Special silica for soles

White carbon black manufacturers introduce the concept of white carbon black

1. Chemical structure of silica

95 to 99% of the composition of silica is SiO2, which is confirmed by X-ray diffraction. The structure of the silica differs depending on the method of preparation. The internal structure of the fumed silica is almost completely arranged in a three-dimensional network of silicic acid. This structure makes the particles less hygroscopic, has strong surface adsorption and strong reinforcing effect. In addition to the three-dimensional structure of silicic acid, the structure of the precipitated white carbon black still has more two-dimensional structure of silicic acid, resulting in loose structure, many capillary structures, and easy to absorb moisture, thus reducing its reinforcement. active.

2. Structure of silica

The structure of silica is carbon black, and its basic particles are spherical. In the production process, these elementary particles collide with each other at a high temperature to form a chain-like structure linked by chemical bonds, and this structure is called a basic aggregate. The chain-like structures are hydrogen-bonded to each other to form a secondary aggregate structure, which is easily destroyed during processing and kneading.

three. Surface chemistry of silica

1. Surface group

Surface model of silica

Adjacent hydroxyl groups (on adjacent silicon atoms), it is very important for the adsorption of polar substances; isolated hydroxyl groups, mainly on the surface of white carbon black to remove moisture. The content of such a hydroxyl group, the gas phase method of white carbon black is more than the precipitation method, and it is not easy to remove at an elevated temperature; the bishydroxy group has two hydroxyl groups attached to one silicon atom.

The groups on the surface of silica have certain reactivity, and the surface reactions include: water loss and hydrolysis reaction, reaction with acid chloride, reaction with active hydrogen, formation of hydrogen bonds, and the like.

2. Adsorption of silica surface

The surface of silica has a strong chemisorption activity, which is related to the surface hydroxyl group. It can be combined with water in the form of hydrogen bonds to form a multimolecular adsorption layer. In addition, it can also adsorb with many small organic molecules.

Polyfunctional amines or alcohols have higher adsorptivity than monofunctional groups, so polyfunctional compounds such as ethanolamine, ethylene glycol and triethanolamine are commonly used as active agents in SiO2 compounds.

3. Thermal behavior

Heating the silica will release moisture, and as the temperature increases, the amount of water released will increase. Before 150~200°C, the water is released most, and after 200°C, it tends to be gentle and has obvious turning points. Before the breakpoint, it was mainly the desorption of adsorbed water, and the breakpoint was followed by the surface hydroxyl condensation reaction.