Micro silica fume

Buyers must prioritize the SiO2 (Silicon Dioxide) content, which should ideally be between 85% and 98% depending on the application. For high-strength concrete, a content of >92% is standard. Additionally, monitor the Specific Surface Area (BET), which should be 15,000–30,000 m²/kg, and the Loss on Ignition (LOI), which must be below 3% to ensure carbon content doesn't interfere with air-entraining agents.

Densified silica fume (bulk density 500–700 kg/m³) is preferred for international shipping as it reduces freight costs and is easier to handle in automated batching plants. Undensified silica fume (bulk density 200–350 kg/m³) is typically used in pre-mixed mortars but incurs significantly higher logistics expenses due to its high volume-to-weight ratio.

Ensure the supplier provides test reports confirming compliance with ASTM C1240 (Standard Specification for Silica Fume used in Cementitious Mixtures) or EN 13263 (European standard). For B2B buyers, a Certificate of Analysis (COA) for every batch is mandatory to verify pozzolanic activity index and moisture content (<3%).

It is primarily used in High-Performance Concrete (HPC) for bridges, marine structures, and high-rise buildings to enhance impermeability and corrosion resistance. It is also a critical component in refractory materials (castables) to improve packing density and in the rubber and polymer industry as a reinforcing filler.

Request a pre-shipment inspection (PSI) by third parties like SGS or Intertek. Since silica fume is a byproduct of silicon metal or ferrosilicon production, quality can fluctuate. Ensure the contract specifies penalties for SiO2 variance and requires sealed samples from the production line before the vessel departs.

Focus on long-term supply stability rather than just the lowest price. Ask for the supplier's annual production capacity to ensure they can handle scale-ups. When sourcing via Made-in-China.com, prioritize Audited Suppliers who offer Trade Resources or secure payment terms to protect your capital during the initial transaction.

Silica fume is highly hygroscopic. Specify Jumbo Bags (500kg/1000kg) with moisture-proof PE liners or 25kg small bags palletized and shrink-wrapped. For sea freight, ensure the container is inspected for holes or condensation issues (container rain) to prevent clumping of the powder.

Verify the correct HS Code (typically 2811.22 or 3824.40) to determine applicable import duties in your country. Be aware of environmental regulations regarding the handling of fine powders; some regions require specific SDS (Safety Data Sheets) highlighting respiratory protection measures during unloading.