Contact Current Density Research Articles

Treatment of real carwash wastewater using high-efficiency and energy-saving electrocoagulation technique

This study focused on the treatment of actual wastewater from a car wash facility using electrocoagulation. The primary objective was to decrease chemical oxygen demand (COD) and eliminate turbidity by employing various electrodes such as Stainless Steel (SS) 304, Galvanized Iron (GI), and aluminum foil (α-Al) in a batch configuration. Several factors including contact time, current density, initial pH, and electrode material were examined to optimize process efficiency. The sludge generated during electrocoagulation was analyzed using Scanning Electron Microscopy/Energy-Dispersive X-ray Spectrometry (SEM-EDS). The results indicated that COD removal efficiency initially decreased between 30 and 60 min before improving. The data for COD, turbidity, and total phosphate reduction aligned well with the pseudo-first-order kinetic model, with R2 values of 0.275, 0.898, and 0.522, respectively. Minor variations were observed in pH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), and alkalinity, while the temperature increased from 12 to 18.6 °C. Optimal removal efficiency for turbidity, total phosphate, and COD was achieved at pH = 6. The study demonstrated that higher current density resulted in enhanced COD reduction and turbidity removal. Chloride levels decreased with increasing applied current. The α-Al electrode exhibited superior performance compared to SS 304 and GI electrodes, with notable pH fluctuations during the process. UV–visible absorption spectra indicated differences in treated wastewater patterns based on the electrode utilized. SEM analysis revealed distinct characteristics of sludge produced by different electrodes. Energy and electrode consumption varied among the electrodes, with SS 304 displaying the lowest values.

Theoretical study on contact current density in the boundary of random rough surfaces

We theoretically calculate here how random roughness affects the contact current density and equivalently contact resistance by utilizing a perturbative expansion method. Then, By taking into consideration self-affine roughness on the surface of the solids, we find the contact current density. The obtained results illustrate the total contact current exhibits significant dependence on the properties of the self-affine rough surface such as root-mean-square of roughness and Hurst exponent. Assuming a lower value of root-mean-square roughness for a solid in a higher potential compared to another which is connected to a lower potential, results in a decrement of the total contact current compared to the current between solids without roughness. By considering similar rough parameters for both solids, the contribution of the perturbed contact current becomes zero. Moreover, repercussions by considering the conductivity contrast between components are explored.

Numerical study on thermal-electrical-mechanical coupling mechanism of electrical connectors considering contact resistance

Electrical connectors are widely used in electromechanical equipment. Their rough surfaces inevitably induce electrical contact resistance (ECR) and thermal contact resistance (TCR), which generates a significant influence on electricity and heat conducting at the faying surface and affects the accuracy of the thermal-electrical-mechanical coupling (TEMC) numerical calculation. Thus, a TEMC model with ECR and TCR of a parallel groove clamp is necessary to investigate the TEMC mechanism. Firstly, appropriate ECR and TCR models are created based on the available experimental results. Secondly, a refined TEMC finite element model is established by optimising the mesh size at the faying surfaces, and the cyclic coupling calculation method is adopted to achieve efficient and consistent numerical calculations. Meanwhile, the validity of the simulation model is verified by experimental results. Finally, the transient real contact area, current density, and heat generation rate (HGR) are obtained to analyse the TEMC mechanism during temperature rise. The results indicate that the mechanical characteristics during temperature rise are different under two loading conditions of tight and loose, thereby resulting in different changing laws in terms of the maximum current density and HGR. In addition, two coupling mechanisms exist until the steady-state temperature is achieved.

Research and Analysis on Contact Resistance of Wheel and Insulated Rail Joint in High-Speed Railway Stations

Insulated rail joint (IRJ) as one of the components of the track circuit will be burned once the electric arc is generated when the train wheel passes through the insulated rail joint and the track circuit occurs the red-light band fault, which has a great impact on the safety of the train. Reducing the voltage at both ends of the insulated rail joint can effectively prevent the occurrence of electric arc. Clarifying the wheel-IRJ contact resistance is the basis for analyzing the voltage of wheel-IRJ. The effective apparent contact area of the wheel-IRJ contact was derived through the mathematical relation. Considering the surface roughness parameters, based on the electrical contact theory and the Greenwood-Williamson (GW) model, the mathematical models of the wheel-IRJ contact resistance and current density were established, and their influencing factors were analyzed. The results show that the contact resistance increased first and then decreased. The influences of load, roughness of the contact interface, and electric arc heat on the contact resistance were greater. Considering the influencing factors of contact resistance and current density, corresponding protective measures were proposed to reduce the potential difference at both ends of the insulated rail joint.

Effect of Holding Time on the Extrusion Force and Microstructure Evolution during the Plastic Forming of Ti-6Al-4V Micro-Gears.

The application of titanium alloy micro-gears in microelectromechanical systems has been severely restricted, as the graphite mold is prone to abrasion or even to crack at high temperatures, mainly due to the forming load. We aimed to manufacture Ti-6Al-4V alloy micro-gears through hot extrusion under an electric field and to clarify the influence of holding time on the extrusion force. The results suggest that the formed gears had a complete filling and clear tooth profile. Moreover, the contact resistance and current density caused a gradient temperature distribution inside the billet, resulting in a carburized layer and inhomogeneous β grains. The extrusion force increased with an increased holding time, which can be ascribed to the increase in the thickness of the carburized layer and the β grain size. Among these two factors, β grain size played a leading role in the extrusion force. Continuous dynamic recrystallization dominated the deformation in a single β phase, and the misorientation of the transformed α laths from β grains followed the Burgers orientation relationship. This study may pave the way for the extrusion forming of other titanium alloy micro-components.

Photo-, cathodic- and electroluminescence-band models in solid (SiC)1-x(AIN)x luminescence centers and SiC/SiC-AIN LEDs

The paper presents models of bands (levels) in solid (SiC)1-x(AlN)x luminescence centers and n-SiC/p-(SiC)1-x(AlN)x heterostructures (light-emitting diodes). The diagram of (SiC)1-x(AlN)x energy gaps shows the positions of luminescence levels, subject to x. A SiC/SiC–AlN series of electroluminescence bands, for the first time, is found to have a continuous relationship between the positions of short-wave and long-wave band maxima in a K-minimum conduction band, respectively, as continuous functions of contact current density.

Application of central composite design (CCD) for optimization of cephalexin antibiotic removal using electro-oxidation process

In this work, the removal of cephalexin (CEX) from aqueous solutions using the anodic oxidation process was studied and four significant independent variables including contact time, pH, current density (CD), and initial CEX concentration were optimized using response surface methodology (RSM) involving a five-level central composite design (CCD). The degradation mechanisms and mineralization pathway of CEX were also proposed. To determine the removal and mineralization rate, chemical oxygen demand (COD) and total organic carbon (TOC) were determined. The optimum conditions were experimentally determined as follows: reaction time 52.68 min, pH 5.00, CD 44.69 mA/cm2 and initial CEX concentration 75.88 mg/L. The predicted and experimental removal efficiencies were obtained 100 and 97.38%, respectively. A good agreement between the experimental and predicted values was also observed with coefficient of determination of 0.95. Moreover, under the optimal conditions, 79.64 and 73.25% efficiencies were obtained for COD reduction and TOC removal, respectively, indicating the effectiveness of the developed method. Regarding the relatively low electrical energy consumption (41.28 kWh/kg COD), it can be claimed that the developed method is preferable to other processes in terms of energy consumption.

Investigation of graphene as a material for electrical contacts in the application of microrelays using finite element modeling

This paper investigates the use of Graphene (Gr) as an electrical contact material for the application of microrelays. Gr is an ideal material for microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). A microrelay has been considered and electrothermal analysis is carried out based on Finite Element Modeling (FEM) using COMSOL Multiphysics simulation tool. Electrical contact surfaces for the material Al, Cu, Ag and Gr have been analyzed. The electrical contact resistance, voltage drop, current density, resistive losses and temperature of the contact interface has been obtained. The results obtained have been verified using theoretical calculations. Also, the combustion voltage of Gr electrical contact has been obtained as 0.2 V at which the Gr reaches its combustion temperature of 623 K. The results show that Gr electrical contact performs better in terms of electrical and thermal performance parameters which would be used in future electrical components.

Analysis of the Melt Erosion Patterns at Rail-Armature Contact of Rail Launcher in Current Range of 10–20 kA/mm

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. This current melt erosion (CME) has been experimentally studied in the current range of 10–20 kA/mm with a 20-mm caliber lab-scale rail launcher, and payload separated method was used to keep the recovered armatures intact. Thus, the onset behavior and erosion patterns of CME can be successfully observed in such relatively low current densities. In this paper, we will further our study to analyze the patterns of CME with the increasing current densities under the effect of different initial mechanical contact force. Results show that CME all start at the side edge, and then spreading longitudinally and transversely with the increase of current. It is found that the starting position of CME appears near the trailing edge at small mechanical contact force and moves to the leading edge with larger mechanical contact force. At the same current magnitude, erosion amounts are much more under small mechanical contact force. Stationary mechanical contact pressures and current distribution of armature surface are simulated to investigate the effect of initial mechanical contact force on starting position of CME. Current distributes at the edges of actual contact zone and the maximum of current density appears at the side edges of armature. As the initial mechanical contact force increases, actual contact zone and current density move toward to the leading edge from trailing edge. It can be confirmed that the erosion starting position is at the side edge along actual contact zone and will move toward to the leading edge from trailing edge with the increase of initial mechanical contact force. Smaller initial mechanical contact force will cause more erosion at the same current magnitude because of larger current density. Furthermore, an average friction coefficient calculation method is proposed to evaluate the melt lubrication effect of CME. The result shows that the lubrication effect becomes better with larger current densities.

Influence of copper content on wear behavior of composites “steel ShKh15/copper” at sliding against copper under electric current of contact density higher than 100 A/cm<sup>2</sup>

Powder composites “steel ShKh15/copper” in alumina ceramics and graphite powders surrounding were sintered in the air. Powder steel was restored from grinding slime of bearings production. It is shown that the steel framework has low level of mechanical properties, but high pore space percolation. Copper concentration increases isolated pores concentration impeding oil impregnation. This effect did not allow making the long and steady sliding electric contact with contact current density higher than 150 A/cm2. The sintered composites based on recycled bearing steel and containing near 15%Cu show high wear resistance at sliding with a contact current density 150–200 A/cm2 under boundary lubrication.

Armature Shape Optimization of an Electromagnetic Launcher Including Contact Resistance

Barrel and pulsed power supply modules are two crucial parts of an electromagnetic launcher (EML), in terms of overall efficiency. One of the most important features of the barrel side is the armature geometry. In this paper, the shape of the armature of an EML with 10-MJ current pulse generator, 1000-kA peak current, and 4.5-ms excitation time is optimized by using independent variables to define the exact geometry of the armature. The main goal is to maximize the muzzle kinetic energy of the projectile with 300-g mass including pressure and contact current constraints. Finite-element method (FEM) is used to calculate the muzzle kinetic energy of the EML for different armature geometries. Genetic algorithm is used as the optimization method. Since the contact resistance between the armature and the rail affects the distribution of contact current density, contact resistance is also modeled in FEM. It is observed that armature shape optimization study increases the muzzle kinetic energy to 596 kJ and the muzzle velocity to 1993 m/s.

The Surface Layer States in Metallic Materials Subjected to Dry Sliding and Electric Current

The structure and properties of surface layers of metallic materials undergoing structural-phase changes as a result of their contact interactions in the form of dry sliding friction on steel in combination with exposure to electric currents are investigated. This impact results in the formation of a composite surface layer whose structural constituents are the particles of FeO oxide, FCC- and BCC-iron, and quasi-amorphous initial material. Sliding of materials at the contact current density higher than 150 A/cm2 gives rise to the formation of local, low-stability structures which, as a result of phase transformations, are observed as sectors of quasiliquid plastic flow on the sliding surface. It is shown that the average temperatures of the Cu – steel material contact do not exceed 300°С, i.e., none of the surface-layer constituents reaches its melting temperature. It is shown that quasi-liquid plastic flow favors stress relaxation and maintains the strength of the surface layer, which ensures its lower wear.

Dry slipping steel–steel contact at high current density

The behavior of steel 3 in dry slipping under the action of high-density electric current is studied. In these conditions, the surface layer undergoes plastic deformation; its temperature rises; and new phases and structural defects are formed. That gives rise to a layer of secondary structures. The basic factor disintegrating the surface layer is the contact current density. The mean contact temperature and layer thickness of the secondary structures increase with increase in current density. The variation in wear rate and electrical conductivity with change in contact temperature is studied. The wear rate depends linearly on the contact temperature in normal wear. Catastrophic wear appears as sharp increase in the wear rate and simultaneous decrease in the contact electrical conductivity at 500—600°C. The thickness of the layer of secondary structures is 50 μm in these frictional conditions.

Wear Resistance of Friction Pair of Metal Composite/Copper under Electric Current

Sliding of metal composites against copper counterbody under severe conditions (i.e. at the contact current density higher 50 A/cm2 and at high roughness of counterbody) is carried out. It is shown that the composite of composition of Cu-30% of graphite shows low wear resistance in these conditions. Higher wear resistance is inherent in the composites containing lead and bearing steel. Impregnation of these composites by industrial oil hasn't led to noticeable increase in wear resistance.

Structure and Worn Surface Morphology on Copper Containing Composites under Dry Sliding with High Contact Current Density

Dry sliding of the sintered composites of compositions Cu-graphite-Fe and Cu-Fe against steel at the contact current density higher 100 A/cm2 has been carried out. The presence of FeO oxide in surface layer was shown. The low content of FeO oxide resulted in high wear intensity. Formation of a liquid phase on a sliding surface was observed. Wear intensity was low in the presence of a liquid phase on the worn surface.

Electrochemical disinfection of simulated ballast water on PbO2/graphite felt electrode

A novel PbO2/graphite felt electrode was constructed by electrochemical deposition of PbO2 on graphite felt and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) analysis. The prepared electrode is a viable technology for inactivation of Escherichia coli, Enterococcus faecalis, and Artemia salina as indicator organisms in simulated ballast water treatment, which meets the International Maritime Organization (IMO) Regulation D-2. The effects of contact time and current density on inactivation were investigated. An increase in current density generally had a beneficial effect on the inactivation of the three species. E.faecalis and A.salina were more resistant to electrochemical disinfection than E. coli. The complete disinfection of E.coli was achieved in <8min at an applied current density of 253A/m2. Complete inactivation of E. faecalis and A.salina was achieved at the same current density after 60 and 40min of contact time, respectively. A. salina inactivation follows first-order kinetics.

Surface layer structure of AISI 1020 steel at different stages of dry sliding under electric current of high density

Wear intensity of the sliding electric contact steel 1020/steel 1045 depending on sliding time is presented at the contact current density higher than 100 A/cm2 without lubricant. It is shown that wear intensity of 1020 steel decreases at increasing of sliding time. Wear intensity is stabilized after some sliding time. This time (burn-in time) decreases at reduction of current density. Structural changes are realized in surface layer. Signs of liquid phase are observed on sliding surface. This liquid isn't a result of melting. It is established using Auger spectrometry that the contact layer contains up to 50 at.% of oxygen.

COLD WORK HARDENING EFFECT ON WEAR OF 0,2% C STEEL IN DRY SLIDING CONTACT AT HIGH CURRENT DENSITY

The current dependences of wear intensity and specific surface electric conductance of sliding electric contact 0,2 % C steel/0,45 % C steel are represented at contact current density higher than 100 A/cm 2 without lubricant. It was shown that the steel having stronger cold work hardening realized has higher wear resistant than the low hardening steel. This fact is represented as a result of the realization of lower cycle stress amplitude in conditions of low cycled fatigue of the material adjoining to real contact spots of stronger hardened steel. It was marked that the contact characteristics of 0,2 % C steel are some higher than known contact characteristics of quenched steels. This is caused by higher plasticity reserve of 0,2 % C steel surface layer comparing with that of quenched steels. Structure changes of sliding surface were observed as a formation of friction induced structure layer containing crystal phases namely oxide FeO, α-Fe and γ-Fe. The optical image of worn surface having the signs of liquid phase appearance is shown. This phase is not a result of melting but it is a result of strong excited atoms appearance in thin surface layer.

Influence of cold working on the wear of AISI 1020 steel in dry sliding contact at high current density

The wear rate and surface electrical conductivity in the sliding electrocontact of 1020 steel and quenched steel are studied as a function of the current, at a contact current density exceeding 100 A/cm2, without lubricant. The wear resistance is greater for steel with greater cold working. This may be attributed to the lower amplitude of the stress in low-cycle fatigue of the material adjacent to the contact spot of the stronger steel. The contact characteristics observed for the 1020 steel are somewhat higher than the known values for quenched steel. This may be attributed to the higher reserve of plasticity of the surface layer in 1020 steel than in quenched steel. Structural changes in the sliding surface are observed: specifically, the formation of a friction induced structure layer containing crystalline phases (FeO, α Fe, and γ Fe). An image of the worn surface shows indications of liquid phase. This phase is the result not of melting but of the appearance of highly excited atoms in a thin surface layer.

Efficient De-colorization of Methylene Blue by Electro-coagulation Method: Comparison of Iron and Aluminum Electrode

In this study, removal of methylene blue by electro-coagulation method using aluminum and iron electrodes was investigated. The influence of the operating parameters such as contact time, current density, anode type, inter-electrodes distance, initial and final pH and energy consumption rate was determined. Dye removal was increased with increases in solution pH, current density and contact time and then decreased for increase in initial dye concentration and electrodes distance. The results show that the electrochemical method has significant efficiency in removal of methylene blue, higher efficiency was observed for iron (Fe) electrode; namely 100% and 95.78% of dye was removed by iron and aluminum electrode; respectively, after 24 min contact time. For a given current density, the removal efficiency and energy consumption rate showed that iron electrode was superior to aluminum in removal of methylene blue. In the case of iron as anode type, the required energy for complete dye decolorization was 3.8 kWh/m 3 ; for 98% dye removal, the required energy was observed to be 4.3kWh/m 3 in the case of aluminum as anode type. In general, complete methylene blue can be removed at operating parameters condition of iron as anode, distance between electrodes of 1cm, solution pH of 9 and current density of 50 A/m 2 for 24 min electro-coagulation time.