Abnormal Glow Discharge Plasma Research Articles

Synthesis of Ti21.5V40Cr38.5 alloy by abnormal glow discharge plasma

The paper describes the structural-phase state and sorption characteristics of the Ti21.5V40Cr38.5 alloy synthesized by melting in abnormal glow discharge plasma and arc melting. X-ray diffraction patterns showed the presence of the main TiVCr phase with a body-centered cubic (bcc) lattice and Ti2O phase with a hexagonal close packed (hcp) lattice. The maximum hydrogen capacity of the samples obtained by melting in abnormal glow discharge plasma after 3 cycles was 3 wt%.

High-rate growth of single crystal diamond in AC glow discharge plasma

The detailed experimental behavior of an AC abnormal glow discharge plasma assisted chemical vapor deposition reactor for single crystal diamond (SCD) synthesis operating within the wide-range (20–250 Torr) pressure regime was presented. Within the discharge operating window absorbed power densities of 250–9000 W/cm3 were achieved and high quality SCD synthesis with growth rate up to 80 μm/h was demonstrated. At the power densities over 2500 W/cm3 the diamond substrates were located directly on water-cooled substrate holder without any intermediate molybdenum holder. The influence of several input experimental variables including pressure, N2 and Ar concentration, CH4 percentage, and discharge current on SCD deposition was explored. The quality of synthesized crystals approved competitive purity level of glow discharge CVD process.

Application of Glow Discharge Plasma for Cleaning (Activation) and Modification of Metal Surfaces while Welding, Brazing, and Coating Deposition

As known, the surface phenomena play a crucial role in the formation of strong interatomic bonds while joining dissimilar materials and the deposition of metal films. Thus, the presence of various contaminants, including oxides, on the metal surface reduces drastically the metal surface energy, thereby, preventing the diffusion processes in the contact zone and wetting them with liquid solder and adhesion of condensed films on the substrate surface. As a result, the processes of cleaning (activating) of metal surfaces before welding or coatings’ deposition begin to play a significant role. In some cases, metal surfaces have to be modified in order to give them the desired properties. Recently, for activation and modification of surfaces before welding and coatings’ deposition, gas-discharge plasma of abnormal glow discharge is widely used. The latter allows treating the surfaces of different configurations, including internal cavities, and various areas from units to tens of thousands of square centimetres. This review contains the results of research on the activation and modification of metal surfaces with low-energy ions (< 10 keV) initiated in the plasma of an abnormal glow discharge for welding, brazing, and coatings’ deposition. Particularly, we present results of studies of ion treatment with the glow discharge surface of samples, which are made of steels С45 and DC04, a number of active metals and alloys as well as chromium-containing steels 41Cr4, X20Cr13, and X6CrNiTi18-10, which possess the chemically and thermally stable Cr2O3 oxides on their surfaces. The decisive influence on the efficiency of purification and modification of metal surfaces with glow discharge by means of such regime parameters as electrode voltage, discharge current density, working chamber pressure, and ion exposure time is indicated. The optimal values of these parameters, in most cases, are determined by the technological conditions of the process and vary in the following ranges: U = 1500–3500 V, J = 0.4–1 mA/cm2, P = 3.99–7.98 Pa, t = 120–300 s, respectively.

Optical radiation from plasma of abnormal glow discharge in various gas mixtures

Optical radiation from plasma of abnormal glow discharge in Ar+N2, He+ N2 and N2+H2 was investigated. Lines of N2 N2+, N, N+, Ar+, Ar, He, Fe, H, H2 and OH were detected by optical spectrometry. Discharge current and intensities of spectral lines of N2, N2+, N, and N+ versus the concentration of Ar, He, and H2 in the gas mixtures were measured at various compositions of the working gas.

Structure and defects evolution at temperature and activation treatments of the TiCr2 intermetallic compound of Laves phase C36-type

In this work, microstructure and defect evolution at a temperature and activation treatment of the TiCr2 intermetallic compound of Laves phase C36-type synthesized in the abnormal glow discharge plasma were investigated. The crystalline structure of the C36TiCr2 powder crushed by hydrogenation-dehydrogenation (HD) method is characterized by the following lattice parameters: a = 4.932 Å and c = 16.059 Å. The dilatation of the crystal lattice under the hydrogenation at the HD crushing process leads to the formation of partial dislocations. For the first time ever the experimental value of the positron lifetime of the synthesized compound of the C36TiCr2 Laves phase, this amounted to (141 ± 2) ps, established by the positron spectroscopy. The optimal activation parameters of the HD-crushing C36TiCr2 powder were established: the temperature should be in the range from 450 to 500 °C, the exposure time in a hydrogen atmosphere at a pressure of (1–8) atm. must be at least 10 min.

Cyclic stability of the C36-type TiCr2 Laves phase synthesized in the abnormal glow discharge plasma under hydrogenation

In this work, the cyclic stability of the C36-type TiCr2 Laves phase synthesized in the abnormal glow discharge plasma was investigated. Melting of titanium-chromium metallic powders by the glow discharge plasma leads to the formation of the TiCr2 hexagonal C36 Laves phase with lattice parameters a = 4.928 Å and c = 15.983 Å. The hydrogenation-dehydrogenation method was used for crushing to increase the effective sorption capacity of the C36-type TiCr2 Laves phase. The stable hydride TiCr2Hx (x ≤ 0.5) phase of structural polytype C36 is formed during the first absorption/desorption cycle at the temperature of 30 °C. After 15 cycles hydride with the stoichiometric composition close to the TiCr2H0.5 phase of C36 polytype with lattice parameters: a = 4.961 Å and c = 16.224 Å was observed by XRD analysis. The hydrogen is localized in the crystal lattice in three main states: in a solid solution trapped by defects, open volume defects, and in the form of hydrides.

Structural Changes in С36 Laves Phase Intermetallic Compound TiCr2 During Hydrogenation–Dehydrogenation Process

The paper deals with melting of titanium and chromium metal powders in plasma of abnormal glow discharge which results in the formation of the hexagonal С36 Laves phase compound TiCr2 with a = 4.928 A and c = 15.983 A lattice parameters. The hydrogenation–dehydrogenation process is used to prepare the powder of C36 Laves phase intermetallic compound TiCr. The hydrogenation–dehydrogenation process is performed at 100°C, 2 atm hydrogen pressure and 30 min ageing followed by vacuum cooling. The prepared metal powder is characterized by rounded lamellar and coarse particles 6 ± 2 μm and 21 ± 7 μm in size, respectively.

The Synthesis Method of Intermetallic Alloys Based on Ti–Cr with C14 and C36 Laves Phases for Hydrogen Storage

The possibility of obtaining hydrogen storage materials based on TiCr2 intermetallic compounds by the methods of melting in abnormal glow discharge plasma and electron beam melting is shown. The use of melting in abnormal glow discharge plasma leads to the formation of a Laves phase of the C36 structural type, while electron beam melting allows the C14-type Laves phase to be obtained. It is established that the formation of Laves phases of different structural types is associated with different cooling rates, which is caused by the specific features of the methods for synthesizing intermetallic compounds.

Pulsed abnormal glow discharge with hollow cathode for nitriding of internal cylindrical surfaces

Possibility of nitriding of internal cylindrical surfaces in plasma of abnormal glow discharge with hollow cathode in the pulse-periodic mode in N2+H2 was investigated. Tubes with internal diameters of 6, 8, and 9 mm and with the aspect ratio from 12 to 50 were made a low carbon steel were used. Regimes of the discharge were investigated. Nitrided layers in different parts of the tubes were analyzed.

Effective secondary electron emission coefficient in DC abnormal glow discharge plasmas

In this work, a self-consistent model has been used to estimate the effective secondary electron emission coefficient (γE) of the cathode in typical abnormal dc glow discharge conditions. Using this model, the value of γE has been obtained for tungsten (W), copper (Cu), and stainless steel (SS304) cathode samples for argon (Ar) and nitrogen (N2) discharges. The γE for W is lower than the Cu cathode under identical operating conditions. The results show possible dependence of γE on the Fermi energy of the cathode material since it influences the probability of electron to be emitted by the incident ion. In addition to this, we found, significant contribution of cathode directed species other than ion to γE. Further, the effect of pressure on γE for the N2 discharge has been investigated in the pressure range of 0.5 mbar to 2.0 mbar and its value increases from 0.38 to 0.47 with pressure for the SS304 cathode. The knowledge of γE successfully explains the governing processes in abnormal glow discharge plasma that cannot be explained by the value of the ion induced secondary electron emission coefficient γi. The measurement of the γE value of the cathode material in typical abnormal glow discharge plasma conditions presents possibilities of exciting advancement in various applications by accurate estimation of discharge characteristics including flux of species, fraction of power carried by ions and electrons, plasma density, discharge current density, etc.

The peculiarities of CVD diamond coatings synthesis in abnormal glow discharge plasma using repetitively-pulsed mode

We report about the features of polycrystalline diamond coatings CVD synthesis in repetitively-pulsed plasma of abnormal glow discharge. The discharge burning time was varied from 0.5 to 10 ms with proportional pauses. The dependences of deposited diamond films growth rate on the durations of the discharge burning and pauses are presented. The mutual influence of two plasma filaments on each other and onto the substrate has unequivocally established. Raman spectroscopy, X-ray diffractometry and SEM were used for identification of phase composition and microstructure of deposited films. Implementation simplicity and reliability of the proposed discharge system may find application in diamond film deposition industries.

Growth of Single-Crystalline Silicon Nanocone Arrays by Plasma Sputtering Reaction Deposition**Supported by the National Natural Science Foundation of China under Grant Nos 11261140327, 11325524, 11475102 and 11575057, the Chinese National Fusion Project for ITER under Grant Nos 2013GB112001, 2013GB107001 and 2014GB108000, the Tsinghua University Initiative Scientific Research Program, and the 221 Program.

Vertically aligned single-crystalline silicon nanocone (Si-NC) arrays are grown on nickel-coated silicon (100) substrates by a novel method i.e., abnormal glow-discharge plasma sputtering reaction deposition. The experimental results show that the inlet / ratio has great effects on the morphology of the grown Si-NC arrays. The characterization of the morphology, crystalline structure and composition of the grown Si-NCs indicates that the Si-NCs are grown epitaxially in the vapor–liquid–solid mode. The analyses of optical emission spectra further reveal that the inlet methane can promote the growth of Si-NCs by raising the plasma temperature and enhancing the ion-sputtering. The understanding of the growth mechanism of the Si-NC arrays will be helpful for fabrication of required Si-NC arrays.

Redistribution of alloying elements in the surface region of titanium alloy VT-23 during glow discharge nitriding

VT-23 titanium alloy is processed in the plasma of abnormal glow discharge in a gas mixture of N2 and Ar under a total pressure of 4 mbar and a partial pressure ratio of N2 : Ar = 3 : 2 at 900°C. The phase composition of the alloy is determined, the cross-section structure is studied by electron microscopy, and maps of the elemental composition in the cross section are obtained. The distribution of alloying elements and nitrogen is found to be inhomogeneous in the surface region.

Effect of glow discharge sintering in the properties of a composite material fabricated by powder metallurgy

Composite samples of 316 stainless steel and SiC were produced by powder metallurgy. Starting materials were mixed in different proportions and compacted to 700MPa. Sintering stage was performed by abnormal glow discharge plasma with direct current in an inert atmosphere of argon. The process was conducted at a temperature of 1200°C±5°C with a heating rate of 100°C/min. This work shows, the effectiveness of plasma sintering process to generate the first contacts between particles and to reduce vacancies. This fact is confirmed by comparing green and sintered density of the material. The results of porosity show a decrease after plasma sintering. Wear tests showed the wear mechanisms, noting that at higher SiC contents, the wear resistance decreases due to poor matrix-reinforcement interaction and by the porosity presence which causes matrix-reinforcement sliding.

Remoción del lubricante adicionado al hierro pulvimetalúrgico, con plasma de la descarga luminiscente anormal

Se emplea el plasma de la descarga luminiscente anormal DLA en la remoción del lubricante de compactos de hierro pulvimetalúrgico en atmósfera de hidrógeno, con el fin de establecer las condiciones óptimas del ciclo térmico en la configuración catódica para mantener las propiedades ofrecidas del hierro. Para la preparación de las mezclas se utiliza un mezclador rotatorio. El material se conforma con presión uniaxial en matriz cilíndrica, calculando su densidad y porosidad. Con TGA y DSC se estudian la descomposición térmica y la eliminación del lubricante, luego, se realizan los ciclos de remoción en la DLA. Con TGA se monitorea el estado de remoción del lubricante de cada ciclo en la DLA. Se caracterizan los compactos en verde y los del proceso de remoción con microscopia óptica y SEM.Se halló una adecuada remoción en la configuración catódica a 400 °C durante 10 minutos, removiéndose la totalidad de lubricante. El ciclo propuesto conviene en aplicaciones industriales por las altas tasas de calentamiento alcanzadas con reducción del consumo de energía, así como de la necesaria en mantener la descarga, referidas a los hornos resistivos utilizados.

Controlled growth of crystalline g-C3N4 nanocone arrays by plasma sputtering reaction deposition

Vertically and neatly arranged crystalline graphitic C3N4 (g-C3N4) nanocone arrays were firstly synthesized on nickel-covered silicon (100) substrates supported on a graphite frame. Synthesis was accomplished using an abnormal glow discharge plasma sputtering reaction deposition method with a feed gas mixture of CH4, N2 and H2. The experimental results show that the morphologies, structures, composition and photoluminescence of the grown nanostructures strongly depend on the CH4/(N2+H2) ratios (0–1/10). The hexagonal g-C3N4 nanocone arrays were well grown at a CH4/(N2+H2) ratio of around 1/150 as a result of the hydrogen ion sputtering of the graphite frame to generate a lot of carbon atoms, the hydrogen ion etching on the growing graphite structures, and the reaction between the active nitrogen atoms and the sputtered carbon atoms. The g-C3N4 nanocone arrays have the characteristic photoluminescence-peak of g-C3N4 and very nice wettability to the polymer absorber layers. At the higher or lower CH4/(N2+H2) ratios, the silicon or diamond nanocone arrays were grown respectively due to the ion-sputtering of the silicon substrate and the inhibition of CHn-radicals on the H+-sputtering of the graphite frame or the mismatch between the sputtered carbon atoms and the dissociated nitrogen atoms.

Effects of experimental conditions on the growth of vertically aligned carbon nitride nanocone arrays

Vertically aligned carbon nitride nanocone (CNNC) arrays were prepared on Ni-covered (100) silicon wafers by an abnormal glow discharge plasma assisted chemical vapor deposition method. In order to control the growth of the CNNC arrays, the distance of the anode tip to the substrate surface was adjusted for it affected the contents and activities of the species in the plasmas leading to the CNNC growth. Based on the characterization of the as-grown thin films and the analysis of the growth environments, the effects of the experimental conditions on the growth of the CNNC arrays were studied and their growth mechanism was discussed. The tip−substrate distance strongly affects the CNNC growth. Under appropriate experimental conditions, the vertically-aligned and intact CNNC arrays with the β-C3N4 microstructure and the minimum tip curvature diameter of only 3–4nm could be fabricated. This kind of CNNC arrays have many potential applications, such as tips for microscopes, electron-emitting units in field emission displays, electron-capture electrodes of solar cells etc.

Characterization of the discharge in array needle cathodes and applications

In this paper, a new direct current (DC) plasma source for surface alloying using array-needle-cathode has been designed and manufactured. The array-needle-cathode is used to produce a stable abnormal glow discharge plasma in a rectangular chamber. During the surface alloying process, it is noticed that the discharge modes severely influenced the plasma parameters including electron density (Ne) and electron temperature (Te). The Te obtained by optical emission spectrometry (OES) through the comparison of the relative intensity of N in 3919Å and 3995Å is between 1.44eV and 5.40eV. The distribution and fluctuation of Te in the two-dimensional planar are revealed by analysis of digital camera images. It is concluded that the discharge by the array- needle-cathode is a kind of new plasma source which can generate stable plasma with a high electron temperature applicable for surface alloying. Lastly, with this array-needle-cathode plasma source (ANCPS), W-Mo-N alloyed layer on Ti alloy is explored in this paper.

Synthesis of Crystalline Carbon Nitride Nanocone Arrays by Direct‐Current Discharge Plasma‐Assisted CVD

AbstractCrystalline carbon nitride nanocone (CNNC) arrays are prepared by a rather simple and facile direct current, abnormal glow discharge plasma‐assisted (PA) CVD method. The CNNCs are grown on the surfaces of (100) silicon wafers covered by Co/Ni intermediate layers. The experiments are carried out in an atmosphere of mixtures of methane and nitrogen, under a total pressure of 4000 Pa, and CH4/N2 pressure ratios in the range 1:50–1:5. The as‐grown CNNCs are vertically aligned in arrays with rather perfect crystallinity, and smallest tip diameters of 2–3 nm. Based on the optical emission spectra from the abnormal glow discharge plasma, the growth mechanism of the as‐grown CNNCs is discussed.

Low temperature brazing of chip inductors by abnormal glow discharge plasma

A novel method, by which Cu was deposited on ferrite ceramics with arc-added glow discharge as a precursory procedure and then brazing the ferrite ceramics with vacuum glow discharge, was investigated. This new method can effectively suppress interfacial diffusion and brazing joint oxidation as well as maintain good adhesion in the joint due to low deposition and brazing temperature, the vacuum atmosphere effect, and the cathode sputter-cleaning action of the abnormal glow discharge plasma. The influence of the brazing process parameters on electrical and magnetic properties of the chip inductors is discussed. The optimal deposition and brazing process parameters are presented. Scanning electron microscope line scanning confirms the brazing electrode joints and detected the interfacial diffusion between the joints and the ferrite ceramics