How to Distinguish between Fumed Silica and Precipitated Silica?

This article provides a comprehensive guide to distinguishing between Fumed Silica and Precipitated Silica. It details their different production processes, unique properties including physical parameters and surface structure, and compares their performance and main application areas.

1.What is silica

Silica, also called silicon dioxide( SiO₂) , is a white amorphous powdery substance. According to different production processes, silica can be divided into Fumed Silica and Precipitated Silica.

Fumed silica can be divided into Hydrophilic Fumed Silica and Hydrophobic Fumed Silica.

2.What is Fumed silica

Fumed silica is an amorphous silica product made by high temperature hydrolysis of halosilanes.

The main synthesis principle:

SiCl₄ + H₂ + O₂ → SiO₂ + HCl

CH₃SiCl₃ + 2H₂ + 3O₂ → SiO₂ + CO₂ + 3HCl + 2H₂O

Its unique synthesis principle gives it a distinctive structure and excellent performance. Fumed silica is a multifunctional additive with reinforcing, thickening, antiprecipitation, matting, etc.; in general, fumed silica is divided into Hydrophilic Fumed Silica and Hydrophobic Fumed Silica products.

The following are its properties:

1. High temperature resistance

2. Non-combustible

3. High electrical insulation

Physical parameters

• Primary particle size: 7-40mm

• Specific surface area: 50m2/g-400m2/g

• SiO₂ content: 99.8%

Main application areas

In rubber, plastics, glue coating, adhesives, industrial catalyst, food, medicine, CMP and heat insulation and thermal insulation materials and many other fields are playing a vital role, and thus known as the best of the silica, favored by the market.

3.What is Precipitated Silica

Precipitated silica, also called Precipitated Hydrated Silica, is made of quartz sand, soda ash, industrial sulfuric acid, etc., and the main component is SiO₂. The properties of precipitated silica are similar to those of carbon black, and the appearance is a white, highly dispersed amorphous or flocculent powder.

The following are its properties:

1. It is insoluble in water and most acids, soluble in caustic soda and hydrofluoric acid.

2. It is chemically stable. High temperature resistance is not easy to decompose and does not burn.

3. Higher electric margin.

4. Higher dispersibility, porous and larger specific surface area.

5. Higher reinforcing properties.

Physical parameters

• Primary particle size: Below 0.3um

• Relative density: 2.319-2.653

• Melting point: ≤ 1750°C

Main application areas

Additives for rubber tires, paints, toothpaste, etc.

4. Difference between Fumed silica and Precipitated Silica

Different preparation processes

Fumed Silica: Generated generally by hydrolysis of silicon tetrachloride (SiCl₄) by reaction with hydrogen and oxygen at high temperature, which belongs to the fumed method; the by-product is HCl.

Precipitated Silica: Precipitated Silicoa is usually prepared by the sol-gel method, which means that solid precipitated Silicon Dioxide is obtained by the reaction of Sodium Silicate (Na₂SiO₃) and Sulfuric Acid (H₂SO₄) in the aqueous phase to produce silicic acid, and then aging, precipitation, drying and other steps to obtain solid precipitated silica.

Fumed Silica		Precipitated Siliba
	Tightly arranged three-dimensional body structure  Filled interior  Low hygroscopicity  Strong surface adsorption and reinforcing action		Three-dimensional and irregular two-dimensional structure inside  Loose structure with many capillary structures  Moisture adsorption easily, weak reinforcing effect

Comparison of Physical Properties

Performance and Application Comparison

For both types of silica, the right product can be selected according to the specific application scenario. Fumed silica has high performance and purity, and is correspondingly expensive; Precipitated silica, due to its low price, is suitable for use in products that are mass-filled and cost-sensitive.