 0.1 μm or less, specific surface area ≥30 m2/g, generally found in high-purity silica powders and relatively rare.
- Median diameter between 0.5-2.0 μm, specific surface area in the range of 5-15 m2/g, very rare.
- Median diameter ≥2.0 μm, extremely rare, and poor performance.
In summary, users should select the appropriate grade of microsilica powder based on their actual needs, achieving both cost-effectiveness and the best results.