High Arc Research Articles

Preparation and characterization of a TiO2-cis photocatalyst for CO2 reduction and utilization.

With the overabundance of detrimental gases in the atmosphere such as carbon dioxide, efforts are being made to not only remove them but to utilize them in artificial photosynthetic pathways. Titanium dioxide nanoparticles are well-known photocatalytic materials for water splitting and CO2 reduction. By introducing semiconductor nanocrystals, the electronic structure of the TiO2 may be altered to improve efficiency and selectivity for synthetic routes. Wet chemistry and inert atmospheric methods were used to synthesize copper indium sulfide (CIS) quantum dots and TiO2 nanomaterials. Characterization results from UV-Vis, fluorescence, and infrared spectroscopy will be presented. A vacuum system, high power arc lamp, and infrared spectroscopy were employed to investigate potential photosynthesis using the TiO2-CIS in the presence of CO2 gas and H2O vapor. Results from these experiments will be provided.

Zirconate Pyrochlore Frustrated Magnets: Crystal Growth by the Floating Zone Technique

This article reviews recent achievements on the crystal growth of a new series of pyrochlore oxides—lanthanide zirconates, which are frustrated magnets with exotic magnetic properties. Oxides of the type A 2 B 2 O 7 (where A = Rare Earth, B = Ti, Mo) have been successfully synthesised in single crystal form using the floating zone method. The main difficulty of employing this technique for the growth of rare earth zirconium oxides A 2 Zr 2 O 7 arises from the high melting point of these materials. This drawback has been recently overcome by the use of a high power Xenon arc lamp furnace for the growth of single crystals of Pr 2 Zr 2 O 7 . Subsequently, large, high quality single crystals of several members of the zirconate family of pyrochlore oxides A 2 Zr 2 O 7 (with A = La → Gd) have been grown by the floating zone technique. In this work, the authors give an overview of the crystal growth of lanthanide zirconates. The optimum conditions used for the floating zone growth of A 2 Zr 2 O 7 crystals are reported. The characterisation of the crystal boules and their crystal quality is also presented.

High vacuum arc ion plating TiAl coatings for protecting titanium alloy against oxidation at medium high temperatures

High vacuum arc ion plating TiAl coatings are explored for protecting titanium alloys against oxidation at temperatures below 700°C. Bi-phased TiAl coatings which are composed of γ-TiAl+α2-Ti3Al were obtained under the substrate bias range of 0V to −350V, which formed Al2O3-rich oxide layers during oxidation. Higher bias induced slight decrease of Al content but dramatically densified the microstructure of the coating, resulting in improved oxidation resistance of the TiAl coatings. Meanwhile, no detrimental interdiffusion phase was observed after oxidation for 100h, showing good protectiveness of the TiAl coatings.

Backward flowing molten metal in weld pool and its influence on humping bead in high-speed GMAW

The additional electromagnetic force generated by the interaction of external magnetic field and the welding current was applied to suppress the momentum of the backward flowing metal and to prevent the occurrence of humping bead in high speed gas metal arc welding. The vision-based observation was utilized to capture the images of the weld pool and the features of the backward flowing molten metal in the weld pool were extracted and compared under different welding speeds and excitation currents of the magnetic field. The velocity of the backward molten metal flow on the surface of the weld pool was calculated and analyzed by the combination of the visual observation and the tracer particle technique. It was found that the velocity of the backward flow metal are decreased and the humping was disappeared when the external magnetic field was applied.

Characterization of mechanical and electric properties of geopolymers synthesized using four locally available fly ashes

Geopolymer can be synthesized using industrial wastes such as fly ash, making it a promising material to replace Ordinary Portland Cement (OPC) as a green binder for concrete materials. One major barrier to prevent the wide application of geopolymer is that its properties heavily depend on the source materials. Aiming to evaluate the effect of fly ash on the properties of synthesized geopolymers, this study used four carefully selected fly ash to synthesize geopolymers. Comprehensive experimental programs have been carried out to characterize both the mechanical and electrical properties of these geopolymers. Mechanical testing shows that similar chemical composition in the source materials doesn’t guarantee similar compressive strengths of the produced geopolymers, and that high content of calcium doesn’t always lead to high compressive strength. Electrical characterization shows that both the magnitude of the electrical impedance and the electrical resistance of the geopolymers at early age measured at frequency of 10kHz increase with the curing time. It has also been found that at the early age, the electric resistance of the geopolymers is mainly determined by the reaction rate. At the late age, this electric resistance is mainly controlled by the chemical composition. Measurements over one year show that the bulk electric resistances or the diameters of the high frequency arcs of all geopolymers increase with age during the one-year testing period, suggesting that the geopolymerization is a very long process.

Designs and preparation of advanced HVOF-PVD duplex coating by combination of HVOF and arc ion plating

Abstract Advanced HVOF-PVD duplex coatings were produced on the medium carbon steel by combinations of High Velocity Oxygen-Fuel (HVOF) and arc ion plating. The microstructures and mechanical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) in association with mechanical property measurement. The results show that the duplex coating are composed of an inner NiCr-Cr 3 C 2 -based HVOF-sprayed layer mainly consisted of γ-NiCr and Cr 3 C 2 phases, and an outmost PVD-AlCrN layer containing fcc-AlCrN phase. Duplex coatings reveal more excellent wear resistance when compared to the HVOF-sprayed coating. The improved wear resistance is mainly related to the outmost AlCrN layer with more excellent wear resistance in comparison to the HVOF-sprayed coating against WC ball. The AlCrN layer deposited on NiCr-75 wt.% Cr 3 C 2 duplex coating reveals higher wear resistance than that of the AlCrN layer deposited NiCr-30 wt.% Cr 3 C 2 duplex coating. The improvement of wear resistance is mainly associated to its higher surface hardness, load capacity and bond strength. The main wear mechanisms of the duplex coatings are adhesive and oxidation wear, whereas the ones of the single HVOF-sprayed NiCr-Cr 3 C 2 -based coating are adhesive wear as well as spalling and chipping wear.

Effect of temperature on the electronic/ionic transport properties of porous LiNi0.5Mn1.5O4 with high voltage for lithium ion batteries

Porous spinel LiNi0.5Mn1.5O4 microspheres were successfully synthesized by a facile method with microspheres MnCO3 template, and characterized by XRD and SEM. The as-synthesized porous LiNi0.5Mn1.5O4 microspheres exhibit high rate capability and good cycle performance, with the specific discharge capacity of 125.5, 125.4, 121 and 97.6 mA h/g at 1, 2, 3 and 5 C, respectively, and the capacity retention of 85.6% at 5 C after 100 cycles, which are attributed to the porous structure. It is found that the EIS features of spinel LiNi0.5Mn1.5O4 cathode are related to the temperature, and the middle to high frequency arc is observed in the Nyquist diagram at temperatures below zero, which is attributed to the electronic properties of the electrode material. In 1 mol/L LiPF6-EC:DEC:DMC electrolyte solutions, the energy barriers for the ion jump related to migration of lithium ions through the SEI film of the spinel LiNi0.5Mn1.5O4 cathode are determined to be 16.89 kJ/mol, the thermal activation energy of the electronic conductivity to be 0.348 eV, and the intercalation-deintercalation reaction activation energies to be 0.619 eV, respectively.

Numerical study of arc in SF6 gas circuit breaker with externally applied magnetic field

The influence of an externally applied magnetic field on the characteristics and the transient behavior of the arc in a gas circuit breaker is examined by means of three‐dimensional time‐dependent numerical simulations. It is assumed that the gas circuit breaker has a ring‐shaped permanent magnet and an arc is exposed to the externally applied magnetic field. Numerical results demonstrate that the rotation of arc induced by the Lorentz force produces a three‐dimensional spiral structure of the arc. As a consequence of the rotation, the arc shrinks and the arc temperature decreases remarkably just before the time when the arc current is zero, so that applying the magnetic field increases the arc voltage. The numerical results also show that a swirling flow generated by the Lorentz force carries a thermal energy toward the thermal puffer room mainly by the convection during the high arc current phase, and as a result the pressure in the thermal puffer room increases. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Numerical analysis of undercut defect mechanism in high speed gas tungsten arc welding

A computational fluid dynamics model is developed to investigate undercut defect formation in high speed gas tungsten arc welding (GTAW) process. Double-ellipse arc shear stress model and modified double-ellipse arc heat source and arc pressure models are used, which are self-adaptive to weld pool surface evolution. The heat and mass transfer in weld pool and solidified weld bead profile are simulated and the undercut mechanism are discussed. The prematurely solidified periphery part at maximum width of weld pool is the initiation of undercut defect and the inward velocity component at trailing periphery due to teardrop-shaped weld pool profile promotes subsequent undercut formation, which provides an explanation to the high tendency of undercut formation during high current and high speed welding. The undercut morphology is unremarkably influenced by Marangoni force and the capillary pressure hinders undercut formation to some extent. The developed model is validated by comparing undercut morphology and gouging region profile from both simulation and experiment.

Electrochemical immittance spectroscopy applied to a hybrid PVA/steel fiber engineered cementitious composite

Alternating current (a.c.) electrical property measurements are presented on an Engineered Cementitious Composite (ECC) reinforced with a hybrid mix of polyvinyl alcohol fibers (fixed dosage) and straight steel fibers of varying dosages (0.15–1.0% by volume), with the aim at elucidating the influence of conductive inclusions on the nature of conduction and polarization processes within the composite. Measurements were undertaken over the frequency range 1Hz–10MHz at 7, 14 and 28days after casting and the data presented in a range of formalisms to aid interpretation. When plotted in the frequency domain, the work shows that steel fibers enhance the polarizability of the material, particularly within the frequency range ~10Hz–10kHz. When presented in Nyquist format, this feature manifests itself as an intermediate arc forming between a high frequency arc (>10kHz) and a low frequency arc (<10Hz), the latter resulting from polarization processes at the sample/electrode interface. The prominence of the intermediate arc was found to be dependent upon steel fiber dosage and curing time. It is shown that the bulk electrical conductivity conforms to the equivalent inclusion theory which is a variant on the effective medium theory.

Enhancement of mechanical property and corrosion resistance of 316L stainless steels by low temperature arc plasma nitriding

Abstract AISI 316 L austenitic stainless steels (316 L SS) were nitrided to enhance their mechanical property and corrosion resistance by a high efficiency low-pressure arc plasma nitriding process at low temperature (~ 400 °C). Arc currents ranging from 55 A to 95 A were applied to generate the arc plasma. The effect of arc current on the microstructure, mechanical property of the nitrided layers was investigated by using XRD, SEM, TEM, Vickers microhardness tester and ball-on-disk tribometer, respectively. The corrosion resistance was also evaluated by potentiodynamic polarization in 3.5% NaCl solution. The results showed that the nitrided layers consisted primarily of the expanded austenite (γN) phase with a trace of a mixture of CrN and Fe3N. The thickness of nitrided layer could reach 15 μm in 1 h at 400 °C in virtue of the high-density and high-energy nitrogen plasma generated from this process, which showed an extremely fast nitriding kinetics. Due to the solution strengthening of the nitrogen super-saturation γN-phase formed on the surfaces of the samples, the surface microhardness and the wear resistance of the nitrided 316 L SS was significantly improved. The worn surfaces revealed that worn behavior of the low current (below 85 A) nitrided samples was remarkably dominated by micro-abrasion and spalling holes, while the 95 A sample was worn in a mode featured by cracks and spalling blocks. Besides, because chromium nitride precipitation was eliminated, the nitrided samples still showed excellent corrosion resistance, which was comparable to untreated 316 L SS.

Influence of Welding Techniques on Heat Affected Zone Softening of Dissimilar Metal Maraging Steel and High Strength Low Alloy Steel Gas Tungsten Arc Weldments

The present investigation reports on a study that has been taken up to understand and control the extent of softening in heat affected zone of dissimilar gas tungsten arc (GTA) welds of high strength steels: AISI 4130 steel and 18 % Ni maraging steel which are in hardened condition i.e., maraging steel in solution treated and aged condition and AISI 4130 steel in hardened and tempered condition before welding. The influence of welding technique on the width of soft zone and in-turn on the hardness has been investigated. All the dissimilar joints have been investigated for microstructures, microhardness and tensile properties. It is observed that continuous current GTA welding process results in a wider soft zone, leading to poor mechanical properties, which can be attributed to softer microstructural constituents.

Electrical and hydrodynamic characterization of a high current pulsed arc

High current pulsed arcs are of significant industrial interest and, aiming to reduce time and cost, there is progressively more and more need for computation tools that describe and predict the behaviour of these arcs. These simulation codes need inputs and validations by experimental databases, but accurate data is missing for this category of electric discharges. The principal lack of understanding is with respect to the transient phase of the current, which can reach thousands of amperes in a few microseconds. In this paper, we present the work realized on an experimental setup that simulates in the laboratory an arc column subjected to five levels of high pulsed current, ranging from 10 kA to 100 kA, with the last one corresponding to the standard lightning current waveform used in aircraft certification processes. This device was instrumented by high speed video cameras to assess the characteristic sizes of the arc channel and to characterize the shock wave generated by the arc expansion. The arc channel radius was measured over time during the axisymmetric phase and reached 3.2 cm. The position and velocity of the shock wave was determined during the first 140 μs. The background-oriented schlieren method was used to study the shock wave and a model for the light deflection inside the shock wave was developed. The mass density profile of the shock wave was estimated and showed good agreement with Rankine–Hugoniot relations at the wave front. Electrical measurements were also used to estimate the time-dependent resistance and conductivity of the arc for times lasting up to 50 μs.

Variable thickness scroll compressor performance analysis—Part II: Dynamic modeling and model validation

In order to investigate the performance of variable thickness scroll compressor, a detail mathematical modeling based on energy and mass balances is established in this two-part. In part II, dynamic modeling and model validation are developed. Temperature, pressure, mass flow of working chambers, friction loss power of moving parts, efficiency, and shaft power are investigated by solving the mathematical modeling. The experimental rig for variable thickness scroll compressor based on involute of circle, high order curve and arc is set up. From the comparison of the simulated and measured data, it can be seen that the compressor model predicts the mass flow, discharge temperature, and shaft power very well. So the proposed mathematical modeling can accurately describe all the suction, compression, and discharge processes for variable thickness scroll compressor.

Effect of Al2O3 Addition in Partially-Stabilized Zirconia Based NOx Sensors

Porous yttria-stabilized zirconia (YSZ) electrolyte based NOx sensors are capable of providing improved sensing capabilities for NO and NO2 gases at concentrations as low as 5 ppm. However, the brittle, porous structure of the electrolyte significantly limits sensor durability. Adding alumina (Al2O3) to YSZ can enhance the mechanical strength and thermal shock resistance of the NOx sensor electrolyte. It is also anticipated that Al2O3 addition to YSZ will improve sensor adhesion to conventional Al2O3-based substrates used for commercial NOx sensors. Although partially-stabilized zirconia (PSZ) has lower ionic conductivity, in comparison to fully-stabilized zirconia, it can provide greater mechanical strength to the NOx sensor. A decrease in ionic conductivity was a common finding in studies where 20 – 30 wt% Al2O3 was added to fully-stabilized zirconia; whereas, the ionic conducting properties were not observed to change for Al2O3 additions below 10 wt%. Keeping these considerations in view, PSZ porous electrolyte based NOx sensors were fabricated with and without the addition of Al2O3 and operated using the impedancemetric method. The aim of this study was to gain understanding of the impact of Al2O3 and the role of ionic transport on NOx sensing behaviour. Standard ceramic processing methods were used to fabricate porous electrolyte based NOx sensors. Partially-stabilized zirconia powder composed of 8 wt% Y2O3-ZrO2 (Advanced Ceramics) was combined with B-76 binder and ball milled in ethanol to form a slurry. A portion of the slurry was dried and the resulting powder was uniaxially pressed at 200 MPa into pellets. Two Au wire electrodes were affixed to the pellets using the remaining PSZ slurry. The Au electrodes were approximately 3 mm apart and were completely covered by the PSZ slurry coating. The entire assembly was co-fired at 1050 for 1 hr. This procedure was repeated with 3.8 wt% Al2O3 (Sigma Aldrich) added to the slurry to form PSZ-Al2O3 electrolyte based sensors. The structure, morphology, and composition of the fabricated sensors were characterized using x-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy dispersive x-ray (EDX). Electrical properties of the sensors were studied using a Gamry Reference 600 to perform impedance spectroscopy for operating temperatures ranging from 550 – 700 °C where the gas concentrations were 0 - 100 ppm for NO and NO2 with 10.5% O2 and N2 as the balance for dry and humidified (3% H2O) conditions. SEM images showed a porous network of particles within the PSZ electrolytes and well dispersed Al2O3 particles throughout the PSZ-Al2O3 material. Using Archimedes method, the porosity for the PSZ and PSZ-Al2O3 electrolytes were determined to be approximately 44% and 42%, respectively. Analysis of the chemical compositions of both sensor electrolytes through EDX and XRD revealed no impurities and presence of α alumina was confirmed. The impedance data for the PSZ and PSZ-Al2O3 sensors contained two distinct arcs describing electrolyte and interfacial reactions. The high and low frequency arcs for the PSZ-Al2O3 sensors were generally about 50% and 25% larger, respectively, than the arcs for the PSZ sensors. This suggested that the alumina addition interfered with ionic transport within the electrolyte, and also limited reaction sites at the electrode/electrolyte interface. Analysis of the capacitance behaviour of the PSZ and PSZ-Al2O3 sensors based on equivalent circuit modelling of the impedance spectra indicated a decrease in capacitance with increasing NOx concentration and operating temperature for both dry and humidified gas conditions. The data also indicated a more substantial capacitance decrease for PSZ-Al2O3 sensors. The capacitance described the oxygen coverage at the electrolyte/electrode interface; and, the data suggests that the addition of Al2O3 further limited oxygen coverage possibly due to Al2O3 occupying O2 sites at the interface. Other key results were determined from the change in capacitance, ΔC = CO2 – CNOx, which is beneficial for interpreting NOx sensitivity as it is independent of frequency, thereby providing a broader interpretation of the NOx response. The terms, CO2 correspond to the capacitance with only 10.5% O2 and N2 present; and, CNOx describe the capacitance with the addition of NO or NO2 in the gas stream. In general, NOx sensitivity based on ΔC for the PSZ-Al2O3 sensors was over 50% higher than sensitivity values determined for PSZ sensors. In addition, it was found that the presence of H2O caused an increase in NOx sensitivity of about 30% for both the PSZ and PSZ-Al2O3 sensors. Overall, based on the operating conditions studied, the addition of 3.8 wt% Al2O3 seemed to limit oxygen at the electrolyte/electrode interface, such that NOx reactions could proceed more readily leading to greater NOx sensitivity.

Effect of spray parameters on the splashing of plasma-sprayed cast iron particles

To understand the effects of spray parameters on the splashing, cast iron particles were plasma-sprayed onto polished surfaces of aluminum substrate to form single splats. Various plasma arc powers and spray distances were applied to adjust the morphology of the splats which was studied using a field emission scanning electron microscope (FESEM). The experimental results showed that the splashing of impinging droplets was significantly restrained for the splats deposited with high arc power (30 kW) and short spray distance (80 mm). This finding would be beneficial to improving the adhesive strength of the coating.

Construction material properties of slag from the high temperature arc gasification of municipal solid waste

Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m3) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self cementing character which supports the elevated LBR results. Preliminary material characterization of the HTAG slag establishes potential for beneficial use; larger and longer term studies focusing on the material’s possibility for swelling and performance at the field scale level are needed.

Optimization of the plasma parameters for the high current and uniform large-scale pulse arc ion source of the VEST-NBI system

A large-scale hydrogen arc plasma source was developed at the Korea Atomic Energy Research Institute for a high power pulsed NBI system of VEST which is a compact spherical tokamak at Seoul national university. One of the research target of VEST is to study innovative tokamak operating scenarios. For this purpose, high current density and uniform large-scale pulse plasma source is required to satisfy the target ion beam power efficiently. Therefore, optimizing the plasma parameters of the ion source such as the electron density, temperature, and plasma uniformity is conducted by changing the operating conditions of the plasma source. Furthermore, ion species of the hydrogen plasma source are analyzed using a particle balance model to increase the monatomic fraction which is another essential parameter for increasing the ion beam current density. Conclusively, efficient operating conditions are presented from the results of the optimized plasma parameters and the extractable ion beam current is calculated.

Interruption Phenomenon in Intermediate-Frequency Vacuum Arc**supported by National Natural Science Foundation of China (No. 51377007), Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20131102130006), and Fundamental Research Funds for the Central Universities of China

In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.

Effect of extrusion on corrosion behavior and corrosion mechanism of Mg-Y alloy

AbstractThe influences of the hot extrusion process on the microstructure, corrosion behavior and corrosion mechanism for Mg-Y magnesium alloy were studied by means of the microstructure observation, weight loss test, electrochemical test and corrosion morphology test. The results showed that with increasing of the extrusion ratio, the shear flow line on the vertical section of the extruded alloy increased, the shear bands parallel lines became more clearly visible, and a large number of fine equiaxed grains distributed in parallel with the flow lines. The open circuit potential had a certain degree of improvement after extrusion, the open circuit potential increased with increment of extrusion ratio, and the corrosion potential of the vertical section was higher than that of the same alloy in the same compression ratio. The shift rate of the corrosion potential relatively became larger with increasing of the extrusion ratio, and the cathode corrosion current corresponding to the branch migration shifted to the positive direction. The high frequency capacitive arc increased with increment of the extrusion ratio, and the radius of capacitive arc of the vertical section was slightly larger than that of the transverse section. The corrosion morphologies of Mg-0.25Y alloy were uniform corrosion, and the corrosion morphologies of Mg-(2.5, 5, 8 and 15) were the pitting corrosion and the small range, deep depth localized corrosion.