Constant Current Experiments Research Articles

Analysis of Convective Mass Transfer by Potential Relaxation: II . Transient Natural Convection Copper Deposition

A transient potential relaxation technique was used to determine mass transfer boundary‐layer thicknesses during steady‐state and pre‐steady‐state natural convection copper deposition at a vertical flat plate cathode. Boundary‐layer thicknesses for constant currents below the limiting current and pulsed currents at 6 Hz were found by matching experimentally measured concentration overpotentials after current interruption to a theoretical surface concentration decay model. The initial growth of constant and pulsed current boundary‐layers with the time of current passage was found to be diffusion controlled. Steady‐state pulsed current boundary‐layer thicknesses were approximately 33% smaller than those obtained from constant current experiments.

Effect of some amino acid chelating agents on the passivation of copper anodes in copper sulfate/sulfuric acid electrolyte

Inhibition of passivation during the anodic dissolution of copper by using organic additives was tested. The ability of four amino-acid chelating agents to delay the onset of passivation of copper anodes was evaluated using the galvanostatic method. Ethylenediaminetetracetic acid (EDTA) gave the most promising results and a more detailed study of this reagent was carried out by using both galvanostatic and staircase voltammetry techniques. The time before the potential of the working electrode exceeded 0.3 V vs. Hg, Hg 2SO 4/K 2SO 4 saturated reference electrode for constant current experiments and the peak current characteristic for the staircase voltammetry, allowed the inhibition efficiency of each additive to be evaluated. The inhibition efficiency of each compound was very dependent on its concentration in the electrolyte. EDTA showed a maximum efficiency to delay copper anode passivation at a concentration of about 0.5% (w/w). Energy dispersive X-ray analysis carried out on samples electrolyzed in the presence and absence of EDTA revealed only metallic copper and/or copper oxide, in both cases. SEM observations showed that the surfaces of the above mentioned samples had different morphologies. No more than metallic copper was detected by X-ray diffraction analysis carried out on the same samples. Interpretations and some consequences of these observations are presented and discussed.

Analysis of the feedback voltage during constant current avalanche hole injection experiments

The behavior of the controlling feedback voltage during constant current avalanche hole injection experiments on metal-oxide-semiconductor capacitors has been analyzed in detail. It is concluded that at dc hole current densities greater than 50 nA/cm2, displacement currents generated in the oxide as a result of a change in the feedback voltage can dominate the injected hole current. The effect of this displacement current on the determination of hole trapping kinetics is evaluated quantitatively. In particular, it is shown that the effect of the displacement current is to reduce the hole current density and cause an apparent delay in oxide charging kinetics. In addition, it is shown that the feedback voltage necessary to maintain current densities larger than 50 nA/cm2 induces a measurable electron current from the gate electrode when the oxide field exceeds 6 MV/cm. Analysis of this phenomenon provides evidence for hole trapping at the Al-SiO2 interface as well as an estimate of the capture cross section for this process. The estimated cross section,1×10−14 cm2, is similar in magnitude to that obtained for hole trapping at the Si-SiO2 interface. It is concluded that while displacement currents and gate electron injection may affect the determination of hole trapping kinetics, these effects can be avoided at current densities below 50 nA/cm2. Finally, consideration of the relative changes in the feedback and flat-band voltage data during low-current density experiments suggests that the feedback voltage does not respond to charge in interface traps.

Zinc electrowinning with 2‐butyne‐1,4‐diol

AbstractThe beneficial effect of 2‐butyne‐1,4‐diol on zinc current efficiency in the presence of nickel impurity has been examined. Several techniques including HPLC, absorption spectrophotometry and constant current deposition experiments have shown that a trimer of 2‐butyne‐1,4‐diol is responsible for the removal of Ni ions from the electrolyte, thus increasing the current efficiency of the zinc electrowinning process from sulphate solutions (60 g/L Zn + 200 g/L H2SO4) in the presence of Ni ions.

Heat Transfer Measurements On Unequally Loaded Underground Power Cables With Constant And Cyclic Currents

A test site was constructed with underground power cables in a typical distribution-type duct bank arrangement. The site can be used to obtain temperatures throughout the duct bank and surrounding soil medium for known cable currents. A personal computer with an analog to digital converter system is used to independently set the currents in each cable to any load so that steady, cyclic, and transient experiments can be performed. Results of a number of constant and cyclic current experiments show good agreement between experimental temperature data and the calculated temperatures from an ampacity computer program.

Dissolution kinetics of copper sulphide anodes

Constant current and voltammetric experiments were carried out with synthetic and natural chalcocite and synthetic digenite anodes in a variety of electrolytes. Rapid dissolution of copper occurred at low potentials until limited by the rate at which copper could be transported from the reaction zone by diffusion through electrolyte held within the porous product layer. At this point, the potential rose sharply (galvanostatic) or the current began to fall (voltammetric) corresponding to the formation of elemental sulphur. Quantitative support for this mechanism was obtained using a simplified model of the pore diffusion process. The complexity of the solid-state reactions occurring in the anode product was revealed by a novel technique which enabled direct observation of the product profile during electrolysis.

Spike frequency of the nodal membrane generated by high-frequency alternating current.

Changes in membrane potential of single frog motor nerve fibres due to alternating current (ac) between 4 kHz and 20 kHz were recorded in the air gap equipment under constant current conditions at 20 degrees C. The experimental findings were compared with the results of computations on the basis of potential clamp data. Ac shifted mean membrane potential (averaged for every ac period) in the direction of depolarization. The mean depolarization Vm depended on current strength I; it disappeared when the sodium permeability was blocked, in the experiments by tetrodotoxin. In a current range between about 1 and 3 fold threshold strength the ac initiated repetitive activity with response frequencies v between averaged 120 Hz and 820 Hz or in the computations even higher; v depended logarithimically on current strength, but was independent of ac frequency. Elimination of current amplitude I from the nonlinear realtions v(I) and Vm(I) led to a linear function between v and Vm. Both v and Vm depended markedly on prepolarization of the node. The results were attributed to the preferred activation of the sodium permeability under maintained high frequency ac stimulation. Differences between computations and constant current experiments occurred for very long stimulus duration when rhythmical discharges died out in the experiment.