What Is Plasma Electrolytic Oxidation?

Plasma (plasma), also called plasma, is an ionized gas-like substance composed of positively and negatively ions generated by the deprivation of some electrons and atomic groups. The scale is larger than the length of Debye. Movement is mainly dominated by electromagnetic forces and exhibits significant collective behavior. It exists widely in the universe and is often regarded as the fourth state of matter except solid, liquid, and gas. Plasma is a very good electrical conductor, and it uses a cleverly designed magnetic field to capture, move, and accelerate the plasma. The development of plasma physics has provided new technologies and processes for the further development of materials, energy, information, environmental space, space physics, and geophysics.

Plasma (plasma) is also called plasma. It is an ionized gas-like substance composed of positive and negative ions generated by the deprivation of some electrons and atomic groups. The scale is larger than the length of Debye. Movement is mainly dominated by electromagnetic forces and exhibits significant collective behavior. It exists widely in the universe and is often regarded as the fourth state of matter except solid, liquid, and gas. Plasma is a very good electrical conductor, and it uses a cleverly designed magnetic field to capture, move, and accelerate the plasma. The development of plasma physics has provided new technologies and processes for the further development of materials, energy, information, environmental space, space physics, and geophysics.

Plasma is the fourth state of matter that is different from solids, liquids, and gases. Matter is composed of molecules, molecules are composed of atoms, and atoms are composed of a positively charged nucleus and negatively charged electrons surrounding it. When heated to a sufficiently high temperature or for other reasons, the outer electrons get rid of the bondage of the atomic nucleus and become free electrons, just like the students after class run to the playground and play at will. When electrons leave the nucleus, this process is called "ionization." At this time, the substance becomes a uniform "paste" composed of positively-charged atomic nuclei and negatively-charged electrons, so people jokingly call it an ion plasma. The total amount of positive and negative charges in these ion plasmas is equal. Therefore, it is approximately electrically neutral, so it is called plasma.

Chinese name: plasma
Foreign name: plasma

Category: physics
Also called: Plasma

Plasma composition

Seemingly "mysterious" plasma is actually a common substance in the universe. Plasma exists in the sun, stars, and lightning, and it accounts for 99% of the entire universe. In the 21st century, people have mastered and used the generation of electric and magnetic fields to control plasma. The most common plasmas are high-temperature ionized gases, such as arcs, neon lights, and luminous gases in fluorescent lamps, such as lightning and aurora. Electron gases in metals, carriers in semiconductors, and electrolyte solutions can also be considered plasmas. On earth, there are far fewer plasma substances than solid, liquid, and gaseous substances. In the universe, plasma is the main form of matter, accounting for more than 99% of the total amount of matter in the universe. Stars (including the sun), interstellar matter, and the ionosphere around the earth are all plasma. In order to study the generation and properties of the plasma to clarify the laws of movement of the plasma in the natural world and use it to serve humankind, with the promotion of astrophysics, space physics, especially nuclear fusion research, magnetohydrodynamics has been formed in the past three to four decades And plasma dynamics.

Plasma consists of a collection of ions, electrons, and non-ionized neutral particles, and it is in a neutral state as a whole. Plasma can be divided into two types: high temperature and low temperature plasma. The temperature of the plasma is expressed by the temperature of the electron and the temperature of the ion. The two are called high-temperature plasma if they are equal; Low temperature plasma is widely used in many

Plasma generator Production area. For example: plasma TV, waterproof coating on the surface of baby diapers, increase the barrier properties of beer bottles. More importantly, the use of etching in computer chips makes the Internet age a reality.

High temperature plasma occurs only when the temperature is high enough. Stars emit this plasma constantly, making up 99% of the universe. Low temperature plasmas are plasmas that occur at normal temperature (although the temperature of the electrons is high). Low temperature plasma can be used for surface treatments such as oxidation and denaturation or precipitation coating treatment on organic and inorganic substances.

Plasma is a form of matter with free electrons and charged ions as its main components. It is widely present in the universe and is often regarded as the fourth state of matter, called the plasma state, or "super gaseous state" Also called "plasma". Plasma has a very high electrical conductivity and has a strong coupling effect with electromagnetic fields. The plasma was discovered by Crooks in 1879, and in 1928 American scientists Irving Langmuir and Tonks first introduced the term "plasma" to physics.

It is used to describe the material form in the gas discharge tube [1]. Strictly speaking, the plasma is a gas cluster with high potential kinetic energy, and the total charge of the plasma is still neutral. The electrons in the outer layer are knocked out by the high kinetic energy of the electric or magnetic field. The nucleus becomes a free electron with high potential energy and high kinetic energy.

Plasma is the fourth state of matter, which is an ionized "gas". It exhibits a highly excited unstable state, which includes ions (with different signs and charges), electrons, atoms, and molecules. In fact, people are not new to the plasma phenomenon. In nature, the blazing flames, dazzling lightning, and the magnificent aurora are all the result of plasma. For the entire universe, almost 99.9% of matter exists in the plasma state. For example, stars and interplanetary space are composed of plasma. Plasma can be generated by artificial methods such as nuclear fusion, nuclear fission, glow discharge, and various discharges. The internal structure of a molecule or atom consists mainly of electrons and nuclei. Under normal circumstances, that is, in the first three forms of the above-mentioned matter, the relationship between electrons and nuclei is relatively fixed, that is, electrons exist around the nuclear field at different energy levels, and their potential energy or kinetic energy is not large.

When the temperature of ordinary gas increases, the thermal motion of gas particles intensifies, causing strong collisions between particles, and a large number of atoms or electrons in the molecules are knocked out. When the temperature reaches 1 million to 100 million k, all gas atoms are ionized. The total negative charge of the ionized free electrons is equal to the total positive charge of the positive ions. This highly ionized, macroscopically neutral gas is called a plasma.

Plasma and ordinary gas have different properties. Ordinary gas is composed of molecules, and the interaction force between molecules is short-range force. Only when the molecules collide, the interaction force between molecules has a significant effect. It is theoretically described by molecular kinematics. In plasma, the Coulomb force between charged particles is a long-range force. The effect of Coulomb force far exceeds the local short-range collision effect that may occur with charged particles. When charged particles in plasma move, they can cause positive or negative charges. The local concentration generates an electric field; the directional movement of the charge causes a current to generate a magnetic field. The electric and magnetic fields affect the movement of other charged particles, and are accompanied by extremely strong thermal radiation and heat conduction; the plasma can be constrained by the magnetic field to make a gyrating motion. These properties of the plasma distinguish it from the fourth state of ordinary gas called matter.

In the universe, plasma is the most important normal state of matter. New technologies such as space research, space development, and satellite, aerospace, and ^[1] energy will enter a new era with plasma research. ^[2]

History of plasma development

Research on gas discharge since the 19th century; research on astrophysics and space physics in the mid-19th century; research on controlled thermonuclear fusion around 1950; and research on the application of low-temperature plasma technology All aspects have promoted the development of this discipline.

In the 1830s, M. Faraday in Britain, followed by JJ Thomson, JSE Townsend, and others successively studied the phenomenon of gas discharge, which is actually the beginning of plasma experimental research. In 1879, W. Crooks of England adopted the term "fourth state of matter" to describe the ionized gas in a gas discharge tube. I. Langmuir of the United States first introduced the term plasma in 1928, and plasma physics was officially introduced. In 1929, L. Tonks and Langmuir of the United States pointed out the dense wave of electron density in plasma (ie Langmuir wave).

The exploration of space plasma also began in the early 20th century. In 1902, in order to explain the phenomenon that radio waves can be transmitted over long distances, O. Heaviside in Britain and other countries speculated that there is an ionosphere over the earth that can reflect electromagnetic waves. This hypothesis was confirmed experimentally by British EV Upton. Britain's DR Hartley (1931) and Upton (1932) proposed the refractive index formula of the ionosphere, and obtained the dispersion equation of the magnetized plasma. In 1941, British S. Chapman and VCA Ferraro believed that the sun would emit a stream of high-speed charged particles, which would surround the geomagnetic field and deform it by compression.

Since the 1930s, magnetohydrodynamics and plasma dynamics have gradually formed. The velocity distribution function of the plasma obeys the Falk-Planck equation. The Soviet Union's .. Landau gave the collision integral form of the collision term in the equation due to the collision of particles in the plasma in 1936. In 1938, the AA Vlasov of the Soviet Union proposed the Vlasov equation, that is, the collision-free equation with the collision term discarded. The introduction of Landau collision integrals and Vlasov equations marks the beginning of dynamics.

In 1942, H. Alvin of Sweden pointed out that when an ideal conductive fluid is in a magnetic field, a shear wave (alwin wave) propagating along the magnetic field lines will be generated. India's S. Chandrasekhar proposed a trial particle model to study the relaxation process in 1942. In 1946 Landau proved that when Langmuir waves propagate, the resonance electrons absorb the energy of the waves and cause the waves to decay, which is called Landau damping. This theory of Landau has opened up new research fields such as wave-particle interaction and micro-instability in plasma.

From 1935 to 1952, HH Bogoriubov of the Soviet Union, M. Born of the United Kingdom, and others, starting from Liu Wei's theorem, obtained an unclosed series of equations named BBGKY chain. Vlasov equation can be derived from it, which lays a theoretical foundation for plasma dynamics.

After 1950, Britain, the United States, and the Soviet Union began to vigorously study controlled thermonuclear reactions, which promoted the vigorous development of plasma physics. The concept of thermonuclear reactions first appeared in 1929, when Atkinson in the United Kingdom and Hautmanns in Austria proposed that the energy released by thermonuclear reactions between the cores of hydrogen in the sun was the source of solar energy, which is natural. Self-controlled thermonuclear reaction. In 1957, JD Lawson of the United Kingdom proposed the conditions of controlled thermonuclear reactions to achieve energy gain, that is, the Lawson criterion.

Since the 1950s, a number of experimental devices for controlled fusion have been completed, such as the US stellar and magnetic mirror and the Soviet Tokamak. These three are magnetically confined thermonuclear fusion experimental devices. After the 1960s, a number of experimental devices for inertial confinement fusion were established.

The equilibrium problem of toroidal magnetic confinement plasma was solved by Soviet VD Shafranov and others. M. Kruska and Shafranov of the United States have derived the most important criterion for plasma instability, that is, twisted instability. In 1958, the US IB Bernstein and others proposed the energy principle for analyzing macro instability. The transport coefficient of the plasma in a ring-shaped magnetic field was first studied by D. Pfirsch et al. (1962) of the Federal Republic of Germany. They gave the diffusion coefficient in the denser region. Fu et al. Gave the diffusion system dispersion in a less dense area (1967). This theory is applicable to the transport process in a toroidal magnetic confined plasma such as Tokamak and is named as the new classical theory.

Since the Soviet Union launched the first artificial satellite in 1957, many countries have successively launched scientific satellites and space laboratories, and obtained many observations and experimental data, which have greatly promoted the development of astronomical and space plasma physics. In 1959, JA Van Allen of the United States predicted the existence of a strong radiant band over the earth. This prediction was confirmed by future experiments, which is called the Van Allen zone. In 1958, EN Parker of the United States proposed the solar wind model. In 1974, the United States' DA Gnett certified that the earth is a radiating star based on satellite data, which is long-wave radiation and thermal infrared radiation ^[3] . The radiation source of the earth's radiation is the earth, and its wavelength range is about 4 to 120 microns, which is long-wave radiation ^[3] . 99% of the radiated energy is concentrated in the wavelength range above 3 microns ^[3] . The strongest wavelength of the earth's radiation is about 9.7 microns ^[3] .

During this period, some low-temperature plasma technologies have been further applied and promoted based on previous gas discharge and arc technologies, such as plasma cutting, welding, sputtering, magnetic fluid power generation, plasma chemical engineering, plasma metallurgy, and Rocket ion propulsion, etc., has promoted research on the properties of low-temperature plasmas with incomplete ionization.

After 30 years of development, the Institute of Plasma Physics of the Chinese Academy of Sciences is at the international advanced level in the field of high-temperature plasma physics experiments and nuclear fusion engineering technology research, and has formed extensive international exchanges and cooperation. Nearly 30 countries and regions such as Australia, Australia and other countries have established stable cooperation and exchange relations, carried out a number of international cooperation projects, and become the "Open Laboratory of the Third World Academy of Sciences" and the "World Laboratory Fusion Research Center". One of the important units of the fusion project ITER China team.

Plasma ion effect

The ionosphere is composed of a spherical surface of the atmosphere with ions that have been ionized by solar radiation. This is the plasma region, forming layers D, E, F1, and F2 with different ion densities. When the spacecraft returns to the atmosphere, due to the high temperature generated by friction, a very dense plasma is formed on the surface of the spacecraft. When the density of these electrons is high enough, the plasma frequency will be very high (generally 8MHz). The communication was blocked, and communication was not resumed until its speed dropped.

Main applications of plasma

When light hits a metal surface, two-dimensional light or plasma is excited. Plasma can be seen as the connection of photons and electrons.

A mixing principle can be established, when the plasma converted from light travels on the metal surface (the wavelength of the plasma is much smaller than the wavelength of the original light wave); the plasma can be processed by two-dimensional optical instruments (mirrors, waveguides, lenses, etc.) The plasma can be converted into light or electrical signals again.

Plasma sensor and cancer treatment instrument: NaomiHalas described how the plasma excites the surface of a small metal layer. The particles in the shape of rice grains have a lot of energy. The light used for spectroscopy experiments is of the order of micromolecules.

plasma The electric field of the plasma at the curved tip of the rice grain particles is much stronger than the electric field used to excite the plasma, and it greatly improves the rate and accuracy of the spectrum. In other words, plasmas on the order of nanometers can be used not only for identification, but also to kill cancer cells.

Plasma microscope: IgorSmolyaninov reports that he and his colleagues can photograph objects with a spatial resolution of 60nm (if it is a practical material, the resolution can reach 30nm), and laser excitation can only reach 515nm. In other words, a microscope made with this resolution will be much better than the usual diffraction method; moreover, this is a far-field microscope-the light source does not need to be placed in a range less than the wavelength of light. Huge light polarization and light transmission: GennadyShvets reports that super prisms (lensed with flat plate materials) are used when the surface phonons are excited by light to make a microscope that is one-twentieth the wavelength of an infrared light microscope. He and his colleagues were able to capture features under the surface of the sample, which they called "giant light transmission," and the light hitting the surface was much smaller than the wavelength of ordinary light.

Futuristic Plasma Circuits at Light Frequency: NaderEngheta supports plasma-excited nanoparticles that can be designed as capacitors, resistors, and inductors (various elements in the circuit) on the order of nanometers.

The circuit can receive broadcast (1010Hz) or microwave (1012Hz) frequencies, but the circuit can reach the optical frequency (1015Hz). This enables miniaturization and the process of detecting optical signals with nano-antennas, nano-waveguides, nano-sensors, and also possible nano-computers, nano-storages, nano-signals, and optical molecular interfaces.

Plasma is mainly used in the following three aspects.

Plasma smelting: used for materials that are difficult to smelt by ordinary methods, such as high melting point zirconium (Zr), titanium (Ti), tantalum (Ta), niobium (Nb), vanadium (V), tungsten (W), etc. Metal; also used to simplify processes, such as directly from ZrCl, MoS, TaO, and TiCl, respectively

plasma Obtain Zr, Mo, Ta and Ti; use plasma melting rapid solidification method to develop hard high melting point powders, such as tungsten carbide-cobalt, Mo-Co, Mo-Ti-Zr-C, etc. The advantages of plasma smelting are products The consistency of the composition and microstructure is good, which can avoid the pollution of the container material.

Plasma spraying: Many parts of equipment should be able to withstand abrasion, corrosion and high temperature. To this end, a layer of material with special properties needs to be sprayed on the surface. Plasma deposition rapid curing method can spray special material powder into hot plasma to melt and spray it on the substrate (parts), so that it can quickly cool and solidify, forming a surface layer close to the network structure, which can greatly improve the quality of spraying .

Plasma welding: It can be used to weld steel, alloy steel; aluminum, copper, titanium, etc. and their alloys. The characteristic is that the welding seam is flat, and can be reprocessed without oxide impurities, and the welding speed is fast. Used for cutting steel, aluminum and its alloys, with large cutting thickness.

Plasma technology

The so-called plasma, in terms of electrical technology, refers to an uncharged ionized substance with ions, electrons and core particles. The plasma includes almost the same number of free electrons and anode electrons. In a plasma, the particles have been separated from the core particles. Therefore, when a plasma includes a large number of ions and electrons, it is the best conductor of electricity, and it will be affected by the magnetic field. When the temperature is high, the electrons will be separated from the core particles.

In recent years, the PDP supported by plasma flat screen technology is really like the sky and the sky. It is the best candidate for true flat TV in the future. In fact, plasma display technology is not a new technology only in the 21st century. As early as 1964, the University of Illinois has successfully developed a plasma display technology.

plasma Sub display flat, but at that time the plasma display was monochrome. Plasma flat screen technology is now the latest technology, and it is the best choice for high-quality images and large flat screens. The large flat screen can watch TV in any environment. The plasma panel has a series of pixels. At the same time, these pixels contain three secondary pixels, which are red, green, and blue. The gas in the plasma state can react with the phosphor in each sub-pixel to produce red, green or blue. This kind of phosphor is the same as that used in cathode ray tube (CRT) devices (such as televisions and ordinary computer monitors). You can get the rich and dynamic colors you expect from each. An advanced electronics-controlled sub-pixel produces 1.6 billion different colors, all of which means you can see the best picture on a display less than 6 inches thick.

Plasma instability

The nature of the plasma's departure from thermodynamic equilibrium. There are two general approaches. One type is the inhomogeneity of the macroscopic parameters of the plasma, such as density, temperature, pressure, and other thermodynamic quantities. The resulting instability causes the overall shape of the plasma to change, which is called macroinstability or configuration space instability. It can be analyzed by magnetohydrodynamics (see Plasma Physics), so it is also called magnetohydrodynamic instability. The other is that the velocity and space distribution function of the plasma deviates from the Maxwell distribution. The resulting instability is called micro-instability or velocity-space instability. It can be analyzed by plasma dynamics, so it is also called dynamical instability. .

Plasma instability (macro or micro) can also be classified by the driving energy that caused it. For example, current instability caused by magnetic energy; exchange instability caused by expansion energy when the plasma expands into a weak magnetic field region; drift instability caused by plasma expansion energy due to density and temperature gradients; non-Maxwell distribution or pressure anisotropy Velocity and space instability caused by free energy corresponding to the opposite sex.

plasma Various instabilities in the plasma can lead to the escape of charged particles or an abnormal increase in the transport coefficient, destroying the constraints of the plasma or limiting the constraint time. Therefore, studying the various instabilities of plasma, elucidating its physical mechanism, and exploring methods of stabilization have been a central topic in the research of controlled thermonuclear fusion, and also an important content of plasma physics.

If the plasma column is constrained only by the angular magnetic field in which the longitudinal current is generated, then after a slight disturbance, the inward magnetic pressure at the contraction point will increase and it will shrink more, and the inward magnetic pressure at the expansion point will decrease and expand more. It is shaped like a sausage, so it is called unstable sausage. It can cut off the plasma and add a longitudinal magnetic field to resist contraction and expansion to stabilize it. If the plasma column carrying the longitudinal strong current is slightly bent by the disturbance, the magnetic field of the concave portion is strengthened, and the convex portion is weakened. The magnetic pressure difference caused by this causes the disturbance to expand, and the plasma column will quickly bend or even form a spiral. Twisting instability, which can be stabilized by longitudinal magnetic field. If water is up and oil is down, a slight disturbance will be exchanged under the action of gravity. Similar instability in the plasma is called exchange instability. The above cases are all macro instability.

Plasma fusion

Nuclear fusion is the main choice for solving future energy sources. High-temperature plasma research to achieve nuclear fusion becomes the goal. Tokamak-type nuclear fusion research is one of the main fusion research approaches in the world today, and it is also the main subject of this institute. The institute has built a number of tokamak nuclear fusion experimental devices and research systems such as HT-6B, HT-6M, HT-7 and EAST, and participated in the International Thermonuclear Fusion Test Reactor (ITER) plan and research. It is planned to build a steady-state tokamak experimental reactor and a Chinese magnetically constrained fusion demonstration reactor in China in the future so as to commercialize pure fusion energy.

During the construction of Tokamak and the development of plasma physics experiments, the Institute has developed diagnostics, power, microwave, low temperature, superconductivity, vacuum, data acquisition and processing, materials, safety and environmental protection, and electrophysics to ensure the operation of Tokamak. A series of high-tech such as precision instrument processing and so on, carried out new reactor conceptual design and related technology research. Technologies in high-power power supplies, large-scale low-temperature refrigeration, superconducting energy storage, high-temperature superconducting, and electrophysical equipment development have been applied to the national economy, and some of them have been industrialized.

Plasma Research Contribution

Since the founding of the People's Republic of China, the Plasma Institute has undertaken a number of major scientific research projects such as the National Development and Reform Commission, the Ministry of Science and Technology, the National Funding Committee, and the Chinese Academy of Sciences. Plasma Institute relied on its own strength to build conventional magnet tokamak devices HT-6B and HT-6M and China's first circular cross-section superconducting tokamak device HT-7; in 2006, the world's first non-circular The cross-section superconducting Tokamak EAST device was independently built at the Institute of Plasma. The successful construction of EAST was evaluated by the international fusion community as "the extraordinary performance of fusion engineering worldwide, and the outstanding achievement and important milestone of fusion energy development worldwide." This major achievement won the first prize of the 2008 National Science and Technology Progress Award, and was selected as the 2006 "China's Top Ten Science and Technology Progress" and "China's Top Ten Basic News".

Plasma where plasma theory and experiments closely related to high temperature thermonuclear fusion plasma physics and engineering research, reactor technology, high power power technology, computer automatic control and data acquisition and processing technology, high vacuum technology, low temperature refrigeration technology, low temperature ultra-low temperature The research achievements of such subjects as high-temperature superconducting technology, high-temperature superconducting technology, special materials technology, large-scale microwave heating, and electric current drive are outstanding, and a comprehensive talent team with different disciplines has been accumulated. Completed multiple plasma physical diagnostic systems, 2 MW wave heating system, 2 MW wave drive current system, AC / DC pulse power system with a total power of 200,000 kW, 110 kV substation, China's largest 2 kW liquid Helium refrigeration system, ultra-high vacuum system, 200,000 Gaussian steady-state hybrid magnets, advanced computer control and data acquisition and processing systems, large superconducting magnet production and testing systems, and other advanced facilities are built into a comprehensive system for plasma physics and Advanced platform for fusion engineering and technology research and development.

Ion beam biological engineering is a new research field of physics and biology pioneered by the researchers of the Institute of Plasma, and has now formed a new branch of interdisciplinary discipline-ion beam biological engineering. This subject mainly studies the effects of low-energy ion radiation on evolution and health in nature. Based on the precise positioning of ion beam and single ion beam cell irradiation platforms, it studies the interaction mechanism of ion beams, ray beams and organisms. Ion beam bioengineering technology has been promoted and applied in industrial biotechnology, agriculture, environmental health and other fields, and has achieved significant social and economic benefits. It has won many important national awards and has become the "leading team" in this field.

Solar materials and engineering research has undertaken a number of projects such as the National Key Basic Research Program 973, the Chinese Academy of Sciences Knowledge Innovation Project, research in the fields of dye-sensitized solar cells, photovoltaic functional materials and polymer crystallization, and has achieved a number of internationally advanced scientific research The results make positive contributions to the development of solar energy with Chinese characteristics.

Combining with the development outline requirements for the construction of an innovative country, the Institute has established research on the application of low-temperature plasma technology in the fields of environment, new energy, chemicals, and new materials. It has obtained a series of independent intellectual property rights that can be important to the national economy. High-tech achievements.

Plasma Science and Technology, edited and published by the Institute of Plasma, is the only English-language academic journal in the domestic plasma profession, and has been included in important international databases such as SCI and SA. ^[4]

The application of plasma in catalysis is mainly concentrated in ^[5] :