Degradation Of CF₄ By Microwave Standing Wave Plasma At Atmospheric Pressure

Carbon tetrafluoride(CF4)has a wide range of applications in the semiconductor and aluminum smelting industries,material modification,etching,etc.due to its low cost and high carbon-to-fluorine ratio.However,with the various applications of CF4,the Greenhouse Effect it brings cannot be underestimated.Due to its stable structure,CF4 has an atmosphere lifetime of 50,000 years,and its Global Warming Potential(GWP)is 7597 times that of carbon dioxide,which is one of the strong greenhouse gases that scientists focus on.At present,the decomposition technologies of CF4 mainly include several application technologies such as thermal decomposition,catalytic decomposition,and plasma decomposition.Plasma decomposition technology is an emerging technology in recent decades,benefiting from the existence of active species,it has unique characteristics and advantages.Plasma can realize many reactions that cannot be happened by traditional methods,and has demonstrated strong application ability in many fields.The microwave plasma used in this paper is a very effective technical means to degrade and transform CF4 due to its.high power and high plasma density.In this study,industrial microwave sources were used to enhance the electric field strength by means of standing wave resonance,generating discharge to achieve high-density plasma,and the decomposition of high-concentration CF4 gas under atmospheric pressure.Flame ionization detector(FID)and thermal conductivity detection(TCD),mass spectrometer,etc.were used to measure and analyze the decomposition rate of CF4,the gas composition and content of the gas.Experimental results showed that this technology had a high decomposition efficiency for CF4 gas.Under the best microwave power and intake gas flow,the decomposition rate of CF4 could reach 100%.For the degradation of pure CF4,the main reaction products were solid C and F2,but because the reactor cannot be completely vacuumed,the air component was mixed into the reaction,and a small amount of gas such as CO and CO2 was generated;while under the condition of adding oxygen,the decomposition products of CF4 were mainly F2 and CO2,and there was no solid carbon in the reactor.The influence of metal electrodes in the plasma degradation process was discussed,and the plasma treatment process was considered as a whole.The spectrum was measured in the plasma negative pressure generation stage and the normal pressure maintenance stage.The type of high-energy particles present in the CF4 was speculated to speculate the decomposition mechanism of CF4.In the early stage of the plasma degradation reaction,the decomposition of CF4 mainly produces a large amount of CFi and F,while during atmospheric pressure degradation,due to the continuous rise of the plasma temperature,CFi would further decompose to produce C and F;when the oxygen was added,COFi will be formed from CFi and finally converted into CO and CO2,and it would be basically converted into CO2 when the oxygen was excessive;F and F atom would combine to become F2.This paper systematically evaluates the ability of microwave standing wave plasma to degrade high-concentration CF4 at atmospheric pressure,provided an effective solution to the problem of eliminating high-concentration CF4,and provided theoretical support for the application of this program in industry so that plasma decomposition technology would have further developed.