Physicochemical properties of precipitated silica

The physical and chemical properties of precipitated silica, also known as precipitated white carbon black, are as follows:

Physical Properties

Appearance: Usually, precipitated silica appears as a white amorphous powder. When its purity is high, it shows a pure white color with no visible impurities, giving a fine and uniform visual impression.

Particle Size: The particle size generally ranges from 10 to 500 nanometers, with a relatively wide distribution. Different production processes and conditions can lead to variations in particle size. The small particle size endows it with a large specific surface area and surface energy.

Specific Surface Area: Precipitated silica has a relatively large specific surface area, typically between 100-300 square meters per gram. The high specific surface area imparts good adsorption properties and surface activity, enabling it to interact physically or chemically with many substances.

Density: The true density is approximately 2.0-2.6 grams per cubic centimeter, while the bulk density is relatively small, generally between 0.1-0.5 grams per cubic centimeter. This makes it lightweight and loose in applications, facilitating its uniform dispersion in some materials.

Pore Structure: White carbon black has a certain pore structure with pores of various sizes, including micropores and mesopores. This pore structure endows it with good adsorption and storage capabilities, allowing it to adsorb gases, liquids, or other substances.

Solubility: Precipitated silica is insoluble in water and most organic solvents. It can form a stable suspension in water, exhibiting good dispersibility and suspension. This property plays an important role in aqueous systems and applications that require suspension stability.

Flowability: The flowability of powdered precipitated silica is poor, and it is prone to agglomeration. This is due to the strong interaction forces between particles resulting from its high specific surface area and surface activity. However, its flowability can be improved through some surface treatments or the addition of additives.

Chemical Properties

Chemical Stability: Precipitated silica has good chemical stability and is not prone to chemical reactions under normal chemical conditions. Under normal temperature and pressure, it can resist the erosion of most acids, alkalis, salts, and other chemical substances, but it can react with hydrofluoric acid and strong alkalis.

Surface Groups: There are a large number of silanol groups (-SiOH) on its surface. These silanol groups endow precipitated silica with strong hydrophilicity and surface activity. The silanol groups can react chemically with active groups in other substances. For example, they can bind to active sites in rubber, playing a reinforcing role. They can also interact with other molecules through hydrogen bonds and other interactions, affecting the properties of the material.

Acidity and Alkalinity: In terms of acidity and alkalinity, precipitated silica is weakly acidic. This is due to the presence of surface silanol groups, which can release hydrogen ions under certain conditions. Its weak acidity can affect the pH value and chemical reactivity of the system in some applications.

Reactivity: Although it is generally chemically stable, it has certain reactivity under specific conditions. For example, it can react with some metal oxides in a solid - state reaction at high temperatures to form silicate compounds. It can also participate in some organic synthesis reactions in the presence of catalysts.