DC Plasma Jet Research Articles

Formation of carbon nanostructures by the plasma jets: synthesis, characterization, application

Carbon nanostructures were synthesized without the use of catalysts by the conversion of hydrocarbons in the DC plasma jet system. The samples of carbon nanotubes, nanofibers, graphene, onion like structures have been characterized by electron microscopy, thermal analysis, Raman spectroscopy. An experimental study of the composition of the gas phase with variation of the type of the plasma-forming gas and the type of carbon source was carried out. The synthesized samples have been used in the composition of the functional ceramic and in electrochemical systems.

Characteristics of helium DC plasma jets at atmospheric pressure with multiple cathodes**Project supported by the National Natural Science Foundation of China (Grant Nos. 11475174 and 11675177) and the Fundamental Research Funds for the Central Universities, China (Grant No. WK2090130021).

A novel DC plasma torch with multiple cathodes is developed for generating laminar, transitional and turbulent plasma jets. The jet’s characteristics, including jet appearance, voltage fluctuation, thermal efficiency, specific enthalpy, and distributions of temperature, pressure, and velocity, are experimentally investigated. The results show that as the gas flow rate increases, the plasma jet transforms first from the laminar state to the transitional state and second to the turbulent state. Compared with the transitional/turbulent jet, the laminar jet possesses not only a better stability and a longer high-temperature zone but also a higher average/core temperature and a higher specific enthalpy at the nozzle’s outlet. With the change of jet states from the laminar to the turbulent flow, the core pressure and velocity at the nozzle’s outlet increase, while the decaying rates of temperature/pressure/velocity along the jet’s axial direction increase sharply. Furthermore, applications of laminar, transitional and turbulent jets for zirconia spray coating are described. The test results indicate that the long laminar jet is favorable for the deposition of a high-quality coating because the powder particles injected into the laminar jet may have better heating and lower kinetic energy.

Comparison of pulsating DC and DC power air-water plasma jet: A method to decrease plume temperature and increase ROS

Most air–water plasma jets are rich in hydroxyl radicals (•OH), but the plasma has higher temperatures, compared to that of pure gas, especially when using air as working gas. In this paper, pulsating direct current (PDC) power was used to excite the air–water plasma jet to reduce plume temperature. In addition to the temperature, other differences between PDC and DC plasma jets are not yet clear. Thus, comparative studies of those plasmas are performed to evaluate characteristics, such as breakdown voltage, temperature, and reactive oxygen species. The results show that the plume temperature of PDC plasma is roughly 5–10 °C lower than that of DC plasma in the same conditions. The •OH content of PDC is lower than that of DC plasma, whereas the O content of PDC plasma is higher. The addition of water leads in an increase in the plume temperature and in the production of •OH with two types of power supplies. The production of O inversely shows a declining tendency with higher water ratio. The most important finding is that the PDC plasma with 100% water ratio achieves lower temperature and more abundant production of •OH and O, compared with DC plasma with 0% water ratio.

Effect of Irradiation with DC Plasma Jet on the Structure Phase Compositions and Properties of Powder Ni and Co – based Coatings

This paper presents new results of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) investigation of the structure-phase compositions of coatings on the base of Ni and Co deposited by plasma-detonation on steel substrates after their modification by DC plasma jet irradiation. The phase structures and morphology of precipitation of strengthening phases from solid solution are defined. The irradiation of the coatings leads to the evolution of the structural-phase state of coatings: an increase in the size of the diffusion zone between the coating and the substrate, an increase in the volume fraction of hardening intermetallic phases, the formation of sufficiently homogeneous fine-grained structure in the irradiated coatings and, consequently, a significant increase of hardness, corrosion and wear resistance of modified coatings. There is a mutual penetration of the substrate main element Fe in the coating and base coating elements (Ni and Co correspondingly) into the substrate as a result of the coating treatment by a pulse DC plasma jet. DOI: http://dx.doi.org/10.5755/j01.ms.22.2.7699

Direct probing of anode arc root dynamics and voltage instability in a dc non-transferred arc plasma jet

The transient dynamics of the anode arc root in a dc non-transferred arc plasma torch is captured through fast photography and directly correlated with the associated voltage instability for the first time. The coexistence of multiple arc roots, the transition to a single arc root, root formation and extinction are investigated for the steady, takeover and re-strike modes of the arc. Contrary to the usual concept, the emerging plasma jet of a dc non-transferred arc plasma torch is found to carry current. An unusually long self-propelled arc plasma jet, a consequence of the phenomenon, is demonstrated.

Diffusion and Filamentary Regime of an Atmospheric Pressure DC Plasma Jet in Nitrogen and Air

An atmospheric pressure direct current plasma jet is produced in nitrogen and air. The active region and afterglow region of the plasma jet at various discharge currents and gas flow rates are investigated. Depending on the gas flow and the current, the discharge can be sustained at diffusion or filamentary modes.

The production mechanisms of OH radicals in a pulsed direct current plasma jet

The production mechanism of OH radicals in a pulsed DC plasma jet is studied by a two-dimensional (2-D) plasma jet model and a one-dimensional (1-D) discharge model. For the plasma jet in the open air, electron-impact dissociation of H2O, electron neutralization of H2O+, as well as dissociation of H2O by O(1D) are found to be the main reactions to generate the OH species. The contribution of the dissociation of H2O by electron is more than the others. The additions of N2, O2, air, and H2O into the working gas increase the OH density outside the tube slightly, which is attributed to more electrons produced by Penning ionization. On the other hand, the additions of O2 and H2O into the working gas increase the OH density inside the tube substantially, which is attributed to the increased O (1D) and H2O concentration, respectively. The gas flow will transport high density OH out of the tube during pulse off period. It is also shown that the plasma chemistry and reactivity can be effectively controlled by the pulse numbers. These results are supported by the laser induced fluorescence measurements and are relevant to several applications of atmospheric-pressure plasmas in health care, medicine, and materials processing.

Deposition of a TMDSO-Based Film by a Non-Equilibrium Atmospheric Pressure DC Plasma Jet

This work deals with the deposition of thin films using an atmospheric pressure direct current nitrogen plasma jet with tetramethyldisiloxane as precursor. The effect of O2 flow and plasma discharge power on film deposition rate and film chemical characteristics is investigated in detail by surface profilometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It is found that a higher deposition rate is obtained at higher oxygen flow rates and higher discharge powers. Increasing discharge power shows a certain amount of capability to transfer low oxygen content bonds to high oxygen content bonds. Organic films can be deposited in a pure nitrogen atmosphere. The film chemical composition can be tuned to a more inorganic structure by admixture of O2 leading to an increase in SiO4 units at high oxygen flow rates.

Three-dimensional flow dynamics of an argon RF plasma with dc jet assistance: a numerical study

Time-dependent three-dimensional numerical simulation based on a large-eddy simulation approach is conducted to ascertain the complicated thermofluid dynamics of an argon radio-frequency (RF) inductively coupled plasma with a direct-current (dc) plasma jet assistance, considering non-uniform densities and properties in time and space as well as turbulence generation and suppression. Using a combination of numerical schemes suitable to capture vortices, the present simulation successfully shows unsteady behaviour of the plasma as well as wave-like interfaces between a high-temperature flow and a low-temperature flow as a result of the balance of fluid-dynamical instability and a viscous diffusion effect. Small cold vortices generated near a dc jet injector are entrained into and merged with vortices generated around the dc jet. Subsequently, they interact with large vortices in an RF induction coil region, which causes a much more complex vortex structure.

Langmuir probe diagnostics of an atmospheric pressure, vortex–stabilized nitrogen plasma jet

Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non–transferred arc torch with a rod–type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min−1. A flat ion saturation region was found in the current–voltage curve of the probe. The ion saturation current to a cylindrical probe in a high–pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processes inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 × 1022 m−3, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying–type plasma jets characterized by electron temperatures in the range 9000–14 000 K.

Thermo-Mechanical Coupled and Fracture in Diamond Film under High Strain Rate

According to the special case of high strain rate for diamond film produced by DC plasma jet method, a transient thermo-mechanical coupled model for the cooling process of diamond film and Mo substrate was developed. The direct coupled finite element method was used to simulate the transient thermal stresses in diamond film during the cooling period after the film deposition. The residual thermal stresses of diamond film were calculated and compared respectively under two conditions of real uneven temperature fields and unreal even temperature fields. Based on the simulated results of stresses, the moment and cause of diamond film cracking were analyzed. The conclusions are as the follows: (1) the thermal stresses in diamond film increase with the increase of cooling time, but the maximum first principal tensile stress may reach the fracture strength of common diamond film before the film cools to room temperature; (2) the excessive tensile stress at the film edge causes the film cracking; (3) in order to reduce the thermal (residual ) stresses and increase the finished product ratio of diamond film, it is essential to further improve the temperature uniformity.

Ultrafast production of silicon via aluminothermic reduction of tetrachlorosilane in a thermal plasma jet

This paper proposed a new route for producing silicon at a high rate via the reduction of tetrachlorosilane with aluminum molten particles by utilizing a thermal plasma jet. High-purity aluminum particles melted and sprayed by an atmospheric dc plasma jet were reacted with tetrachlorosilane vapor. Silicon generation was confirmed in the reacted particles. The residence time was calculated to be a few milliseconds. The obtained results demonstrate the feasibility of the aluminothermic reduction process in a thermal plasma jet for rapid silicon production.

The effect of applied electric field on pulsed radio frequency and pulsed direct current plasma jet array

Here we compare the plasma plume propagation characteristics of a 3-channel pulsed RF plasma jet array and those of the same device operated by a pulsed dc source. For the pulsed-RF jet array, numerous long life time ions and metastables accumulated in the plasma channel make the plasma plume respond quickly to applied electric field. Its structure similar as “plasma bullet” is an anode glow indeed. For the pulsed dc plasma jet array, the strong electric field in the vicinity of the tube is the reason for the growing plasma bullet in the launching period. The repulsive forces between the growing plasma bullets result in the divergence of the pulsed dc plasma jet array. Finally, the comparison of 309 nm and 777 nm emissions between these two jet arrays suggests the high chemical activity of pulsed RF plasma jet array.

Fabrication and Simulation of Shell Diamond Film

Shell diamond film prepared using DC plasma jet CVD (DCPJCVD) is studied by those techniques. The relationships between morphology, microstructure, and the quality of diamond film are investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy, respectively. The results show that, high nucleation density was attained when molybdenum substrate was polished by different size diamond powder and was etched by atom hydrogen. Diamond film grows in the columnar way, and the microstructure of diamond film is compact, continuous, and uniform. (111) faces were dominant in polycrystalline texture diamond film. Raman spectrum indicates that there is only diamond characteristic peak in shell diamond film, furthermore, the velocity, pressure, and temperature fields of reaction chamber were simulated by finite element methods, which help to prepare high-quality shell diamond film. It also shown that although velocity and pressure fields fluctuated, which caused negative influence on the quality of diamond film, the temperature field is uniform, which is very important to grow normal diamond film, and it is in accordance with the experience results.

Advancement of In-Flight Alumina Powder Spheroidization Process with Water Droplet Injection Using a Small Power DC-RF Hybrid Plasma Flow System

The correlation between plasma thermofluid characteristics and alumina powder spheroidization processes with water droplet injection using a small power DC-RF hybrid plasma flow system was experimentally clarified. Micro-sized water droplets with a low water flow rate were injected into the tail of thermal plasma flow so as not to disturb the plasma flow directly. Injected water droplets were vaporized in the thermal plasma flow and were transported upstream in the plasma flow to the torch by the backflow. After dissociation of water, the production of hydrogen was detected by the optical emission spectroscopy in the downstream RF plasma flow. The emission area of the DC plasma jet expanded and elongated in the vicinity of the RF coils. Additionally, the emission area of RF plasma flow enlarged and was visible as red emission in the downstream RF plasma flow in the vicinity below the RF coils due to hydrogen production. Therefore, the plasma flow mixed with produced hydrogen increased the plasma enthalpy and the highest spheroidization rate of 97% was obtained at a water flow rate of 15 Sml/min and an atomizing gas flow rate of 8 Sl/min using a small power DC-RF hybrid plasma flow system.

Research of CBN Film and its Application Prospect on Cutting Tool

Tool material has been one of the focuses in tool research. Diamond and cubic boron nitride (c-BN) are materials of exceptional and very similar properties that make them extremely valuable not only for the aesthetics of diamond. C-BN is a material synthesized rather recently that has rapidly spurred technological and scientific interest. Presently, both materials have found commercial applications. There is still a long way for the practical application of cBN film. The main problems are such as adhesion, thickness, purity, nucleating, and growth mechanism. We will develop a new way of DC plasma jet CVD way to synthesis the cBN film. The deposition of cBN films can be performed in a DC jet plasma CVD reactor by using an Ar-N2-BF3-H2 gas mixture, on the basis of deposition of diamond has been achieved.

Solution precursor plasma deposition of nanostructured CdS thin films

Cadmium sulfide (CdS) films are used in solar cells, sensors and microelectronics. A variety of techniques, such as vapor based techniques, wet chemical methods and spray pyrolysis are frequently employed to develop adherent CdS films. In the present study, rapid deposition of CdS thin films via plasma spray route using a solution precursor was investigated, for the first time. Solution precursor comprising cadmium chloride, thiourea and distilled water was fed into a DC plasma jet via an axial atomizer to create ultrafine droplets for instantaneous and accelerated thermal decomposition in the plasma plume. The resulting molten/semi-molten ultrafine/nanoparticles of CdS eventually propel toward the substrate to form continuous CdS films. The chemistry of the solution precursor was found to be critical in plasma pyrolysis to control the stoichiometry and composition of the films. X-ray diffraction studies confirmed hexagonal α-CdS structure. Surface morphology and microstructures were investigated to compare with other synthesis techniques in terms of process mechanism and structural features. Transmission electron microscopy studies revealed nanostructures in the atomized particulates. Optical measurements indicated a decreasing transmittance in the visible light with increasing the film thickness and band gap was calculated to be ∼2.5eV. The electrical resistivity of the films (0.243±0.188×105Ωcm) was comparable with the literature values. These nanostructured polycrystalline CdS films could be useful in sensing and solar applications.

Heat and Mass Transfer Within an Evaporating Solution Droplet in a Plasma Jet

Solution precursors have been injected into the plasma gases to produce finely structured ceramic coatings with nano- and sub-micrometric features. The trajectory history and heat and mass transfer within individual solution droplets play a very important role in determining the coating microstructure. A mathematical model is developed to analyse the thermal behavior of individual precursor droplets travelling in the high temperature plasma jet. This model involves the motion and evaporation of the precursor droplet in a DC plasma jet and the heat and mass transfer within the evaporating droplet. The influence of Stefan flow, as well as the variable thermo-physical properties of the solution and the plasma gas, is considered. The internal circulation due to the relative velocity between the droplet and the plasma jet, which may be approximated by the Hill vortex, is considered as well. The trajectory, temporal droplet surface temperature, and radius variation are predicted. The temporal temperature and concentration distributions within the evaporating droplet are presented for different injection parameters.

Synthesis and Numerical Analysis on Velocity and Pressure Field of Convex Diamond Film

Maths model based on wo-dimensionalhas was built to simulate the velocity and pressure field of the growth of diamond film. Firtstly，the plasma jet flow is supposed as steady state incompressible gas, which meets with Reynolds-averaged Navier–Stokes equations. The model of the growth of convex diamond film considers different convex height of Mo substrate. The velocity and pressure field were simulated by CFD respectively.The simulational results show that, the distributions of velocity and pressure fields were fluctuant in reaction chamber. When convex height of Mo substrate was 9mm, DC plasma jet was smoother than the other heights, thus, we predicts that diamond film easily grows. Meanwhile, we prepared four diamond films in different heights of substrate, by DCPJCVD. Raman spectra were used to investigate the quality of convex diamond film. It was found that, when the height of convex substrate was 9mm, convex diamond film had only diamond characteristic peak. It is obvious that numerical analysis help us predict the distributions of velocity and pressure fields and synthesize high quality convex diamond film.

Fabrication and Simulation of Shell Diamond Thin Film

Shell diamond film prepared using DC plasma jet CVD (DCPJCVD) is characterized by those techniques. The relationships between morphology, microstructure, and film quality are investigated by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy, respectively. The results show that, after molybdenum substrate was polished by series of diamond powder, atom hydrogen etching, a much higher nucleation density can be achieved. Synthetic diamond film is compact, continuous and uniform, and diamond film grows with the columnar spreading from the nucleation surface to the growth surface. (111) Faces were dominant in polycrystalline texture diamond film. Raman spectrum indicates that there is only diamond characteristic peak in diamond film; furthermore, the velocity, pressure, and temperature fields of reaction chamber were simulated by finite element methods respectively, which is help to prepare high quality shell diamond film. It also showed that, though uneven velocity and pressure fields’ distributions have negative influence on the growth of diamond film, the temperature field is uniform, which guarantees to grow normally diamond film, and it accords with the experience results.