Fumed silica powder, also called pyrogenic silica, is a very fine, non-crystalline form of silicon dioxide. It is made using a high-temperature flame process. In this process, silicon tetrachloride vapor burns in a hydrogen-oxygen flame. This creates tiny particles that join together in branched, chain-like shapes. These shapes give fumed silica its special features, like a large surface area and strong thickening ability. (Ref. Fumed silica – Wikipedia)
The Chemical Abstracts Service (CAS) number for fumed silicas (silica, amorphous, fumed) is 112945-52-5. This number is essential for safety data sheets (SDS) and regulatory compliance.
Grades are usually categorized by their specific surface area, measured in square meters per gram (m²/g) using the BET method. A higher surface area indicates smaller primary particle sizes, which typically enhances thickening and reinforcement capabilities. Common grades vary from 150 m²/g to 380 m²/g or more.
The key difference is surface chemistry.
| Grade | Surface Chemistry | Ideal System | Key Benefit |
|---|---|---|---|
| Hydrophilic | Untreated, contains silanol groups (Si-OH) | Polar liquids (e.g., water, alcohol, epoxy resins) | Maximum thickening and thixotropy in polar media |
| Hydrophobic | Surface-treated with silanes (e.g., DMS) | Non-polar liquids (e.g., oils, solvents, polyester resins) | Easier dispersion, lower moisture absorption, and improved corrosion protection |
No. All these are types of synthetic amorphous silica, but they are made in different ways and have different structures.
- Fumed Silica (Pyrogenic): Made in a gas-phase process. It has the highest purity and the smallest particle size. It is very effective for controlling rheology.
- Precipitated Silica: Made in a liquid-phase process. It has larger particles and is often used as a cost-effective filler, like in tires.
- Silica Gel: Made by adding acid to a silicate solution. It forms a rigid, porous gel that is mainly used as a drying agent.
It is made of tiny particles with a large surface area. These particles create a three-dimensional network in a liquid or paste. This happens through hydrogen bonding or hydrophobic interactions. The network holds the liquid, which makes the mixture thicker. This property is called thixotropy. It means the material becomes less thick when stirred or brushed. When it is still, it thickens again. This helps prevent sagging on vertical surfaces and keeps pigments from settling.
| Industry Sector | Primary Function | Example Applications |
|---|---|---|
| Coatings & Paints | Thickening, Anti-Settling, Anti-Sagging | High-performance industrial coatings, marine paints, powder coatings. |
| Adhesives & Sealants | Viscosity Control, Reinforcement | Silicone sealants, epoxy adhesives, construction mastics. |
| Elastomers | Reinforcing Filler | RTV and HTV silicone rubber, rubber compounds, cable insulation. |
| Plastics & Composites | Flow Aid, Anti-Blocking | Film production, gel coats, pultrusion resins. |
| Cosmetics & Pharma | Thickening, Suspension, Carrier | Toothpaste, lipsticks, tablet coatings, pharmaceutical suspensions. |
Fumed silicas are an important filler in the silicone industry. It is the main reinforcing agent for Room Temperature Vulcanizing (RTV) and High Temperature Vulcanizing (HTV) silicone rubber. It changes a liquid polymer into a strong, durable elastomer. (Ref. Fumed Silica – an overview – ScienceDirect) This reinforcement is crucial for products that need high stability and long-lasting reliability. Examples include automotive parts and medical devices.
The ideal concentration depends on the viscosity and polarity of the liquid system, the desired final thickness, and the specific grade used. Generally, concentrations vary from 0.5% to 5% by weight. We recommend starting with a low concentration and gradually increasing it while observing any changes in rheology.
Absolutely! It is widely used as a thixotropic thickening agent in epoxy systems. This helps create non-sag pastes and putties ideal for vertical applications, fiberglass composites, and adhesives.
Proper mixing is important for the best performance. You usually need high-shear mixing. This can be done with a high-speed mixer, homogenizer, or bead mill. This helps break down the powder clumps and create a strong thixotropic network. For the best results:
- Add slowly into the swirling liquid while mixing hard.
- Do not add large clumps all at once.
- For tough mixtures, try pre-mixing the silica in some of the liquid or use a polar solvent to wet hydrophilic grades.
- Keep mixing until you have a smooth, even mixture.
Some food-grade and cosmetic-grade products are approved by regulatory agencies, such as the FDA and the EU, for use as anti-caking agents (E551) in powders and thickeners found in toothpaste and cosmetics, provided they meet specific purity standards.
While it is typically regarded as low in toxicity, this fine powder can irritate the respiratory system if inhaled in large amounts. To ensure safety during handling, it is important to implement effective dust control measures, maintain good ventilation, and use personal protective equipment (PPE).
Store in a cool, dry place in its original, tightly sealed container. This helps prevent moisture absorption, which is important for hydrophilic grades. Since it is a fine powder, use dust control measures when handling. This includes local exhaust ventilation and dust masks to avoid inhalation. For more information, refer to the Safety Data Sheet (SDS) for handling and safety details.
Partner with a Trusted Fumed Silica Supplier
Ensuring a steady supply of high-quality material is essential for the integrity and performance of your final products. As a trusted supplier, we are dedicated to delivering materials that meet the highest standards of purity and surface area. Our expert technical team is here to assist you with grade selection and dispersion techniques, helping you maximize the benefits of this outstanding material.
