Silica Fume / Microsilica (Densified & Undensified)

Densified and undensified microsilica at 85–96% SiO₂ for high-performance concrete and refractories

Silica fume is the ultrafine amorphous silica collected in the baghouse of a silicon or ferrosilicon furnace: primary particles around 0.15 micron, roughly a hundredth the size of a cement grain, which is why a few percent in a concrete mix fills the space between cement particles and reacts with the lime the cement liberates. The buyer specifies it on SiO₂ (85% is the ASTM C1240 floor; Chinese grades are sold as 85, 90, 92, 94 and 96%), loss on ignition and moisture, oversize on the 45 micron sieve (ASTM C1240 caps it at 10%), BET specific surface, and the accelerated pozzolanic strength activity index in which 10% of the cement is replaced and the mortar cured a day at 23 °C and six days at 65 °C. EN 13263-1 is the European specification for silica fume as a Type II addition under EN 206. The second decision is physical form. Undensified fume leaves the filter at 200–350 kg/m³, loads about 10–12 t in a 20-ft container and disperses easily, so refractory makers and dry-mix producers prefer it; densified fume is tumbled with air until it agglomerates to 500–700 kg/m³, loads 20–24 t per box and suits ready-mix and precast plants with good mixing energy. Dosage in high-performance concrete is usually 5–10% of cement weight, up to about 15% in specialised mixes. Refractory-grade microsilica for low-cement and ultra-low-cement castables is a distinct product with its own carbon and alkali limits.

Customs heading 2811.22 covers all silicon dioxide, so precipitated and fumed silica sit inside the same trade figures. UN Comtrade 2024 export declarations under HS 2811.22 total about USD 3.45 billion and 2.47 million MT across reporters; China declared 1.33 million MT at about USD 630/MT, and the origins whose tonnage and unit value point to furnace silica fume rather than chemical silica include Norway (91,000 MT at about USD 473/MT), India (86,000 MT, USD 960/MT), Malaysia (75,000 MT, USD 434/MT) and Brazil (20,000 MT). Norway's producers collect microsilica at ferrosilicon and silicon plants and sell a refractory-benchmark grade alongside concrete grades. CBIL is a commodity brokerage company and brokers silica fume from furnace operators and processors in China, Norway, India and Brazil to ready-mix, precast, shotcrete, dry-mortar, oil-well cementing and refractory buyers, against an SGS, Bureau Veritas or Intertek certificate of SiO₂, LOI, moisture, 45 micron residue, specific surface and activity index, a safety data sheet, and a certificate of origin, in 20–25 kg bags palletised or 500–1,000 kg jumbo bags in 20-ft containers, on FOB, CFR and CIF terms; bulk pneumatic parcels are quoted for plants with silo intake. There are no export bans or licence requirements on silica fume from these origins that we know of, and no CBAM listing under HS 2811. Price is agreed per MT on grade, form and pack. Send your SiO₂ floor, densified or undensified, the standard you certify to, monthly tonnage and discharge port and the enquiry is screened and worked against it.

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Excluded origins are not offered, including product re-exported, blended or re-processed through a third country. Every lot moves with a certificate of origin naming the producing plant, mine or grower country, and nothing is quoted before the seller and loading point are known.