The size of the nanoparticles is 1~100m. In addition to the common characteristics of the above-mentioned nanomaterials, the excellent absorption performance of the nanoparticles also comes from: ① With the refinement of the particles, the surface effect of the particles becomes prominent, and the interface of the nanoparticles is extremely Chemical and multiple scattering have become important absorption mechanisms; ②The quantum size effect of nanoparticles splits the electronic energy levels of the nanoparticles, and the interval is in the microwave energy range (10-5~10-eV), which leads to new absorption. aisle. Nano coating refers to the use of nanoparticles in coatings to obtain coatings with certain special functions. On the one hand, the conventional mechanical properties of nano coatings such as adhesion, impact resistance and flexibility will be improved; on the other hand, it is possible to improve the aging resistance, corrosion resistance and radiation resistance of the coating. In addition, nano coatings may also exhibit some special functions, such as self-cleaning, antistatic, invisible wave absorption, flame retardant and other properties. At present, three types of nanoparticles used in coatings are metal oxides; such as TiO2, ZnO2, Al2O3, Fe2O3, etc.; the second is nano metal powder, such as A, T, Cr, Nd, Mo, etc.; the third is inorganic salts, such as CaCO3 And layered silicates, such as one-dimensional nano-scale clay.
The unique structure of nanopowders makes it have quantum size effect, macro-quantum tunneling effect and interface effect, etc. The electromagnetic shielding coating prepared by using it as a filler has the characteristics of wide frequency band, good compatibility, low areal density and thin coating. Nano-metal powder absorbing composite materials have high microwave permeability and good temperature stability (the Curie temperature is as high as 770K). Magnetic nanoparticles, nanoparticle films and multilayer films are the main forms of nanomaterials used as stealth materials. Magnetic nanoparticles have high coercivity, and ferromagnetic metal nanoparticles have a strong interaction with electromagnetic waves, which can cause large hysteresis loss and increase the absorption of electromagnetic waves. The "super black powder" nano-wave absorbing material developed by the United States has an absorption rate of more than 99% for radar waves. The absorbing material with metal nano-chips as filler developed by France has good absorbing performance in 50MHz-50GHx. Nano soft magnetic metals and alloys have large saturation magnetic induction, high hysteresis loss, high coercive force, resulting in high eddy current loss, high Curie point and high operating temperature, wide wave absorption frequency and other properties. Studies have shown that nano-particles have much stronger microwave absorption capacity than non-nano-sized particles. Many nano-materials such as nano-alumina, titanium oxide, silicon oxide, silicon carbide, etc. have strong absorption of infrared, and are compatible with microwave infrared absorption, Broadband absorption and low reflectivity. The high-efficiency absorbing properties of nano-materials will also help reduce the quality of materials.
Some researchers have tested the relative complex permeability P, relative complex permittivity E, magnetic loss tangent and electrical loss tangent of the nano-material Fe3O4/SiC in different frequency ranges through experiments, and the results show that the Fe3O4 sample is near 1.4GHz There is strong magnetic loss, strong dielectric loss appears near 12GHz and 14.6GHz, SiC sample appears strong dielectric loss near 10GHz and 15GHz. Through the optimized design and simulation of the absorption efficiency of single and double-layer absorbing materials that meet certain conditions in the frequency range of 8-18 GHz, it is found that the absorption efficiency of Fe3O4 is mainly manifested in the Ku band (12-18 GHz), while the absorption of SiC The wave efficiency is mainly manifested in the X-band (8~12GHz), where the single-layer reflection loss is as low as about 25dB, the reflection loss is less than 10dB, the bandwidth is close to 5GHz, the lowest peak of the double-layer reflection loss is about 53dB, and the reflection loss is less than -10dB. The frequency bandwidth is about 4GHz. According to the optimized results and the experimental conditions, the corresponding single-layer and double-layer nano-absorbent coatings were prepared, and the microwave anechoic chamber was used to measure the absorbing effect of the experimental coating samples. The results show that the developed double-layer absorbing material has better performance. Absorbing performance.
For the absorbing coating on the equipment surface, in addition to the absorbing effect, it must also have sufficient mechanical properties. Using rigid nanoparticles to toughen polymers with certain brittle mechanical properties is another feasible method to improve the mechanical properties of polymers. With the development of inorganic particle miniaturization technology and particle surface treatment technology, the toughening modification of plastics has completely broken through the previous practice of adding rubber elastomers to plastics, and the toughness of elastomers is often at the expense of the precious rigidity and size of the material. At the expense of stability and heat resistance. From the point of view of composite materials, if the particles are rigid and bond well with the matrix resin, the rigid inorganic particles can also withstand tensile stress and play a role of toughening and strengthening. Regarding the toughening modification mechanism of ultrafine inorganic particles, it is generally believed that: ①The existence of rigid inorganic particles produces a stress concentration effect, which is easy to cause micro-cracking of the surrounding resin and absorbs a certain deformation work; ②The existence of rigid particles prevents the crack propagation of the matrix resin and hinders and Passivation, the final termination of the crack will not develop into destructive cracking: ③With the finer of the filler, the specific surface area of the particles increases, so the contact area between the filler and the matrix increases. When the material is impacted, due to the rigidity of the nanoparticles and the matrix resin Poisson's ratio is different, it will produce more micro-cracks, absorb more impact energy and prevent the material from breaking. However, if the amount of filler is too large and the particles are too close, microcracks will easily develop into macro cracks, and the performance of the system will deteriorate.
The use of nano-rigid particles filled with polymer resin will not only improve the toughness and strength of the material, but also its performance-price ratio will be unmatched by other materials. In addition, due to the high price of some engineering plastics, people hope to use the secondary materials in the processing and production process as much as possible, but the various properties of the thermoplastic resin will be reduced to varying degrees after the secondary processing. A certain modification can effectively improve the waste utilization rate of thermoplastic engineering plastics and reduce costs, thereby alleviating the problems of resource shortage and environmental pollution. High polymer/rigid nanoparticle composite materials represented by CaCO3 and SiO2 have been widely produced and applied.
In addition, the composite of metal oxide nanopowders and polymers often have characteristics that conventional materials do not have. If these nanomaterials are combined with polymers, polymer composite materials with some specific functions will be obtained, and there will be broad room for development in various high-tech industries. Metal nano powder has a special absorption effect on electromagnetic waves. Iron, cobalt, zinc oxide powder and carbon-coated metal powder can be used as military high-performance millimeter wave stealth materials, visible light infrared stealth materials and structural stealth materials, as well as mobile phone radiation concealment materials. In addition, iron, cobalt, and nickel nanopowders have very good magnetic properties; copper nanopowders have excellent electrical conductivity; zinc oxide nanopowders have excellent antibacterial properties. Using them to compound with high polymers will bring many new 0 functions to high polymer resins, so that they can be more widely used in the technological advancement and upgrading of high industries such as military, aerospace, and electronics, and serve the society. Progress and development.