Papers by Keyword: Current Density

Abstract: Proton exchange membrane fuel cell (PEMFC) system is an advanced power system for the future that is sustainable, clean and environmental friendly. The flow channels present in bipolar plates of a PEMFC are responsible for the effective distribution of the reactant gases. Uneven distribution of the reactants can cause variations in current density, temperature, and water content over the area of a PEMFC, thus reducing the performance of PEMFC. By using Serpentine flow field channel, the performance is increased. Two types of serpentine flow field channels are implemented such as curved serpentine flow field channel and normal serpentine flow field channels. The result shows that curved serpentine flow field channel gives better current density and power density, thus increasing the performance of PEMFC.

Abstract: A 3-D computational model was developed to examine the proton exchange membrane fuel cell (PEMFC) performance using Lung channel design bipolar plate. The model was developed using ANSYS FLUENT-15.0 software and simulations were carried out at 100 % humidity conditions. The parameters such as pressure distribution, hydrogen and oxygen concentrations and proton conductivity were briefly presented. The simulation results of Lung channel are presented in the form of polarization curves. The results of a Lung channel compare with the conventional flow channel and observed that the Lung channel gives a less pressure drop, uniform distribution of reactants and high cell voltage at a particular current density. From the observation from the polarization data, the Lung channel performance was 17% higher than triple serpentine flow channel. Keywords: Humidity conditions, Simulation, Lung channel, Polarization curves, Current density.

Abstract: Among physical and mechanic properties of coatings the internal stresses are of special interest. Internal stresses include stresses which exist and are counterbalanced within a rigid body in cases when there is no external action which caused them. In coatings obtained on the basis of nickel, chrome they can decrease the adhesive strength, cause cracking, peeling, anticorrosion properties deterioration. But the definite level of internal stresses leads to increase of hardness and coatings wear resistance and also facilitates porous coatings obtaining. The results of theoretical and experimental investigations of the internal stresses that appear in oxide ceramic coatings formed by plasma-electrolytic oxidation (PEO) on aluminum surfaces are presented.

Abstract: To understand the effects of temperature and injection current density on expansion of Shockley stacking faults (SSFs) from basal-plane dislocations in 4H-SiC p-i-n diodes, the threshold current density for SSF expansion was investigated at eight temperatures by electroluminescence image observation. The threshold injection current density was found to decrease at lower temperatures and to increase at higher temperatures. We identified the origin of this temperature dependence and found that the limiting factor for expansion differed depending on the temperature.

Abstract: In order to obtain a titanium-based PbO₂ electrode with high electrocatalytic activity and good stability, A porous β-PbO₂ electrode is prepared by electrodepositing on titanium substrate Sn-Sb-RuOx coating. The surface morphology and phase analysis of the porous β-PbO₂ electrode prepared at different current density were investigated by SEM and XRD. Results showed that the current density changes the surface morphology and active surface area of the porous β-PbO₂ electrode. When the current density is 2 A/dm², the surface of the porous β-PbO₂ prepared by electrodeposition has a uniform porous morphology with a pore diameter of 50-200 µm with main crystal phase of β-PbO₂. Influence of current density on the electrochemical activity of the electrode was analyzed using anodic polarization curve, electrochemical impedance spectroscopy and galvanostatic polarization. Results revealed that with the increase of current density, the oxygen evolution potential of the porous β-PbO₂ electrode decreases first and then increases while the exchange current density first increases and then decreases. When the current density is 2 A/dm², the oxygen evolution potential is 2.0075 V(at 0.05 A/cm²) and the maximum exchange current density is 1.77×10^-4 A/cm². According to the electrochemical impedance spectroscopy, when the current density is 2 A/dm², Q_f and Q_dl are the largest, R_f and R_ct are the smallest, and the R_F first increases and then decreases with the current density increases. When the current density is 2 A/dm², the maximum R_F value is 655.7. The results with galvanostatic polarization at current density of 0.05 A/cm² showed that the electrode has a minimum electrode voltage of 2.05 V at a current density of 2 A/dm². Accelerated life experiments were carried out in 2 g/L Cl^- and 150 g/L H₂SO₄ bath at 25 °C, and the porous β-PbO₂ electrode obtained under the current density of 2 A/dm² has the longest life, and the electrode life is 68 h, which is 2.5 times of the PbO₂ electrode obtained under the current density of 4 A/dm².

Abstract: The effect of nanosized nickel ferrite (NiFe₂O₄) addition on (Tl_0.85Cr_0.15)Sr₂CaCu₂O_7-δ superconductors has been investigated. (Tl_0.85Cr_0.15)Sr₂CaCu₂O_7-δ high temperature superconductors was prepared via solid-state reaction method using high purity oxide powders. Nanosized NiFe₂O₄ was added to the compound at composition x = 0 - 0.003 wt.%. Samples were studied using scanning electron microscopy (SEM), X-ray diffraction method (XRD), electrical resistance versus temperature, transport critical current density J_c and AC susceptibility measurements. SEM micrographs showed close-packed microstructure with low porosity. XRD patterns showed a dominant phase of Tl-1212 with a minor phase of Tl-1201 for all samples. All of the samples displayed metallic normal state behavior before the onset transition temperature (T_c-onset) which was between 102 and 104 K. The transition temperature (T_cχ’) from AC susceptibility measurement also showed the similar results between 101 and 103 K. T_c-zero was slightly suppressed with the addition of nanosized NiFe₂O₄. The peak temperature T_p from the imaginary part of the susceptibility χ” was found between 77 - 91 K for all samples. The highest transport critical current density (J_c) at 77 K was shown by sample x = 0.001 wt.% at 2213 mAcm^-2. Nanosized NiFe₂O₄ has significantly enhanced the J_c of (Tl_0.85Cr_0.15)Sr₂CaCu₂O_7-δ superconductor.

Abstract: Under the condition of controlling the relevant electrolysis process parameters, 12μm-thick electrolytic copper foils were prepared by adjusting the electrodeposition time under different current densities. The surface morphology, mechanical properties and textures of the electrolytic copper foil at different current densities were studied using SEM, XRD, EBSD and universal testing machines. The fracture mechanism of the copper foil at different current densities was also analyzed in this paper. The results show that as the current density increases, the surface of the copper foil become larger and sharper. The main orientation of the crystal surface is {220}, and the preference firstly increases and then decreases. The high preference of the {220} crystal surface of the copper foil reduces its tensile strength. When the current density is from 8 to 14 A/dm², the preferential degree of {111} decreases with the increase of current density, while the preferential degree of {220} increases, and the tensile strength of copper foil decreases. When the current density is from 14 to 26 A/dm², the preferential degree of {111} and {311} increases with the increase of current density, while the preference of {220} crystal surface decreases, and the tensile strength of copper foil increases. The elongation of copper foil is affected by the fracture mechanism. When the current density is 8 A/dm², the copper foil is plastically fractured and has high elongation. When the current density is 14A/dm², the copper foil is brittle fracture and the elongation is low. When the current density is 26 A/dm², the copper foil is plastically fractured but the effect of hydrogen evolution at high current density reduces the plasticity of the copper foil.

Abstract: In order to improve the corrosion resistance of shock absorber for ships, the alumina ceramic coatings are carried out on the surface of aluminum alloy shock absorber by micro arc oxidation (MAO) technology. The microstructure and anti-corrosion performance of the MAO coatings were investigated experimentally. This paper mainly focuses on the experimental work to determine the effect of current density on the structural characteristics and corrosion resistance of MAO coatings. The results show that the current density has a significant influence on the preparation of MAO coating during the process. The surface of the coating becomes more compact and smooth with the cathode voltage of 7 A.dm^-2. Furthermore, the anti-corrosion performance of the MAO coatings can effectively be improved at the current density of 7 A.dm^-2.

Abstract: The influence of varying the emitter-base geometry, i.e., the emitter width (W_E), emitter contact–emitter edge distance (W_n), and base contact–emitter edge (W_p) on the on-state characteristics in 5.6 kV implantation free 4H-SiC BJTs are investigated. The BJTs present a clear emitter size effect pointing out that surface recombination has a significant influence on current gain (β). The results show that the influence of varying W_p on the β is higher than W_n. A distance of 3 μm between emitter contact and base contact to the emitter edge (W_n = W_p = 3 μm) is the optimized value to have a BJT with a high β, and low on-resistance (R_ON) at a given W_E.

Abstract: Stainless steel (SS) is one of the most commonly used metallic food contact materials. It may be classified based on its microstructure whether ferritic, austenitic, martensitic, duplex or precipitation hardened. Austenitic SS, among mentioned grades, has the largest contribution to market due to its numerous industrial and domestic applications. In this study, the corrosion behavior of AISI 202 SS – a cheaper grade of stainless steel, in three different solution temperatures of citric acid was investigated using different electrochemical techniques such as open-circuit potential (OCP) measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results were compared to that obtained from conventional AISI 304 SS. OCP, polarization and impedance measurements agreed that AISI 202 SS has comparable resistance to that of AISI 304 SS in citric acid at ambient temperature and at 50 °C. At 70 °C, results of OCP measurements suggest that AISI 304 SS exhibited greater performance as indicated by more positive OCP values in the designated solution. EIS results indicate that the two alloys have identical corrosion resistance even at 70 °C as indicated by their comparable polarization resistance (R_p). The corrosion mechanism in both alloys is charge-transfer controlled as indicated by depressed semi-circular appearance of the generated Nyquist plots. The values of corrosion current densities (i_corr) extracted from polarization curves indicate that the initial corrosion rates were higher in AISI 304 than AISI 202 SS suggesting that formation of more protective film may have occurred on the former alloy.