What is the Difference Between Fumed Silica and Precipitated Silica?

Fumed silica and precipitated silica are both synthetic amorphous silicas, but they differ in their manufacturing process, particle size, and properties. Here are the main differences between the two:

1. Manufacturing Process: Fumed silica is produced through a pyrogenic process, where high purity silane is hydrolyzed in a flame of oxygen and hydrogen at very high temperatures. On the other hand, precipitated silica is manufactured using a wet-chemical process, where dilute sodium silicate (water glass) is neutralized by concentrated sulfuric, hydrochloric, or carbonic acids.
2. Particle Size: Fumed silica has a much smaller particle size, with an average particle size of 7-40 nm. In contrast, precipitated silica has a larger particle size, ranging from 1-100 micrometers.
3. Microsctructure: Fumed silica consists of microscopic droplets of amorphous silica fused into branched chainlike 3D secondary structures. Precipitated silica appears as a white, powdery material with a porous structure and a particle diameter ranging between 5-100 nm.
4. Chemical Properties: Fumed silica has a high specific surface area (7-40 m²/g) and small aggregate size (150-300 nm), with 99.8% silica content and low moisture content. Precipitated silica has a larger particle size (1-100 µm), around 90% silica content, and high moisture content.
5. Product Functions: Fumed silica has better performance in thickening, thixotropy, sag resistance, reinforcement, and caking resistance. Precipitated silica is mainly used as a reinforcing agent for rubbers or as a friction agent in brake pads.
6. Environmental Impact: Precipitated silica is considered more environmentally friendly than fumed silica, as its manufacturing process does not produce any harmful byproducts.

In summary, fumed silica is typically used for applications requiring high heat resistance and reinforcement, while precipitated silica is more suitable for environmental friendly applications where hardness and abrasion resistance are important factors.

Comparative Table: Fumed Silica vs Precipitated Silica

Fumed silica and precipitated silica are both synthetic amorphous silica, but they have different properties and applications. Here is a comparison between the two:

Fumed silica is produced through a pyrogenic process, where it is synthesized from the hydrolysis of high purity silane in a flame of oxygen and hydrogen. On the other hand, precipitated silica is manufactured in a wet-chemical process, involving the controlled neutralization of dilute sodium silicate (water glass).

Fumed silica has a smaller particle size, higher silica content, and lower moisture content compared to precipitated silica. As a result, fumed silica is known for its better performance in thickening, thixotropy, sag resistance, reinforcement, and caking resistance. In contrast, precipitated silica is mainly used as a reinforcing agent for rubbers or as a friction agent in brake pads.