Application of pulsating overpotential regime on the formation of copper deposits in the range of hydrogen co-deposition

Electrodeposition of copper by pulsating overpotential (PO) regime in the range of hydrogen co-deposition was examined by scanning electron microscopy. It was found that the increase of the pause-to-pulse ratio produced a strong effect on the morphology of electrodeposited copper. Honeycomb-like copper structures were formed with the pause-to-pulse ratios up to 5. Up to this value of the pause-to-pulse ratio, the diameter of the holes formed by attached hydrogen bubbles was decreasing, while their number was increasing by the application of PO regime. The compactness of the formed honeycomb-like structures was also increasing with the increasing pause duration. The increase of the pause-to-pulse ratio suppressed a coalescence of neighboring hydrogen bubbles. Copper dendrites in the interior of the holes and at their shoulders were formed with the higher pause-to-pulse ratios. The size of the formed dendrites, as well as their number, increased with the increasing pause duration. Depth of holes was decreasing with the increasing pause duration. The increased compactness of the obtained structures was explained by the use of a set of equations describing the effect of square-wave PO on electrodeposition process.     

Optimization of process of the honeycomb-like structure formation by the regime of reversing current (RC) in the second range

Journal of Solid State Electrochemistry - Formation of the honeycomb-like electrodes of copper by the regime of reversing current (RC) in the second range has been investigated. Morphological and...     

The overpotential components on the palladium hydrogen electrode

When a polarization current is applied or switched off, the Pd hydrogen electrode exhibits characteristic overpotential transients due to extensive dissolution of hydrogen in Pd. The physical significance of the overpotential components are discussed in some detail. This was shown to be an excellent system to investigate the detailed mechanism of the hydrogen electrode reaction. Individual affinity values and kinetic parameters of the constituent steps were readily obtainable. Some examples are presented.     

The effects of the underpotential and overpotential deposition of lead and thallium on silver on the Raman spectra of adsorbates

It is shown that the underpotential deposition (UPD) and dissolution of monolayers of Pb and Tl onto Ag surfaces roughened in a controlled oxidation-reduction cycle produces a Ag surface which shows diminished surface enhanced Raman scattering (DSERS). Significantly enhanced Raman spectra can still be obtained from electrodes covered by complete UPD and overpotential deposited (OPD) layers of the metals. Correct choice of electrolytes for the UPD of the metal reduces the loss of enhanced Raman scattering; chloride ions, constituents of many electrolytes used in the investigation of surface enhanced Raman scattering (SERS), are shown to be especially active in causing the loss of SERS.     

Morphology and internal structure of copper deposits electrodeposited by the pulsating current regime in the hydrogen co-deposition range

The effect of the regime of pulsating current (PC) on copper electrodeposition in the hydrogen co-deposition range was examined by the techniques of scanning electron and optical microscopes. The quantities of evolved hydrogen and morphologies of electrodeposited copper strongly depended on the applied parameters of square waves PC, such as the current density amplitude (or the amplitude of the cathodic current density), deposition pulse, and pause duration. The increase of the current density amplitude led to intensification of hydrogen evolution reaction, and the change of morphology of electrodeposited copper from dendrites and shallow holes to dish-like holes was observed. For the constant pause duration, the prolonging deposition pulses intensify hydrogen evolution reaction leading to the formation of the honeycomb-like structures. The set of modified equations considering the effect of hydrogen generated during metal electrodeposition processes by the pulsating current regime is also presented. The concept of “effective overpotential amplitude” was proposed to explain the change of copper surface morphology with the intensification of hydrogen evolution reaction.     

The effects of boron and lithium on the ratio of induced to spontaneous fission in natural uranium

The presence of boron and lithium in natural uranium systems in altering the ratio of induced fission of ²³⁵U is significant. For systems containing 0.06% boron and 0.038% lithium with respect to uranium (low Z/U atom to atom ratio equals 1.32 × 10⁻²), the induced to spontaneous fission ratios were measured to be 1.4 and 0.60 respectively. The increase in the neutron flux is attributed to (α, n) reactions on the low Z elements present in the systems.     

The influence of surfactant mixing ratio on nano-emulsion formation by the pit method

The formation of O/W nano-emulsions by the PIT emulsification method in water/mixed nonionic surfactant/oil systems has been studied. The hydrophilic-lipophilic properties of the surfactant were varied by mixing polyoxyethylene 4-lauryl ether (C12E4) and polyoxyethylene 6-lauryl ether (C12E6). Emulsification was performed in samples with constant oil concentration (20 wt%) by fast cooling from the corresponding HLB temperature to 25 degrees C. Nano-emulsions with droplet radius 60-70 nm and 25-30 nm were obtained at total surfactant concentrations of 4 and 8 wt%, respectively. Moreover, droplet size remained practically unchanged, independent of the surfactant mixing ratio, X(C12E6). At 4 wt% surfactant concentration, the polydispersity and instability of nano-emulsions increased with the increase in X(C12E6). However, at 8 wt% surfactant concentration, nano-emulsions with low polydispersity and high stability were obtained in a wide range of surfactant mixing ratios. Phase behavior studies showed that at 4 wt% surfactant concentration, three-liquid phases (W+D+O) coexist at the starting emulsification temperature. Furthermore, the excess oil phase with respect to the microemulsion D-phase increases with the increase in X(C12E6), which could explain the increase in instability. At 8 wt% surfactant concentration, a microemulsion D-phase is present when emulsification starts. The low droplet size and polydispersity and higher stability of these nano-emulsions have been attributed, in addition to the increase in the surface or interfacial activity, to the spontaneous emulsification produced in the microemulsion D-phase.     

The structural determinants that lead to the formation of particular oligomeric structures in the pancreatic-type ribonuclease family

Pancreatic-type ribonucleases are a family of RNA degrading enzymes that share different degrees of sequence identity but a very similar 3D-structure. The prototype of this family is bovine pancreatic ribonuclease or ribonuclease A. This enzyme has been the object of landmark work on the folding, stability, protein chemistry, catalysis, enzyme-substrate interaction and molecular evolution. In the recent years, the interest in the study of pancreatic-type ribonucleases has increased due to the involvement of some members of this family in special biological functions. In addition, dimeric and also higher oligomeric structures can be attained by the members of this family. The oligomers described structurally to date are mainly formed by 3D-domain swapping, a process which consists of the exchange of identical domains (i.e. identical structural elements, usually the N- and C-termini) between the subunits and is considered to be a mechanism for amyloid-type aggregate formation. This review compares the dimeric and oligomeric structures of different members of the pancreatic-type ribonuclease family which are able to acquire these structures, namely, bovine seminal ribonuclease, ribonuclease A and its human counterpart, human pancreatic ribonuclease. A specific focus is placed on what is known about the structural determinants that lead to the acquisition of a particular oligomeric structure and on the proposed mechanism of 3D-swapping.     

Molecular fibers based on the honeycomb-like self-assembly of an alpha-helical polypeptide

We have succeeded in fabricating well-grown molecular fibers of a polypeptide on substrates by using a conventional solution spin-coating and drying process. These molecular fibers were found to consist of a honeycomb-like molecular assembly formed via the hexagonal close packing of the polypeptide chains in the alpha-helix conformation.     

Neural networks prediction of different frequencies’ effects on calcareous deposits formation under pulse cathodic protection

This paper deals with the calcareous deposition by using pulse cathodic protection on steel structures submerged in the synthetic sea water. In order to fully characterize the complex underlying mechanism of this process and evaluate the effects of a thorough range of frequencies, a prediction model is developed using a hybrid of Neural Networks and Genetic Algorithms (GA). Process variables, i.e. time, frequency and final required current, have been experimentally studied with the aid of chronoamperometric technique. A portion of this dataset is used to train the prediction model, while the rest is set aside to test its predictive performance. This hybrid Neural Networks model uses GA to achieve its optimal architecture for prediction. Finally, it is concluded that the proposed model has an excellent prediction capability of final current density in the various range of frequencies by comparing the results with the experimental data. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 10, pp. 1198–1204. The text was submitted by the authors in English.     

Effect of citrate to nitrate ratio on the decomposition characteristics and phase formation of alumina

This paper reports the effect of the variation of citrate to nitrate ratio on the thermal decomposition characteristics of alumina precursor and the properties of nanocrystalline alumina synthesized using this auto-ignition process. The technique involves the auto-ignition of a citrate-nitrate gel occurring between Al(NO₃)₃ and citric acid to yield an ash powder that upon calcination at 1373 K produced α-alumina. The auto-ignition was restricted to a particular range of citrate to nitrate ratio in the gel. The resulting powder exhibited large surface area (40–50 m² gm^?1) and fine crystallite size. It was established from various characterization techniques that the alumina powder prepared with a C/N ratio of 0.3 has got the optimum powder characteristics compared to the rest of the batches, thus establishing the importance of maintaining a stoichiometric or near stoichiometric C/N ratio. The process has a higher degree of reproducibility and a good potential for large-scale production of alumina.     

Influence of nucleants on the formation of shear-induced structures in polypropylene

The interaction between the type of nucleating agent and base polymer was investigated for a combination of three commercial nucleants and polypropylenes each. Both the crystallisation behavior under DSC conditions and the mechanical and optical properties were determined for all materials. For both the influences of the nucleant and of the base polymer, the present study has provided qualitative indications as to the triggered crystal morphology and shear-induced superstructure. Especially the latter can be related to the differences between optical and mechanical effects of the nucleation process.     

The plasma-electrolytic formation of cerium-containing surface structures on titanium and aluminum

The possibility of obtaining cerium-containing structures on aluminum and titanium by the plasma-electrolytic method with the use of aqueous solutions of electrolytes containing Ce³⁺ polyphosphate complexes was demonstrated. The amount of cerium in the films obtained depended on the molar ratio n = [polyphosphate]/[Ce³⁺] in the electrolyte. The films contained crystalline CePO₄. The growth of films on titanium was characterized by the formation of secondary layers by the mechanism involving the appearance of new phase nuclei followed by their expansion.     

Competitive ionization processes of anthracene excited with a femtosecond pulse in the multi-photon ionization regime

To clarify the ionization mechanism of large molecules under multi-photon ionization conditions, photo-electron spectroscopic studies on anthracene have been performed with electron imaging technique. Electron kinetic energy distributions below a few eV reveal that three kinds of ionization channels coexist, viz., vertical ionization, ionization from Rydberg states, and thermionic hot electron emission. Their relative yield is determined by the characteristic of the laser pulse. The duration in particular influences the ratio between the first two processes, while for higher intensities the last process dominates. Our results provide strong evidence that internal conversion plays an important role for the ionization of the molecule.     

Ablation thresholds and morphological changes of poly-l-lactic acid for pulse durations in the femtosecond-to-picosecond regime

Biodegradable polymers such as poly-l -lactic acid (PLLA) are essential tools for a wide range of medical applications because of their mechanical robustness and bio-affinity. Laser processing is commonly used to construct various structures from biodegradable polymers. However, in general, polymers deteriorate rapidly owing to laser-induced heating effects. In this study, we investigate the optimum irradiation conditions for PLLA processing, using an ultrafast laser and finely controlling the pulse duration over the femtosecond-to-picosecond range. We report on the morphological characteristics of the craters generated by single-shot and multiple-shot laser irradiation under pulse duration control. Our results show that crater morphology and damage threshold in the single-shot regime depend on pulse duration and that the degree of crater unevenness is insensitive to pulse duration in the multishot regime.     

Free-surface effects on the response of nematic liquid crystal films to a laser pulse

Abstract

The dynamic response of 5CB films with a free surface to a laser pulse is investigated. A magnetic field above the Fréedericksz transition is applied initially to induce a starting angle on the molecular orientation. A single 1·06 μm laser pulse with e ^?1 pulse width 0·2 ms is incident normally upon the films. When the laser pulse polarization is perpendicular to the magnetic field, only a thermal effect is involved. While it is parallel to the magnetic field, both molecular orientation and thermal effects are involved. The results from films with a free surface are compared with those from films sandwiched between two glass substrates. The free surface effect, beam size effect, and thermal effect are discussed by comparing with theoretical analysis.     

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint

In the present work, the resonance Raman, UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about approximately 300 nm in diameter) and nanofibers (about approximately 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1, 632 cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609 cm(-1) of PANI fibers is correlated with the extended PANI chain conformation.     

The effects of high-voltage pulse electric discharges on ion adsorption on activated carbons

The effects of high-voltage pulse electric discharges (HPED) on sorption of boron and sulfate ions on activated carbons of different kinds (KM-2, BAU, DAK) were investigated. The effect of HPED activation on the sorption characteristics of the systems was found to be similar to the temperature effect.