Silica Fume (Microsilica)

Silica fume (microsilica, CAS 69012-64-2) is an ultra-fine powder of amorphous SiO₂ produced as a by-product of electric arc furnace operations during the production of silicon metal or ferrosilicon alloys. Particles have a diameter of approximately 0.15 µm — about 100 times smaller than Portland cement — and a BET specific surface area of 15,000–30,000 m²/kg. Certified technical parameters (Oriental IMEX inspection report, last shipment 03.2026): • SiO₂: 83.92% (requirement ≥ 70%) ✓ • Fineness (sieve): 8.9% (requirement ≤ 12%) ✓ • Al₂O₃: 0.97% • Fe₂O₃: 2.46% • CaO: 2.87% • MgO: 1.83% • K₂O: 3.91% • Na₂O: 0.37% • Chloride ion: 0.015% • Bulk density: 0.93 g/cm³ • Moisture: 0.58% • Strength activity index: 89.8% (requirement ≥ 70%) ✓ • Overall result: QUALIFIED Mechanisms of action: 1. Fill effect — ultra-fine particles fill the voids between cement grains, densifying the microstructure of the concrete matrix. 2. Pozzolanic effect — SiO₂ reacts with Ca(OH)₂ released during cement hydration, forming additional C-S-H gel that increases strength and durability. Applications: • High-performance concrete (HPC/UHPC): bridges, tunnels, deep foundations, industrial slabs • Fiber-cement composites and wood-wool cement boards • Dry-mix systems (drywall/AAC): improved adhesion and moisture resistance • Refractory materials: castables and refractory concrete for steel and cement kilns • Oil and gas well cementing (API standards) • Paints and sealants: micro-filler improving rheology Standards: • ASTM C1240 (Standard Specification for Silica Fume) • EN 13263-1 (Silica fume for concrete) • Testing performed by accredited laboratory; full COA documentation available for each batch. Logistics: Available in 25 kg bags, 1,000 kg big-bags or bulk. Ports: Shanghai, Ningbo, Qingdao, Tianjin, Guangzhou, Shenzhen. MOQ: 10 MT. SGS/BV certification available on request.