Fumed Silica

CAS Number:

112945-52-5 (for fumed/colloidal silica) or 7631-86-9 (for amorphous silica).

Chemical  Name:

Silicon Dioxide, amorphous (Fumed). Also called Pyrogenic Silica or Colloidal Silicon Dioxide.

Chemical Formula:

SiO2

Molecular Weight:

60.08 g/mol (for the SiO? unit)

Common Form:

Fluffy, white, ultra-fine, and lightweight powder composed of nanoscale primary particles fused into branched, chain-like aggregates

Uses:

Fumed silica is a versatile multi-functional additive used primarily as a rheology modifier, thickener, and reinforcing agent due to its enormous surface area and surface chemistry.

Primary Applications:

· Coatings, Adhesives, Sealants & Elastomers (CASE): A key rheology control agent to prevent sagging, settling, and provide thixotropy.

· Silicone Rubber: Acts as a reinforcing filler to dramatically improve tensile strength, tear resistance, and hardness.

· Pharmaceuticals: Used as a glidant and anti-caking agent in powders and tablets (e.g., Colloidal Silicon Dioxide, NF/Ph. Eur. grade).

· Cosmetics & Personal Care: Provides viscosity control, suspension, and anti-settling in creams, toothpaste, and lotions.

· Chemical & Industrial Processes: Used as a free-flow agent for powders, a viscosity modifier for inks and resins, and a matting agent for coatings.

What does Fumed Silica  do in a formulation?

• Thickening & Rheology Control (Thixotropy): Its primary function. Surface silanol groups form a reversible 3D hydrogen-bond network in liquids, creating gel-like structure that breaks under shear (thins) and recovers at rest (thickens).
• Reinforcing Filler: In rubber and composites, its nanoscale particles form strong interactions with the polymer matrix, significantly improving mechanical properties.
• Anti-settling & Suspension: Prevents pigments and heavy fillers from settling in coatings and pastes.
• Free-Flow & Anti-caking Agent: Coats powder particles to reduce moisture absorption and static, improving flowability (e.g., in spice blends, instant powders).
• Matting Agent: Scatters light to reduce gloss in coatings and films.

Safety Profile:

· Hazard Classification: Generally considered low toxicity but a physical hazard. Classified as a respiratory irritant. Powder may cause mechanical eye irritation. It is not classified as a carcinogen (amorphous form).

· Inhalation Hazard (Dust): The primary concern. Repeated inhalation of fine dust may cause lung damage (silicosis), but the risk is considered significantly lower for synthetic amorphous silica than for crystalline silica (e.g., quartz). Use dust control.

· Skin/Eye Contact: Inert, but dry powder can be drying or mildly irritating.

· Required PPE: Use dust masks (NIOSH N95 or better) and safety goggles when handling powder to prevent inhalation and eye contact. Wear protective clothing to avoid skin dryness.

· Storage: Store in a dry place in a sealed container. It is hygroscopic and can absorb moisture, which affects its performance.

Technical profile: