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 produced.
Nanostructured materials are referred to as nanomaterials for short, which means that the size 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, it
The properties of optics, heat, electricity, magnetism, mechanics and chemistry will be obviously 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.
Nanotechnology is still in its infancy all over the world. Although a few countries such as the United States, Japan and Germany have begun to take shape, they are still studying, and the emergence of new theories and technologies is still in the ascendant. China strives to catch up with advanced countries, and its research team is growing.
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Discovery and Development of Nanomaterials
186 1 year, with the establishment of colloid chemistry, scientists began to study the particle system with the diameter of 1~ 100nm.
The truly conscious study of nanoparticles can be traced back to the "smoke deposition experiment" conducted by Japan for military needs in the 1930s. However, due to the limitation of the test level and conditions at that time, although the first batch of ultrafine lead powder in the world was prepared by vacuum evaporation, its light absorption performance was very unstable.
In 1960s, people began to study discrete nanoparticles. In 1963, Uyeda prepared metal nanoparticles by gas evaporation and condensation, and studied them by electron microscope and electron diffraction. Gleiter of Saarland University in Germany and Siegal of Argonne Laboratory in the United States successfully prepared pure nano-powders ranging from 65438 to 0984. Gleiter pressed iron particles with a diameter of 6nm in situ under high vacuum and sintered them to obtain nanocrystalline blocks, which made the research of nanomaterials enter a new stage.
1990 the first international nanotechnology conference was held in the United States in July. Technology), officially announced that nano-materials science is a new branch of materials science.
Since the advent of nano-particle materials in 1970s, its research connotation and characteristics can be roughly divided into three stages:
The first stage (before 1990): mainly explore the preparation of nano-particle powders or synthetic blocks of various materials in the laboratory, study the methods of evaluation and characterization, and explore the special properties of nano-materials different from ordinary materials; The research object is generally limited to single material and single-phase material, which is usually called nanocrystalline or nano-phase material internationally.
The second stage (1990~ 1994): People pay great attention to how to use the physical and chemical properties of nano-materials to design nano-composites, and the synthesis and physical properties exploration of composite materials once became the dominant direction of nano-materials research.
The third stage (1994 up to now): the nano-assembly system and nano-structured material system synthesized by artificial assembly are becoming the new focus of nano-materials research. Internationally, this kind of material is called nano-assembly material system or nano-pattern material. Its basic connotation is that nanoparticles and their nanowires and tubes are assembled and arranged in one-dimensional, two-dimensional and three-dimensional space to form a system with nanostructures.
Nanostructure
Nanostructure is a new system based on nano-scale material units and constructed according to certain rules. It includes nano-array system, mesoporous assembly system and thin film mosaic system. At present, the research on nano-array system mainly focuses on the binary system formed by the orderly arrangement of metal nanoparticles or semiconductor nanoparticles on insulating substrates. However, due to the characteristics of nanoparticles and some new effects caused by coupling with interface matrix, the assembly system of nanoparticles and mesoporous solids has become a research hotspot. According to the types of carriers, it can be divided into inorganic mesoporous composites and polymer mesoporous composites, and according to the state of carriers, it can be divided into ordered mesoporous composites and disordered mesoporous composites. In the film mosaic system, the study of nano-particle films is mainly based on the electromagnetic characteristics of the system. American scientists use self-assembly technology to form hundreds of single-walled carbon nanotubes into crystal cable "rope", which has metallic characteristics and room temperature resistivity is less than 0.0001ω/m; Nano-lead triiodide is assembled on nylon-1 1 and has photoconductivity under X-ray irradiation, which lays the foundation for the development of digital radiography.
Technical indicators
Nanometer alumina looks like white powder.
γ phase of nanometer alumina crystal.
The average particle size (nm) of nano-alumina is 20 5.
The content of nano-alumina is more than 99.9%.
Melting point: 20 10℃-2050℃
Boiling point: 2980℃
Relative density (water = 1): 3.97-4.0.
applied range
1, natural nanomaterials
Turtles lay eggs on beaches in Florida, USA, but after being born, young turtles have to swim to the waters near Britain in order to survive and grow. Finally, adult turtles will return to Florida to lay eggs. It takes about 5-6 years to go back and forth like this. Why can a turtle travel tens of thousands of kilometers? They rely on nano-magnetic materials in their minds to navigate accurately.
When biologists study why pigeons, dolphins, butterflies, bees and other creatures never get lost, they also find that there are nano-materials in these creatures to navigate for them.
2. Nanomagnetic materials
Most of the nano-materials used in practice are manufactured artificially. Nanomagnetic materials have very special magnetism, such as small size of nanoparticles, single domain structure and high coercivity. Magnetic recording materials made of nano-magnetic materials not only have good sound quality, image and signal-to-noise ratio, but also have a recording density several times higher than that of γ-Fe2O3. Superparamagnetic strong magnetic nanoparticles can also be made into magnetic liquids, which are used in electro-acoustic devices, damping devices, rotary sealing, lubrication and mineral processing.
3. Nanometer ceramic materials
In traditional ceramic materials, the grains are not easy to slide, the materials are fragile and the sintering temperature is high. The grain size of nano-ceramics is small, and the grains are easy to move on other grains. Therefore, nano-ceramic materials have extremely high strength, high toughness and good ductility, so that nano-ceramic materials can be cold-worked at room temperature or sub-high temperature. If nano-ceramic particles are processed and shaped at sub-high temperature, and then the surface is annealed, nano-materials can become a high-performance ceramic with the hardness and chemical stability of conventional ceramic materials on the surface and the ductility of nano-materials on the inside.
4. Nanosensors
Nano-zirconia, nickel oxide, titanium dioxide and other ceramics are very sensitive to temperature changes, infrared rays and automobile exhaust. Therefore, they can be used to make temperature sensors, infrared detectors and automobile exhaust detectors, and their detection sensitivity is much higher than that of ordinary similar ceramic sensors.
5. Nano-tilt functional materials
In the space hydrogen-oxygen engine, the inner surface of the combustion chamber needs to be resistant to high temperature, and its outer surface needs to be in contact with the coolant. Therefore, the inner surface should be made of ceramics and the outer surface should be made of metal with good thermal conductivity. But it is difficult to combine bulk ceramics with metals. If the composition of metals and ceramics is gradually changed in the production process, so that metals and ceramics can be combined into an inclined functional material, that is to say, the change of composition is like an inclined ladder. When metal and ceramic nanoparticles are mixed and sintered according to the requirements of gradual content change, the requirements of high temperature resistance inside the combustion chamber and good thermal conductivity outside can be achieved.
6. Nanometer semiconductor materials
Nanomaterials made of semiconductor materials such as silicon and gallium arsenide have many excellent properties. For example, the quantum tunneling effect in nano-semiconductors makes the electron transport of some semiconductor materials abnormal, and the conductivity decreases with the decrease of particle size, or even appears negative. These characteristics play an important role in large-scale integrated circuit devices, optoelectronic devices and other fields.
A new type of solar cell with high photoelectric conversion efficiency can be prepared by using semiconductor nanoparticles, which can work normally even in rainy days. Because the electrons and holes generated by nano-semiconductor particles when irradiated by light have strong reduction and oxidation ability, they can oxidize toxic inorganic substances, degrade most organic substances, and finally generate non-toxic and odorless carbon dioxide, water and so on. Therefore, inorganic matter and organic matter can be decomposed by solar energy with the help of semiconductor nanoparticles.
7, nano catalytic materials
Nano-particles are an excellent catalyst, because of their small size, large surface volume fraction, different surface chemical bond states and electronic states, and incomplete coordination of surface atoms, which leads to the increase of surface active sites, making them have the basic conditions as catalysts.
Nanoparticles of nickel or copper-zinc compounds are excellent catalysts for hydrogenation of some organic compounds, which can replace expensive platinum or palladium catalysts. Nano-platinum black catalyst can reduce the temperature of ethylene oxidation reaction from 600℃ to room temperature.
8. Medical applications
The size of red blood cells in blood is 6 000~9 000 nm, while the size of nanoparticles is only a few nanometers, which is actually much smaller than red blood cells, so they can move freely in blood. If all kinds of nanoparticles with therapeutic effects are injected into various parts of the human body, the lesions can be examined and treated, and the effect is better than that of traditional injections and drugs.
Using nanotechnology can make the drug production process more and more elaborate, and directly use the arrangement of atoms and molecules to manufacture drugs with specific functions on the scale of nano-materials. Nano-material particles will make the transmission of drugs in human body more convenient. Smart drugs wrapped in several layers of nanoparticles can actively search and attack cancer cells or repair damaged tissues after entering the human body. New diagnostic instruments using nanotechnology can diagnose various diseases by using protein and DNA in a small amount of blood.
9. Nanocomputers
The world's first electronic computer was born in 1945. It was successfully developed by American universities and the War Department. A * * used 18 000 electron tubes, with a total weight of 30 t and an area of about 170 m, which can be regarded as a giant. However, that was in 65438.
Half a century later, due to the development of integrated circuit technology, microelectronics technology, information storage technology, computer language and programming technology, computer technology has developed rapidly. Today's computers are small and exquisite, and can be placed on the computer desk. Its weight is only one tenth of that of our ancestors, but its operation speed is far faster than that of the first generation of electronic computers.
If nanotechnology is used to build electronic computer equipment, then this future computer will be a kind of "molecular computer", and its pocket size is far from today's computer, which will also bring considerable benefits to society in saving materials and energy.
Card readers that can read from hard disks and nano-material memory chips with storage capacity thousands of times that of current chips have been put into production. After the widespread use of nano-materials, computers can be simplified as "handheld computers".
10, carbon nanotubes
In 199 1, experts from the Nippon Electric Company prepared a material called "carbon nanotubes", which is a tube composed of many hexagonal ring carbon atoms, or it can be composed of several coaxial tubes nested together. As shown in the figure, both ends of such single-layer and multi-layer pipes are usually sealed.
This tube made of carbon atoms is called carbon nanotubes because its diameter and length are in the order of nanometers. Its tensile strength is 100 times higher than that of steel and its electrical conductivity is higher than that of copper.
Carbon nanotubes are heated to about 700℃ in the air, so that the carbon atoms at the top seal of the tube are destroyed by oxidation and become open carbon nanotubes. Then the low melting point metal (such as lead) is evaporated by the electron beam and condensed on the open carbon nanotubes, and the metal enters the hollow core of the carbon nanotubes due to siphon effect. Because the diameter of carbon nanotubes is extremely small, the metal wires formed in the tubes are also very thin, which are called nanowires, and their size effect is superconducting. Therefore, carbon nanotubes and nanowires may become new superconductors.
Nanotechnology is still in its infancy all over the world. Although a few countries such as the United States, Japan and Germany have begun to take shape, they are still studying, and the emergence of new theories and technologies is still in the ascendant. China strives to catch up with advanced countries, and its research team is growing.
1 1, household appliances
Nano-material multifunctional plastic is made of nano-material, which has antibacterial, deodorizing, anti-corrosion, anti-aging and anti-ultraviolet effects, and can be used as antibacterial and deodorizing plastic in refrigerator and air conditioner shell.
12, environmental protection
Nanofilms with unique functions will appear in the field of environmental science. This membrane can detect pollution caused by chemical and biological agents, and can filter these agents to eliminate pollution.
13, textile industry
Nano-silica, nano-zinc oxide and nano-silica composite powder materials are added into synthetic fiber resin, and after spinning and weaving, underwear and clothing with sterilization, mildew resistance, deodorization and ultraviolet radiation resistance can be made, which can be used to make antibacterial underwear and articles, and can also be made into functional fiber with ultraviolet radiation resistance to meet the requirements of national defense industry.
14, machinery industry
Using nano-material technology, coating nano-powder on the metal surface of key mechanical parts can improve the wear resistance, hardness and service life of mechanical equipment.
Classification of nano-materials
Nano-materials can be roughly divided into four categories: nano-powder, nano-fiber, nano-film and nano-block. Among them, nano-powder has the longest development time and the most mature technology, which is the basis for the production of other three types of products.
Nanometer powder
Also known as ultrafine powder or ultrafine powder, it generally refers to powder or particles with a particle size below 100 nm, which is a solid particulate matter in an intermediate state between atoms, molecules and macroscopic objects. Can be used for: high-density magnetic recording materials; Absorb stealth materials; Magnetic fluid material; Radiation protection materials; Monocrystalline silicon and polishing materials for precision optical devices: microchip heat-conducting substrate and wiring materials; Microelectronic packaging materials; Photoelectric materials; Advanced battery electrode materials: solar battery materials; Efficient catalyst; Efficient combustion improver; Sensitive element; High toughness ceramic materials (ceramics that are not easy to break, used in ceramic engines, etc. ); Human body repair materials; Anticancer preparations, etc.
Nano fiber
Refers to the linear material with nanometer diameter and large length. Can be used for: microfilament, microfiber (an important part of quantum computer and photonic computer in the future) materials; New laser or LED materials, etc. Electrospinning is a simple method to prepare inorganic nanofibers at present.
Nanometer thin film
Nano-membranes are divided into granular membranes and dense membranes. Particle film is a thin film with nano-particles stuck together, with a very fine gap in the middle. Dense film refers to the thin film with dense film layer but nanometer grain size. Can be used for: gas catalysis (such as automobile exhaust treatment) materials; Filter material; High density magnetic recording materials; Photosensitive material; Flat panel display materials; Superconducting materials, etc.
Nanoblock
Nano-block is a nano-particle material obtained by high-pressure molding of nano-powder or controlling crystallization of metal liquid. The main uses are: ultra-high strength materials; Intelligent metal materials, etc.
Preparation method:
(1) Evaporation and condensation in inert gas. Usually, it is made of particles with clean surface and particle size of 1- 100nm by high pressure molding, and nano-ceramics need to be sintered. A variety of nano-solid materials, including metals and alloys, ceramics, ionic crystals, amorphous and semiconductors, have been successfully developed abroad by using the above inert gas evaporation and vacuum in-situ pressurization methods. China has also successfully used this method to manufacture nano-materials such as metals, semiconductors and ceramics.
(2) Chemical method: 1 hydrothermal method, including hydrothermal precipitation, synthesis, decomposition and crystallization, is suitable for preparing nano-oxides; Hydrolysis methods include sol-gel method, solvent volatile decomposition method, latex method and evaporation separation method.
(3) Comprehensive method. A preparation method combining physical vapor phase method and chemical deposition method. Other methods usually include ball milling and spray machining.
Nanotechnology content
Nanotechnology includes the following four main aspects:
1. Nanomaterials: When a substance reaches the nanometer scale, which is about 0. 1- 100 nanometer, the properties of the substance will suddenly change and special properties will appear. This kind of material with special properties different from the original atoms, molecules and macroscopic substances is called nano-material.
If only nano-scale materials have no special properties, they cannot be called nano-materials.
In the past, people only paid attention to atoms, molecules or cosmic space, and often ignored this intermediate field, which actually exists in nature in large quantities, but did not realize the performance of this scale range before. Japanese scientists were the first to truly recognize its characteristics and introduce the concept of nano. In 1970s, they prepared ultramicro ions by evaporation, and found that a kind of conductive copper-silver conductor lost its original properties after being made into nano-scale, neither conducting electricity nor conducting heat. The same is true of magnetic materials, such as iron-cobalt alloys. If the size is about 20-30 nanometers, the magnetic domain will become a single magnetic domain, and its magnetism will be 1000 times higher than the original. In the mid-1980s, people formally named this kind of materials as nanomaterials.
Why does the magnetic domain become a single magnetic domain, and its magnetism is 1000 times higher than the original one? This is because the arrangement of single atoms in a magnetic domain is not very regular, but there is a nucleus in the middle of a single atom surrounded by electrons, which is the reason for the formation of magnetism. However, after becoming a single magnetic domain, the single atoms are arranged regularly and show strong magnetism to the outside.
This characteristic is mainly used to manufacture micro-motors. If the technology is developed for a certain period of time and used to manufacture magnetic levitation, a faster, more stable and more energy-saving high-speed train can be manufactured.
2. Nano-dynamics: mainly micro-machines and micro-motors, or micro-electromechanical systems (MEMS), which are used as micro-sensors and actuators for transmission machinery, optical fiber communication systems, special electronic equipment, medical and diagnostic instruments, etc. It adopts a new technology similar to the design and manufacture of integrated appliances. The feature is that the parts are very small, the etching depth often needs tens to hundreds of microns, and the width error is very small. This process can also be used to manufacture three-phase motors, ultra-high-speed centrifuges or gyroscopes. In the research, micro-deformation and micro-friction at quasi-atomic scale should be detected accordingly. Although they have not really entered the nanometer scale at present, they have great potential scientific and economic value.
Theoretically, micro-motor and detection technology can reach nanometer level.
3. Nano-biology and nano-pharmacology: for example, fixing dna particles on mica surface with colloidal gold with nano-particle size, conducting experiments on the interaction between biomolecules with interdigital electrodes on the surface of silica, conducting double-layer planar biofilm of phospholipids and fatty acids, and fine structure of dna. With nanotechnology, you can also put parts or components into cells through self-assembly to form new materials. About half of the new drugs, even the fine powder of micron particles, are insoluble in water; However, if the particles are nanoscale (i.e. ultrafine particles), they can be dissolved in water.
When nano-organisms develop to a certain technology, nano-biological cells with recognition ability can be made of nano-materials, and the biomedical absorption of cancer cells can be injected into the human body for targeted killing of cancer cells. This is an old way of raising money.
4. Nano-electronics: including nano-electronic devices based on quantum effect, optical/electrical properties of nanostructures, characterization of nano-electronic materials, atomic manipulation and assembly. The current trend of electronic technology requires devices and systems to be smaller, faster, colder and smaller, which means faster response. Being colder means that a single device consumes less power. But smaller is not infinite. Nanotechnology is the last frontier of builders, and its influence will be enormous.