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What is nanomaterial?

Edit: Ccdanni 2020-01-23 Mobile

  What are nanomaterials?

  Nanomaterials have gradually penetrated into our lives. The general public has not yet had a deeper understanding and understanding of nanomaterials. However, the application of nanomaterials is not surprising, such as nano-coatings, nano-care products, and nano-water repellents. and many more.

  What is nanomaterial

  So what is a nanomaterial? Nano-structured materials are simply referred to as nanomaterials. Since nanomaterials are materials that have been concerned and applied in recent years, they are also understood as new materials of nanostructures. In a broad sense, at least one dimension in the three-dimensional space is in the nanoscale range. Generic term for fine particle materials.

  According to the definition adopted by the European Commission on October 18, 2011, a nanomaterial is a powdery or agglomerated natural or artificial material composed of basic particles with one or more three-dimensional dimensions ranging from 1 nanometer to 100 Between nanometers, and the total number of this elementary particle accounts for more than 50% of the total number of all particles in the entire material.

  Nanomaterials have certain uniqueness. When the scale of matter is small to a certain extent, it is necessary to use quantum mechanics instead of traditional mechanics to describe its behavior. When the size of powder particles decreases from 10 microns to 10 nanometers, their particle size Although it is changed to 1000 times, when converted to volume, it will be as large as 9 times to 10 times, so there will be a significant difference in behavior between the two.

  Structure of nanomaterials

  A nanostructure is a new system built on the basis of nanometer-scale material units and constructed or constructed according to certain rules.

  Nanoarray system

  Existing research results The research on the nano-array system is focused on the binary system formed by the metal nano-particles or semiconductor nano-particles arranged neatly on an insulating substrate.

  2D nanomaterial array

  Mesoporous assembly system

  The nanoparticle and mesoporous solid assembly system has become a research hotspot due to the characteristics of the microparticles and the coupling with the matrix of the interface, which can be divided into inorganic mesopores according to the type of support. Complexes and polymer mesoporous complexes can be divided into ordered mesoporous complexes and disordered mesoporous complexes according to the state of the support.

  Mesoporous assembly of nanomaterials

  Thin film mosaic system

  In the thin film inlay system, the main research on the nanoparticle film is based on the electrical and magnetic properties of the system. American scientists use self-assembly technology to form hundreds of single-walled carbon nanotubes into a crystal rope "Ropes". This rope has metallic properties and has a resistivity of less than 0.0001 Ω / m at room temperature; nano-lead triiodide is assembled into nylon-11 In the past, it has photoconductivity under X-ray irradiation. Using this property has laid a foundation for the development of digital radiography.


  Properties and Applications of Nanomaterials

  Surface and interface effects

  Refers to the change in properties caused by the ratio of the surface atomic number of the nanocrystalline particles to the total atomic number increasing sharply as the particle size becomes smaller. It shows that the diameter decreases and the number of surface atoms increases.

  The smaller the diameter of the surface of the nanomaterial, the greater the number

  The surface of ultrafine particles has high activity, and the metal particles in the air will rapidly oxidize and burn. If you want to prevent spontaneous combustion, you can use surface coating or consciously control the oxidation rate to make it slowly oxidize to form a very thin and dense oxide layer to ensure surface stability. Utilizing surface activity, metal ultrafine particles are expected to become a new generation of efficient catalysts, gas storage materials and low melting point materials.

  Small size effect

  When the size of a nanoparticle is equal to or smaller than the physical characteristic size of the wavelength of the light wave, the De Broglie wavelength of the conducting electron, the coherence length of the superconducting state, and the depth of transmission, its periodic boundary is destroyed, so that its Electrical, magnetic, thermodynamic and other properties show a "novelty" phenomenon. As the amount of particle size changes, a qualitative change in the nature of the particles is caused under certain conditions. Changes in macroscopic physical properties due to smaller particle sizes are called small size effects. For ultrafine particles, the size becomes smaller and the specific surface area increases significantly, resulting in the following properties:

  1.Special optical properties

  All metals appear black in the state of ultrafine particles. The smaller the size, the darker the color, silver-white platinum (platinum) becomes platinum black, and metallic chromium becomes chrome black.

  Metal ultrafine particles are black

  Metal appears black in ultrafine particles

  It can be seen that the reflectivity of metal ultrafine particles to light is very low, usually less than 1%, and the thickness of about a few micrometers can completely extinction. By using this feature, high-efficiency photothermal, photoelectric conversion materials can be manufactured, and solar energy can be converted into thermal energy and electric energy with high efficiency. In addition, it may be applied to infrared sensitive components and infrared stealth technology.

  2.Special thermal properties

  When a solid substance has a large size, its melting point is fixed. After ultra-micronization, it is found that its melting point will be significantly reduced, especially when the particles are smaller than 10 nanometers. The melting point of ultrafine particles has a certain attraction for the powder metallurgy industry.

  3.Special magnetic properties

  In the process of studying nanomaterials, scientists found that ultra-fine magnetic particles exist in organisms such as pigeons, dolphins, butterflies, bees, and magnetotactic bacteria living in water, allowing such organisms to distinguish directions under the guidance of the geomagnetic field and have a returning ability.

  Magnetic nanomaterials

  Small-sized magnetic ultrafine particles are significantly different from bulk materials. Large pieces of pure iron have a coercive force of about 80 amps / meter, and when the particle size is reduced below 2 × 10-2 microns, its coercive force can increase by a factor of 1,000. If its size is further reduced, when it is less than about 6 × 10-3 microns, its coercive force will instead be reduced to zero, showing superparamagnetism.

  Utilizing the characteristics of magnetic ultrafine particles with high coercive force, magnetic recording magnetic powder with high storage density has been made, which is widely used in magnetic tapes, magnetic disks, magnetic cards, and magnetic keys. Utilizing superparamagnetism, people have made magnetic ultrafine particles into magnetic liquids with a wide range of uses.

  4.Special mechanical properties

  American scholars have reported that calcium fluoride nanomaterials can be largely bent without breaking at room temperature. Research shows that the reason why human teeth have high strength is that they are made of nanomaterials such as calcium phosphate. Nano-grained metals are 3 to 5 times harder than traditional coarse-grained metals. Metal-ceramic composite nanomaterials can change the mechanical properties of materials in a wider range, and their application prospects are very broad.

  The small size effect of ultrafine particles is also manifested in superconductivity, dielectric properties, acoustic properties, and chemical properties.

  Carbon nanotubes are 300 times stronger than steel

  Carbon nanotubes are a new type of super material, which can reach 300 times the strength of steel

  Quantum size effect

  When the size of the particle reaches the nanometer level, the electron energy level near the Fermi level is split into a continuous energy level by a continuous state. When the energy level distance is greater than thermal, magnetic, electrostatic, magnetostatic, photon, or cohesive energy of superconducting states, quantum effects of nanomaterials will occur, which will cause their magnetic, optical, acoustic, thermal, electrical, and superconductive properties Variety.

  Fermi level structure

  Energy level structure

  Quantum size effect: When the size of the particle drops to a certain value, the phenomenon that the electronic energy level near the metal Fermi level changes from quasi-continuous to discrete levels and the highest occupied molecular orbital and the lowest Widening of the energy gap between occupied molecular orbital energy levels.

  In nanopowder, because each particle has few constituent atoms and the surface atoms are in a unstable state, the amplitude of the surface lattice vibration is large, so it has a high surface energy, which causes the unique thermal properties of ultrafine particles, that is, the melting point is reduced. At the same time, nano-powder will be easier to sinter at a lower temperature than traditional powder, and become a good sintering promotion material.

  Macro quantum tunnel effect

  The ability of microscopic particles to penetrate a barrier is called the tunneling effect. Nanoparticles also have tunneling effects such as magnetization. They can pass through the barriers of the macroscopic system to produce changes. This type of macroscopic quantum tunneling is called nanoparticles.

  Macro quantum tunnel effect

  The macroscopic quantum tunneling effect is one of the basic quantum phenomena, that is, when the total energy of a microscopic particle is less than the barrier height, the particle can still pass through the barrier. In recent years, it has been found that some macroscopic quantities, such as the magnetization of microparticles and magnetic flux in quantum coherent devices, also have tunneling effects, called macroscopic quantum tunneling effects.

  The above-mentioned small size effect, surface effect, quantum size effect, macro quantum tunnel effect, and dielectric limit should be the basic characteristics of nano particles and nano solids. This series of effects has led to the melting point, vapor pressure, and optical properties of nano materials. Many physical and chemical aspects, such as chemical reactivity, magnetic properties, superconductivity, and plastic deformation, have shown special properties. It makes nano particles and nano solids show many strange physical and chemical properties.

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