In previous studies on plasma-particle interaction, as far as we know, the rf plasma flow and temperature fields are all simulated by the non-self-consistent one-dimensional electromagnetic (1-D EM) field model. In th...In previous studies on plasma-particle interaction, as far as we know, the rf plasma flow and temperature fields are all simulated by the non-self-consistent one-dimensional electromagnetic (1-D EM) field model. In the present paper, the complete self-consistent two-dimensional electromagnetic (2-D EM) field model in- corporating the axial Lorentz force component, which is neglected in the 1-D model, is firstly adopted to calculate the aluminium particle trajectory and thermal history in atmospheric rf Ar plasma with the particle evaporation effect included. The cru- cial effect of reverse flow within the coil region on the particle trajectory is discovered and the results show that the 2-D EM field model must be adopted instead of the 1-D model when the plasma-particle interaction is studied. The effect of carrier gas flux on the particle movement and heating are also studied, resulting in some useful conclusions for both plasma theory and application.展开更多
This paper deals with the topic of RF plasma sources and their application inhigh-power neutral beam heating systems for nuclear fusion devices. RF sources represent aninteresting alternative to the conventional arc d...This paper deals with the topic of RF plasma sources and their application inhigh-power neutral beam heating systems for nuclear fusion devices. RF sources represent aninteresting alternative to the conventional arc discharge sources. Due to the absence of hotfilaments they exhibit an inherent simplicity both in mechanical and electrical aspects andconsequently offer advantages in terms of cost savings, gain in availability and reliability andreduced maintenance. This renders the RF plasma source attractive for any long pulse (> 10 sec) NBIsystem and in particular for the ITER NBI system. The latter, however, requires that the RF plasmasource is also capable of delivering negative rather than positive hydrogen ions. In the first partof the paper the types, characteristics and operation experience of RF plasma sources for positiveions in operation are described. The second part is devoted to the development for ITER NBI: thebasic requirements, physics and technology issues and the present status are discussed.展开更多
In this study,numerical simulation and discharge current tests were conducted on an inductively coupled radio frequency(RF)plasma cathode.Numerical simulations and experimental measurements were performed to study the...In this study,numerical simulation and discharge current tests were conducted on an inductively coupled radio frequency(RF)plasma cathode.Numerical simulations and experimental measurements were performed to study the factors influencing the electron extraction characteristics,including the gas type,gas flow,input power and extracting voltage.The simulation results were approximately consistent with the experimental results.We experimentally found that the RF input power mainly determines the extracted electron current.An electron current greater than 1 A was acquired at 270 W(RF input power),2.766 sccm(xenon gas).Our results prove that an inductively coupled RF plasma cathode can be reasonable and feasible,particularly for low power electric propulsion devices.展开更多
Organosilicone thin films were prepared through plasma polymerization(pp)in a plasma enhance chemical vapour deposition(PECVD)system,utilizing hexamethyldisilazane(HMDSN)as a monomer precursor,at varying distances(25 ...Organosilicone thin films were prepared through plasma polymerization(pp)in a plasma enhance chemical vapour deposition(PECVD)system,utilizing hexamethyldisilazane(HMDSN)as a monomer precursor,at varying distances(25 mm,35 mm,45 mm,55 mm,and 65 mm)from the plasma source to the substrate.Research has examined how the distance between the substrate and plasma source impacts the properties of thin films,including their thickness,surface morphology,and photoluminescence(PL).It was discovered that as the distance increased,both film thickness and PL intensity also increased.Additionally,the film was observed to be more uniform and smoother when deposited 45 mm below the plasma source.展开更多
Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a for...Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm-3 to 11.041 g cm-3. Alloying element tantalum can reduce the tendency to micro- crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta （%wt） powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.展开更多
A simple method for measuring RF plasma parameters by means of a DC-biased Langmuir probe is developed. The object of this paper is to ensure the reliability of this method by using the other methods with different pr...A simple method for measuring RF plasma parameters by means of a DC-biased Langmuir probe is developed. The object of this paper is to ensure the reliability of this method by using the other methods with different principles. First, Langmuir probe current response on RF voltage superimposed to DC biased probe was examined in DC plasmas. Next, probe current response of DC biased probe in RF plasmas was studied and compared with the first experiment. The results were confirmed by using an emissive prove method, an ion acoustic wave method, and a square pulse response method. The method using a simple Langmuir probe is useful and convenient for measuring electron temperature , electron density , time-averaged space potential , and amplitude of space potential oscillation in RF plasmas with a frequency of the order of .展开更多
Spherical tungsten and titanium powders were prepared by radio frequency inductively coupled plasma torch with irregular shaped tungsten and titanium hydride （TiH2） powders, respectively. The effect of the feed rate...Spherical tungsten and titanium powders were prepared by radio frequency inductively coupled plasma torch with irregular shaped tungsten and titanium hydride （TiH2） powders, respectively. The effect of the feed rate on spheroidization efficiency was investigated. The phase composition, oxygen content, morphology, and particle size distribution of the powders before and after spheroidization were characterized by X-ray diffraction （XRD）, nitrogen/oxygen analyzer, scanning electron microscopy （SEM）, and laser micron sizer （LMS）. The results show that both kinds of plasma-processed powders have good dispersity, smooth surface, and single phase. A maximum of 100 % of spheroidization efficiency can be achieved at a lower feed rate. The spherical titanium powder obtained by the plasma treatment consists of particles with mean diameter of 33.34 gin, while the mean diameter of ori- ginal Till2 powder is 136.56 μm. The apparent density and flowability of the spherical tungsten powder are 6.3 g.cm-3 and 0.16 s.g-1, respectively. The apparent density and flowability of the spherical titanium powder are 2.8 g.cm-3 and 0.52 s.g-1, respectively. With the increase of the feed rate, the sphemidization efficiency of raw powders drops gradually.展开更多
Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a pr...Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a precursor containing Ni（～5‐μm diameter） and CeO2（～200‐nm diameter）powders were heated simultaneously using an RF plasma at a power level of ～52 kVA and a powder feeding rate of ～120 g/h. From the X‐ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles（ 50‐nm diameter） on their surfaces. The catalytic performance was evaluated under atmospheric pressure at 500 °C and a CH4：O2 molar ratio of 2：1 with Ar diluent. Although the Ni content was high（～50 mol%）, the experimental results reveal a methane conversion rate of 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on‐stream test at 550 °C for 24 h.However, at 750 °C, the on‐stream test revealed the formation of filament‐like carbons with an increased methane conversion rate over 90%.展开更多
Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposi-tion (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical the...Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposi-tion (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical thermodynamic equilibrium in the system, a computer program based on chemical thermodynamics was used to cal-culate the compositions of the system at different initial concentrations and final temperatures. At first, five elements and thirty-four species were considered. The effects of temperatures, and concentrations of ammonia, hydrogen and nitrogen on the equilibrium compositions were analyzed. It was found that the optimal reaction temperature range should be 1200 to 1500 K to obtain the highest conversion and yield of Si3N4. The inlet position of ammonia should be lower than that of silicon tetrachloride, and both should be located at the tail of the plasma torch. The best mole ratio of ammonia to silicon tetrachloride was found to be about 6. Later, the influences of water (and oxygen) were considered, and 17 additional species were included in the computations. It was found that oxygen or water content in the raw materials should be as low as possible in order to have high nitride content in the produced Si3N4. Nitrogen or hydrogen might be used to replace some or even all the argon to improve the yield of silicon nitride and reduce the cost. The ratio of ammonia to silicon tetrachloride should be high enough to obtain high conversion, but not exces-sively high to reduce the oxygen content due to the existence of water in ammonia. The simulated results were veri-fied by experiments.展开更多
Improvement of the bonding strength and durability between the dentin surface and the composite resin is a challenging job in dentistry. In this paper, a radio-frequency atmosphericpressure glow discharge(RF-APGD) pla...Improvement of the bonding strength and durability between the dentin surface and the composite resin is a challenging job in dentistry. In this paper, a radio-frequency atmosphericpressure glow discharge(RF-APGD) plasma jet is employed for the treatment of the acid-etched dentin surfaces used for the composite restoration. The properties of the plasma treated dentin surfaces and the resin–dentin interfaces are analyzed using the x-ray photoemission spectroscopy, contact angle goniometer, scanning electron microscope and microtensile tester.The experimental results show that, due to the abundant chemically reactive species existing in the RF-APGD plasma jet under a stable and low energy input operating mode, the contact angle of the plasma-treated dentin surfaces decreases to a stable level with the increase of the atomic percentage of oxygen in the specimens; the formation of the long resin tags in the scattered clusters and the hybrid layers at the resin–dentin interfaces significantly improve the bonding strength and durability. These results indicate that the RF-APGD plasma jet is an effective tool for modifying the chemical properties of the dentin surfaces, and for improving the immediate bonding strength and the durability of the resin-dentin bonding in dentistry.展开更多
This paper reports the effects of long- distance and direct argon radio frequency (RF) plasma surface treatment on polyvinyl chloride (PVC) films in terms of changes in surface wettability and surface chemistry. The s...This paper reports the effects of long- distance and direct argon radio frequency (RF) plasma surface treatment on polyvinyl chloride (PVC) films in terms of changes in surface wettability and surface chemistry. The surface properties are char- acterized by the water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scan- ning electron microscopy (SEM). The mechanism is further analyzed and the role of all kinds of active species, e.g. electrons, ions and free radicals in- volved in plasma surface modification is further evaluated. Results show that the long-distance and direct RF plasma treatments modify the PVC surface in morphology and composition, and both modifica- tions cause surface oxidation of PVC films, in the forming of functional groups enhancing polymer wet- tability. The effect of the long-distance argon RF plasma is more notable. This suggests that long-distance argon RF plasma could restrain the ion and electron eroding effect and enhance free radical reaction.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
The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been inves- tigated experimentally. As the pressure increases, the shapes of charge-voltage Lissajous curves vary, a...The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been inves- tigated experimentally. As the pressure increases, the shapes of charge-voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa, the electron temperature is estimated to be 4.139 eV, the electron density and the vibrational temperature of plasma are /peak /lPeak which describes the electron temper- 4.71 x 10^11 cm-3 and 1.27 eV, respectively. The ratio of spectral lines ＂391.4/＇380.5 ature hardly changes when the pressure varies between 5000-30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spec- trum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin-pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.展开更多
Measurement of the oxygen dissociation fraction in RF low pressure oxygen/argon plasma using optical emission spectrometry is presented. The oxygen dissociation fraction and its evolutions as functions of operational ...Measurement of the oxygen dissociation fraction in RF low pressure oxygen/argon plasma using optical emission spectrometry is presented. The oxygen dissociation fraction and its evolutions as functions of operational parameters were determined using argon as the actinometer. At a pressure of 30 Pa, the oxygen dissociation fraction decreased from 13.4% to 9.5% as the input power increased from 10 W to 70 W. At an input power of 50 W, the oxygen dissociation fraction decreased from 12.3% to 7.7% when the gas pressure increased from 10 Pa to 40 Pa. The influences of operational parameters on the generation of atomic oxygen were also discussed.展开更多
Surfaces of optical elements are deposited by antireflection coatings (ARCs) to decrease the reflection of light. Surface needs treatment before depositing the ARC one of treatment processes by plasma for adhesion imp...Surfaces of optical elements are deposited by antireflection coatings (ARCs) to decrease the reflection of light. Surface needs treatment before depositing the ARC one of treatment processes by plasma for adhesion improvement and surface hardening. A comparison of RF and DC glow discharges treated CR-39 polymer films gives insight into the mechanism of these surface processes. The surface properties of the plasma-treated samples are examined by microscopy techniques include contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared (IR) spectroscopy and refractive index measurements. Results show that the plasma treatment modifies the polymer surface in both composition and morphology. It is found that the surface wettability is enhanced after plasma treatment. It is found that, RF plasma is more effective than DC plasma in CR-39 surface modification, as it implants more oxygen atoms into the surface and makes the contact angle declining to a lower level.展开更多
The tokamak plasma flows induced by the local radio frequency （RF） forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant pa...The tokamak plasma flows induced by the local radio frequency （RF） forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term （i.e. the parallel component of the resonant ponderomotive forces）. Different momentum balance relations are em- ployed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated.展开更多
Hα（Balmer-alpha）, Hβ （Balmer-beta） and Hγ （Balmer-gamma） spectral line inten- sities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectra...Hα（Balmer-alpha）, Hβ （Balmer-beta） and Hγ （Balmer-gamma） spectral line inten- sities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectral lines are detected by increasing the input power （0-6 kW） of ICPs （inductively coupled plasmas）. With the increase of net input power, the intensity of Hα im- proves rapidly （0-2 kW）, and then reaches its dynamic equilibrium; the intensities of Hβ can be divided into three processes： obvious increase （0-2 kW）, rapid increase （2-4 kW）, almost constant （4-6 kW）; while the intensities of Hγ increase very slowly. The energy levels of the excited hydro- gen atoms and the splitting energy levels produced by an obvious Stark effect play an important role in the results.展开更多
为解决大口径红外元件类金刚石(Diamond-Like Carbon,DLC)膜层的镀膜工艺难题,满足长焦距、大视场光学系统的技术需求,采用射频等离子增强化学气相沉积(Radio Frequency Plasma Enhanced Chemical Vapor Deposition,RF-PECVD)制备工艺方...为解决大口径红外元件类金刚石(Diamond-Like Carbon,DLC)膜层的镀膜工艺难题,满足长焦距、大视场光学系统的技术需求,采用射频等离子增强化学气相沉积(Radio Frequency Plasma Enhanced Chemical Vapor Deposition,RF-PECVD)制备工艺方法,基于容性耦合等离子体驻波效应及趋肤效应机理,在大口径红外元件基底制备了红外类金刚石膜。通过优化改进等离子体电场均匀性,有效降低了膜层应力并提升了其可靠性及膜层厚度均匀性。依据光学薄膜元件环境试验要求进行了高温、低温及湿热等试验,试验后膜层未出现膜层起皮、褶皱及脱落现象。结果表明,大口径红外类金刚石膜具备良好抗温度冲击及腐蚀等特性,满足光学元件镀膜的正常需求,进一步拓展了大口径DLC薄膜的制备工艺能力。展开更多
文摘In previous studies on plasma-particle interaction, as far as we know, the rf plasma flow and temperature fields are all simulated by the non-self-consistent one-dimensional electromagnetic (1-D EM) field model. In the present paper, the complete self-consistent two-dimensional electromagnetic (2-D EM) field model in- corporating the axial Lorentz force component, which is neglected in the 1-D model, is firstly adopted to calculate the aluminium particle trajectory and thermal history in atmospheric rf Ar plasma with the particle evaporation effect included. The cru- cial effect of reverse flow within the coil region on the particle trajectory is discovered and the results show that the 2-D EM field model must be adopted instead of the 1-D model when the plasma-particle interaction is studied. The effect of carrier gas flux on the particle movement and heating are also studied, resulting in some useful conclusions for both plasma theory and application.
文摘This paper deals with the topic of RF plasma sources and their application inhigh-power neutral beam heating systems for nuclear fusion devices. RF sources represent aninteresting alternative to the conventional arc discharge sources. Due to the absence of hotfilaments they exhibit an inherent simplicity both in mechanical and electrical aspects andconsequently offer advantages in terms of cost savings, gain in availability and reliability andreduced maintenance. This renders the RF plasma source attractive for any long pulse (> 10 sec) NBIsystem and in particular for the ITER NBI system. The latter, however, requires that the RF plasmasource is also capable of delivering negative rather than positive hydrogen ions. In the first partof the paper the types, characteristics and operation experience of RF plasma sources for positiveions in operation are described. The second part is devoted to the development for ITER NBI: thebasic requirements, physics and technology issues and the present status are discussed.
基金supported by Joint Fund for Equipment Preresearch and Aerospace Science and Technology(No.6141B061203)。
文摘In this study,numerical simulation and discharge current tests were conducted on an inductively coupled radio frequency(RF)plasma cathode.Numerical simulations and experimental measurements were performed to study the factors influencing the electron extraction characteristics,including the gas type,gas flow,input power and extracting voltage.The simulation results were approximately consistent with the experimental results.We experimentally found that the RF input power mainly determines the extracted electron current.An electron current greater than 1 A was acquired at 270 W(RF input power),2.766 sccm(xenon gas).Our results prove that an inductively coupled RF plasma cathode can be reasonable and feasible,particularly for low power electric propulsion devices.
基金the AECS for its financial support of this study
文摘Organosilicone thin films were prepared through plasma polymerization(pp)in a plasma enhance chemical vapour deposition(PECVD)system,utilizing hexamethyldisilazane(HMDSN)as a monomer precursor,at varying distances(25 mm,35 mm,45 mm,55 mm,and 65 mm)from the plasma source to the substrate.Research has examined how the distance between the substrate and plasma source impacts the properties of thin films,including their thickness,surface morphology,and photoluminescence(PL).It was discovered that as the distance increased,both film thickness and PL intensity also increased.Additionally,the film was observed to be more uniform and smoother when deposited 45 mm below the plasma source.
文摘Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated. By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from 6.916 g cm-3 to 11.041 g cm-3. Alloying element tantalum can reduce the tendency to micro- crack during tungsten laser melting and rapid solidification process. Spherical W-6Ta （%wt） powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.
文摘A simple method for measuring RF plasma parameters by means of a DC-biased Langmuir probe is developed. The object of this paper is to ensure the reliability of this method by using the other methods with different principles. First, Langmuir probe current response on RF voltage superimposed to DC biased probe was examined in DC plasmas. Next, probe current response of DC biased probe in RF plasmas was studied and compared with the first experiment. The results were confirmed by using an emissive prove method, an ion acoustic wave method, and a square pulse response method. The method using a simple Langmuir probe is useful and convenient for measuring electron temperature , electron density , time-averaged space potential , and amplitude of space potential oscillation in RF plasmas with a frequency of the order of .
基金financially supported by the National Natural Science Foundation of China(No.51274039)the Research Fund for the Doctoral Program of Higher Education of China(No.20120006110007)
文摘Spherical tungsten and titanium powders were prepared by radio frequency inductively coupled plasma torch with irregular shaped tungsten and titanium hydride （TiH2） powders, respectively. The effect of the feed rate on spheroidization efficiency was investigated. The phase composition, oxygen content, morphology, and particle size distribution of the powders before and after spheroidization were characterized by X-ray diffraction （XRD）, nitrogen/oxygen analyzer, scanning electron microscopy （SEM）, and laser micron sizer （LMS）. The results show that both kinds of plasma-processed powders have good dispersity, smooth surface, and single phase. A maximum of 100 % of spheroidization efficiency can be achieved at a lower feed rate. The spherical titanium powder obtained by the plasma treatment consists of particles with mean diameter of 33.34 gin, while the mean diameter of ori- ginal Till2 powder is 136.56 μm. The apparent density and flowability of the spherical tungsten powder are 6.3 g.cm-3 and 0.16 s.g-1, respectively. The apparent density and flowability of the spherical titanium powder are 2.8 g.cm-3 and 0.52 s.g-1, respectively. With the increase of the feed rate, the sphemidization efficiency of raw powders drops gradually.
基金supported by Renewable Energy Technologies Development Program(No.2008NFC02J0200002009)Technology Innovation Program(No.10048910)funded by the Ministry of Trade,Industry and Energy(MI,Korea)
文摘Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a precursor containing Ni（～5‐μm diameter） and CeO2（～200‐nm diameter）powders were heated simultaneously using an RF plasma at a power level of ～52 kVA and a powder feeding rate of ～120 g/h. From the X‐ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles（ 50‐nm diameter） on their surfaces. The catalytic performance was evaluated under atmospheric pressure at 500 °C and a CH4：O2 molar ratio of 2：1 with Ar diluent. Although the Ni content was high（～50 mol%）, the experimental results reveal a methane conversion rate of 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on‐stream test at 550 °C for 24 h.However, at 750 °C, the on‐stream test revealed the formation of filament‐like carbons with an increased methane conversion rate over 90%.
文摘Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposi-tion (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical thermodynamic equilibrium in the system, a computer program based on chemical thermodynamics was used to cal-culate the compositions of the system at different initial concentrations and final temperatures. At first, five elements and thirty-four species were considered. The effects of temperatures, and concentrations of ammonia, hydrogen and nitrogen on the equilibrium compositions were analyzed. It was found that the optimal reaction temperature range should be 1200 to 1500 K to obtain the highest conversion and yield of Si3N4. The inlet position of ammonia should be lower than that of silicon tetrachloride, and both should be located at the tail of the plasma torch. The best mole ratio of ammonia to silicon tetrachloride was found to be about 6. Later, the influences of water (and oxygen) were considered, and 17 additional species were included in the computations. It was found that oxygen or water content in the raw materials should be as low as possible in order to have high nitride content in the produced Si3N4. Nitrogen or hydrogen might be used to replace some or even all the argon to improve the yield of silicon nitride and reduce the cost. The ratio of ammonia to silicon tetrachloride should be high enough to obtain high conversion, but not exces-sively high to reduce the oxygen content due to the existence of water in ammonia. The simulated results were veri-fied by experiments.
基金supported by National Natural Science Foundation of China (Nos. 11475103 and 81200805)Beijing Natural Science Foundation (No. 7162204)
文摘Improvement of the bonding strength and durability between the dentin surface and the composite resin is a challenging job in dentistry. In this paper, a radio-frequency atmosphericpressure glow discharge(RF-APGD) plasma jet is employed for the treatment of the acid-etched dentin surfaces used for the composite restoration. The properties of the plasma treated dentin surfaces and the resin–dentin interfaces are analyzed using the x-ray photoemission spectroscopy, contact angle goniometer, scanning electron microscope and microtensile tester.The experimental results show that, due to the abundant chemically reactive species existing in the RF-APGD plasma jet under a stable and low energy input operating mode, the contact angle of the plasma-treated dentin surfaces decreases to a stable level with the increase of the atomic percentage of oxygen in the specimens; the formation of the long resin tags in the scattered clusters and the hybrid layers at the resin–dentin interfaces significantly improve the bonding strength and durability. These results indicate that the RF-APGD plasma jet is an effective tool for modifying the chemical properties of the dentin surfaces, and for improving the immediate bonding strength and the durability of the resin-dentin bonding in dentistry.
基金supported by the National Natural Science Foundation of China(Grant No.20174030)the specialized research Fund for the Doctoral Program of Higher Education(20010698007)the Scientific Research Star Fund for the Study Abroad Returnee and the Key Scientific Technique Item of Shaanxi Province(2001[345]).
文摘This paper reports the effects of long- distance and direct argon radio frequency (RF) plasma surface treatment on polyvinyl chloride (PVC) films in terms of changes in surface wettability and surface chemistry. The surface properties are char- acterized by the water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scan- ning electron microscopy (SEM). The mechanism is further analyzed and the role of all kinds of active species, e.g. electrons, ions and free radicals in- volved in plasma surface modification is further evaluated. Results show that the long-distance and direct RF plasma treatments modify the PVC surface in morphology and composition, and both modifica- tions cause surface oxidation of PVC films, in the forming of functional groups enhancing polymer wet- tability. The effect of the long-distance argon RF plasma is more notable. This suggests that long-distance argon RF plasma could restrain the ion and electron eroding effect and enhance free radical reaction.
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Project supported by the National Natural Science Foundation of China(Grant Nos.11472306,51336011,and 51407197)
文摘The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been inves- tigated experimentally. As the pressure increases, the shapes of charge-voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa, the electron temperature is estimated to be 4.139 eV, the electron density and the vibrational temperature of plasma are /peak /lPeak which describes the electron temper- 4.71 x 10^11 cm-3 and 1.27 eV, respectively. The ratio of spectral lines ＂391.4/＇380.5 ature hardly changes when the pressure varies between 5000-30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spec- trum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin-pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.
基金supported by the Beijing Municipal Education Commission of China(No.KM201010015005)Beijing Key Laboratory of Printing & Packaging Materials and Technology of Beijing Institute of Graphic Communication of China(No.KF201005)
文摘Measurement of the oxygen dissociation fraction in RF low pressure oxygen/argon plasma using optical emission spectrometry is presented. The oxygen dissociation fraction and its evolutions as functions of operational parameters were determined using argon as the actinometer. At a pressure of 30 Pa, the oxygen dissociation fraction decreased from 13.4% to 9.5% as the input power increased from 10 W to 70 W. At an input power of 50 W, the oxygen dissociation fraction decreased from 12.3% to 7.7% when the gas pressure increased from 10 Pa to 40 Pa. The influences of operational parameters on the generation of atomic oxygen were also discussed.
文摘Surfaces of optical elements are deposited by antireflection coatings (ARCs) to decrease the reflection of light. Surface needs treatment before depositing the ARC one of treatment processes by plasma for adhesion improvement and surface hardening. A comparison of RF and DC glow discharges treated CR-39 polymer films gives insight into the mechanism of these surface processes. The surface properties of the plasma-treated samples are examined by microscopy techniques include contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared (IR) spectroscopy and refractive index measurements. Results show that the plasma treatment modifies the polymer surface in both composition and morphology. It is found that the surface wettability is enhanced after plasma treatment. It is found that, RF plasma is more effective than DC plasma in CR-39 surface modification, as it implants more oxygen atoms into the surface and makes the contact angle declining to a lower level.
基金supported by National Natural Science Foundation of China(Nos.11405218,11325524,11375235 and 11261140327)in part by the National Magnetic Confinement Fusion Science Program of China(Nos.2013GB111002,2013GB112001 and 2013GB112010)the Program of Fusion Reactor Physics and Digital Tokamak with the CAS"One-Three-Five"Strategic Planning
文摘The tokamak plasma flows induced by the local radio frequency （RF） forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term （i.e. the parallel component of the resonant ponderomotive forces）. Different momentum balance relations are em- ployed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2011GB108011 and 2010GB103001)the Major International(Regional) Project Cooperation and Exchanges(No.11320101005)
文摘Hα（Balmer-alpha）, Hβ （Balmer-beta） and Hγ （Balmer-gamma） spectral line inten- sities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectral lines are detected by increasing the input power （0-6 kW） of ICPs （inductively coupled plasmas）. With the increase of net input power, the intensity of Hα im- proves rapidly （0-2 kW）, and then reaches its dynamic equilibrium; the intensities of Hβ can be divided into three processes： obvious increase （0-2 kW）, rapid increase （2-4 kW）, almost constant （4-6 kW）; while the intensities of Hγ increase very slowly. The energy levels of the excited hydro- gen atoms and the splitting energy levels produced by an obvious Stark effect play an important role in the results.
文摘为解决大口径红外元件类金刚石(Diamond-Like Carbon,DLC)膜层的镀膜工艺难题,满足长焦距、大视场光学系统的技术需求,采用射频等离子增强化学气相沉积(Radio Frequency Plasma Enhanced Chemical Vapor Deposition,RF-PECVD)制备工艺方法,基于容性耦合等离子体驻波效应及趋肤效应机理,在大口径红外元件基底制备了红外类金刚石膜。通过优化改进等离子体电场均匀性,有效降低了膜层应力并提升了其可靠性及膜层厚度均匀性。依据光学薄膜元件环境试验要求进行了高温、低温及湿热等试验,试验后膜层未出现膜层起皮、褶皱及脱落现象。结果表明,大口径红外类金刚石膜具备良好抗温度冲击及腐蚀等特性,满足光学元件镀膜的正常需求,进一步拓展了大口径DLC薄膜的制备工艺能力。
