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Nanoparticle magnetic material equipment process and application

In addition to the unique effects of nanoparticles in general, magnetic nanomaterials developed in recent years have excellent magnetic properties and have broad application prospects. In order to further develop the application potential of nanoparticle magnetic materials, there are still many problems that need further study, such as the development and improvement of nanoparticle magnetic material preparation technology and self-assembly technology, to expand the scope of preparation (such as preparation with magneto-optical, magnetoelectric and magnetic Thermal properties of the new nanocomposites); to strengthen the theoretical study of magnetic nanoparticles, the use of a variety of characterization methods in-depth study of its structure and performance, so that this new material really play its greatest potential.

When the ferromagnetic material particles are in a single domain size, the coercive force (Hc) will show a maximum value and the particles will enter a superparamagnetic state. These special properties have made the research on the preparation methods and properties of various nanoparticle magnetic materials more and more important [1]. Initially, pure iron (-Fe) nanoparticles were mostly used as the research object, and almost all of the preparation processes used chemical deposition methods. Later, there have been many new preparation methods, such as wet chemical methods and physical methods, or a combination of two or more methods to prepare nanoparticle magnetic materials with special properties. These particles have broad application prospects in magnetic recording materials, magnetic fluids, biomedicine, sensors, catalysis, permanent magnetic materials, pigments, radar wave absorbing materials, and other fields.

The reason why nanoparticle magnetic material has a broad application prospect is because it has many unique effects that are different from conventional materials, such as quantum size effect, surface effect, small size effect and macroscopic quantum tunneling effect, etc. These effects make nanoparticle magnetic material Has different optical, electrical, acoustic, thermal, magnetic, and sensitive properties than conventional materials.
When the particle size of the nanoparticle magnetic material is smaller than its superparamagnetic critical size, the particles enter a superparamagnetic state without coercivity and remanence. It is known that for bulk magnetic materials (such as Fe, Co, and Ni), multi-domain structures are often formed in the body to reduce the demagnetization energy of the system. Nanoparticles have a high coercivity when they have a single domain critical size [3]. The small size effect and surface effect result in a lower Curie temperature of the nanoparticle magnetic material. In addition, the saturation magnetization (Ms) of the nanoparticle magnetic material is lower than that of a conventional material, and its specific saturation magnetization decreases with decreasing particle size. When the particle size is reduced to nanometers, the magnetic material may even undergo a magnetic phase transition.
Nanoparticle magnetic material synthesis method
The preparation of nanoparticle magnetic materials is the basis of its application. At present, many kinds of synthesis and preparation methods have been developed, and they can be generally divided into chemical methods and physical methods. Tables 1 to 3 summarize the preparation processes, characteristics, and applications of these methods.
Application of Nanoparticle Magnetic Materials
1. Applications in magnetic recording materials. At present, the magnetic recording medium is still mainly composed of magnetic oxide fine-particle magnetic media. In order to increase the magnetic recording density, the general trend of the magnetic recording media is to develop toward high coercivity. In a granular magnetic storage medium, the size of the recording unit becomes smaller and smaller, and the size of the magnetic particles has transitioned to the nanoscale direction. Since the magnetic material of the nanoparticle has a single magnetic domain structure and high coercivity, It can increase the signal-to-noise ratio, improve the image quality, and create conditions for high-density magnetic storage.
Strontium ferrite particles containing Co and Ti have attracted great interest as high-density magnetic recording media. Cobalt-precipitated, hydrothermally synthesized nano-sized Co-exchanged Fe2O3, Co-Ti substituted BaFe12O19 oxide particle magnetic powders, metal nanoparticle magnetic powders, continuous film media made by vacuum evaporation, sputtering, etc. Successively put on the market, promoted the rapid development of high-density magnetic recording.
2, in the application of magnetic liquids. The use of nanoparticle magnetic superparamagnetic magnetic material developed into a magnetic fluid (also known as ferrofluid), which is the nanoparticle magnetic material coated by a surfactant, so that it is evenly and stably dispersed in a certain base (load) Stabilized colloidal material formed in the liquid. This material has the fluidity of the liquid and the magnetism of the magnet. Its basic parameter is the saturation magnetization, which is mainly determined by the magnetic particles that make up the colloid. The initial magnetic particles are metal (Fe, Co, Ni) or alloy particles prepared by vacuum chemical vapor deposition (CVD) or ball milling and have an average particle size of 5 to 7 nm, and the magnetic liquid made of 120 to 150 mT. Later, it also made a low-cost oxide (Fe3O4, etc.) particle magnetic liquid, its ≈40mT. Magnetic fluids are used in hard disk drive (HDD) sealing, space suits, bearings, lubrication, up and down, damping, speaker damping, magnetic dyes, magnetic fuels, shift register displays, magnetic fluid drugs, photocopying, and industrial waste processing. Have applications;
3. Applications in medicine and biology. The use of nanoparticle magnetic materials for the manufacture of targeted delivery medical drugs is a hot topic in pharmaceutical research. After the nanoparticle magnetic material is coated with a macromolecule material and then combined with a protein on the outside, the nanoparticle magnetic material containing the macromolecule and the protein is used as a drug carrier, injected into a living body, and subjected to the action of an external magnetic field. The magnetic orientation of nanoparticles makes it easier for drugs to move to the lesion, enhance their targeting to the diseased tissue, help to improve the efficacy, achieve the purpose of targeted therapy, and thus change the normal cells and cancer cells in current radiotherapy and chemotherapy. All were killed. Animal clinical experiments confirmed that Fe3O4 nanoparticles magnetic material is the most promising carrier for this technology, and it can be naturally excreted by the human liver and spleen after treatment is completed;
4, in the application of the sensor. Because of its huge surface and interface, nano-particles are very sensitive to external environment such as temperature, light, humidity, etc. Changes in the external environment will quickly cause changes in surface or interface ion valence and electron transport, and are the most promising for sensors. s material. Such as the use of nano-Fe2O3 carrier temperature effects caused by resistance changes, can be made of temperature sensors. In addition, the gas-sensing materials made of nano-Fe2O3 have the characteristics of fast response, strong selectivity, high sensitivity and good stability. Under non-doping conditions, they have certain sensitivity to gases such as C2H5OH, H2, and CH4.
5, in the application of catalysis. Nanoparticles have many advantages such as large specific surface area, high surface reactivity, many surface active sites, high catalytic efficiency, and strong adsorption capacity, which provide the necessary conditions for nanoparticle as a catalyst, and it has important applications in chemical catalysis. For example, Fe2O3 nanoparticles have been used directly as a catalyst for the oxidation, reduction and synthesis reactions of high molecular polymers, which can greatly increase the reaction efficiency and control the reaction speed and temperature well. The nano-Fe2O3 is made into hollow spheres that float on the surface of wastewater containing organic matter, and sunlight can be used for organic degradation. The United States and Japan use this method to deal with the pollution caused by offshore oil spills. Guo Guangsheng et al. studied the effect of nano-iron oxide particles on the activity of ethylbenzene dehydrogenation catalyst and found that multi-component catalysts prepared with special processes using nano-iron oxide as the main raw material generally have lower strength and are easily crushed when calcined. If the main catalyst is a mixture of ordinary iron oxide and nano-iron oxide, it can not only increase the activity of the catalyst, but also increase the strength of the catalyst [40]. When -Fe2O3 reaches nanoscale, the combustion velocity of the solid propellant made from the combustion catalyst can be increased by 1 to 10 times compared with the ordinary propellant, which is very favorable for the manufacture of high-performance rockets and missiles;
6, used as a permanent magnet material. Siemens Ltd. of Germany used rare-earth nano permanent magnetic materials, such as Nd-Fe-B and Sm-Fe-N magnets, to develop mechanical alloying methods and subsequent solid-state reactions. Nanoparticles Magnetic materials are single-domain particles. The residual magnetic moment is proportional to the volume of the particles. Its magnetization mechanism is rotation magnetization. Even if it is not magnetized, it is a permanent magnet. Therefore, it can be used as a permanent magnetic material. For example, bulk soft iron generally exhibits soft magnetic properties, but for 16 nm iron powder, its coercive force is very high, so it can be used as a permanent magnetic material. For example, it can be used as a magnetic recording material to improve recording density and signal to noise ratio.
7, in the field of pigment applications. Iron oxide pigments are important inorganic raw materials for the coating industry. The nano iron oxide particles with a particle size of less than 100 nm have the same chemical composition and even crystal structure as the bulk material, but they have many unique properties. Nano iron oxide is used as a pigment to keep both The general inorganic pigment has good heat resistance and ultraviolet absorption effect, and can be well dispersed in the oil carrier. The coating or ink prepared with it has satisfactory transparency;
8. Applications in radar wave absorbing materials. The radar wave absorbing material (RAM) can effectively reduce the target's RCS (radar cross section), improve the penetration ability and survivability of various operational weapons platforms, and can effectively suppress electromagnetic radiation, leakage, improve the electromagnetic environment, and improve the overall Machine security, confidentiality. Due to the special magnetic, infrared stealth and shielding effects of nanoparticle magnetic materials, they are widely used in RAM. Currently, the materials studied mainly include absorbents, and M, Z, Y, and W sheet-like hexagonal ferrite absorbents. The latter is mainly focused on absorbents;
9, in other areas of application. Magnetic sensors fabricated using the giant magneto-impedance effect of nanoparticle magnetic materials have been developed. Soft ferrite nanomaterials have been widely used in radio communications, radio and television, automatic control, space navigation, radar navigation, measuring instruments, computers, printing, home appliances and other fields. O 3 -type composites and multilayered 2 - 3 composites formed of nanoparticles, polymers such as metals and ferrites, can absorb and attenuate electromagnetic and acoustic waves, reduce reflections and scattering, and provide electromagnetic stealth and acoustic stealth. It has an important role to play. Coatings made of nano-Fe2O3 with semiconducting properties can be electrostatically shielded due to their strong electrical conductivity.

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