What is the concept of nanomaterials?

Nano-structured materials, referred to as nano-materials, are broadly defined as ultra-fine particle materials with at least one dimension in the three-dimensional space within the nanometer scale. According to the definitions adopted by the European Commission on 20 1 10, 18, nanomaterial is a kind of powdery and massive natural or man-made material composed of elementary particles, and its one or more dimensions range from 1 nm to 100 nm.

In terms of size, the size of fine particles that usually cause significant changes in physical and chemical properties is below 0. 1 micron (note 1 m = 100 cm, 1 cm = 1000 micron, 1 micron =/kloc) Therefore, particles with a particle size of 1 ~ 100 nm are called ultrafine materials and also nano-materials.

Nano-metallic materials were successfully developed in the mid-1980s, and then nano-semiconductor films, nano-ceramics, nano-ceramic materials and nano-biomedical materials were developed.

Nanostructured materials are referred to as nanomaterials for short, which means that the size range of their structural units is between 1 nm and 100 nm. Because its size is close to the coherence length of electrons, its properties have changed greatly because of the self-organization brought by strong coherence. Moreover, its scale is close to the wavelength of light, and it has the special effect of large surface, so its characteristics, such as melting point, magnetism, optics, heat conduction and electricity conduction, are often different from those of matter in the whole state.

Nanoparticle materials, also known as ultrafine particle materials, are composed of nanoparticles. Nanoparticles, also known as ultrafine particles, generally refer to particles with the size of 1 ~ 100 nm, which are in the transition region between atomic clusters and macroscopic objects. Generally speaking, such a system is neither a typical micro system nor a typical macro system, but a typical mesoscopic system with surface effect, small size effect and macro quantum tunneling effect. When people subdivide a macroscopic object into ultrafine particles (nano-scale), it will show many strange characteristics, that is, its optical, thermal, electrical, magnetic, mechanical and chemical properties will be significantly different from those of bulk solids.

The broad scope of nanotechnology can include nano-material technology and nano-processing technology, nano-measurement technology, nano-application technology and so on. Among them, nano-material technology focuses on the production of nano-functional materials (ultrafine powder, coating, nano-modified materials, etc.). ) and performance testing technology (chemical composition, microstructure, surface morphology, physical, chemical, electrical, magnetic, thermal and optical properties). Nano-machining technology includes precision machining technology (energy beam machining, etc. ) and scanning probe technology.

Nano-materials have certain uniqueness. When the size of matter is small enough, it is necessary to use quantum mechanics instead of traditional mechanics to describe its behavior. When the particle size of powder is reduced from 10 micron to 10 nanometer, although its particle size becomes 1000 times, it will be as large as 10 times when converted into volume, so there will be obvious differences between the two behaviors.

Nanoparticles are different from bulk materials because of their large surface area, that is, the surface of ultrafine particles is covered with a stepped structure, which represents unstable atoms with high surface energy. These atoms are easy to adsorb and bond with foreign atoms, and at the same time, due to the reduction of particle size, they provide larger surface active atoms.

As far as the melting point is concerned, nano-powder has a high surface energy because there are fewer atoms in each particle and the surface atoms are in an unstable state, which leads to a large vibration amplitude of its surface lattice, thus producing a unique thermal property of ultrafine particles, that is, the melting point is reduced. At the same time, nano-powder will be easier to sinter at lower temperature than traditional powder and become a good sintering promoting material.

Generally, common magnetic materials belong to a collection of multiple magnetic regions. When the particle size is too small to distinguish their magnetic regions, a magnetic material with a single magnetic region is formed. Therefore, when magnetic materials are made into ultrafine particles or films, they will become excellent magnetic materials.

The particle size of nanoparticles (10 nm ~ 100 nm) is smaller than the wavelength of light wave, so it will have complex interaction with incident light. Under proper evaporation and deposition conditions, ultrafine particles of black metal which can easily absorb light, called metallic black, can be obtained, which is in sharp contrast with the glossy surface with high reflectivity formed by metallic coating in vacuum. Nanomaterials can be used as infrared sensor materials because of their high light absorption rate.