Effects Of Different Current Densities Research Articles

Preparation of Co–Pt–P thin films by magnetic electrodeposition

Magnetic fields perpendicular to the electric field were applied during an electrodeposition process to obtain Co–Pt–P thin films from alkaline baths. Effects of different current densities and magnetic intensities on the composition, microstructure and magnetic properties of Co–Pt–P thin films were studied. It was found that the deposition rate and films thickness increased gradually with the increase of the current density and magnetic intensity. Almost all of the deposited films were crystalline and showed Co(002), CoPt(111) peaks. With the increase in the magnetic intensity, the intensity of CoPt(111) peak decreased while the intensity of Co(002) rose gradually. Magnetic fields would induce cobalt growing along (002) orientation. The films were densely covered with typical nodular structure. When the current density increased to 100 A m−2, rougher and agglomerate nodular structures would be formed. Films of smaller grain size and smooth surface could be formed under high magnetic intensity (0·5 T) as a result of impact of magnetic force and MHD effects. Furthermore, higher current density induced larger Magnetisation and lower coercivity. Largest coercivity could be achieved when current density equals to 70 A m−2. With the increase in magnetic intensity, cobalt contents in films increase gradually which lead to the rise on magnetisation.

Increased nitrous oxide accumulation by bioelectrochemical denitrification under autotrophic conditions: Kinetics and expression of denitrification pathway genes

Under autotrophic conditions, we investigated the effects of different current densities on bioelectrochemical denitrification (BED). In this study, nitrate consumption and nitrous oxide (N2O) production, microbial diversity and population dynamics, and denitrification pathway gene expressions were explored in continuous flow BED reactors at different current densities (0.2, 1, 5, 10 and 20 A/m2). We found that, under the autotrophic conditions, N2O accumulation was increased with increase in current density. The maximum rate of denitrification was 1.65 NO3−–N (g/NCCm3.h), and approximately 70% of the reduced N was accumulated as N2O. After each current density was applied, pyrosequencing of the expressed 16S rRNA genes amplified from the cathodic biofilms revealed that that 16 genera were active and in common at all currents, and that eight of those showed a statistically significant correlation with particular current densities. The relative expression of napA and narG was highest, whereas nosZ was low relative to its level in the inoculum suggesting that this could have contributed the high N2O accumulation. Kinetic analysis of nitrate reduction and N2O accumulation followed Michaelis–Menten kinetics. The Vmax for nitrate consumption and N2O accumulation were similar, however the Km values determined as A/m2 were not. This study provides better understanding of the community and kinetics of a current-fed, autotrophic, cathodic biofilm for evaluating its potential for scale-up and for N2O recovery.

Electrocoagulation for the removal of phenol and aldehyde contaminants from resin effluent

This paper is a report on a study which aimed to investigate the effect of different current density, pH, temperature, and cathode-anode combination on the removal of phenol and aldehyde in two samples of actual resin effluent through the process of electrocoagulation using solar energy. Current density 60 A/m(2) and pH 6 proved to be the best levels for both contaminants. As for the effect of temperature, although the highest degree of phenol and aldehyde removal was achieved at 15 °C, 25 °C was taken to be the optimum temperature for economic reasons. The Fe-Fe combination of electrodes was found to be the best as it led to nearly 93% of phenol removal and approximately 95% of aldehyde removal. Also, the effect of electrode combination on energy consumption was studied. It was observed that the Fe-Fe combination consumed the least amount of energy (0.7-4.3 kWh/m(3) of wastewater in the case of phenol and 0.8-4 kWh/m(3) of wastewater in the case aldehyde). Moreover, the Fe-Fe combination brought about the best results in terms of chemical oxygen demand removal: 93% in both cases. Finally, an economic analysis was performed for the electrocoagulation process.

Influence of electropolishing current densities on sulfur generation at niobium surface

We report the effect of different current densities on sulfur generation at Nb surface in the electropolishing (EP) with aged electrolyte. In this regard, we conducted a series of electropolishing (EP) experiments in aged EP electrolyte with high (≈50mA/cm2) and low (≈30mA/cm2) current densities on Nb surfaces. The experiments were carried out both for laboratory coupons and a real Nb single cell cavity with six witness samples located at three typical positions (equator, iris and beam pipe). Sample's surfaces were investigated by XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectroscopy). The surface analysis showed that the EP with a high current density produced a huge amount of sulfate/sulfite particles at Nb surface whereas the EP with a low current density was very helpful to mitigate sulfate/sulfite at Nb surface in both the experiments.

Effect of the Current Density on Oxygen Overpotential and Corrosion Rate of the Al/Pb-Ag-Co Anodes for Zinc Electrowinning

Lead-silver-cobalt was electrodeposited on the aluminum matrix, which was used as anode for zinc electrowinning. Scanning electron microscopy (SEM), linear sweep voltammetry(LSV), Tafel curve were used to study the effect of different current density on the surface morphology, electrocatalytic activity and corrosion resistance of Al/Pb-Ag-Co anode. The results showed that the Ag content change slightly with the current density change, but the Co content change big with the current density change; the value of a and b oxygen evolution of Pb-Ag-Co composite coating electrode obtained under 1 Adm-2were the smallest, respectively, was 1.436 V, 0.930 V; and the corrosion potential was 0.272 V; surface microstructure was smooth and dense.

Effect of different current densities on optical properties of porous silicon carbide using photo-electrochemical etching

The morphological and optical characterizations of porous silicon carbide (PSC) were studied after photo-electrochemical etching of silicon carbide (SiC) substrates using various current densities. Atomic force microscopy results demonstrated that the current density is an outstanding parameter that controls the morphology of pores. The Raman intensities of the PSC samples with higher current densities were enhanced because of the increase in the specific surface area. An evident red-shift in the position of the A1 (LO) mode of phonon vibrations was observed compared with that of non-porous crystalline 6H-SiC. These results show that tensile stress was induced in PSC nanocrystallites.

Effects of different current densities on properties of MAO coatings embedded with and without α-Al2O3 nanoadditives

Ceramic coatings have been synthesised on 6063 aluminium alloy by microarc oxidation (MAO) technique in the solution of NaAlO2 electrolyte with and without α-Al2O3 nanoadditive. Effects of different current densities on the properties of ceramic coatings have been studied in this paper. The phase composition and microstructure of the MAO coatings were investigated by X-ray diffraction and scanning electron microscopy analyses respectively. Microhardness, adhesion and wear resistance tests were also performed. X-ray diffraction shows that the ceramic coating prepared in NaAlO2 electrolyte with α-Al2O3 nanoadditive has better crystallisation in comparison with that prepared without α-Al2O3 nanoadditive. Scanning electron microscopy shows that the surface of the coating prepared with α-Al2O3 nanoadditive became denser and smoother and the number of pores decreased with increasing current density from 15 to 20 A dm−2. Mechanical property tests show that values of microhardness and adhesion of the ceramic coatings increase with increasing current density, while the samples prepared under the current density of 20 A dm−2 with α-Al2O3 nanoadditive have better wear resistance than the others, which is mainly attributed to its dense surface, high hardness and relatively low friction coefficient.

Electrochemical treatment of effluents containing Cr(VI). Influence of pH and current on the kinetic

Compounds of Cr(VI) are very toxic and their reduction to Cr(III) is necessary to allow their further precipitation or adsorption. Chemical methods for Cr(VI) reduction are usually used for this purpose. As an alternative, electrochemical methods using three-dimensional electrodes, such as reticulated vitreous carbon (RVC) and polyaniline-modified RVC, have been used successfully. Since the pH affects reaction of Cr(VI) reduction, in this work its effect on the reaction rate was studied using electrodes of RVC and RVC/PANI. While a maximum in reaction rate was found for a pH 1.5 using the RVC, the RVC/PANI showed no differences in reaction rates in the range of pH between 0 and 1. Practically, no reaction was observed for any pH greater than 3. The effect of different current densities using optimized pH was also evaluated and the RVC/PANI electrode showed the best reaction rates, current efficiencies and energy consumption as a result of the polyaniline electrocatalytic effect.

Tailoring surface properties of biomedical polymers by implantation of Ar and He ions

Ion implantation at 25 and 100 keV has been used as a tool for the modification of the surface properties of two biomedical polymers. The modulation induced by the different energy dispersion mechanisms of Ar and He have allowed satisfactory modifications for both the activation of the surfaces of chemically functional polycaprolactone (PCL) and the stabilization of anti-fouling poly(ethylene glycol) (PEG). In both cases the implantations have been performed at doses of 10 14 cm −2 by taking into account the effect of different current densities, which are shown to distinctly influence the fragmentation-crosslinking of the target polymers. The resultant films were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectroscopy and atomic force microscopy. Both shifts in zeta potential versus pH curves and the alteration of the polar components of the surface free energy (contact angle measurements) were correlated with the composition analysis. The response of the modified surfaces towards biomolecular interaction is demonstrated by the induction of preferential adsorption on irradiated PCL and the inhibited adsorption onto implanted PEG regions for selected oligopeptides and proteins.

Influence of electrical parameters in the iontophoretic delivery of a small peptide: in vitro studies using arginine–vasopressin as a model peptide

The present investigation was carried out to understand the influence of electrical parameters on iontophoretic transport of a small peptide like arginine–vasopressin (AVP). In vitro studies using rat skin were conducted to assess the effect of different current densities (CDs), durations, duty cycles and alternating polarity on vasopressin permeation. HPLC was used for ensuring electrochemical stability of the peptide whereas FT-IR and TGA were used to understand the biophysical changes caused in skin due to passage of current. Application of CD > 0.75 mA/cm 2 was found to compromise skin barrier integrity as well as electrochemical stability. Periodic current did not show any significant difference in permeation compared to continuous current. Alternating polarity was useful in reducing pH shift however, was less efficient compared to continuous direct current. FT-IR and TGA studies showed that skin hydration increased as a function of CD and duration and all the results could be explained on the basis of increased skin hydration.

A mathematical model of polymer electrolyte fuel cell with anode CO kinetics

We develop a mathematical model of solid polymer electrolyte fuel cell with anode CO kinetics, which is essentially a model that marrying the work of Bernardi and Verbrugge (J. Electrochem. Soc. 139 (1992) 2477) with that of Springer et al. (J. Electrochem. Soc. 148 (2001) A11). Two cases of study were carried out. First, the water self-sufficiency of fuel cell operation was conducted under different current density, temperature, pressure differential across the membrane-electrode-assembly (MEA), hydraulic permeability and electro-kinetic permeability. Comparison of superficial water velocities in the MEA under the effect of different current density with those from Bernardi and Verbrugge was conducted. Results showed that, treating the catalyst layers as interfaces instead of regions as simplified by Bernardi and Verbrugge, would significantly underestimate the water velocities in the MEA and the error is particularly large at high current density operations. Second, the effect of CO poisoning of fuel cell was presented in terms on cell polarization. The prediction covered 0, 25, 50, 100 and 250 ppm of CO concentration in hydrogen feedstock and results were validated by experimental data obtained from Springer et al. The trends of anode polarization curve due to CO poisoning were explained.

PH and potential measurements on mild steel and cast iron during periodic cathodic polarization at 20° and 90°C

A recently described pH measuring method has been applied to simultaneous pH and potential measurements at cast iron and mild steel cylinder surfaces during periodic cathodic polarization at 20 and 90°C. Observed effects of different current densities and of electrolytes NaCl, MgSO 4 and NaOH on the pH-potential measurements and on the corrosion tendency are described. The measured pH and potential values are compared with equilibrium diagrams and theories of the corrosion and protection mechanisms discussed.

Electrical model of the injection laser

The simplest electrical model of the injection laser assumes that the active layer, the layer in which spontaneous and stimulated radiative recombination take place, is a homogeneous layer. The only parameters of such an electrical model are the thickness of the active layer, and the electron and hole concentrations and quasi-Fermi levels. If such a model is combined with an optical model with no k -selection rule, one obtains reasonable agreement with experimental threshold current densities, particularly if energy band tails are taken into account. The theory, however, predicts a superlinear relation between gain constant and current density near room temperature, while the observed relation is linear. An alternative electrical model by Pikus assumes that the quasi-Fermi levels of electrons and holes are constant in the active layer. This model, when combined with an optical model having a k -selection rule, gives a strong superlinear dependence of gain on current and is therefore also in disagreement with experiment. A realistic electrical model of the injection laser requires a knowledge of the impurity concentration at each point and solution of the equations governing the motion of electrons and holes. We are carrying out such calculations, using a method of solution developed by J. W. Cooley and G. Hachtel. Preliminary results show that at room temperature the spontaneous emission rate and the stimulated emission rate may have substantially different spatial dependences. The calculations will give information about the effect of different impurity profiles on injection laser performance and on the effect of different current densities on the electron and hole distributions. A detailed account of this work Will be submitted for publication later.