Properties and applications of nano-white carbon black

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As one of the first nanomaterials in China to be produced on a large scale, nano-silica (nano-white carbon black) possesses unique properties that conventional materials lack, which has drawn extensive attention from the scientific and technological community as well as the business world. The particle size of this product is only a few dozen nanometers; it possesses high hardness and excellent stability, as well as high melting and boiling points. It also exhibits good chemical inertness and thermal stability. It is mainly used for: (1) In the ceramics industry: it can improve the toughness and surface finish of ceramic products ； (2) Synthetic mullite: It possesses high thermal conductivity and excellent mechanical properties, making it one of the best raw materials for packaging materials in the electronics industry ； (3) Rubber modification: By controlling the particle size of SiO2, rubbers resistant to ultraviolet radiation, infrared-reflecting rubbers, and highly insulating rubbers can be prepared ； (4) Binder: Nanoscale SiO2 particles form a network structure that prevents the flow of the colloid, results in a fast curing rate, enhances the bonding effect, and simultaneously improves the sealing properties of the adhesive ； (5) Coating: Utilizing the transparency of nano-SiO2 and its absorption properties for ultraviolet light ； (6) Functional fiber additives: for manufacturing infrared-shielding artificial fibers, UV-resistant artificial fibers, and fibers with excellent high dielectric insulation properties, etc ； (7) Plastic modification: Used as a reinforcement for plastics, it makes the plastics more dense, thereby improving the transparency, strength, and toughness of the films, **as well as enhancing their water resistance ； (8) Anti-paint aging additives: Improve the aging resistance and finish of various types of paint ； (9) Advanced grinding media: Used to make polishing solutions for grinding or polishing the surfaces of electronic materials such as silicon wafers ； (10) Others: used for artificial teeth, paper surface coatings (porcelain clay), etc. 1. Physical properties of nano-silica: As observed under a transmission electron microscope, the average size of the original particles of nano-silica is around 10 nm ； As determined by dynamic laser particle size analysis, the particle size of the nano-silica particles falls within the range of 10–20 nm, with a very narrow distribution range ； As determined by BET analysis, the specific surface area of nano-silica is as high as 640 m2/g (in other words, the surface area of 1 gram of this nanopowder is roughly equivalent to that of 1 mu of land). Its surface contains a large number of unsaturated residual bonds as well as hydroxyl groups in various bonding states; due to oxygen deficiency on the surface, it deviates from the stable siloxane structure, which is why this material exhibits high reactivity. 2. Optical properties of nano-silica: Nano-silica exhibits high reflectivity for both ultraviolet and visible light, which is distinctly different from the absorption properties of other nanomaterials. Its reflectance for short-wavelength ultraviolet light (200–280 nm) is 70%–80% ； The reflectance for ultraviolet medium-long wavelengths (280–400 nm) is 80–85% ； The reflectance for visible light (400nm–800nm) is over 85% ； The reflectance for near-infrared light in the 800–1350 nm range is also over 70%. 3. Structural properties of nano-silica: Analysis of nano-silica using a specific surface area and porosity analyzer revealed that its surface contains numerous nanoscale pores, with pore sizes ranging from 0.5 to 1 nm, and a porosity of over 60%. 4. Applications of nano-silica in coatings: 4.1 Scrub resistance Research on the use of nano-silica in conventional acrylic coatings shows that, after modification with a small amount of nano-silica, the scrub resistance of these coatings increases from a few thousand cycles to over ten thousand cycles ； Nanosilica can significantly improve the wash resistance of mid-to-low grade latex paints. 4.2 Weather resistance Research on the fundamentals and applications of nano-composite building coatings shows that when traditional mid-to-low quality latex paints are modified with nanomaterials such as nano-silica, nano-titanium dioxide, and nano-zinc oxide, their weather resistance can increase by about 3 times. The addition of a certain amount of nano-silica can raise the resistance of traditional coating products to ultraviolet aging from 350 hours to over 600 hours. 4.3 Stain resistance and self-cleaning property Studies have shown that the stain resistance and self-cleaning property of coatings can be improved through the following approaches: one is to utilize the highly porous structure of nano-silica, and by employing certain processing techniques to create on the coating surface interface structures at the nanoscale where the geometric shapes complement each other (such as alternating convex and concave patterns), thereby enabling the adsorption of air and the formation of a stable gas-barrier layer on the surface ； Second, the surface of the nano-silica particles is treated to give them amphiphilic or hydrophobic properties, thereby effectively improving the wetting of the building coating film by rainwater as well as reducing the adhesion of dust, and enhancing the film’s resistance to staining and its self-cleaning ability. 4.4 Antibacterial property Studies on the antibacterial properties of nanomaterials in mercerized coatings have shown that when the addition amount of nano-silica exceeds 0.5%, the modified mercerized coating samples exhibit significant antibacterial effects. Nanosilver-loaded antibacterial materials using multi-porous nano-silica as a carrier have been successfully applied to provide antibacterial and antifungal properties in water-based building coatings. Application of nano-antibacterial agents (using silica as a carrier and Ag+ as the main antibacterial component) in powder coatings: Adding about 2% of nano-antibacterial agents to conventional powder coatings significantly improves their antibacterial properties; tests using the film-coating method show a killing rate of over 99% against E. coli and Staphylococcus aureus (at 37°C for 23 hours). Nanocomposite latex paint modified with nanomaterials such as nano-silica, nano-titanium dioxide, and nano-zinc oxide can effectively kill a range of bacteria including Escherichia coli and Staphylococcus aureus; the killing rate of Escherichia coli can exceed 99% within about 3 hours, and the antibacterial effect remains quite persistent. 4.5 Hydrophobic Corrosion Resistance: Hydrophobic anti-corrosion coatings containing nano-silica not only possess good adhesion and corrosion resistance, but also high density and resistance to ion penetration. Its preparation method: Particles such as nano-silica are dispersed in the coating in the form of a sol, rather than using the conventional preparation method for nano-modified coatings (which involves selecting appropriate process conditions such as dispersion time and dispersion medium) ； Using existing coating production equipment such as sand mills, ball mills, three-roll mills, colloid mills, and high-speed dispersers is more conducive to the dispersion of nanomaterials. When preparing nano-hydrophobic anti-corrosion coatings, attention must be paid to electrical compatibility; otherwise, electrical neutralization may occur, leading to colloid aggregation. 4.6 Transparency: Since the particle size of nanoparticles (10–20 nm) is much smaller than the wavelength of visible light (400–750 nm), they allow light to pass through, thereby not affecting the transparency of the coating system. For nano-silica, as it is an inorganic non-metallic white powder, it does not cause masking when properly dispersed; therefore, nano-SiOX ensures the transparency of nano-modified coatings. High-wear-resistant transparent coatings can be produced using nano-silica, increasing their wear resistance by more than twice compared to before. 4.7 Hardness Studies on the hardness of polyurethane coatings incorporating nano-silica particles have shown that the addition of a small amount of nano-silica can rapidly increase the hardness of such resin coatings. Studies on the relationship between the film hardness of UV-curable coatings and the amount of nano-silica added have shown that when the nano-silica particles are uniformly dispersed as individual particles within the organic material, these nanoparticles act like rigid chains to reinforce the organic material, thereby increasing the film hardness of the UV-curable coatings by more than 2.5 times. 4.8 Thermal Stability Studies on UV-curable coatings have shown that nano-silica can increase the glass transition temperature of the coating film. This is due to some interaction between the nano-silica and the oligomer segments in the coating film, which hinders the movement of these segments and thereby raises the glass transition temperature. 4.9 Viscosity Upon studying the effect of nanoparticles on the properties of high-solid-content polyester-polyurethane coatings and films, it was found that the addition of nano-silica particles can significantly increase the viscosity of the coatings. Meanwhile, if it is desired to adjust the viscosity of the system, this can be achieved by adding an appropriate amount of nano TiO2. 4.10 Other properties: In interior and exterior wall coatings, the addition of nano-silica can significantly improve the opening performance of the coating; it does not separate into layers, and possesses good thixotropy, anti-sagging properties, and workability. For different types of coatings, the addition amount of nano-silica is generally 0.1~1.0%, with a maximum of no more than 5%. 5. Prospects for the application of nano-silica: The modifying effect of nano-silica on coatings relies, on the one hand, on its unique physical properties (basic physical properties, optical properties, and structural properties); on the other hand, it is achieved by combining it with other nanomaterials, thereby allowing the advantages of two or more nanomaterials to complement each other and create a synergistic effect, which significantly improves the performance of nano-modified coatings. It should be particularly noted that the addition technique and degree of dispersion of nanopowder materials in fields such as coatings are directly related to the extent of performance improvement in the modified products. 5.1 Thermal reflectivity (insulation) The unique optical properties of nano-silica imply great potential for its use in solar heat-reflective coatings. If combined with high-performance solar heat-reflecting resins, high-performance coatings suitable for various high-temperature environments can certainly be developed. 5.2 Ultra-weather resistance: By combining nano-silica with rutile-phase nano TiO2 to form a particle structure with silicon on the outside and titanium on the inside, it is possible for nano-silica to reflect the majority of the ultraviolet rays in sunlight first, while the remaining rays are absorbed by nano TiO2. This approach holds promise for the development of ultra-weather-resistant coatings. 5.3 Super-dryness: Through the structural control and surface treatment of nanoparticles such as nano-silica and nano-titanium oxide, specially structured nano-silica can play a unique role in super-dry coatings. In addition, nano-silica can also be used in various functional coatings, endowing the coating film with special properties such as air purification, self-repair, and antistatic effects. 6. Other applications: Plastics: When nano-silica is fully dispersed in plastic materials such as polypropylene (PP) and polyvinyl chloride (PVC), it can significantly enhance the strength, toughness, wear resistance, and aging resistance of plastic products. Materials such as nano-modified PP meet or exceed the performance standards of the engineering plastic nylon 6 in terms of key indicators such as water absorption rate, insulation resistance, compressive residual deformation, and flexural strength. The weather resistance of these materials is more than twice that of nylon 6, allowing them to replace nylon 6 in certain applications. For colored rubber: by adding a small amount of nano-silica (as a substitute for carbon black) to rubbers such as solvated styrene-butadiene, rubber products with improved toughness, strength, elongation, impact resistance, and aging resistance can be produced, and these properties meet or exceed those of ethylene-propylene-diene monomer rubber. Magnetic materials: Iron coke powder is modified by adding a composite powder primarily composed of nano-silica. Tests have shown that the key performance parameters of these products reach the highest levels among existing similar products in the United States; for example, the residual magnetic induction strength is greater than 4100 Gs, the intrinsic coercivity is greater than 3000 Oe, and the magnetic energy product is greater than 4 mGOe. At the same time, the production cost of these materials is significantly reduced.