Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The...Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The potential structure inside the torch and its dependence on the plasma current and gas flow rate are also investigated. The arc voltage is seen to exhibit negative characteristic for a current below 150 A and positive characteristic above that current value. The voltage drop near the electrodes is found to decrease with the increase in plasma current. 25~ of the total voltage is dropped near the cathode at a plasma current of 50 A and a argon plasma gas flow rate of 10 liter per minute (LPM), and it decreases to 12% with the current increasing to 300 A, and to 17% with a gas flow rate of 25 LPM. The variation in the torch efficiency with the gas flow rate and plasma current is also reported. The efficiency of the torch is found to be between 36% and 48%. In addition, the plasma gas temperature at various positions of the reactor and for different currents and voltages are measured by calorimetric estimation with a heat balance technique.展开更多
A Magnetic DC plasma torch has been developed. Magnetic field distributions of solenoid coils have been calculated electrodynamically. For Ar +H2 plasma, the effects of an akial magnetic field and gas flow rate on the...A Magnetic DC plasma torch has been developed. Magnetic field distributions of solenoid coils have been calculated electrodynamically. For Ar +H2 plasma, the effects of an akial magnetic field and gas flow rate on the characttristics of the plasma jet were studied. Electron temperature, density and plasma velocity at 80 mm from the nozzle have been measured using a floating double probe and a Mach probe. The values of the heat fluxes to substrate were derived from experimental data.展开更多
The contacting interface between the substrate and water-cooled base is vital to the substrate temperature during diamond films deposition by a DC (direct current) plasma jet. The effects of the solid contacting are...The contacting interface between the substrate and water-cooled base is vital to the substrate temperature during diamond films deposition by a DC (direct current) plasma jet. The effects of the solid contacting area,conductive materials and fixing between the substrate and the base were investigated without affecting the other parameters. Experimental results indicated that the preferable solid contacting area was more than 60% of total contacting areal; the particular Sn-Pb alloy was more suitable for conducting heat and the concentric fixing ring was a better setting for controlling the substrate temperature. The result was explained in terms of the variable thermal contact resistance at the interface between substrate and base. The diamond films were analyzed by scanning electron microscopy (SEM) for morphology, X-ray diffraction (XRD) for the intensity of characteristic spectroscopy and Raman spectroscopy for structure.展开更多
TiN coating samples with narrow stitch or deep hole of different sizes and real dies with complex shape were processed by a larger scale pulsed plasma enhanced CVD(PECVD) reactor. Scanning electron microscopy, optical...TiN coating samples with narrow stitch or deep hole of different sizes and real dies with complex shape were processed by a larger scale pulsed plasma enhanced CVD(PECVD) reactor. Scanning electron microscopy, optical microscopy, Vickers hardness and interfacial adhesion tests were conducted to find the relation between the microstructure and properties of TiN coating on a flat and an inner surface. The results indicate that the inner wall of holes ( d >2 mm) and inner surface of narrow stitches ( d >3 mm) can be coated with the aid of pulsed DC plasma in an industrial scale reactor. The quality of coatings on different surfaces is almost the same. The coating was applied to aluminum extrusion mould, and the mould life was increased at least by one time.展开更多
DC plasma is a very promising technology for processing different materials, and is becoming especially interesting when low environmental impact and high-performance treatments are needed. Some of the intrinsic chara...DC plasma is a very promising technology for processing different materials, and is becoming especially interesting when low environmental impact and high-performance treatments are needed. Some of the intrinsic characteristics of DC plasma technology, which make it suitable for powder metallurgy (PM) and powder injection molding (PIM) parts production, are low- pressure processing and plasma environment high reactivity. Moreover it can be considered as a highly competitive green technology. In this work, an overview of some of the important DC plasma techniques applied to PM and PIM parts processing is presented. Emphasis is given to the descriptions of the main characteristics and the technique potentials of plasma-assisted nitriding, plasma-assisted thermal debinding, plasma-assisted sintering, and simultaneously plasma-assisted sintering and surface alloying. The aspects presented and discussed in this paper indicate that DC plasma processes are promising and competitive techniques for PM and PIM parts processing.展开更多
This paper is about the diamond films fabricated by dc plasma jet method. Scanning electron microscopy(SEM), X-ray diffractometry and Roman scattering spectroscopy have been used to characterize the diamond films depo...This paper is about the diamond films fabricated by dc plasma jet method. Scanning electron microscopy(SEM), X-ray diffractometry and Roman scattering spectroscopy have been used to characterize the diamond films deposited under different experimental conditions and different substrates.展开更多
Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view tow...Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current (AC) component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc.展开更多
在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后...在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。展开更多
This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the depo...This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar) could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.展开更多
Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and th...Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.展开更多
The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and ...The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.展开更多
In order to treat hazardous municipal solid waste incinerator's (MSWI) fly ash, a new DC arc plasma furnace was developed. Taking an arc of 100 V/1000 A DC as an example, the heat transfer characteristics of the DC...In order to treat hazardous municipal solid waste incinerator's (MSWI) fly ash, a new DC arc plasma furnace was developed. Taking an arc of 100 V/1000 A DC as an example, the heat transfer characteristics of the DC arc plasma, ablation of electrodes, heat properties of the fly ash during melting, heat transfer characteristics of the flue gas, and heat loss of the furnace were analyzed based on the energy conservation law, so as to achieve the total heat information and energy balance during plasma processing, and to provide a theoretical basis for an optimized design of the structure and to improve energy efficiency.展开更多
We developed a one-dimensional hybrid model to simulate the DC/RF combined driven capacitively coupled plasma for argon discharges. The numerical results are used to analyze the influence of the DC source on the plasm...We developed a one-dimensional hybrid model to simulate the DC/RF combined driven capacitively coupled plasma for argon discharges. The numerical results are used to analyze the influence of the DC source on the plasma density distribution, ion energy distributions (IEDs) and ion angle distributions (IADs) on both the RF and DC electrodes. The increase in DC voltage drives more high-energy ions to the electrode applied to the DC source, which makes the IEDs at the DC electrode shift towards higher energy, and the peaks in the IADs shift towards small angle regions. At the same time, it also decreases the ion energy at the RF electrode and enlarges the incident angles of the ions, which strike the RF electrode.展开更多
A direct current(DC) source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using ...A direct current(DC) source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using optical and electrical methods,the discharge characteristics are investigated for the diffuse plasma plume.Results indicate that the discharge has a pulse characteristic,under the excitation of a DC voltage.The discharge pulse corresponds to the propagation process of a plasma bullet travelling from the anode to the cathode.It is found that,with an increment of the gas flow rate,both the discharge plume length and the current peak value of the pulsed discharge decrease in the laminar flow mode,reach their minima at about1.5 L/min,and then slightly increase in the turbulent mode.However,the frequency of the pulsed discharge increases in the laminar mode with increasing the argon flow rate until the argon flow rate equals to about 1.5 L/min,and then slightly decreases in the turbulent mode.展开更多
Under argon DC glow plasma, the nitrogen removal from molten steel was studied. The experimental result showed that nitrogen mass percent could be reduced to 0000 8%. The change of polarity had no impact on nitrogen r...Under argon DC glow plasma, the nitrogen removal from molten steel was studied. The experimental result showed that nitrogen mass percent could be reduced to 0000 8%. The change of polarity had no impact on nitrogen removal when the nitrogen mass percent was low. The mechanism of denitrogenation of molten steel under argon DC glow plasma was discussed.展开更多
Optical emission spectroscopy (OES) was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition (CVD). C2 radical was ...Optical emission spectroscopy (OES) was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition (CVD). C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments (DOE). An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.展开更多
A three dimensional steady-state magnetohydrodynamic model is developed for the arc plasma in a DC submerged electric arc furnace for the production of fused MgO. The arc is generated in a small semi-enclosed space fo...A three dimensional steady-state magnetohydrodynamic model is developed for the arc plasma in a DC submerged electric arc furnace for the production of fused MgO. The arc is generated in a small semi-enclosed space formed by the graphite electrode, the molten bath and unmelted raw materials. The model is first used to solve a similar problem in a steel making furnace, and the calculated results are found to be in good agreement with the published measurements. The behavior of arcs with different arc lengths is also studied in the furnace for MgO production. From the distribution of the arc pressure on the bath surface it is shown that the arc plasma impingement is large enough to cause a crater-like depression on the surface of the MgO bath. The circulation of the high temperature air under the electrode may enhance the arc efficiency, especially for a shorter arc.展开更多
In this paper, the double-discharge plasma generated by radio frequency (RF) and direct current (DC) has been investigated. In comparison with their single-frequency counterpart, the interaction between the two ex...In this paper, the double-discharge plasma generated by radio frequency (RF) and direct current (DC) has been investigated. In comparison with their single-frequency counterpart, the interaction between the two excitations is significant and beneficial. The results show that the RF discharge can effectively increase the DC discharge current and decrease the DC voltage; meanwhile the DC discharge is favorable to feed abundant high energy seed electrons to the ICP discharge sustaining at 13.56 MHz for the latter to acquire higher plasma density and lower plasma potential by increasing the ionization rate. The innovative design has been demonstrated to facilitate more homogeneous performance with higher plasma density.展开更多
文摘Dependence of the current-voltage characteristics of a non-transferred DC cascaded plasma torch used for nanoparticle synthesis, on the plasma current and the plasma argon gas flow rate are reported in this paper. The potential structure inside the torch and its dependence on the plasma current and gas flow rate are also investigated. The arc voltage is seen to exhibit negative characteristic for a current below 150 A and positive characteristic above that current value. The voltage drop near the electrodes is found to decrease with the increase in plasma current. 25~ of the total voltage is dropped near the cathode at a plasma current of 50 A and a argon plasma gas flow rate of 10 liter per minute (LPM), and it decreases to 12% with the current increasing to 300 A, and to 17% with a gas flow rate of 25 LPM. The variation in the torch efficiency with the gas flow rate and plasma current is also reported. The efficiency of the torch is found to be between 36% and 48%. In addition, the plasma gas temperature at various positions of the reactor and for different currents and voltages are measured by calorimetric estimation with a heat balance technique.
文摘A Magnetic DC plasma torch has been developed. Magnetic field distributions of solenoid coils have been calculated electrodynamically. For Ar +H2 plasma, the effects of an akial magnetic field and gas flow rate on the characttristics of the plasma jet were studied. Electron temperature, density and plasma velocity at 80 mm from the nozzle have been measured using a floating double probe and a Mach probe. The values of the heat fluxes to substrate were derived from experimental data.
基金the National Natural Science Foundation of China for the financial support under the contract Nos.50275076 and 50605032.
文摘The contacting interface between the substrate and water-cooled base is vital to the substrate temperature during diamond films deposition by a DC (direct current) plasma jet. The effects of the solid contacting area,conductive materials and fixing between the substrate and the base were investigated without affecting the other parameters. Experimental results indicated that the preferable solid contacting area was more than 60% of total contacting areal; the particular Sn-Pb alloy was more suitable for conducting heat and the concentric fixing ring was a better setting for controlling the substrate temperature. The result was explained in terms of the variable thermal contact resistance at the interface between substrate and base. The diamond films were analyzed by scanning electron microscopy (SEM) for morphology, X-ray diffraction (XRD) for the intensity of characteristic spectroscopy and Raman spectroscopy for structure.
文摘TiN coating samples with narrow stitch or deep hole of different sizes and real dies with complex shape were processed by a larger scale pulsed plasma enhanced CVD(PECVD) reactor. Scanning electron microscopy, optical microscopy, Vickers hardness and interfacial adhesion tests were conducted to find the relation between the microstructure and properties of TiN coating on a flat and an inner surface. The results indicate that the inner wall of holes ( d >2 mm) and inner surface of narrow stitches ( d >3 mm) can be coated with the aid of pulsed DC plasma in an industrial scale reactor. The quality of coatings on different surfaces is almost the same. The coating was applied to aluminum extrusion mould, and the mould life was increased at least by one time.
文摘DC plasma is a very promising technology for processing different materials, and is becoming especially interesting when low environmental impact and high-performance treatments are needed. Some of the intrinsic characteristics of DC plasma technology, which make it suitable for powder metallurgy (PM) and powder injection molding (PIM) parts production, are low- pressure processing and plasma environment high reactivity. Moreover it can be considered as a highly competitive green technology. In this work, an overview of some of the important DC plasma techniques applied to PM and PIM parts processing is presented. Emphasis is given to the descriptions of the main characteristics and the technique potentials of plasma-assisted nitriding, plasma-assisted thermal debinding, plasma-assisted sintering, and simultaneously plasma-assisted sintering and surface alloying. The aspects presented and discussed in this paper indicate that DC plasma processes are promising and competitive techniques for PM and PIM parts processing.
文摘This paper is about the diamond films fabricated by dc plasma jet method. Scanning electron microscopy(SEM), X-ray diffractometry and Roman scattering spectroscopy have been used to characterize the diamond films deposited under different experimental conditions and different substrates.
基金supported by National Natural Science Foundation of China (Nos.50336010,50276065)
文摘Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current (AC) component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc.
文摘在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。
文摘This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar) could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.
基金National Natural Science Foundation of China(Nos.11675177,11875256)the Anhui Province Scientific and Technological Project(No.1604a0902145).
文摘Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.
基金Projects(U0734001, 50874050) supported by the National Natural Science Foundation of ChinaProjects(2006A11002001, 2007B010600007, 2007B010600043)supported by the Guangdong Provincial Science & Technology Program of ChinaProjects(2006Z2-D0121, 2006Z2-D0131, 2006Z3-D0281) supported by the Guangzhou Civil Science & Technology Program of China
文摘The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.
基金supported by the Knowledge Innovation Project in the Chinese Academy of Sciences (No. O45CF3A211)
文摘In order to treat hazardous municipal solid waste incinerator's (MSWI) fly ash, a new DC arc plasma furnace was developed. Taking an arc of 100 V/1000 A DC as an example, the heat transfer characteristics of the DC arc plasma, ablation of electrodes, heat properties of the fly ash during melting, heat transfer characteristics of the flue gas, and heat loss of the furnace were analyzed based on the energy conservation law, so as to achieve the total heat information and energy balance during plasma processing, and to provide a theoretical basis for an optimized design of the structure and to improve energy efficiency.
基金supported by the Scientific Foundation from Ministry of Education of China (No.N090305004)Doctor Startup Foundation Program of Liaoning Province (No.20111008)
文摘We developed a one-dimensional hybrid model to simulate the DC/RF combined driven capacitively coupled plasma for argon discharges. The numerical results are used to analyze the influence of the DC source on the plasma density distribution, ion energy distributions (IEDs) and ion angle distributions (IADs) on both the RF and DC electrodes. The increase in DC voltage drives more high-energy ions to the electrode applied to the DC source, which makes the IEDs at the DC electrode shift towards higher energy, and the peaks in the IADs shift towards small angle regions. At the same time, it also decreases the ion energy at the RF electrode and enlarges the incident angles of the ions, which strike the RF electrode.
基金supported by National Natural Science Foundation of China(Nos.10805013,11375051)Funds for Distinguished Young Scientists of Hebei Province,China(No.A2012201045)+1 种基金Department of Education for Outstanding Youth Project of China(No.Y2011120)Youth Project of Hebei University of China(No.2011Q14)
文摘A direct current(DC) source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using optical and electrical methods,the discharge characteristics are investigated for the diffuse plasma plume.Results indicate that the discharge has a pulse characteristic,under the excitation of a DC voltage.The discharge pulse corresponds to the propagation process of a plasma bullet travelling from the anode to the cathode.It is found that,with an increment of the gas flow rate,both the discharge plume length and the current peak value of the pulsed discharge decrease in the laminar flow mode,reach their minima at about1.5 L/min,and then slightly increase in the turbulent mode.However,the frequency of the pulsed discharge increases in the laminar mode with increasing the argon flow rate until the argon flow rate equals to about 1.5 L/min,and then slightly decreases in the turbulent mode.
文摘Under argon DC glow plasma, the nitrogen removal from molten steel was studied. The experimental result showed that nitrogen mass percent could be reduced to 0000 8%. The change of polarity had no impact on nitrogen removal when the nitrogen mass percent was low. The mechanism of denitrogenation of molten steel under argon DC glow plasma was discussed.
基金the National High-Tech Research and Development Program of China (No.2002AA305508)the National Natural Science Foundation of China (No.50472095)+1 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars (No.2003-14)Beijing Novel Project (No. 2003A13).]
文摘Optical emission spectroscopy (OES) was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition (CVD). C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments (DOE). An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.
基金supported by the National High Technology Research and Development Program of China (No. 2008AA03A325)
文摘A three dimensional steady-state magnetohydrodynamic model is developed for the arc plasma in a DC submerged electric arc furnace for the production of fused MgO. The arc is generated in a small semi-enclosed space formed by the graphite electrode, the molten bath and unmelted raw materials. The model is first used to solve a similar problem in a steel making furnace, and the calculated results are found to be in good agreement with the published measurements. The behavior of arcs with different arc lengths is also studied in the furnace for MgO production. From the distribution of the arc pressure on the bath surface it is shown that the arc plasma impingement is large enough to cause a crater-like depression on the surface of the MgO bath. The circulation of the high temperature air under the electrode may enhance the arc efficiency, especially for a shorter arc.
基金supported by National Natural Science Foundation of China(No.11475038)
文摘In this paper, the double-discharge plasma generated by radio frequency (RF) and direct current (DC) has been investigated. In comparison with their single-frequency counterpart, the interaction between the two excitations is significant and beneficial. The results show that the RF discharge can effectively increase the DC discharge current and decrease the DC voltage; meanwhile the DC discharge is favorable to feed abundant high energy seed electrons to the ICP discharge sustaining at 13.56 MHz for the latter to acquire higher plasma density and lower plasma potential by increasing the ionization rate. The innovative design has been demonstrated to facilitate more homogeneous performance with higher plasma density.