Fumed silica (commonly known as nano white carbon black) is an artificial amorphous white liquid powder. It is a loose, amorphous, non-toxic, odorless, odorless, non-polluting non-metallic oxide nanomaterial. Its primary particle size is between 7 and 80 nm, and its specific surface area is generally greater than 100 m2/g, which is one of the most important nano-scale inorganic raw materials. Due to its nano-effects, it exhibits excellent reinforcement, thickening, thixotropic, insulating, matting, anti-sagging properties, etc., and is widely used in rubber, plastics, coatings, adhesives, sealants and other polymer industries. field. As a liquid thixotropic agent and thickener, anti-sedimentation, anti-sagging; improve the suspension and dispersibility of pigment filler in liquid system; use as dispersion and grinding aid; improve coating corrosion resistance; improve powder fluidity , storage stability; improve powder charge and charge stability; improve water resistance; improve paint film scratch resistance; improve color vividness; fix special effects; improve paint film physical and mechanical properties; improve paint film adhesion and flexibility Improve rubber, elastomer viscoelastic properties, reinforcement; defoaming effect in antifoaming agent; improve coating surface hardness, scratch resistance; prevent adhesion in film and elastomer; as adsorbent and carrier; Print coating; advanced filler as a dental material; as a catalyst carrier, significant thermal insulation for low temperature and high temperature insulation.

1. Introduction to the production method of fumed silica
Chemical vapor deposition (CAV), also known as pyrolysis, dry or combustion. The raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are formed by reaction at a high temperature. The reaction formula is: SiCl4 + 2H2 + O2 -> SiO2 + 4HCl. The air and hydrogen are respectively subjected to pressurization, separation, cooling and dehydration, silica gel drying, dust removal and filtration, and then sent to a synthetic hydrolysis furnace. After the silicon tetrachloride raw material is sent to the rectification column for rectification, it is heated and evaporated in an evaporator, and sent to the synthetic hydrolysis furnace with the dried and filtered air as a carrier. After the silicon tetrachloride is gasified at a high temperature (flame temperature of 1000 to 1800 ° C), gas phase hydrolysis is carried out with a certain amount of hydrogen and oxygen (or air) at a high temperature of about 1800 ° C; the fumed silica particles formed at this time Very fine, forming an aerosol with gas, not easy to capture, so it is first aggregated into larger particles in the concentrator, then collected by cyclone separator, then sent to the deacidification furnace, and the fumed silica is purged with nitrogen-containing air. To the PH value of 4 to 6, it is the finished product.

The fumed silica is roughly classified into two types, one is hydrophilic fumed silica, and the other is hydrophobic fumed silica.

Hydrophilic fumed silica: Hydrophilic fumed silica is produced by hydrolysis of volatile chlorosilanes in an oxyhydrogen flame. From a chemical point of view, these loose white powders are composed of high purity amorphous silica. Hydrophilic silica can be wetted with water and dispersed in water. In addition to applications in traditional industrial applications such as polyesters, silicones, paints and coatings, hydrophilic fumed silica products are increasingly used in high-tech applications. The nanoparticle properties and high purity of fumed silica have played a leading role in the electronics and fiber industries. The hydrophilic fumed silica product has an amorphous structure by X-ray analysis.

Hydrophobic fumed silica: Hydrophobic fumed silica is produced by chemical reaction of a hydrophilic fumed silica with a reactive silane such as chlorosilane or hexamethyldisilazane. It is hydrophobic (hydrophobic) and cannot be dispersed in water. In order to solve some special technical problems in the industry, various types of hydrophobic fumed silica have been developed. If a hydrophobic fumed silica is produced by treating a modified hydrophilic grade fumed silica with silane or siloxane, in the final product, the chemical treatment agent is chemically bonded to the original hydrophilic oxide. on. In addition to the above advantages of the hydrophilic product, the hydrophobic fumed silica product is characterized by low hygroscopicity, good dispersibility, and rheology adjustment capability even for polar systems. Some products, after structural modification on the basis of hydrophobic treatment, can further help customers develop new products and improve product performance. For example, in a liquid system, the hydrophobic fumed silica can achieve a high addition amount with little effect on the viscosity of the system.

Second, the gas phase method of silica in various fields:
1. Electronic packaging materials
For example, organic electroluminescent device (OELD) is a new type of flat display device newly developed, but the service life of OELD device can not meet the application requirements. One of the technical difficulties to be solved is the packaging material and packaging technology of the device. . By fully dispersing the surface-treated fumed silica in the silicone-modified epoxy resin encapsulant matrix, the curing time of the encapsulant can be greatly shortened (2.0-2.5 h), and the curing temperature can be lowered to At room temperature, the sealing performance of the OELD device is significantly improved, increasing the service life of the OELD device.

2, resin composite materials
By fully and uniformly dispersing the fumed silica particles into the resin material, the purpose of comprehensively improving the performance of the resin-based material can be achieved. Improves strength, elongation, wear resistance, improves the surface finish of the material and enhances anti-aging properties.

3, plastic
The use of fumed silica for light transmission and small particle size can make the plastic more compact. Adding fumed silica to the polystyrene plastic film not only improves its transparency, strength and toughness, but also has waterproof and anti-aging properties. Also significantly improved. The hardness, smoothness and anti-aging properties of plastic steel doors and windows produced by adding a small amount of fumed silica to ordinary plastic polyvinyl chloride are greatly improved.

4, paint
China is a big country in the production and consumption of paints, but the current domestic coatings generally have performance shortcomings, resulting in the import of a large number of high-quality paints every year. Some paint manufacturers in Shanghai, Beijing, Hangzhou, Ningbo and other places have successfully realized the application of fumed silica in coatings. This nano-modified coating has changed the defects of the previous products, and its main performance indicators have been tested. The ratio has remained the same, and the rest have increased substantially.

5, rubber
Rubber is an elastic body with excellent stretchability. In the process of producing rubber products, carbon black is usually added to the rubber to improve strength, wear resistance and aging resistance, but the products are black due to the addition of carbon black. The fumed silica has laid a material foundation for the production of a new generation of rubber products with novel colors and excellent performance. After adding a small amount of fumed silica to ordinary rubber, the strength, wear resistance and aging resistance of the product meet or exceed the high-grade rubber products, and the color can be kept unchanged for a long time. The nano-modified color EPDM waterproofing membrane has obvious improvement in wear resistance, tensile strength, folding resistance and anti-aging property, and has bright colors and excellent color retention effect.

6, ceramic
The use of fumed silica instead of nano-A1203 is added to the ceramic, which can act as a nanoparticle, and it is a second phase particle, which not only improves the strength and toughness of the ceramic material, but also improves the hardness and elasticity of the material. Modulus and other properties, the effect is more ideal than adding A1203.

7, sealant, adhesive
Adding hydrophobic fumed silica to the sealant will quickly form a silica structure, that is, the nano-SiOX small particles form a network structure to inhibit colloidal flow, accelerate the curing speed, and improve the bonding effect due to the gas phase white carbon black particles. The small ruler also increases the sealing and impermeability of the product.

8, cosmetics
The fumed silica has strong UV resistance and good stability. It does not decompose after being irradiated by ultraviolet rays, does not change color, and does not react with other components in the cosmetic formulation. These outstanding features of fumed silica have laid a good foundation for the upgrading of sunscreen cosmetics.

It can be seen from the partial application profile of the above-mentioned fumed silica that its application spans many fields of modern industry and has a very broad market prospect.