Pulsed submerged arc (SA) treatment of aqueous methylene blue (MB) solutions was studied in the reactor with multiple mobile iron (Fe) based electrodes. The discharges were carried out between these electrodes, which are repetitively brought into collision contact with fixed electrodes, connected to the power supply. The new reactor allows electrical discharges and MB decomposition in a large (600ml) volume of liquid. The effects of alternating filtration, electrode type, arcing energy, vibration, aging of the solutions after arcing and the added H2O2 concentration on MB decomposition were studied. The ratio between the number of milliliters of the treated solution that reached complete removal of MB to the time required for this is greater by factor of 7.5 than this ratio for two electrode system obtained for the same SA conditions. The treatment efficiency in multi electrode reactor is explained by the numerous collisions of multiple electrodes leading to the formation of eroded nano-particles with the surface catalytically active towards MB oxidation.

Low voltage, low energy submerged pulsed arcs with a pulse repetition rate of 100 Hz, energy of 48 mJ and duration of 20 mu s were used to determine the electrode erosion rate during treatment of 10 mg l(-1) methylene blue (MB) dissolved in 40 ml of deionized water, with and without the addition of 0.5% H2O2. Anode/cathode pairs of Fe/Fe, Ti/Ti, Cu/Cu, Cu/Fe, Fe/Cu, Ti/Fe, Fe/Ti, Cu/Ti and Ti/Cu were used. Smaller cathode erosion was measured, in the solutions without H2O2, with copper cathodes than with other cathodes. Smaller anode erosion in the same conditions was demonstrated by using pairs with a Ti anode than with other anodes and larger erosion was found for Cu anodes. By adding H2O2 to the treated solution, smaller cathode erosion was measured by using pairs with a Ti cathode than with other cathodes and larger rates were measured for Fe cathodes. The largest anode erosion was observed for a Cu anode. The erosion of the anode and cathode depends on material combination of the electrode pairs, i.e. on the thermo physical properties of the electrode materials. The correlations of anode/cathode erosion ratio (G(a)/G(c)) with ratio (q(am)/q(cm)) for various electrode materials were found, where q(am) and q(cm) are heat fluxes in the body of the anode and cathode, respectively. The experimental data were fitted by curves described with equation G(a)/G(c) = A(q(a)/q(c))(-b) where A and b are experimental constants.

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.

Powders of C and Ni-C nanoparticles were synthesized using a pulsed arc between C and Ni electrode pairs, respectively, submerged in ethanol. The arc was ignited by inter-electrode breakdown. The ethanol was arc treated for 5 min with 1ms duration pulses, at a repetition rate of ~1 kHz. The pulse energy was 50mJ. The samples were examined by HRSEM, TEM, EDX and XRD. Magnetic properties were studied in a SQUID magnetometer. The magnetization curve of “raw” C powder, i.e. containing all of the particles produced, whether magnetic or not, at 20 and 300 K showed hysteresis, with saturation magnetization M s ~0.90‐0.93emu/g, residual magnetization M r =0.022 and 0.018emu/g, and coercive force H c =11 and 8Oe, respectively. Magnetic C particles were separated from non-magnetic particles using a Bio-Ferrograph. SEM examination of the separated magnetic particles showed that they were agglomerates of ~30-50 nm diam spheres, and nanotubes and nano-rods with lengths of 50-250 nm and diameters of 20-30 nm. The powder produced using the Ni electrodes consisted of carbon particles and nickel-carbon alloy particles coated with carbon. The carbon concentration in the Ni alloy was approximately triple that of the maximum solid equilibrium solubility. 95% of the particles had a diameter of less than 30 nm. The material was superparamagnetic in a wide temperature interval T>T B = 8 K and had a very narrow hysteresis loop H c <8Oe (i.e. it is a soft magnet) in the superparamagnetic state. When reducing the temperature to T≈T B , the magnetic moment of the particles began to increase very quickly, interaction between Ni particles increased and the material transformed to the blocked state. The energy barrier between these states was observed experimentally as a sharp maximum at 8 K in the χ’’(T) dependence.

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 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.

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.

Texturing of contact surfaces has a remarkable influence on their tribological properties. Various texturing techniques such as machining, ion beam texturing, etching techniques and laser texturing are employed for preparation of micrometer-sized valleys. Modern modification of surface layers for friction applications combines surface texturing and filling of textured layers by solid lubricant MoS2/WS2 or other compositions. In this work pulsed air arc treatment (PAAT) was used to texture the surface layers. The textured surfaces were obtained and then filled by solid lubricant. Some burnishing methods were used to deposit solid lubricant films on steel surfaces. The tribological properties of solid the lubricant films on textured surfaces were compared with the behavior of solid lubricant films burnished on ground surfaces. The wear rate and wearability of solid lubricant films were assessed. It was shown that application of PAAT and filling of micro-reservoirs by solid lubricant particles provide longevity under dry friction conditions.

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.

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.

Powder consisting nickel and carbon particles were synthesized using a pulsed arc between Ni electrodes submerged in pure ethanol. The ethanol was are treated for 5 min with 20 and 40 mu s duration pulses, at a repetition rate of 100 Hz. The pulse energy was varied in a range of 7.7-192 mJ. 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. Dependencies of the particle structure and size distribution, and the powder production rate and composition, on the pulse energy and duration were studied.The powder samples consisted of nickel and carbon particles. The surface of the nickel particle had a carbon coating. The Ni concentration increased from 32% to 46%, and the C concentration decreased from 68% to 54%, when the pulse energy was increased from 7.7 to 100 mJ with 20 mu s pulses. For 40 mu s pulses the same changes of Ni and C concentrations were obtained when the pulse energy increased from 60 to 100 mJ. The production rate of the Ni and C particles linearly increased with pulse energy.The particle quantity and size distribution width increased with pulse energy. The maximum particle diameter increased from 70 to 550 nm while its minimum diameter remained similar to 50 nm when the pulse energy increased from 7.7 to 48 mJ with pulse duration of 20 mu s. (c) 2005 Elsevier B.V. All rights reserved.

Nanoparticles were synthesized using a pulsed arc submerged in ethanol. Two electrode configurations, (a) a 1×4 mm and a 10×10 mm graphite electrodes, and (b) Ni, W, and steel rod electrode pairs, were used. The liquid was arc treated for 5 min with 100 A peak current, 20 μs duration pulses, at a repetition rate of 100 Hz. Samples were obtained by extracting liquid from the top of the treatment vessel, and by allowing the liquid to evaporate from the vessel, and collecting the residue. The samples were examined by HRTEM, HRSEM, XRD, and X-ray photoemission spectroscopy (XPS). Carbon nanoparticles with an onion-like structure, i.e., composed of concentric spherical layers, were found in the samples from the top of the liquid vessel after arcing with either C or Ni electrode pairs. These particles typically had an o.d. of 15–20 nm, and the diameter of the interior void was approximately 5–8 nm. In some cases, the onions were clustered together, such that a typical cluster size was 50–60 nm. Ni and W nanoparticles were produced by treatment with Ni and W electrodes, respectively. The particles could be electrically collected by applying a potential difference between a pair of collection electrodes submerged in the fluid. The Ni particles with sizes of ∼15 μm drifted in the direction generally towards the positive electrode with velocities of approximately ∼2.5–3.5 mm/s in a d.c. electric field of 100 V/mm.