Direct Current Arc Discharge Plasma Research Articles

A novel approach of waste tires rubber utilization via ambient air direct current arc discharge plasma

Waste tires rubber utilization is one of the most important problems worldwide that affects environmental and energy aspects. In this work, we propose a method for obtaining ultrafine carbon product, as well as mixture of methane and synthesis gas, which is based on the generation of an electric arc plasma in an open-air environment. During arcing the resulting gas flow screens the reaction zone, which prevents the oxidation of the feedstock and synthesis products. This approach allows avoiding a vacuum and gas equipment as a part of a plasma reactor, which greatly simplifies its design and reduces the specific energy consumption. As a result of a series of experiments, two types of products were obtained: 1) ultrafine carbon powder containing micro and nanoscale objects with a graphite-like structure; 2) a mixture of gases, which contains up to 27, 15, and 3 vol% of methane CH4, hydrogen H2 and carbon monoxide CO, respectively.

One-Step Synthesis of SnO2/Carbon Nanotube Nanonests Composites by Direct Current Arc-Discharge Plasma and Its Application in Lithium-Ion Batteries

Tin dioxide (SnO2)-based materials, as anode materials for lithium-ion batteries (LIBs), have been attracting growing research attention due to the high theoretical specific capacity. However, the complex synthesis process of chemical methods and the pollution of chemical reagents limit its commercialization. The new material synthesis method is of great significance for expanding the application of SnO2-based materials. In this study, the SnO2/carbon nanotube nanonests (SnO2/CNT NNs) composites are synthesized in one step by direct current (DC) arc-discharge plasma; compared with conventional methods, the plasma synthesis achieves a uniform load of SnO2 nanoparticles on the surfaces of CNTs while constructing the CNTs conductive network. The SnO2/CNT NNs composites are applied in LIBs, it can be found that the nanonest-like CNT conductive structure provides adequate room for the volume expansion and also helps to transfer the electrons. Electrochemical measurements suggests that the SnO2/CNT NNscomposites achieve high capacity, and still have high electrochemical stability and coulombic efficiency under high current density, which proves the reliability of the synthesis method. This method is expected to be industrialized and also provides new ideas for the preparation of other nanocomposites.

Synthesis of submicron titanium carbide in a direct current arc discharge plasma by a vacuumless method

This paper studies the possibility of obtaining ultrafine cubic titanium carbide in the direct current arc discharge initiated between graphite electrodes in ambient air. According to X-ray diffraction data, there are 3 crystalline phases in the synthesized powder: graphite, initial titanium and cubic tungsten carbide. Based on transmission electron microscopy data, particles with sizes of 100-300 nm containing titanium and carbon are identified in the synthesis product. These objects are characterized by a structure corresponding to the cubic phase of titanium carbide. The applied vacuumless electrotechnical method is known for its ease of implementation, high productivity, and high energy efficiency in comparison with electrical analogues.

Characterization of low-pressure high-current cascaded arc plasma in large volumes

A comprehensive study of behavior and parameters of the low-pressure (1–20 mTorr) large-area plane–symmetric direct current arc discharge plasma in pure Ar and Ar-N2 mixtures was carried out. A low-pressure arc discharge was ignited in a large chamber between a planar vacuum arc cathode with magnetic steering of arc spots and a surrounding grounded primary anode while a long-length remote arc discharge was extended toward a remote linear anode parallel to the cathode plate. The arc column moved up and down along the cylindrical cathode target positioned perpendicular to the cathode-to-remote anode direction, following the motion of the cathodic arc spots. Current-voltage characteristics of the low-pressure direct current arc discharge, electron density, electron temperature, electron energy distribution function (EEDF), ion energy distribution function (IEDF) and dissociation of nitrogen molecules in the discharge were studied using electro-technical methods, electrostatic probes, a microwave resonant probe, an ion energy analyzer and optical emission spectroscopy (OES) methods. A number of OES methods were used to determine temperature and density of electrons in the discharge: the Te was measured using 1) the IArI,415/IArI,306 intensity ratio, 2) an intensity ratio of the (0–0) vibrational bands of 1st negative and 2nd positive systems of N2; the ne was obtained by 1) the IArII,487/IArI,451 intensity ratio and 2) ratio of N2(C3Πu,v = 1) and N2(C3Πu,v = 0) populations. In addition, the nitrogen dissociation degree was monitored using INI,868.03/IArI,852.14 and INI,862.92/IArI,852.14 intensity ratios. Spectral and probe measurements of Te and ne in the large-area arc discharge show reasonable agreement. The electron population analysis based on the second derivative of the Langmuir probe current-voltage characteristics allowed accurate measurements of electron population parameters in the discharge including EEDF, electron drift velocity along with plasma potential, electron density and energy. Modeling of the low-pressure large-volume arc discharge using the axially symmetric drift-diffusion approximation exhibited good qualitative and acceptable quantitative agreement between calculated plasma parameters and experimental data.

A Vacuum-Free Method for Producing Cubic Titanium Carbide in the Plasma of Low-Voltage Direct-Current Arc Discharge

The results of a study on the production of cubic titanium carbide in direct-current arc discharge plasma initiated in open air are presented. A feature of the method is its implementation without the use of gas or liquid protective media preventing the oxidation of products and initial reagents with air oxygen. According to the X-ray diffraction data, graphite gC, hexagonal titanium α-Ti, and cubic titanium carbide TiC are identified in the composition of the powder product. The TiC particles are represented by objects with a regular characteristic cut and sizes from units to tens of micrometers.

Optical emission spectroscopy diagnosis of energetic Ar ions in synthesis of SiC polytypes by DC arc discharge plasma

Silicon carbides are basilic ceramics with proper bandgaps (2.4–3.3 eV) and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fast and facile direct current (DC) arc discharge plasma method. The influence of Ar atmosphere on the formation of nanocrystal SiC polytypes was investigated by optical emission spectroscopy (OES) diagnoses on the arc discharge plasma. Boltzmann’s plot was used to estimate the temperatures of plasma containing different Ar concentrations as 10,582 K (in 2 × 104 Pa of Ar partial pressure) and 14,523 K (in 4 × 104 Pa of Ar partial pressure). It was found that higher energy state of plasma favors the ionization of carbon atoms and promotes the formation of α-SiC, while β-SiC is generally coexistent. Heat-treatment in air was applied to remove the carbon species in as-prepared SiC nanopowders. Thus, the intrinsic characters of SiC polytypes reappeared in the ultraviolet–visible (UV–vis) light absorbance. It was experimentally revealed that the direct bandgap of SiC is 5.72 eV, the indirect bandgap of β-SiC (3C) is 3.13 eV, and the indirect bandgap of α-SiC (6H) is 3.32 eV; visible quantum confinement effect is predicted for these polytypic SiC nanocrystals.

Continuous preparation of structure-controlled carbon nanoparticle via arc plasma and the reinforcement of polymeric composites

Environmental-friendly continuous process of manufacturing structure-controlled carbon black (CB) nanoparticles has been developed by the combination of advantages of alternative-current (AC) gliding arc plasma and direct-current (DC) arc discharge plasma. In this process, methane was first decomposed in the low temperature AC gliding arc plasma and then further thermally pyrolyzed in the DC arc discharge plasma area. CB was generated in the AC arc plasma area and then continued to grow or surface modified by DC arc plasma according to different arc positions, which was determined by the operating gas flow rate. The effects of AC arc and DC arc on the yield, size, morphology and structure of particles have been investigated. The connection of AC and DC plasma areas might cause totally different growth process of nanoparticles. Formation mechanism has been discussed based on series of physical characterizations to illustrate the different growth process. The essential properties of CB prepared by plasma have been compared with three kinds of CB purchased, and then all the CB nanoparticles have been blended with acrylonitrile-butadienestyrene/ethylene-propylene-diene monomer composites. Electrical conductivity and mechanical properties as well as the morphology of fracture surface of composites have been characterized. The results indicate that CB prepared from AC plasma process shows excellent mechanical reinforcement and CB from AC+DC plasma process owns outstanding electrical conductivity.

Glycerol steam reforming for hydrogen and synthesis gas production

In this experimental study, glycerol conversion to hydrogen and synthesis gas was carried out by utilizing thermal plasma technology. An entrained-flow reactor equipped with a direct current arc discharge plasma torch, which was used to heat plasma-forming gas via Joule heating effect, and superheated water vapor, which was used to form the plasma, as a main reaction agent and a source of active radicals generation during steam reforming process of glycerol, set up a core of the glycerol conversion system. Glycerol, which is a by-product of biodiesel production during transesterification process, is considered to be a potential feedstock for renewable energy, biofuels, and high value-added chemicals production, such as methanol, hydrogen, etc. The reforming of glycerol was performed at various experimental conditions by changing the flow rate of water vapor and glycerol as well as the plasma torch power. The obtained results showed that the main reaction products were hydrogen and carbon monoxide with total concentration up to 75%. Moreover, the process was quantified in terms of cold gas efficiency, energy efficiency, carbon conversion, and specific energy requirement. Generally, the performed study indicates that hydrogen and synthesis gas could be effectively produced from glycerol by employing thermal plasma technology.

Adsorption Performance of Methylene Blue onto Nanoparticles of Carbon-Encapsulated Magnetic Nickel

Nanoparticles of carbon encapsulated nickel (Ni@C NPs) were in-situ synthesized by direct current arc-discharge plasma method through evaporating pure Ni in methane atmosphere. Transmission electron microscopy observation revealed that the nanoparticles (Ni@C NPs) exhibited an encapsulation structure with Ni metal as core and carbon 3-5 nm in thickness as shell. The BET surface area of the prepared Ni@C NPs is 38.82 m·g according to N2 adsorption-desorption isotherm. Surface modification with hydrogen peroxide was carried to graft oxygen-containing groups on carbon, which can improve the wettability and hydrophilicity of the Ni@C NPs. Then the effect of contact time, adsorption time and *国家重点基础研究发展计划2011CB936002和国家自然科学基金51271044、51331006、51171033资助项目。 2014年10月8日收到初稿; 2014年11月13日收到修改稿。 本文联系人:董星龙,教授

Phase Formation and Microstructure of BaTiO3 Ceramics Prepared by Direct Current Arc Discharge Process

BaTiO3 (BT) ceramics are prepared above 2000°C by direct current arc discharge plasma process in argon atmosphere. The results show the formation of the perovskite structure. However, the coexisting of tetragonal phase and hexagonal phase is found in the structure. It is also found that a small amount of BaTi4O9 compound appears. With the sintering temperature increasing, the structure becomes more homogeneous because of interdiffusion of constituent ions and phase transition. The hexagonal phase gradually disappears and BaTi4O9 compound could also be traced.

Raman Spectra of SrTiO<sub>3</sub> Prepared by Direct Current Arc Discharge Plasma Process

The XRD patterns of Strontium Titanate (SrTiO3) prepared by direct current arc discharge plasma technique show that the well crystallized cubic structure. A Raman spectra study is performed to investigate SrTiO3 ceramics and powders compared with earlier investigations. The observed Raman spectra in this work have been interpreted primarily as second order and derived from combinations, overtones and differences of phonon frequencies.

Phase formation and microstructure of BaxSr1−xTiO3 ceramics prepared by direct current arc discharge plasma process

BaxSr1−xTiO3 (BST) ceramics are prepared above 2000°C by direct current arc discharge plasma process in the argon atmosphere. The microstructure, phase and morphology are investigated. The results of samples show the formation of the perovskite BST phase. However, the biphasic phases are formed, which is consisted of Ba-rich and Sr-rich phases. It is found that with the Ba content increasing, a small amount of BaTi4O9 compound appears. It is beneficial for the crystal growth in the Ba-rich phase and Ba is more readily incorporated into BST crystal.

Infrared spectra study associated with hydrogen impurity in low pressure CVD diamond films

The infrared absorbance peaks at 2 852.4, 2 924.3, 2 963.0 and 3 034.9 cm−1 have been observed in diamond films made by the direct current arc discharge plasma chemical vapor deposition. Three former absorbance peaks have been assigned to C—H stretching in SP3 configuration, 3 034.9 cm−1 has been assigned to C—H stretching in SP2 configuration. The effect of methane concentration and H2 gas flow rate on absorption in the “C—H stretch” range has been investigated. Electron spin resonance analysis indicated that a considerable amount of defects exist in diamond films produced by low pressure chemical vapor deposition.

Purification of diamond films by applying current into the plasma stream in the arc discharge plasma jet chemical vapor deposition technique

A synthesis method that provides high-purity diamond films is proposed employing direct current arc discharge plasma jet chemical vapor deposition. In the method, an electric current was supplied to a plasma jet stream by applying a bias voltage between a cathode and the substrate on which diamond films were deposited. The Raman spectral analysis showed that the purity of the synthetic diamond was remarkably improved by the application of the bias voltage during deposition. The alternating current calorimetric method was employed to measure the thermal diffusion coefficient of the synthesized diamond films. The thermal diffusion coefficient greatly increased for films deposited with biasing. This improved thermal diffusion coefficient suggests higher purity diamond films. Emission spectral analysis revealed that the quantity of the dissociated hydrogen contributing to the plasma emission near the substrate is greater when biasing is used. Thus, the dissociated and excited hydrogen atoms are considered to play a key role in removing the carbon allotropes other than diamond.

プラズマジェットＣＶＤ法によるダイヤモンド成膜面積の拡大

A direct current arc discharge plasma jet Chemical Vapor Depositon (CVD) method has achieved very high growth rates of diamond by spraying a plasma jet onto a water-cooled substrate. The initial, experimental scale diamond films thus synthesized on a substrate were small in area, less than 10 mm in diameter. A large area of diamond film formed with a high growth rate is presupposed to be required, but this only has partially been obtained. By rotating a tungsten, substrate during spraying, the area of diamond deposited on the substrate was observed to be about 4 times as large as that on a fixed tungsten substrate. Raman spectroscopy determined the diamond obtained by this method included a small quantity of amorphous carbon. However, diamond Raman spectra obtained from within the diamond indicated the diamond had a diameter of about 20 mm. More recently, a diamond film that has a diameter of about 30 mm has been obtained by rotating the substrate while moving it horizontally.