Direct Current Method Research Articles

Ferromagnetic anisotropy in scandium-doped AlN hierarchical nanostructures

We experimentally fabricated uniformly distributed single-, double- and six-sided Sc-doped AlN (AlN:Sc) nanodendrites by a plasma-assisted direct current arc discharge method. The crystal structure, composition, morphological and microstructures were characterized, and the physical mechanisms governing the formation of AlN:Sc nanodendrites were examined. It was found that the morphology and the crystal orientation of the AlN nanodendrites can be controlled by tuning the N2 pressure. The incorporation of Sc induces native point defects in AlN that contribute to the growth of hierarchical structures and affect the room-temperature photoluminescence. The AlN:Sc nanodendrites exhibit room-temperature anisotropic ferromagnetism, and this is strongly depend on the orientation of the nanodendrites. This work provides a facile strategy to fabricate complex hierarchical AlN:Sc nanostructures with manipulated magnetic properties which may find promising applications in spintronic nanodevices.

Incorporating graphene into a sintered ceramic tape: Structural and magnetic properties of a zirconia-graphene composite

We report an experimental investigation of the structural and magnetic properties of a zirconia-graphene composite. Specifically, we employed tape casting and direct current plasma method to incorporate graphene into a sintered ceramic tape. By considering experiments of rheology, thermogravimetric analysis, X-ray diffractometry, Raman spectroscopy, and Scanning Electron Microscopy, we confirmed that the graphene is embedded in the structure of the zirconia-graphene composite. Further, through the magnetic characterization, we disclosed the ferromagnetic response of the sintered composite. Our findings demonstrated that the employed route successfully functionalizes graphene nanoplatelets and also promotes a magnetic response in ceramics composites, thus opening new possibilities of technological applications for Carbon-based composite materials.

Electrical conductivities and microstructures of LSM, LSM-YSZ and LSM-YSZ/LSM cathodes fabricated on YSZ electrolyte hollow fibres by dip-coating

Lanthanum strontium manganite – La0.80Sr0.20MnO3 (LSM), LSM-Yttria stabilised zirconia (LSM-YSZ) composite and LSM-YSZ/LSM double-layer cathodes were separately fabricated on Yttria stabilised zirconia (YSZ) electrolyte hollow fibres by dip coating; their electrical conductivities and microstructures were then determined by the direct current four-probe method and scanning electron microscopy (SEM), respectively. Excellent cathode-electrolyte and cathode-cathode adhesion without delamination were achieved by the dip-coating fabrication method. The apparent electrical conductivities of porous LSM, LSM-YSZ and LSM-YSZ/LSM cathodes manufactured on YSZ hollow fibre by dip-coating and sintered at various temperatures in the range 1273–1473 K for 3 h, were 1.8 × 103–5.5 × 103 S/m, 0.32–209 S/m and 1.3 × 103–5.5 × 103 S/m, respectively, at measurement temperatures of 673–1073 K. The operating temperature dependence of the apparent electrical conductivity of the LSM, LSM-YSZ and LSM-YSZ/LSM cathodes was defined by the Arrhenius equation for electrical conductivity. The activation energies for electrical conductivity were derived as 0.106–0.147 eV, 0.83–0.94 eV, and 0.104–0.146 eV for the LSM, LSM-YSZ and LSM-YSZ/LSM cathodes, respectively. The LSM-YSZ and LSM-YSZ/LSM cathodes were strongly influenced by the YSZ and LSM phases, respectively.

The electrochemical degradation of malachite green with lead dioxide electrodes by pulse current oxidation methods

ABSTRACT The pulse current oxidation methods were used to degrade the malachite green (MG) using lead dioxide as anodes. The influences of operating parameters, including pulse frequency, pulse current density and pulse duty cycle, on the MG removal efficiency were investigated. The results indicate that MG removal efficiency can reach 99.6% after 90 min with the pulse frequency at 10 Hz, pulse current density at 30 mA cm−2 and pulse duty cycle at 0.6. The pulse degradation processes follow the pseudo-first-order kinetics. Comparison with direct current oxidisation methods, pulse oxidisation methods can enhance MG and COD removal efficiency and reduce the energy consumption. Moreover, pulse oxidisation methods can increase the amount of hydroxyl radicals generation and reduce side reactions (such as oxygen evolution) in the degradation process of MG. Finally, a possible degradation pathway of MG in pulse current modes was proposed based on the intermediate products identified by GC/MS.

Fabrication and magnetic properties of Tb–Fe–B nanotubes prepared by electrochemical deposition

Tb–Fe–B magnetic nanotubes were firstly prepared via direct current (DC) electrochemical deposition method in anodic aluminum oxide (AAO) templates, and its formation mechanism was illustrated. Scanning electron microscopy (SEM) analyses showed that the Tb, Fe, and B elements were deposited into the nanotubes successfully. X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) were performed to investigate the morphology, micro-crystal structure, and magnetic properties of the ternary system Tb–Fe–B nanotubes at different solution concentrations. The results indicated that the nanotubes have the same one-dimensional structure as nanowires and the direction of the axis was easy to be magnetized. The as-deposited nanotubes consisted of soft magnetic phases (Fe3B and TbB6) and amorphous phase, which exhibited soft magnetic properties. After annealing at 600 °C for 2 h, the hard magnetic phases of Fe3Tb and Tb2Fe14B appeared and the nanotubes transformed from an incomplete crystalline state to a complete crystalline state with a larger diameter. Due to the exchange coupling between hard and soft magnetic phases, Tb–Fe–B nanotubes obtained good hard magnetic properties with an improved coercivity. When the concentration of Tb ion is 0.04 mol/L, the relative intensity of the diffraction peaks and coercivity is the largest. Therefore, Tb–Fe–B rare-earth alloy nanotubes would be one promising magnetic storage and recording material.

Properties and application of multi-functional and structurally colored textile prepared by magnetron sputtering

Adopting magnetron sputtering continuous automatic production line equipment for industrial production, polyester fabrics as the substrates were coated with nano-Ag/TiO2 composite films prepared by direct current sputtering method and direct current/radio frequency reactive sputtering method, respectively. The microstructure of Ag/TiO2 composite films deposited on the surface of the fabrics was dense and uniform. Structural colors were generated on the surface of the fabrics coated with the composite films and the coloring mechanism was consistent with the single-layer film interference principle. The color fastness, mechanical properties, comfortable properties were not significantly changed and had better antistatic property, anti-ultraviolet property, and antibacterial property compared with the original polyester fabrics. Therefore, the multi-functional and structurally colored fabrics can be prepared by magnetron sputtering technology, and can achieve industrial production, and have wide application prospects in apparel, home textile, and so on.

Degradation behaviors and failure of magnetron sputter deposited tantalum nitride

A reactive direct current magnetron sputtering method with a controlled total gas flow rate was used to fabricate thin films of tantalum nitride (TaN) on SiO2/Si and multilayer ceramic substrates. In order to identify the total gas flow rate that produced the lowest variation in the sheet resistance and the temperature coefficient of resistance (TCR), TaN films deposited under total gas flow rates of 30, 40, 60, and 80 sccm were characterized in terms of their structural and electrical properties. The optimum total gas flow rate was 60 sccm revealing the lowest deviation of sheet resistance and TCR. Next, the durability and reliability at high temperatures, after heating and cooling cycles, and exposure to induced current were tested. The degradation behaviors and failure of TaN films were investigated by measuring the sheet resistance variation. To further explain the degradation of TaN films, additional analysis of their crystallinity was conducted. The results showed that TaN-based thin film resistors have high durability and reliability and are suitable for embedded passive resistors.

Impact of the dangling bond defects and grain boundaries on trapping recombination process in polycrystalline 3C SiC

The bulk polycrystalline (pc) 3C SiC of n- and p-type obtained by thermal decomposition of methyltrichlorosilane vapor have been studied by applying the electron paramagnetic resonance (EPR), direct current (DC) conductivity, photoconductivity (PC) and PC time-resolved decay methods. The energy level of the two donor-like minority carrier traps at ε1 = 77 meV and ε2 = 92.6 meV located at the grain boundaries (GB) of pc-3C SiC has been obtained using the measurements of the temperature dependence of DC conductivity and PC in the range of 80–600 K. The minority carrier traps assigned to carbon and silicon dangling bonds with the carbon back bonds were observed in the EPR spectra of pc-3C SiC of n- and p-type at g = 2.0029(3), g = 20042(3), respectively. The PC time decay after the termination of the photo-excitation was studied in monocrystalline and pc-3C SiC of n- and p-type at 80 K. The persistent relaxation of PC has been described by kinetic equations accounting the trapping, ionization, and recombination processes of non-equilibrium charge carriers bound dynamically to shallow donors and acceptors. We have concluded that the main process responsible for the long-lived relaxation of the PC is trap-assisted electron-hole recombination in n-type pc-3C SiC and ionization of boron acceptors, as well as the hole escape/capture at the boron level in p-type pc-3C SiC. The differences in the relaxation process of the PC in n- and p-type pc-3C SiC were explained by the presence of the potential barrier height of about 8.6 meV at GB for the capture of the majority carriers in p-type pc-3C SiC.

Determining Proton Transport in Pseudo Catalyst Layers Using Hydrogen Pump DC and AC Techniques

Optimizing electrode morphology with a more uniform ionomer distribution is key to reducing ohmic losses and increasing electrocatalyst utilization in polymer electrolyte fuel cells (PEFCs). Inherent ionomer conductivity, volume fraction and tortuosity determine effective ionic conductivity. We use hydrogen pump (HP) method to measure effective ionic conductivity of a pseudo catalyst layer (PCL) comprised of Vulcan XC-72 carbon black and 3M 825 EW ionomer with ionomer to carbon (I/C) ratios of 0.6, 1 and 1.4 and relative humidity (RH) range of 50 to 120%. These direct current (DC) experiments are then compared with electrochemical impedance spectroscopy (EIS). Both DC and EIS methods show good agreement, indicating that EIS can be used as an alternative to DC method in HP experiment. Ionic conductivity for PCL with I/C of 1 and 1.4 was found to be about one order of magnitude higher than I/C of 0.6 for most of the RH range. At 90% RH tortuosities for I/C = 1 and 1.4 were close to 1, whereas tortuosity for I/C = 0.6 was 3. With decrease in relative humidity tortuosities increased linearly and at 50% relative humidity a PCL with I/C = 0.6 had the highest tortuosity of 6.1.

Crack Detection and Localization with Multiple Potential Drop Measurements

The direct current potential drop method (DCPD) is commonly used to measure the crack length in fatigue tests. Due to a propagating crack the cross section of the specimen is reduced leading to a densification of potential field lines, whereby the measured potential difference increases. First experiments on notched round bars have shown that the location of a crack can be determined with a multiple potential drop measurement (Hartweg and Bär, 2019).In this study single-edge notched specimens were equipped with three potential probes – on the frontside (Uf), on the backside (Ub) and on the narrow side (Un) of the specimen. During the fatigue test the three potentials were measured simultaneously using amplifiers of the control electronics. To enable a direct comparison between the potential drop measurement and the real crack geometry, the crack front was marked on the fracture surface by introducing overloads in defined intervals.The measured potential values were normalized on the starting potential and quotients of the potentials were formed (Pf/Pn and Pb/Pn). By plotting the potential quotients over the cycle number, the time as well as the location of the crack initiation site can be identified. In addition, it was possible to identify subsequent cracks and to determine the shape of the crack front of long fatigue cracks based on the measured potential data.

Advanced detection and analysis of inclined shaft passing through aquifer in the mine of western China

The thick sandstone aquifer of the Cretaceous Yijun formation is rich in water and poor in predictability. Under this circumstance, the issue of the main inclined shaft of the mine in western China has been studied. Then, the comprehensive geophysical method is used in the field for advanced exploration and prediction. Based on the mine transient electromagnetic method and direct current resistivity method, the comprehensive advanced detection is carried out. Furthermore, the low resistance area in front is determined, the geological anomaly position and characteristics in front of the head are judged, and the water rich area of the detection is qualitatively evaluated, which provides support for the formulation of production technology scheme. The driving construction verification shows that the result of comprehensive geophysical exploration is basically consistent with the actual one of the shaft, and the detection accuracy of the relatively rich water area reaches over 80% which demonstrates that the comprehensive geophysical exploration method can be effectively applied into the construction of inclined shaft driving.

Effect of the base material condition on the structure and properties of Al2O3 oxide layers

The paper presents a new method for modelling oxide layers for tribology related needs. The most recent world trendsin the machine-building sector, in particular with reference to piston machines, are heading towards reducing theirlubrication and cooling. Hence, a question arises, what the upper layer of a ceramic material should be like in order tomaintain low wear and low frictional resistance. An oxide layer for tribological needs has been formed on an AlMg2 alloy asa result of hard anodizing in SAS electrolyte. This electrolyte enables the control of oxide layer production parameters,which allowed obtaining for the tests an oxide coating with a wide range of changes in porosity and micro-hardness μHV.Anodizing has been carried out by means of the direct-current method, using a stabilized feeder, GPR-25H30D, for aconstant electrical charge density of 180 Amin/dm2. A lead plate has been acted as the cathode in the anodizing process. Bymeans of a scanning electron microscope (SEM), the surface morphology and structure, and the chemical composition of thelayers have been analyzed.

High-pressure topological transport study of Bi2Se3 single crystal

Herein we report the topological transport on compressed Bi2Se3 single crystal, one of ideally topological insulators, based on a combination of in-situ alternating current (AC) impedance spectra and direct current (DC) conductivity methods at room temperature. The insulating bulk and metallic surface states of the sample are well divided into two relaxation processes according to their different responses on electric excitation. We find that the surface state conductivity remains constant in the face of one order of magnitude increase in the bulk state conductivity. The first-principles calculations are adopted to account for the bulk transport results. The band structures calculations reveal the gradual decrease in the intrinsic bandgap with pressure elevation. The variations of charge density difference demonstrate the strengthened interatomic interactions and the formation of small polarons due to the electrons overlap assisted by the lattice shrinking under high pressure. By the pressure dependences of electrical parameters and the relationship between them, a reasonable electrical model of topological insulators is well established and opens up a new way for the exploration of topological architectures under extreme conditions.

Effects on p-type buffer layers for semitransparent organic photovoltaics using indium zinc oxide transparent electrode

The present study used transparent conductive oxide films as the top electrode of semitransparent organic photovoltaic (ST-OPV) cells. Indium zinc oxide (IZO) was fabricated by a facing direct current magnetron sputtering method for the top electrode of ST-OPV cells with an inverted structure, and then, the effect of selecting a p-type buffer material applicable to IZO films was investigated. Three kinds of p-type buffer materials were examined, namely, molybdenum trioxide (MoO3), tungsten trioxide-nanoparticles (WO3-NPs), and dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HATCN). The MoO3-, WO3-, and HATCN-based cells yielded power conversion efficiencies (PCEs) of 4.02%, 3.60%, and 3.14%, respectively. After optimization of MoO3 thickness, the 15 nm thick MoO3-based cell reached a PCE of 4.84% and a transmittance of 19.9% at a wavelength of 550 nm.

Hopping conductivity in V2O5-P2O5 glasses: Experiment and non-constant force field molecular dynamics

Glasses in xV2O5–(100-x)P2O5 system within x range from 35 to 95 mol% are obtained by a melt-quenching method and characterized by X-ray powder diffraction, atomic emission spectroscopy and red-ox titration. The dependences of density and molar volume of glasses on V2O5 concentration are linear up to 90 mol% of vanadium oxide and can be expressed via formulas: ρ = 2.64 + 0.36·xV2O5 g cm−1 and Vmol = 54.17 + 6.36·xV2O5 cm3 mol−1. The electronic conductivity of glasses is measured by both impedance spectroscopy and direct current methods. The glass composition of 95V2O5·5P2O5 shows the highest electrical conductivity value of ~1.0 × 10−4 S cm−1 at 50 °C. The concentration dependence of the conductivity is described at a qualitative level with non-constant force field molecular dynamics.

Non-Evaporable Getter Ti-V-Hf-Zr Film Coating on Laser-Treated Aluminum Alloy Substrate for Electron Cloud Mitigation

For improving the vacuum and mitigating the electron clouds in ultra-high vacuum chamber systems of high-energy accelerators, the deposition of Ti-V-Hf-Zr getter film on a laser-treated aluminum alloy substrate was proposed and exploited for the first time in this study. The laser-treated aluminum surface exhibits a low secondary electron yield (SEY), which is even lower than 1 for some selected laser parameters. Non-evaporable getter (NEG) Ti-V-Hf-Zr film coatings were prepared using the direct current (DC) sputtering method. The surface morphology, surface roughness and composition of Ti-V-Hf-Zr getter films were characterized and analyzed. The maximum SEY of unactivated Ti-V-Hf-Zr getter film on laser-treated aluminum alloy substrates ranged from 1.10 to 1.48. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate that the Ti-V-Hf-Zr coated laser-treated aluminum alloy could be partially activated after being heated at 100 and 150 °C, respectively, for 1 h in a vacuum and also used as a pump. The results were demonstrated initially and the potential application should be considered in future particle accelerators.

Piping process: Genesis and network characterization through a pedological and geophysical approach

Piping is a soil erosion process initiated by concentrated subsurface water flow, which can develop in both natural and anthropogenic landscapes and causes various environmental impacts. The piping process acts as a relief modifier, leading to soil subsidence on a short time scale. This paper aims to provide a more comprehensive characterization of the piping process in a tropical forested area of Brazil. First, we sought to understand and examine the subsurface environment of the soil, using field description and soil sampling for chemical and physical analyses (pH, CEC, bulk density, total porosity, flocculation degree). Based on this information, we performed geophysical tests using Direct Current resistivity method (DC resistivity), with six lines of electrical resistivity tomography (ERT), to map the pipes and check the connection between subsurface tunnels. Data on the basic properties of the soil aided our interpretation of the geophysical results and the genesis of the piping process. The soil of the study area presented horizons in which textural variations accompanied changes in total porosity, bulk density and flocculation degree. The DC resistivity method efficiently detected the pipes (resistive zones of values >4000 O.m and high contrast with adjacent zones) and revealed the connection and continuity of the pipe network. While various factors may contribute to the subsurface erosive process in the study area, the decisive factor triggering the process seems to be the presence of a permeable layer that lies just above the impermeable layer, which may stop water infiltration and facilitate the lateral water movement.

Mitigation of high voltage induction effect on ICCP system of gas pipelines: a field case study

An analysis of the high voltage induction effect on the impressed current cathodic protection (ICCP) system on pipelines parallel toward high voltage power lines was employed in this research. Mitigation of high voltage effect throught human and environment is necessary to implemented. Direct current induction was used to increase the electrical potential of the gas pipeline, from Klumpang to sicanang area, Indonesia. During the mitigation process, the highest induction value was obtained 0.00574 KV which is previously was 0.01732 KV, and occurred at the limit of the allowable secure touch tension value of 0.015 KV. The data that acquire from the measurement of test point of ICCP underneath the transmission line revealed a comparison data between field measurements occurred of mitigation process. The direct current induction method is found to be safe for ICCP system and environment.

Roof and floor anomalous response of mine resistivity method

As the exploitation level of coal seams increases in China, mine water inrush is becoming increasingly serious. Effectively detecting the roof and floor anomalous bodies of mines in whole space has always been the focus and challenge of research with the direct current (DC) resistivity method. Based on the finite element theory and the ANSYS finite element software, the ANSYS parametric design language (APDL) of 600 m pole–dipole array A-MN or MN-B of the mine DC resistivity method is given, and the floor model with a distance of 40 m from the abnormal body to the roadway and the roof and floor model with a distance of 40 m, 30 m, 20 m, and 10 m from the abnormal body to the roadway are established, respectively. According to the analysis of calculation error, the maximum relative average error is 2.18%, which shows the correctness of the calculation of model. The calculation results of the above model are plotted, and then the anomalous response characteristics of the roof and floor of the pole–dipole array in the whole-space are obtained by comparing the figures. According to the anomalous response characteristics of roof and floor, it is conducive to accurately interpret the measured data.

The Invariant to Direct Current Signal Non-Coherent Harmonic Alternating Current Signals Vectors Sets Measurement

A high-accuracy fast-acting simple in implementation and invariant to interferences in the form of direct current signal method of non-coherent harmonic alternating current signals vectors sets measurement is described. The solution of stated in the general view problem is gained on the base of so called the splitting sets of samples method and invariant theory approach to measurement process organization. The implementation of the method is illustrated on example of a synthesis of the measurement algorithm for the case of three harmonic signals. The analysis of the gained results is given.