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Influence of atmospheric pressure low temperature plasma energy density

Influence of atmospheric pressure low temperature plasma energy density

In a normal pressure flow plasma reactor, the main factors affecting the plasma energy density are the feed gas flow rate F and the plasma injection power P. The feedstock gas flow rate is one of the main factors affecting the density and collision probability of the active particles in the reaction system. The plasma injection power is the energy source for the generation of various active particles in the plasma (high-energy electrons, reactive oxygen species, methyl radicals, etc.). The dynamic synergistic effect of the two can be described by energy density Ed(kJ/mol). Influence of atmospheric pressure low temperature plasma energy density on methane conversion: With the decrease of plasma energy density, the conversion rate of methane decreases, but the C2 hydrocarbon selectivity increases with the decrease of energy density, and the C2 hydrocarbon yield does not fluctuate much.   In a flow plasma reactor, the injected plasma energy and the total gas flow rate are two important factors affecting plasma chemical reactions. This is because the former is the energy source of various active particles in the plasma, while the latter is the determinant of the density and collision probability of the active particles in the reaction system. When the injected energy is constant, the gas flow rate increases, that is, the energy absorbed by the gas per unit flow rate decreases. Therefore, low flow rate is conducive to improving the yield. However, when the flow rate is too low, the target product is prone to further cracking to form C, resulting in the decrease of the yield of C2 hydrocarbon. Therefore, appropriate plasma energy density must be adopted to obtain the high yield of Hydrocarbon C2.   There is a serious problem of carbon deposition in the conversion of pure methane by plasma. In the low temperature plasma activation reaction at atmospheric pressure, a layer of carbon deposition will be formed on the reactor wall. The longer reaction time or the greater the input energy, the more carbon deposition will be. The increase of carbon deposition will directly affect the conversion rate of CH4, which will make the reaction unable to continue in severe cases.

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On-line vacuum plasma cleaning machine

On-line vacuum plasma cleaning machine

The main structure of on-line vacuum plasma cleaning machine includes: rack, automatic feeding equipment and automatic cleaning equipment; The upper and lower material pushing mechanism, the upper and lower material taking and placing platform, the upper and lower material conveying system, the upper and lower material shifting mechanism, reaction bin, main structure of equipment and electrical control system, etc. On-line vacuum plasma cleaning machine has simple structure, easy to use and high efficiency. The machine has compact structure, comprehensive performance, uniform and stable treatment effect, flexible configuration and high cost performance. And can be manually or before the process of automatic completion of feeding, feeding, positioning, open the material door, feeding, cleaning and discharging, and then by manual feeding or in accordance with the process of automatic completion of feeding, feeding, feeding. On-line vacuum plasma cleaning machine is a design concept of automatic material handling. Compared with the traditional plasma cleaning system, it reduces the cost of manual handling and improves the automation level of the equipment.   Online type vacuum plasma cleaning belongs to high precision dry cleaning, its principle is to use rf source to produce the high voltage ac electric field, such as oxygen, argon, hydrogen process gas into a highly active or high-energy ion, the workpiece surface by chemical reactions or physical function, at the molecular level of pollutant removal, improve the surface activity. The ideal cleaning effect can be achieved by adopting different cleaning techniques for different pollutants.   In the vacuum of vacuum plasma cleaning, the plasma reacts or collides with organic pollutants and micro-particle pollutants to form volatile substances, which are removed by working air stream and vacuum pump, so as to achieve surface cleaning effect of the workpiece. Plasma cleaning is a kind of stripping cleaning, which has no pollution to the environment after cleaning. On - line plasma equipment is based on mature plasma technology and equipment manufacturing, adding automatic functions such as feeding and feeding. Precleaning the lead frame in IC packaging, such as gluing pieces, chip bonding and plastic sealing before cleaning, greatly improves the performance of bonding and bonding strength, and avoids secondary pollution caused by human factors to long-term contact with the lead frame and damages to the chip at the same time.   On-line plasma cleaning is widely used in gluing, welding, printing, coating and other occasions, through plasma acting on the surface of the product, improve its surface activity, and activate the surface performance, can significantly improve the product, has become an essential equipment for the surface performance treatment of middle and high-grade products. On-line vacuum plasma cleaning machine focuses on plasma surface modification or plasma surface treatment applications. It is the high energy and instability of plasma that is used to clean, activate and activate the surface of treated materials, thus changing the microstructure, chemical properties and energy of the surface.   The interaction of plasma with the surface of an object can be divided into physical interaction (ion bombardment) and chemical interaction. The mechanism of physicochemical reaction is that the active particles are bombarded on the surface to be cleaned, so that the pollutants can be separated from the surface and sucked out by the vacuum pump. The chemical reaction mechanism is that all kinds of active particles react with pollutants to produce volatile substances, and then the volatile substances are sucked out by vacuum pumps.   Plasma cleaning is mainly based on physical reaction, and there is no chemical reaction on its own. No oxide is left on the surface of cleaning, which can keep the chemical purity of the cleaned object. The disadvantage is that there is a small amount of damage to the surface, which will produce a large thermal effect. The different substances on the surface of the object to be cleaned have poor selectivity and low corrosion rate.   Chemical reaction plasma is used for cleaning, which has the advantages of high cleaning speed, good selectivity, and can remove organic matters more effectively, while the disadvantage is that it can produce oxides on the surface. Compared with physical reaction, the disadvantage of chemical reaction is not easy to overcome. The influence of the two reaction mechanisms on the surface morphology is significantly different. The physical reaction can make the surface become more "rough" at the molecular level, thus changing the surface adhesion property.   In addition, the reaction mechanism of plasma cleaning on the surface, the physical and chemical reaction plays an important role, also is the reactive ion etching and reactive ion beam etching

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Cleaning features of non-standard industrial automatic cleaning equipment

Cleaning features of non-standard industrial automatic cleaning equipment

Surface cleaning can be defined as a cleaning process that removes excess material adsorbed on the surface that can adversely affect the process and performance of the product. Cleaning is an essential process in advanced manufacturing. The removal of excess material from the workpiece surface should be accomplished in the industrial cleaning process at a low cost with the least possible environmental impact. Can be used for metal processing and mechanical operation, the surface modification of tool, electronic industry, jewelry, plastic and glass surface, optical device and the surface cleaning of medical apparatus, etc., each area of the cleaning program has a specific cleaning technology, with the development of science and technology, non-standard custom automatic cleaning device, make cleaning technology and development in the direction of more efficient and rapid.   According to the requirements of fineness, industrial cleaning can be divided into conventional industrial cleaning, precision industrial cleaning and ultra-precision industrial cleaning. According to the cleaning method can be divided into physical and chemical; According to the cleaning medium can be divided into wet method and dry method. No matter how classified, automatic, environmental and efficient cleaning methods are the development direction of the industrial cleaning industry.   Advantages of non-standard automatic cleaning equipment:   Automatic cleaning equipment is to make full use of science and technology, so that the cleaning work fully automated, mechanized, systematic, safe and humanized cleaning system.   1. At present, China's labor cost is rising year by year. Automatic cleaning system can realize automatic mechanized cleaning in the process of industrial cleaning without manual cleaning, which saves a lot of manpower for production enterprises and greatly reduces the cost of employing people.   2, time is efficiency, comprehensive mechanization of automatic cleaning equipment work efficiency is often several times or even tens of times of manual cleaning, industrial automatic cleaning system efficiency can greatly save the cost of production time.   3. Through professional research and system design, automatic cleaning equipment can make the edges and gaps that are difficult to be cleaned manually more effectively.   4. At present, the automatic cleaning system mostly adopts pollution-free and environmental protection technology. Compared with the chemical cleaning method, the odorless, tasteless and non-toxic water medium causes less pollution to the environment and is more environmentally friendly.   5. Due to the high degree of automation of the cleaning system, the program control operation is more stable, which changes the extensive management of the traditional cleaning process, and the control is not strict. Especially for chemical tank truck cleaning and other dangerous industries, automatic cleaning system greatly improves the safety of cleaning.   At present, the cleaning industry has penetrated into almost all industrial fields, including petroleum, chemistry, energy, electric power, metallurgy, construction, machinery and electronics, transportation, textile, printing, and even nuclear industry, and has been widely recognized by the society. Non-standard customized automatic cleaning system makes industrial cleaning with energy saving, high efficiency, consumption reduction, safety, stability and other characteristics, in improving product quality, speed up the production speed, extend the service life of equipment, reduce environmental pollution, purification and beautification of the environment has made a great contribution to the industrial cleaning industry to move forward.   According to incomplete statistics, the market share of Industrial cleaning equipment and industrial cleaning agents in China has reached several hundred billion YUAN, and the production, management and construction enterprises of various cleaning equipment have exceeded 10,000, and the production and sales enterprises of cleaning agents have reached thousands. Now only cleaning supplies manufacturers, distributors and agents in the domestic more than 4000, industrial cleaning has formed a huge industry.   In the industrial green development plan issued by the Ministry of Industry and Information Technology, the overall level of industrial green development will be improved, and industrial cleaning will inevitably need more application of automatic cleaning system. How to realize the comprehensive system automation of industrial cleaning has become an inevitable trend, and will also become the research direction of industrial cleaning enterprises.

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Application of special gas in plasma etching

Application of special gas in plasma etching

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Plasma cleaning machine gas action

Plasma cleaning machine gas action

Before using the plasma cleaning machine to clean the object, the object and dirt should be analyzed first, and then select the corresponding gas. According to the action principle of plasma, the selected gases can be divided into two types, one is hydrogen, oxygen and other reactive gases, among which hydrogen is mainly used to clean oxides on the metal surface for reduction reaction. The oxygen introduced by the plasma cleaner is mainly used to clean the organic matter on the surface of the object.   The other is plasma cleaner filled with argon, helium, nitrogen and other non-reactive gases. Nitrogen plasma treatment can improve the hardness and wear resistance of the material. Argon and helium are stable, and the discharge voltage is low (the ionization energy of argon atom is 15.57eV), and metastable atoms are easy to form. On the one hand, the plasma cleaning machine USES the physical action of its high-energy particles to clean the objects that are easy to be oxidized or reduced. Ar+ bombarding dirt forms volatile dirt, which is removed by vacuum pump to avoid the reaction of surface substances. On the other hand, metastable atoms are easily formed by argon, and then charge conversion and combination occur when they collide with oxygen and hydrogen molecules, forming oxygen and hydrogen active atoms acting on the surface of the object.   Although it is effective to clean the surface oxides with pure hydrogen in the plasma cleaning machine, the stability and safety of discharge are mainly considered here, and the mixture of argon and hydrogen gas is more suitable for the plasma cleaning machine. In addition, for the material easy oxidation or easy reduction of the material plasma cleaning machine can also be used to reverse the oxygen and argon hydrogen gas cleaning order to achieve the purpose of thorough cleaning.   Application examples of gas in plasma cleaning machine:   1. Degreasing and cleaning of metal surface:   Metal surface often has grease, grease, oxide layer and other organic matter. Prior to sputtering, painting, bonding, bonding, brazing, and PVD and CVD coatings, plasma treatment is required to obtain a completely clean and oxide free surface. In this case, plasma treatment has the following effects:   Oxide removal:   Metal oxides react with the treated gases. The treatment USES hydrogen or a mixture of hydrogen and argon. Sometimes two steps are used, one is to oxidize the surface with oxygen for 5 minutes, the second is to remove the oxide layer with a mixture of hydrogen and argon, or several gases can be used simultaneously.   2. Plasma etching:   In the plasma etching process, the etched object will change into a gas phase under the action of the processing gas, the processing gas and matrix materials are pumped out, and the surface is continuously covered by the fresh processing gas. The unneeded etched parts should be covered with a material (for example, chromium is used as a covering material in the semiconductor industry).   Plasmas are also used to etch plastic surfaces into which the filling mixture can be oxidized by oxygen. Etching methods such as polyformaldehyde, polyphenylene sulfide, and polytetrafluoroethylene are pretreated in their printing and bonding, and plasma treatment can greatly increase the bonding wetting area.   3. Etching and ashing:   PTFE etching:   Teflon cannot be printed or bonded without treatment. It is well known that active alkali metals can increase adhesion, but this method is not easy to master and the solution is toxic. Using the plasma method can not only protect the environment, but also achieve better results. The plasma structure can enlarge the surface and form an active layer on the surface, so that PTFE can be better adhesive printing.   Etching of PTFE mixture:   The PTFE mixture must be etched very carefully to avoid overexposure of the filler, thereby weakening adhesion. The treated gases may be oxygen, hydrogen and argon. It can be used in polyethylene, polytetrafluoroethylene, thermoplastic elastomer, polyformaldehyde, etc.   4. Surface activation and cleaning of plastics, glass and ceramics:   Like polypropylene and polytetrafluoroethylene, plastics, glass and ceramics are not polar, so these materials should be processed before printing, bonding and painting. At the same time, the glass and ceramics surface slight metal contamination can also be cleaned with plasma. Compared with combustion treatment, plasma treatment does not damage samples. At the same time, the whole surface can be treated uniformly, without poisonous gas generation, and hollow and interstitial samples can be treated.   Commonly used plasma cleaning machine gas: compressed air, oxygen, argon, argon mixed gas, CF4 and so on.

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Mechanism analysis of methane conversion under the action of simple plasma

Mechanism analysis of methane conversion under the action of simple plasma

At present, most researchers believe that the mechanism of plasma activated methane conversion is the free radical reaction process. Plasma discharge excites a large number of high-energy electrons. These high-energy electrons inelastic collide with methane molecules, splitting stable methane molecules into different active groups, which are coupled with each other to form C2 hydrocarbon products.   From the perspective of energy, under the action of plasma, the energy of high-energy electrons (1 ~ 20 eV) is enough to break the C-H bond of CH4 molecules (the average c-H bond energy is 4.3eV, and the dissociation energy of CH3-H is 4.5eV), thus forming CHx(x=0~3) free radicals in the gas phase. The CHx radical is then directionally recombined on solid surfaces such as the wall and electrode to form products that are desorbed from the surface. In the plasma system, the main role of plasma is to activate methane molecules to form CHx free radicals. The type and concentration of free radicals are determined by the plasma source and its energy-related parameters. The surface properties of free radicals were used to regulate the directed compound reaction of free radicals on the surface and transfer energy for the compound reaction of free radicals.   The emission spectrum in situ diagnosis technology can be excited state of atmospheric pressure plasma methane diagnosis to active species, in 250 ~ 800 nm wavelength range, can be concluded that under the action of plasma conversion of methane generated in the process of the main active species for: CH (430.1 ~ 438.7 nm), C (563.2 nm and 589.1 nm) and C2 (512.9 nm and 516.5 nm) and H (434.1 nm and 486.1 nm and 656.3 nm).   In plasma discharge areas, high-energy electrons are first produced. These high-energy electrons collide inelastic with methane molecules, thus generating a large number of active species and active free radicals, which further collide and combine to form new substances.   CH4+e*—>CH3+H+e               （3-1） CH3+e*—>CH2+H+e               （3-2） CH2+e*—>CH+H+e                 （3-3） CH+e*—>C+H+e                      （3-4） CH4+e*—>CH2+2H(H2)+e      （3-5） CH4+e*—>CH+3H(H2+H)+e    （3-6） CH4+e*—C+4H(2H2)+e            （3-7）   Coupling reactions between free radicals occur and the following products are generated (M is the third body, reactor wall, etc.) :   CH3+CH3+M—>C2H2+M          （3-8） CH2+CH2+M—>C2H4+M          （3-9） CH3+CH2+M—>C2H4+H+M     （3-10） CH +CH +M—>C2H2+M            （3-11） CH +CH2+M—>C2H2+H+M      （3-12） CH3+C+M—>C2H2+H+M         （3-13）   Since the particles with high concentration in the system are methane molecules, it is also an important way that methane molecules collide with various methyl radicals to initiate new radicals and generate various C2-hydrocarbon products.   CH2+CH4+M—>C2H6+M       （3-14） CH+CH4+M—>C2H4+H+M    （3-15） C+CH4+M—>C2H4+M            （3-16） C+CH4+M—>C2H2+H2+M    （3-17）   At the same time, the presence of C2 species in the emission spectra of methane plasma suggests that acetylene can also be generated by the following pathways:   C2+H+M—>C2H+M            （3-18） C2H+H+M—>C2H2+M        （3-19）   In atmospheric pressure pulsed corona plasma, high-energy electrons have a wide energy distribution range, so the concentration of various free radicals in methane plasma is different. The main products of the reaction are acetylene and hydrogen, while the secondary products are ethylene and ethane. CH and C were the main components of CHx free radical distribution in methane plasma, followed by CH3 and CH2.   C2H6 is the primary product of methane dehydrogenation coupling reaction, and C2H4 and C2H2 are the secondary products of further dehydrogenation of C2H6 and C2H4, respectively. Therefore, the following reaction pathways exist:   CH4→C2H6→C2H4→C2H2    （3-20）   To this end, we respectively investigates the pure ethane, ethylene in pulse corona plasma in the dehydrogenation reaction, the results showed that the pure ethane dehydrogenation reaction is the main product of the C2H4 and C2H2, pure ethane dehydrogenation reaction is the main product of C2H2, shows that under the action of plasma methane dehydrogenation coupling reaction do exist such as type (3-20) as shown in the reaction.   In the plasma, C2H6 and C2H4 generated by methane dehydrogenation will further interact with high-energy electrons to form radicals such as C2H5 and C2H3. Therefore, it can be speculated that trace C3 and C4 products are generated by methane dehydrogenation mainly in the following ways:   CH3+C2H5 +M→C3H8 + M         （3-21） CH2 +C2H6 +M→C3H8 + M       （3-22） CH3+C2H3 +M→C3H6 + M         （3-23） CH2+C2H4 +M→C3H6 + M        （3-24） C2H5 +C2H5 +M→C4H10 +M    （3-25）   The results of spectroscopic analysis show that the dehydrogenation of methane is mainly a free radical process under the action of plasma. However, in the methane d

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