Nano powders, also known as nanoparticles, generally refer to ultrafine particles between 1 and 100nm in size. Some people call them ultrafine particles. It is larger than a cluster of atoms and smaller than ordinary particles. In terms of its size, assuming that each atom is one angstrom in size, it contains between 1000 and 1 billion atoms. It’s smaller than a normal living cell, about the size of a virus. Nanoparticles are spherical, plate-like, rod-shaped, angular, spongy and so on. The components of nanoparticles can be metals, oxides or other compounds.
The preparation method of nanometer powder is always the hot technology in powder industry. The common preparation methods of nano powders include chemical method and physical method. The following physical preparation methods of nano powders are introduced to you.
1. Laser concentrated atomic deposition method
Use a laser to control the movement of atomic beam in the nanoscale, the atomic deposition in order to realize the parallel structure of nanomaterials have the purpose of laser on the atomic beam by two ways, namely the instantaneous force and I together near the resonance condition, atomic beam laser standing wave effect in sedimentary process and gathered themselves together, and gradually deposited on silicon substrate, form specified shapes such as linear.
2. Evaporation and condensation method
Evaporation and condensation method refers to the evaporation methods of metal samples after evaporation under high vacuum conditions, including arc discharge, generation of high-energy electrical pulse or high frequency induction, etc., to produce high-temperature plasma and make the metal evaporate. When metal evaporation, metal particles are the surrounding gas molecules collide, condensing on the condenser pipe into about 10 nm nanoparticles, its size can be controlled by adjusting the evaporation temperature, gas pressure, most small to the particle size of 2 nm is prepared by evaporation condensation superfine particle has the following characteristics: (1) (2) with high purity narrow particle size distribution (3) good crystallization and easy clean surface (4) the granularity control, etc. Ag, Au, Cu and Pb particles with average particle size of 3nm can be prepared by this method.
3. Mechanical ball grinding
Mechanical ball grinding takes crushing and grinding as the main body to realize the nano-ization of powder. Nanocrystalline metal nanocrystalline with BCC structure (such as Cr, Nb, W, etc.) and HCP structure (such as Zr, Hf, Ru, etc.) can be prepared by high-energy ball grinding of nanocrystalline metal elements and alloys. However, FCC structured metals (such as Cu) are not easy to form nanocrystals.
4. Mechanical alloying
Mechanical alloying is a technique developed by American INCO company for preparing Ni – based oxide particle dispersion strengthening alloy. This method has simple process and high preparation efficiency, and can prepare high-melting metal alloy nanomaterials that are difficult to obtain by conventional methods. In recent years, physical grinding method and ultrasonic grinding method of grinding aid have been developed, which can produce particles with particle size less than 100nm.
5. Amorphous crystallization method
For example, the Ni80P20 amorphous alloy strip is treated with isothermal heat treatment at different temperatures to produce nanoscale alloy grains. The growth of nanoscale alloy grains is related to the grain boundary type. This method plays an active role in the research of nanometer permanent magnet.
6. Ion implantation
With isotope separator has a certain energy ion stiff embedded in a solid state with it miscibility of the substrate, and then heat annealing, let it segregation out its formation of the nanometer crystallite in the substrate depth distribution and particle size can be by changing the ion energy and dose, and annealing temperature to control under the certain condition of injection, after a certain content of hydrogen protection heat treatment received in Cu, Ag, Al, a – Fe of SiO2 nano crystalline Fe and C double injection, The formation of Fe3O4 and fe-n nanocrystalline nanocrystalline prepared by Fe and C double injection is related to thermal diffusion coefficient and diffusion length.
7. Method of atom
What wonder did science ever wonder if it could one day arrange atoms and molecules according to man’s will? The scanning tunneling microscope (STM) has revealed a “visible” world of atoms and molecules with unprecedented resolution. STM has been developed into a tool that can arrange atoms. Since 1990, when STM was first used to conduct atomic and molecular operations, it has become a reality to manufacture nanoscale ultrafine powders by atomic method.
To sum up, in the current physical preparation methods of nanomaterials, physical crushing and mechanical alloying have simple processes and high yield, but impurities are easily introduced in the preparation process. Evaporation and condensation method is widely used, and the preparation device is easy to be realized. However, the development of this method has been restricted by the large number of technological parameters that affect the particle size of powder and the low yield of powder. However, the prospect of physical preparation of nanometer powders is broad and worth further research and exploration.
05
Jul
