Application of sulfur hexafluoride in oxidation and reduction of high frequency plasma tests- SF6在线监测系统_SF6检漏仪_SF6传感器_SF6密度继电器

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Application of sulfur hexafluoride in oxidation and reduction of high frequency plasma tests

发布时间：2020-07-10 来源：ydlcb 浏览次数：21次

Sulfur hexafluoride, molecular formula SF6, relative molecular weight is 146.06, at normal temperature and pressure for colorless, tasteless, non-toxic, non-corrosive, non-flammable, non-explosive gas, density of about 5 times the air, the standard state density of 6.0886kg cubic meters. It is liquid at low temperature and under pressure and becomes a white solid when frozen. The sublimation temperature is -63.9℃, the melting point is -50.8℃, the critical temperature is 45.55℃, and the critical pressure is 3.759MPa. Sulfur hexafluoride has good chemical and thermal stability, excellent electrical insulation and arc extinguishing performance.

The liquefaction temperature of sulfur hexafluoride gas is -62℃ at one atmospheric pressure (i.e. 0.1MPa). Under the pressure of 1.2MPa, the liquefaction temperature is 0℃. Generally, the pressure of sulfur hexafluoride gas charged into the circuit breaker is 0.35 ~ 0.65MPa (specifically determined by the ambient temperature at the time of inflation), and the liquefaction temperature is -40℃.

The critical temperature is the high temperature at which sulfur hexafluoride gas liquefaction occurs. The critical pressure indicates the gas pressure required for liquefaction to occur at this temperature. Sulfur hexafluoride can only remain gaseous when the temperature is above 45 degrees, under normal conditions of use, it has the possibility of liquefaction, so sulfur hexafluoride can not be used at low temperatures and too low pressure.

The electrical strength of sulfur hexafluoride is about 2.5 times that of air, and the arc extinguishing capacity is more than 100 times that of air, so it has completely replaced insulating oil and compressed air in the category of ultra-high pressure and ultra-high pressure, and has become the circuit breaker arc extinguishing medium.

Sulfur hexafluoride (chemical formula SF6) is a colorless, odorless, non-toxic gas, non-flammable, slightly soluble in water, and it is also a member of the greenhouse gas. Solving the problem of SF6 exhaust emissions is of great significance for protecting the environment. The researchers used a high-frequency plasma system to decompose sulfur hexafluoride (SF6) at room temperature by adding oxidizing agents (O2) or reducing agents (H2 or H2S). The main operating parameters are input power and reactant flow ratio (O2SF6, H2SF6 to H2SSF6 ratio). The contents of the study include discussing the decomposition reaction of the reactants and the distribution of the final products, the toxicity equivalent analysis of oxidized plasma and reduced plasma products, deducing the reaction path of the plasma system, constructing the SF6Ar plasma model for numerical simulation and comparison with the experimental values, and finally proposing the best treatment method of SF6.

The results showed that both input power and reactant flow ratio were the main factors affecting decomposition rate (ηSF6) and product distribution. In terms of decomposition rate, ηSF6 increases with the increase of power in both oxidation and reduction systems. However, when the input power is less than 40W, ηSF6 has a different trend in oxidation and reduction systems. With the increase of O2SF6 ratio, the free radical formation from electron collision is inhibited, and the decomposition of SF6 is reduced. Because fluorine free radicals are easy to form stable HF products with hydrogen, ηSF6 increases significantly when the ratio of H2SF6 or H2SSF6 is increased. However, when the power is increased to 40W, ηSF6 in the oxidation and reduction system is less affected by the reactant inflow ratio.

In terms of product distribution, the main co-decomposed products of oxidation and reduction plasma system are SiF4, SO2, SO2F2, SOF2 and SOF4. However, HF and sulfur deposits are only found in reducing plasma systems. In the oxidized plasma system, F2 is the main product containing fluorine when SF6 is decomposed, and it increases obviously with the increase of power. In the reduction plasma system, HF is the main product containing fluorine in the decomposition of SF6, which also increases with the increase of power. SiF4 is produced by the etching action of fluorine free radicals on SiO2 reactors. In both oxidation and reduction plasma systems, SiF4 tends to increase with the increase of power. However, in the reduction plasma system, HF formation competes with SiO2 etching for fluorine radicals, so SiF4 formation is less obvious. In the reduction plasma system, the deposition of sulfur element is the main product containing sulfur, and it increases with the increase of power. However, no sulfur deposits were found in the oxidized plasma system. The input power is an important parameter affecting the generation of SO2 in the system. In the oxidized plasma system, the sulfur-containing products are mainly fluoro-oxysulfide and SO2 at low power, while the sulfur-containing products change from fluoro-oxysulfide to SO2 at high power. In the reduction plasma system, the formation of SO2 or fluoro sulfide is subject to SiO2 etching.

The reactant flow ratio is also an important factor affecting product distribution. In the oxidized plasma system, the decomposition rate of SF6 decreases with the increase of oxygen addition ratio, resulting in the decrease of F2 generation, and the formation of SiF4 by etching also decreases. The fluorine oxide sulfide gradually increased with the increase of O2SF6 ratio, however, the SO2 production gradually decreased with the increase of O2SF6 ratio. When hydrogen or hydrogen sulfide is added to the reducing plasma system, HF production increases rapidly with the increase of hydrogenation ratio, F2 also disappears from the system due to the competitive reaction of hydrogen, and the etching effect is inhibited, resulting in the formation of SiF4. In the reduction plasma system, SO2 generation is obviously inhibited due to the lack of oxygen supply released by etching, and most of the sulfur-containing products are present in elemental sulfur. In addition, with the increase of H2SF6 ratio, fluoro-oxysulfide disappears from the reducing plasma system.

The toxicity equivalent (TEQ) of oxidized plasma and reduced plasma is higher in SF6O2Ar than in SF6H2Ar plasma. In the SF6O2Ar plasma system, TEQ toxicity increased rapidly with the increase of power, but in the SF6H2Ar plasma system, TEQ toxicity did not increase significantly with the increase of input power. Inflow H2SF6 than for oxidation and reduction with O2SF6 plasma system TEQ toxicity, no significant effect. Since the recovery of HF can reduce systemic toxicity, the recovery of elemental sulfur can reduce SO2 emissions, and avoid the trouble of subsequent treatment of large amounts of emissions, therefore, the reduction RF plasma treatment of SF6-containing emissions will be a better choice.

High purity sulfur hexafluoride also can carry on the processing of the polymer material surface, make the structure change of the material surface. Plasma surface treatment is a very effective polymer material surface treatment technology, the use of plasma surface treatment, can introduce specific surface properties on the surface of the polymer material, and will not affect the polymer material itself original overall. Sulfur hexafluoride plasma can handle soft materials well.

In the experiment, we used high frequency plasma (Electron Cyclotron Resonance) to study the surface modification of Poly ethylene terephthalate (PET). We observed that when sulfur hexafluoride gas SF6 was used, The changing trend of the surface modification effect of the film is closely related to the reaction gas, power and reaction time. In the process, a mask is placed on the surface of the substrate and the distance between the substrate and the mask is controlled, and both hydrophilic and hydrophobic surface characteristics can be obtained at the same time. It shows that the treated mask area can react with a large number of oxygen atoms in the atmosphere to form hydrophilic surface characteristics, and the difference of water contact Angle can reach more than 100 degrees. We will also further study the changes of hydrophilicity and surface chemical structure.

Chemical tips: sulfur hexafluoride gas is widely used in electrical industry because of its good insulation and arc extinguishing performance; As a refrigerant for refrigeration industry, the cooling range can be between -45 ° C and 0 ° C; Because of its chemical inert, non-toxic, non-combustible and non-corrosive, it is also widely used in metal smelting (such as magnesium alloy melting furnace protection gas), aerospace, medical (X-ray machine, laser machine), meteorological (tracer analysis), chemical (advanced automobile tires, new fire extinguishers) and so on.