I. Nano-knowledge
Nanometer is a unit of length, one nanometer is one-hundred-thousandth of a meter, equivalent to the length of ten hydrogen atoms arranged one by one. Fifty nanometers is one thousandth of a hair.
The emergence of nanomaterials is an outstanding contribution of materials science to human progress in the 20th century. Scientists have proved that when normal substances are processed to nanoscale (1-100 nm), there will be special physical and chemical properties, and their magnetic, optical, electrical, acoustic, thermal, mechanical and chemical properties will undergo surprising changes. If the original conductive copper will not be conductive at a certain nanometer limit; the original insulated silicon dioxide will start conducting at a certain nanometer limit; silver nanoparticles used in conductive coatings in electronic devices can be sintered at 1000C, so that the materials of circuit substrates can be changed from ceramics to resins and plastics; when all metals are processed to nanometer scale. There will be black powder which can absorb light, etc. This is because nanomaterials have the characteristics of small particle size, large specific surface area and large proportion of surface atoms, as well as the basic physical effects such as quantum size effect, small size effect, surface effect, macroscopic quantum tunneling effect, Coulomb blocking effect, dielectric confinement effect and so on. The emergence of nanomaterials has greatly expanded the imagination space of science, and it is possible to breed a new technological revolution. Authoritative experts predict that nanotechnology, information technology and biotechnology will become the three pillars of social and economic development in the 21st century, and become the strategic commanding heights contested by all countries in the world today.
Metal nanopowder preparation and product development play an important role in the future development of science and technology. Its industrialization prospects are bright. At present, some technologies have entered the stage of industrialization. With the continuous development of science and technology, metal nanoparticles and composite materials have shown extremely important application value in metallurgy, machinery, chemical industry, light industry, electronics, national defense, nuclear technology, aerospace and other fields. Authoritative experts predict that with the breakthroughs in the future research on application products of metal nano-powders, the demand for metal nano-powders in China will reach about 200 tons in the near future. Great efforts will be made to develop industrialized preparation and product development technology of high-yield and high-quality metal nano-powders with broad prospects.
Scientists tell us that the magic nanotechnology - ldquo; silent moistening - rdquo; has quietly entered the lives of ordinary people, and penetrated into the clothing, food, housing, transportation and other fields. Adding metal nanoparticles to traditional materials will make many traditional products, such as ldquo, new look and rdquo, not necessarily expensive, but can achieve a series of new functions or greatly improve the performance of products, thus making your products more competitive in the market. Let's work together to create a rich and colorful nano-world!
PREPARATION OF METAL NANOPOWDERS
The preparation of high-quality metal nano-powder is the key to the research, development and application of metal nano-powder materials. Its main requirements and development directions are: clean surface of particles; controllable particle shape, particle size and particle size distribution; small particle aggregation tendency; easy collection; better thermal stability; easy preservation; production efficiency. High yield, high yield, etc. At present, there are dozens of preparation methods of nano-metal particles developed at home and abroad, including: (1) gas phase method: mainly gas phase condensation method, active hydrogen-mdash; molten metal reaction method, sputtering method, flow surface vacuum evaporation method, electrically heated evaporation method, mixed plasma method, laser-induced chemical vapor deposition method. Cumulative method, explosive wire method, chemical vapor condensation method (CVC) and combustion flame-mdash; chemical vapor condensation method. (2) liquid phase method: precipitation method, spray method, hydrothermal method, solvent volatilization method, sol &mdash method, gel method and radiation chemical synthesis method. In addition, it includes physical vapor deposition (PVD), chemical vapor deposition (CVD), microwave plasma, low pressure flame combustion, electrochemical deposition, thermal decomposition and precipitation of solution, etc. (3) Solid phase method: mainly thermal decomposition method, solid phase reaction method, spark discharge method, dissolution method, high energy ball milling method. However, in the preparation of high purity metal nanopowders,. (4) Mechanical method: using wet ultra-fine nano-grinding equipment, high-energy ball milling method
High-energy ball milling is a method of preparing nano-powders developed in recent years. The main purpose of ball milling is to reduce the size of ions, solid-state alloying, mixing or fusion, and change the shape of ions. The nanoparticles of pure elements, alloys or composites can be obtained by ball milling under appropriate conditions. Due to the introduction of a large number of strains, defects and nano-scale microstructures in this process, the thermodynamics and kinetics of the preparation process are different from the ordinary solid-state reaction process, and it is possible to prepare new nanomaterials which are difficult to prepare by conventional methods. Its characteristics are simple operation and low cost, but the product is easy to be polluted, so the purity is low and the particle distribution is uneven. Nano-ZnO with different particle sizes was synthesized by ball milling. Lin et al. synthesized magnetic nano-Fe3O4 at different annealing temperatures by ball milling. The particle size ranged from 12.5 to 46 nm, the corresponding saturation magnetization ranged from 52 to 66.4 nm, and the coercivity reached the maximum at 22.2 nm. Goya synthesized a series of magnetic particles with different narrow distribution in organic carrier solution by ball milling. All the particles exhibited superparamagnetism at room temperature, and the magnetism disappeared when the temperature was 10-20K. Zduji? Et al. used high-energy ball milling method to completely convert α -Fe2O3 powder into Fe3O4 in air atmosphere. At present, the more recognized industrialization direction is still vapor evaporation condensation method. Relatively speaking, the prepared metal nano-powders have the characteristics of high purity, good particle shape, narrow particle size distribution and wide application range. However, there are still some problems in this method, such as low yield, high cost and high equipment investment.
In view of the industrialization trend of high purity, high yield and low cost metal nanopowders, our company has developed a continuous preparation equipment for metal nanopowders by high vacuum multi-gun plasma evaporation, which has a high vacuum (up to 5-acute; 10-5Pa) compared with the existing production lines at home and abroad.Domestic equipments are all in the range of 10-1-10-2 Pa; process parameters can be adjusted in a wide range; continuous feeding, continuous production, continuous packaging under vacuum; low energy consumption; multi-gun structure and other characteristics, have formed unique features in high yield, low cost, automatic continuous preparation, application scope and so on. On this basis, through a large number of theoretical and experimental studies, we have successfully mastered the production control technology of various pure and composite metal nano-powders (Fe, Ni, Cu, Ag, Al, Mg, Cu-Ni, etc.). At present, we have the industrial production conditions, and can undertake the preparation of metal nano-powders of different specifications (average particle size is 20-1000 nm). Prepare.
DISPERSION AND SURFACE MODIFICATION OF METAL NANOPOWDERS
In theory, the unique physical and chemical properties of metal nano-powders are possessed by single-particle nanoparticles. In order to give full play to its special properties in practice, it is necessary to disperse metal nano-powders into single-particle nano-powders as far as possible in the process of product development. However, due to the properties of metal nano-particles, metal nano-powders must be dispersed into single-particle nano-powders. It is easy to agglomerate between nanoparticles because of its high activity and the existence of various attractions between nanoparticles. Therefore, before the application of metal nano-powders. Generally, it needs to be dispersed and modified. Surface modification of nanoparticles can not only improve the stability of nano-dispersion system, but also endow the system with new functions.
At present, many kinds of surface modification and modification technologies of metal nano-powders have been developed at home and abroad. Generally speaking, according to the principle, it can be divided into: surface physical modification; surface chemical modification. According to the process, it can be divided into: high-energy surface modification (ultrasound, g, X-ray, plasma); mechanical-chemical reaction modification; local chemical reaction (such as adding coupling agent, grafting polymer, etc.); surface coating modification (surfactant, etc.); capsulation modification (coated uniform membrane); precipitation reaction modification. However, there is a big gap in the surface modification and modification technology of metal nano-powders at home and abroad, which is also a major problem that directly restricts the industrialization of metal nano-powders and the development of metal nano-powders products in China.
After years of research, our company has accumulated rich experience in the dispersion, surface modification and development of nano-metal/ceramic composite lubrication products of Cu, Ni, Fe, Cu-Ni and other metal nano-powders.
IV. Application of Metal Nanopowders
Metal nano-powders have attracted much attention in various fields since their birth, mainly because they are often & ldquo; with great skill & rdquo; have excellent performance and unique performance when compounded with other materials, so they can be widely used in batteries, ceramic capacitors, large-scale integrated circuits, etc. Catalysts, magnetorheological fluids, stealth absorbing materials, lubricating materials, high-performance magnetic recording materials, high-performance polishing materials and various nanocomposite additives are summarized as follows:
1. Catalyst materials: metal nanoparticles can catalyze the breaking of H— H, C— H, C— C— O bonds under appropriate conditions. The selectivity of hydrogenation catalyst made of nano-Ni, Cu and Zn particles under the same heating conditions is 5-10 times higher than that of Renni Ni. In addition, using the catalytic properties of nanoparticles and using polymers as carriers, nanoparticles can not only play a highly catalytic and selective catalytic role, but also make them have long-term stability through the stabilization of polymers. Nanoparticles of Ni and Cu&mdash and Zn compounds are excellent catalysts for the hydrogenation of some organic compounds. They can replace expensive Pt and Pd catalysts. The reaction rate of organic chemical hydrogenation and dehydrogenation can be increased by 10 times when the particle size of Ni is 30 nm. The temperature of ethylene hydrogenation reaction decreased from 6000C to room temperature with nano platinum black catalyst. Ultrafine Fe, Ni, g&mdash and Fe2O3 mixed light sintered bodies can replace precious metals as catalysts for automobile exhaust purification, which have been tried out in developed countries such as the United States and Britain. Copper and its alloy nano-powders can be used as catalysts in the synthesis of methanol from carbon dioxide and hydrogen with high efficiency and selectivity. The preparation of nanoparticles from iron, copper, nickel, palladium and platinum can greatly improve the catalytic effect. With the improvement of metal nanoparticles loading technology and thermal stability of metal nanoparticles, catalyst industry will be one of the important applications of metal nanoparticles.
2. Electromagnetic functional materials: nano-Fe and Co powders have important application prospects in high-performance magnetorheological fluids. They can be widely used in dynamic sealing of rotating axles, new lubricants, damping, specific gravity separation, enhancing loudspeaker power of household appliances and improving sound quality. The coercivity of 16 nm iron powder is very high. It can be used as a permanent magnet material. For example, as a magnetic recording material, the recording density and signal-to-noise ratio can be improved. With the advantages of high recording density, high coercivity (up to 9.4kA/m), high signal-to-noise ratio and good oxidation resistance, the performance of magnetic tapes and large-capacity hard and soft disks can be greatly improved. It is anticipated that the magnetic fluid production industry will also be one of the important markets for some metal magnetic nano-powders in the future.
3. Conductive paste: Using nano-silver instead of micro-silver to make conductive paste can save the amount of silver; using nano-copper and nickel powder instead of precious metal powder to prepare electronic paste with superior performance can greatly reduce the cost. This technology can promote the further optimization of microelectronics process. Microelectronic conductive slurry industry has become one of the main markets of metal nano-Cu and Ni powders.
4. Surface coatings and vacuum brazing materials for microelectronics industry: nano-aluminium, copper and nickel powders have highly activated surfaces, and can be coated at temperatures below the melting point of powders in the absence of oxygen. This technology can be applied to the production of microelectronic devices. The surface coatings with nano-titanium powder have excellent corrosion resistance. Vacuum brazing flux prepared by nanometer metal powder can be used for high vacuum sealing of microwave tubes.
5. Magneto-conductive slurry: Using the characteristics of high saturation magnetization and high permeability of nano-iron powder, magnetic-conductive slurry can be made for bonding structure of fine magnetic head, etc.
6. Stealth absorbing material: Metal nano-powder as absorbing material has the advantages of wide bandwidth, good compatibility, small quality and thin thickness. In infrared detectors, infrared transmissionSensors, millimeter wave stealth and visible-infrared stealth play an important role. It is expected that stealth absorbing materials for military industry and microwave attenuation materials for microelectronics industry will also be one of the main markets for metal nano-powders in the future.
7. Hydrogen storage materials: Mg and Ni powders with average grain size of 20-30 nm can directly form chemical equivalent Mg2Ni by ball milling, and their hydrogen absorption performance is much better than that of ordinary polycrystalline materials. The hydrogen absorption activation performance of nanocrystalline FeTi is better than that of ordinary polycrystalline materials.
8. Sensor materials: Metal nano-powder can be used to prepare high sensitivity, miniaturization, low energy consumption, multi-functional sensors such as gas sensors, infrared sensors, piezoelectric sensors, temperature sensors, humidity sensors and optical sensors.
9. Anti-bacterial and bactericidal materials: nano-silver powder has strong inhibition and killing effect on dozens of pathogenic microorganisms such as Escherichia coli and Staphylococcus aureus. As a new anti-infective product, this nano-silver anti-bacterial powder is different from all anti-infective drugs at present. It has many properties, such as broad-spectrum, non-drug resistance, not affected by acid-base value and so on. Antimicrobial and anticorrosive coatings with nano-Ni and Ag powder can also be successfully used in the protection of cultural relics. With the improvement of people's living standard, the market of medical and health care products will be one of the main markets of metal nano-powder in the future.
10. High-efficiency combustion aids: Adding nano-iron, nickel and aluminium powder to solid fuel propellant of rocket can greatly improve the combustion heat, combustion efficiency and combustion stability. Some studies have shown that adding 0.5% nano-aluminium or nickel powder to rocket solid fuel can increase combustion efficiency by 10% - 25% and accelerate combustion speed by tens of times.
11. Electrostatic shielding material: Adding metal nanoparticles to chemical fibre products can solve its electrostatic problem and improve its safety. Adding metal nano-powder to organic glass or other polymer materials can realize electrostatic shielding and improve the transmittance. It is expected that there will be great development prospects in household appliances, electronic shielding and other industries.
12. Medical Material: From the current research results, metal nano-powders will be used in medical imaging, drug carrier, cell staining, cell separation, disinfection and sterilization in the future.
13. Additive Materials for Nanocomposites: Nanocomposites are new composites made of metal nanoparticles and polymer or ceramic materials. Their properties can be greatly improved. For example, when Fe ultrafine particles are coated with a polymer layer of 5-20 nm, a large number of proteins or enzymes can be immobilized to control biochemical reactions, which can be used in biochemical technology and enzyme engineering. The sintering temperature of powder metallurgy products and high temperature ceramics products can be greatly reduced by using sintering additives made of nano-nickel powder and aluminium powder.
14. Metal Nano-lubricating additives: Because most of the actual mechanical equipment are metal friction pairs, and only the expansion coefficient of solid lubricants containing nano-metal powder is close to that of metal friction pairs, and metal nano-powder has good thermal conductivity, therefore, the lubricating additives containing metal nano-powder have a wider application range. 。 The research shows that the products of metal Nano-lubricating additives have the following characteristics: (1) super-strong anti-wear performance, prolonging the service life of equipment by 2-3 times, prolonging the replacement cycle of lubricating oil, saving about 40% of lubricating oil consumption, greatly reducing the maintenance of equipment and the replacement times of components; (2) remarkable energy saving and efficiency enhancement, which can increase the utilization rate of fuel oil by 1. 0-32%, increase the power of engine by 20%; (3) reduce the temperature of engine parts, reduce the mechanical noise, reduce the pollution of exhaust gas and black smoke of vehicles, and effectively prevent the phenomena of shivering and burning oil caused by old or overloaded machinery and equipment; (4) excellent thermal stability, which can make machinery in hot summer. Maintaining the minimum temperature and stable operation required by the equipment can also make the engine start quickly in cold winter, run easily, and start current is small; (5) It has excellent oil solubility, increases the various properties of lubricating oil, and prolongs the deformation, aging and embrittlement time of oil seal, rubber and plastic pad. Because most of the mechanical equipment involves the lubrication of friction pairs, and the use of nano-lubrication additives represents the future development trend, it is expected that nano-lubrication additives products will also be one of the main consumption markets of metal nano-powders in the future.
With the further understanding of the properties of metal nano-powders, more application markets will be developed. In addition, the application of metal compound nano-powder is more. Here are no more examples.