Fumed white carbon black (commonly known as nano white carbon black) is a synthetic amorphous white fluidity powder, which is a loose, amorphous, non-toxic, tasteless, odorless, non-polluting non-metallic oxide nanomaterial. Its primary particle size is between 7 and 80nm, and its specific surface area is generally greater than 100㎡/g. It is one of the extremely important nanoscale inorganic raw materials. Due to its nano effect, it exhibits excellent properties such as reinforcement, thickening, thixotropy, insulation, extinction, and anti-sagging in materials, so it is widely used in polymer industries such as rubber, plastics, coatings, adhesives, and sealants. field. As a liquid thixotropic agent and thickener, anti-sedimentation, anti-sag; improve the suspension and dispersion of pigment fillers in liquid systems; used as dispersion and grinding aids; 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 brightness; fix special effects; improve paint film physical and mechanical properties; improve paint film adhesion and flexibility ;Improve the viscoelastic properties of rubber and elastomer, reinforce; defoaming effect in defoamer; improve coating surface hardness, anti-scratch; prevent adhesion in film and elastomer; as adsorbent and carrier; used for inkjet Printing coating; as advanced filling of dental materials; as catalyst carrier, remarkable thermal insulation, for low temperature and high temperature insulation.
1. Introduction to the production method of fumed silica
Chemical vapor deposition (CAV) method, also known as pyrolysis method, dry method or combustion method. Its raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are reacted at high temperature. The reaction formula is: SiCl4+ 2H2+ O2—>SiO2+4HCl. Air and hydrogen are sent to the synthetic hydrolysis furnace after being pressurized, separated, cooled and dehydrated, dried on silica gel, and dust-removed and filtered. Send the silicon tetrachloride raw material to the rectification tower for rectification, then heat and evaporate in the evaporator, and use the dried and filtered air as the carrier to send it to the synthetic hydrolysis furnace. After silicon tetrachloride is gasified at high temperature (flame temperature 1000-1800°C), it is hydrolyzed with a certain amount of hydrogen and oxygen (or air) at a high temperature of about 1800°C; the fumed silica particles produced at this time It is very fine, forms an aerosol with gas, and is not easy to capture, so it is first aggregated into larger particles in the collector, then collected by the cyclone separator, and then sent to the deacidification furnace, and the fumed silica is purged with nitrogen-containing air To PH value of 4 ~ 6 is the finished product.
Fumed silica is roughly divided into two categories, one is hydrophilic fumed silica, and the other is hydrophobic fumed silica.
Hydrophilic fumed silica: Hydrophilic fumed silica is produced by hydrolyzing volatile chlorosilanes in an oxygen-hydrogen flame. Chemically, these loose white powders consist of high-purity amorphous silica. Hydrophilic silica is wettable and dispersible in water. In addition to the application in traditional industrial fields, such as polyester, silicone, paint and coating, hydrophilic fumed silica products are more and more successfully used in high-tech fields. The nanoparticle characteristics and high purity of fumed silica play a leading role in its application in the electronics and optical fiber industries. Hydrophilic fumed silica products have an amorphous structure by X-ray analysis.
Hydrophobic fumed silica: Hydrophobic fumed silica is produced by chemically reacting hydrophilic fumed silica with active silanes such as chlorosilane or hexamethyldisilazane. It is hydrophobic (water repellent) 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. For example, hydrophobic fumed silica is produced by treating 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. superior. In addition to the above-mentioned advantages of hydrophilic products, hydrophobic fumed silica products are characterized by low hygroscopicity, good dispersibility, and rheological adjustment ability even for polar systems. Some products undergo structural modification on the basis of hydrophobic treatment, which can provide further help for customers to develop new products and improve product performance. For example: In a liquid system, hydrophobic fumed silica can be added in a high amount with little effect on the viscosity of the system.
2. Application of fumed silica in various fields:
1. Electronic packaging materials
For example: organic electroluminescent device (OELD) is a new type of flat display device newly developed at present, but the service life of OELD device cannot meet the application requirements, and one of the technical difficulties that needs to be solved is the packaging material and packaging technology of the device . Fully dispersing the surface-active treated fumed silica in the silicone-modified epoxy resin encapsulation adhesive matrix can greatly shorten the curing time of the encapsulation material (2.0-2.5h), and the curing temperature It can be lowered to room temperature, so that the sealing performance of the OELD device is significantly improved, and the service life of the OELD device is increased.
2. Resin composite material
Fully and uniformly dispersing fumed silica particles into the resin material can achieve the purpose of comprehensively improving the performance of the resin-based material. Improve the strength, elongation, wear resistance, improve the surface finish of the material and enhance the anti-aging performance.
3. Plastic
Using fumed white carbon black to transmit light and have a small particle size can make the plastic more dense. After adding fumed white carbon black to polystyrene plastic film, it not only improves its transparency, strength, toughness, but also waterproof performance and anti-aging performance. also significantly improved. The hardness, smoothness and anti-aging properties of plastic-steel doors and windows produced by adding a small amount of fumed white carbon black to ordinary plastic polyvinyl chloride are greatly improved.
4. Coating
my country is a big country in the production and consumption of coatings, but the current domestic coatings generally have insufficient performance, resulting in the need to import a large number of high-quality coatings every year. Some coating manufacturers in Shanghai, Beijing, Hangzhou, Ningbo and other places have successfully realized the application of fumed silica in coatings. This kind of nano-modified coating has changed the shortcomings of previous products. Except for the ratio unchanged, the rest have increased significantly.
5. Rubber
Rubber is an elastic body with excellent stretchability. During the production of rubber products, carbon black is usually added to the rubber compound to improve strength, wear resistance and aging resistance, but the products are all 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 can reach or exceed that of high-grade rubber products, and the color can be kept unchanged for a long time. Nano-modified colored EPDM waterproofing membrane, its abrasion resistance, tensile strength, flexural resistance, and anti-aging performance are all significantly improved, and the color is bright and the color retention effect is excellent.
6. Ceramics
Adding fumed white carbon black instead of nano-A1203 to ceramics can not only play the role of nanoparticles, but also the second-phase particles, which not only improves the strength and toughness of ceramic materials, but also improves the hardness and elasticity of materials. Modulus and other properties, the effect is more ideal than adding A1203.
7. Sealants and adhesives
Adding hydrophobic fumed silica to the sealant will quickly form a silica structure, that is, small nano-Si0X particles form a network structure to inhibit the colloidal flow, accelerate the curing speed, and improve the bonding effect. The small size also increases the sealing and anti-seepage performance of the product.
8. Cosmetics
Fumed white carbon black has strong ultraviolet reflection ability and good stability. It will not decompose and change color after being irradiated by ultraviolet rays, and will not chemically react with other components in cosmetic formulations. These outstanding characteristics of fumed silica have laid a good foundation for the upgrading of sunscreen cosmetics.