Low voltage, low energy submerged pulsed arcs with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 10–40 μs, followed by aging in the dark, were used to decompose 10 mg/l methylene blue (MB) dissolved in 40 ml of water, with the addition of 0.5 % H2O2. Electrode pairs composed of Fe/Fe, Ti/Ti, Cu/Cu, Cu/Fe, Fe/Cu, Ti/Fe, Fe/Ti, Cu/Ti and Ti/Cu were used. MB degraded during arc treatment, and during post arc treatment aging. The aging degraded MB faster (by a factor of ~2–3) when the MB solution was subjected to arcing with dissimilar electrodes when one of them was Cu, than for arcing with other used electrode pairs. The impact of the arc treatment time and the electrode materials on the MB removal ratio (C0–Cta)/C0 was determined as a function of aging time ta, where C0 and Cta are the MB concentrations initially and after ta. For a pulse duration of 10 μs and pulse energies of 2–20 mJ, the MB removal rate increased linearly with treatment time and its growth rate increased with pulse energy. The linear dependence of the MB removal rate on treatment time was violated with pulse duration of 40 μs and pulse energies of 30–200 mJ. Kinetics of the MB degradation during aging of the arc treated solution was well described by the 1st order linear rate equation.

The pulsed submerged arc (SA) can decompose contaminant molecules in water. Recently, SA decomposition of Methylene Blue (MB) contamination in aqueous solutions was demonstrated. The particles eroded from the electrodes were shown to influence the decomposition efficiency. However, no comparative studies of effects of the particles eroded from Fe and Ti electrodes were conducted. The objective of this work was to determine the effects of Fe and Ti electrodes on the efficiency of MB decomposition in aqueous solutions. Electrode pairs of the same material (Fe or Ti) and combinations of these materials were used. Solutions were treated using a SA with Fe and Ti electrodes in the presence of H2O2 and without it, and then aged. The treated solutions were examined by Raman and absorption spectroscopy. The produced particles were studied by SEM, XPS and XRD. In the absence of H2O2 in the solutions, the decontamination ratio after SA treatment was higher with Fe/Fe than with Ti/Ti electrodes. In the presence of H2O2 in the solutions, SA treatment with Ti/Ti electrodes was more effective than with Fe/Fe electrodes. One week aging of the solutions treated in the presence of H2O2 with all electrode pairs very effectively decontaminated the solutions, reaching a decontamination ratio close to 99 %). According to the XPS and Raman spectroscopy analysis, titanium peroxide was formed by SA treatment with Ti electrodes on the surface of particles eroded from the electrodes. We believe that Ti-peroxide forms on the surface of eroded particles during SA treatment and gradually oxidizes MB during aging. A similar processes can proceed on the surface of the particles eroded from Fe electrodes owing to Fe-peroxide compounds formed in Fenton chemistry during discharge.

Low voltage, low energy submerged pulsed arcs between Ti electrodes with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 10–40 μs, followed by aging in the dark, were used to decompose 10 mg/l methylene blue (MB) contamination in 40 ml aqueous solutions, with and without the addition of 0.5 % H2O2. The impact of the arc treatment on the MB removal ratio (C0–Cta)/C0 was considered as a function of aging time ta, where C0 and Cta are the MB concentrations initially and after ta (the time needed to complete removal of MB after cessation of exposure of the arc). Particles eroded from the electrodes during the discharge enabled MB decomposition during aging. The particles were studied by XRD, XPS and Raman analysis, and titanium oxides and peroxides were found. MB decomposition during aging is explained by the formation of a surface layer of titanium peroxide that forms by the interaction of titanium dioxide with H2O2, which produce radicals which oxidize the MB. The 99.6 % MB removal yield (G99.6 = 90 g/kWhr) of the submerged pulsed arc process with Ti electrodes and addition of 0.5 % H2O2 was more than 60 times larger than obtained at 50 % removal with other plasma methods.

Anode mass loss was studied in pulsed air arcs between two electrode pairs, 99.99% Ni/Ni and 99.5% Cu/Cu, in a transverse magnetic field. In both cases the anode mass loss decreased (by a factor of 2 for Cu and by a factor of 6 for Ni) when the magnetic field was increased up to 15–20 Oe and then remained approximately constant for Cu and decreased weakly for Ni. The observed dependences of anode mass loss were explained by the published behaviour of an arc motion in a magnetic field. The lattice parameter was decreased by the discharge treatment. The decrease was attributed to residual tensile stress produced on the arced surface. The lattice parameter of Ni increased with magnetic field, while for Cu it did not change substantially. The different behaviour is attributed to the magneto-plastic effect on magnetic Ni, which increases the plasticity with magnetic field.

Low voltage, low energy submerged pulsed arcs between a pair of carbon or iron electrodes with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 20, 50 and 100 μs were used to remove methylene blue (MB) contamination from 30 ml aqueous solutions. The MB concentration decreased exponentially with rates of 0.0006–0.0143 s −1 during processing with the carbon electrode pair. With the iron electrodes, the MB concentration initially decreased faster (0.030 s −1 ) than with the carbon electrodes, but later saturated. However when microparticles produced with the iron electrodes were periodically filtered, the high removal rate was maintained. Under these conditions, the volume of water which can be treated per unit energy expenditure was much higher with the submerged arc than with other plasma processes. A kinetic model based on MB degradation by OH· radicals formed by the discharge was formulated. The higher initial MB removal rate with iron electrodes is explained by additional OH· production from Fenton’s reaction between Fe ++ and H 2 O 2 produced by the discharge. This rate is maintained if the eroded iron particles are filtered, but if eroded iron particles accumulate, degradation slows down and stops, possibly because the iron particles catalytically decompose H 2 O 2 and hence stops Fenton’s reaction, and either directly or via increased Fe ++ dissolved from the particles, scavenge the OH· radicals.

Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition of 5010 and 01 steel. The arc produced local heating and eroded the steel surface forming craters, and the subsequent modification depended on the crater density. X-ray diffraction showed that the volume fraction of ferrite decreased while that of austenite increased with crater density. Cementite was practically absent in 5010 steel, while its volume fraction in O1 steel increased with crater density. PAAT increased the microhardness of the surfaces by 10–40% over that of the virgin surfaces. PAAT increased the lifetime of a lubricant film applied to the surface by more than an order of magnitude, by forming craters on the surface which retained the lubricant.

The steady state of a quasi-neutral bulk of a cylindrical, current-carrying, fully ionized, collisional plasma confined by two coaxial metallic cylinders was analysed both analytically and numerically, using a magneto-hydrodynamic model. The plasma is magnetized by a uniform magnetic field, imposed parallel to the wall. The analysis did not assume Boltzmann equilibrium for the electrons, and the dependence of the mean electron–ion collision frequency on the varying plasma density was considered. The first integral of the model equations was found to be an algebraic relation between the self-consistent electric potential and the ion radial velocity. Radial distributions of characteristic plasma parameters (electric potential, density, velocities and currents) in the quasi-neutral region were calculated, and their dependences on the magnetic field strength, voltage and current were analysed. Trial and error was used in numerical calculations to choose the ‘initial’ ion radial velocity at the inner cylinder so that boundary conditions at the outer cylinder were satisfied. The results show that the variation in the radial ion velocity determined is mainly by competition between the Amperian force, which accelerates the ions, and the centrifugal force, which decelerates them. The competition may lead to non-monotonic variation in the ion velocity and density with the radial coordinate, depending on the electric current, while the electric potential in the plasma bulk is a monotonic function of the radial coordinate. The plasma rotates around the system axis with the frequency proportional to the electric current to the outer wall. The plasma azimuthal velocity calculated taking into account the ion viscosity is a non-linear function of the distance from the system axis. The calculated dependence of the current to the wall from the potential drop in the plasma bulk shows a monotonic transition from ion to electron current to the wall by increasing the voltage from negative to positive magnitudes. The current decreases with the increase in the magnetic field.

The pulsed submerged arc is a high-current electrical discharge between two electrodes in a liquid, in which the electrical current is conducted via a plasma bubble consisting of vaporized and partially ionized liquid and electrode material. The submerged arc discharge has the potential to kill harmful pathogens by a combination of several mechanisms. In this preliminary investigation, the ability of the pulsed arc to sterilize water was tested, hydroxyl radical (OH·) production and the radiation spectrum were measured, and shock wave production was estimated.

Low voltage, low energy submerged pulsed arcs were used to break-down Sulfadimethoxine (SDM) contamination in aqueous solutions. The SDM concentration decreased exponentially with rate constants of 0.13–1.9 min−1 during processing by pulsed arcs with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 20, 50 and 100 μs. The electrical energy consumption was minimized with short duration pulses––1.5 kW-hr/m3 with 7.5 mJ, 20 μs pulses for 90% SDM removal.

Pulsed arc production of tungsten carbide (W-C) powders in deionized water and analytical (99.8%) ethanol was studied. The arc was ignited between two submerged electrodes: one of 99.99% graphite (C) and the other of 99.5% W. The pulse energy and duration were in the ranges of 7.7–192 mJ and 25–65 μs, respectively. The WC1−x production rate was maximized by configuring the C electrode as the anode and the W electrode as the cathode. The rate was greater in ethanol than in water. The rate of producing ∼10 nm particles in ethanol was two orders of magnitude greater when using W anode -C cathode configuration, than with the opposite polarity.

Powders of Ni–C nanoparticles were synthesized using a pulsed arc between Ni electrodes submerged in pure ethanol. The arc was ignited by inter-electrode breakdown. The ethanol was arc treated for 5min with 1μs duration pulses, at a repetition rate of ∼1kHz. The pulse energy was in a range of 0.01–0.05J. Powder samples were obtained by extracting liquid from the treatment vessel after a pre-determined sedimentation time, or by allowing the liquid to evaporate from the vessel, and collecting the residue. The samples were examined by HRSEM, EDX and XRD.

The sheath criterion was considered for electronegative as well as electropositive plasma in contact with a material boundary that is either more negative than the plasma space potential or more positive than the space potential. A fluid model accounted for the inertia and pressures of all the plasma components and the Sagdeev potential in the whole sheath without any power series expansion were used. The criterion was specified for several special cases of both electronegative and electropositive plasmas. In the cases, a cold ion critical velocity at the sheath entrance was greater by a factor of 1.585 for qϕ>0 than that for qϕ<0, where q is the ion charge and ϕ is the electrical potential in the sheath. In the case of a plasma with Boltzmann electrons and positive ions and a cold ion beam, this conclusion is true only for q<0 and ϕ<0.

The relation between plasma parameters determining a steady-state charged sheath at a plasma-wall boundary was derived and analyzed using a fluid model, which accounted for inertia and partial pressure of both plasma components. The relation generalizes the well-known Bohm criterion and, in particular, shows that a steady-state sheath may be formed in some cases where the Bohm criterion is not satisfied. Conditions allowing formation of a double sheath structure were formulated and analyzed. It was shown that the structure may be formed only if a) the generalized Bohm criterion is satisfied, and b) the Sagdeev potential has a minimum. The double sheath structure consists of two sub-sheath of different polarity, which depends on the wall potential polarity and the relation between the plasma component temperatures and inertia. For positive wall potential, the sub-sheath adjacent to the plasma (the sheath edge) is enriched by negative particles, and the sub-sheath adjacent to the wall is enriched by positive particles, while the sub-sheath polarities are reversed for negative wall potential. An analytical theory was formulated and illustrated by numerical solutions of the Poisson equation for special cases. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon powder was produced by a pulsed arc ignited between two carbon electrodes submerged in ethanol, and was comprised of both micro- and nano-particles. The measured magnetic properties of the mixed “raw” powder at 20 and 300K were: saturation magnetization Ms∼0.90–0.93emu/g, residual magnetization Mr=0.022 and 0.018emu/g, and coercive force Hc=11 and 8Oe, respectively. The data lead to conclusion that the powder consisted of ferromagnetic particles with a critical temperature much higher than 300K. Magnetic particles in solution were separated by means of bio-ferrography. It was found that the magnetically separated particles included chains of ∼30–50nm diameter spheres, and nanotubes and nanorods with lengths of 50–250nm and diameters of 20–30nm. In contrast, the residual particles which passed through the bio-ferrograph consisted of 1μm and larger micro-particles, and nano-particles without any definite shape.

Electrode erosion was studied in pulsed arcs ignited between two electrodes comprised of 99.99% C (graphite) and 99.5% W submerged in deionized water or analytical (99.8%) ethanol. In the both cases the erosion rate increased proportionally to the pulse energy, and the total electrode erosion per unit energy was inversely proportional to the discharge pulse duration. Fifteen and sixty-μF discharge capacitors were used for formation of the pulses in water. It was obtained that, respectively (a) erosion of the tungsten anode (Wa) was by factors of 5–6 and ∼10 greater than that of the carbon (Cc) cathode; (b) erosion of the carbon anode (Ca) was by a factor of 1.34 greater and by a factor of 2.65 less than that of the tungsten cathode (Wc); (c) the total erosion rate of both electrodes (anode and cathode) per unit pulse energy for the Wa–Cc pair was greater by factors of 11 and 12.5 than that for the Wc–Ca pair.

A novel method of ZnO nanorods growth is presented based on low temperature (300 degrees C) air annealing of ZnO film while applying an electric field (similar to 10 V/cm) parallel to the film. The films were deposited on glass substrates using a filtered vacuum arc deposition system equipped with a Zn cathode, at an arc current of 160 A, oxygen pressure of 3.2 mTorr, and deposition time of 30 s. Cu tape electrodes were applied on each end of the coated sample, and used to apply the electric field. The samples were annealed in a quartz furnace at 200, 300, 400 degrees C for 20 or 60 min. Each sample surface was examined using a Scanning Electron Microscope (SEM) and a High Resolution SEM (HRSEM) to study its micro- and nano-structure. The film crystallographic structure was studied using X-ray diffractometry (XRD). ZnO rods with lengths of similar to 3 mu m were observed on the samples annealed a(t) 300 degrees C for 20 min with an electric field of similar to 10(3) V/m, while separated conical forms with lengths of similar to 0.5 mu m and base width of similar to 150 mn were observed after annealing under the same conditions but without any electric field. The rod growth rate and area density were similar to 2.0-2.5 nm/s, and similar to 3 x 10(7) cm(-2), respectively. (c) 2006 Elsevier B.V. All rights reserved.

It is shown that a presheath near a wall in fully ionized collisional plasma is unstable due to resistive excitation of electrostatic drift waves. The instability depends on the plasma inhomogeneity and resistivity but is independent of the particle flows to the wall. The wave spectrum and growth rate were calculated using a fluid model of the plasma and the Wentzel-Kramers-Brillouin approximation. The electron-wave collision frequency and the additional diffusion flux of the particles were calculated. The resistive instability may be a cause of the fluctuations in plasma parameters observed in transporting vacuum arc plasma beams through magnetized ducts.

A charged sheath between a multi-component plasma and an absorbing and conducting wall was considered analytically in the framework of a hydrodynamic model. The model accounted for the inertia and pressures of all the plasma components and both wall polarities. An existence criterion for the steady sheath with a monotonous distribution of the electric potential was derived based on analysis of the Sagdeev potential. The model was applied to some special cases of two-and three-component plasmas such as a plasma with macroparticles, and electro-positive and -negative plasmas.

Ni–C powders were synthesized using a pulsed arc between Ni electrodes submerged in pure ethanol. The arc pulses with energies 7.7, 22.7 or 48 mJ and 20 μs duration, and a repetition rate of 100 Hz were applied for 5 min. Powder samples were obtained by extracting liquid from the treatment vessel after a pre-determined sedimentation time, or by collecting the residue after the liquid evaporated. The particles size distribution was studied using a High Resolution Transmission Electron Microscope (HRTEM). The particle diameters after 25 min sedimentation time were in the range of 3–30 nm, and the distribution depended weakly on the discharge energy. Effects of applied electric and magnetic fields on the particle motion in ethanol were also studied. The particles moved in an applied electric field with velocities increasing with the field strength and the particle diameter. The as-produced particles with diameter ∼80 μm had velocities ∼2–2.5 mm/s in an electric field of ∼800 V/cm. The powder had soft ferromagnetic properties at room temperature, and the particles in the liquid moved in the direction of increasing magnetic field.