Pulsed Electrochemical Method Research Articles

A study of electrodischarge machining–pulse electrochemical machining combined machining for holes with high surface quality on superalloy

Noncircular holes on the surface of turbine rotor blades are usually machined by electrodischarge machining. A recast layer containing numerous micropores and microcracks is easily generated during the electrodischarge machining process due to the rapid heating and cooling effects, which restrict the wide applications of noncircular holes in aerospace and aircraft industries. Owing to the outstanding advantages of pulse electrochemical machining, electrodischarge machining–pulse electrochemical machining combined technique is provided to improve the overall quality of electrodischarge machining-drilled holes. The influence of pulse electrochemical machining processing parameters on the surface roughness and the influence of the electrodischarge machining–pulse electrochemical machining method on the surface quality and accuracy of holes have been studied experimentally. The results indicate that the pulse electrochemical machining processing time for complete removal of the recast layer decreases with the increase in the pulse electrochemical machining current. The low pulse electrochemical machining current results in uneven dissolution of the recast layer, while the higher pulse electrochemical machining current induces relatively homogeneous dissolution. The surface roughness is reduced from 4.277 to 0.299 µm, and the hole taper induced by top-down electrodischarge machining process was reduced from 1.04° to 0.17° after pulse electrochemical machining. On account of the advantages of electrodischarge machining and the pulse electrochemical machining, the electrodischarge machining–pulse electrochemical machining combined technique could be applied for machining noncircular holes with high shape accuracy and surface quality.

Fabrication of uniform 4H-SiC mesopores by pulsed electrochemical etching.

In this letter, the uniform 4H silicon carbide (SiC) mesopores was fabricated by pulsed electrochemical etching method. The length of the mesopores is about 19 μm with a diameter of about 19 nm. The introduction of pause time (Toff) is crucial to form the uniform 4H-SiC mesopores. The pore diameter will not change if etching goes with Toff. The hole concentration decreasing at the pore tips during the Toff is the main reason for uniformity.

The Study of Hydroxyapatite Coating on Titanium Surfaces though Electrochemical Technology

Hydroxayapatite coating was prepared on titanium (Ti) substrate by pulsed electrochemical method. Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to investigate the microstructure of the coatings. The results showed that Hydroxyapatite coating was successful prepared on titanium substrate by pulsed electrochemical method.

Development and validation of an indirect pulsed electrochemical detection method for monitoring the inhibition of Abl1 tyrosine kinase

A new method for monitoring the enzyme inhibition of Abl1 tyrosine kinase by liquid chromatography–indirect pulsed electrochemical detection (LC–InPED) was developed. In this method, adsorption of a peptide analyte at the noble metal electrode suppresses the oxidation of polyols under alkaline condition to elicit an indirect response resulting in a negative peak of the target peptide. Among the reagents tested, d-gluconic acid sodium salt gave the best overall signal to noise (S/N) values for the indirect detection of p-Abltide, the product of Abl1 enzymatic reaction. 50μM d-gluconic acid sodium salt dissolved in a mixture of 78% water–22% acetonitrile–0.03% trifluoroacetic acid (TFA) was used as the mobile phase. Chromatographic separation was achieved on an Alltima C18 (I.D. 5μm; 250mm×4.6mm) column with the mobile phase flow rate of 0.5ml/min. 0.5M sodium hydroxide was added post-column to maintain alkaline conditions in the PED cell. The limit of quantification (LOQ) was 0.2μM for p-Abltide, which was about 50-fold lower than direct PED analysis. The residual plot of the linear calibration curve indicated a good fit with a linear model within the investigated concentration range of p-Abltide. Intra- and inter-day precision was not more than 6.5% and accuracy was from −5.75% to +1.54%. The validated LC–InPED method was successfully applied for monitoring of p-Abltide in Abl1 enzyme reaction and the inhibition study of Abl1. The determined IC50 values of model inhibitors, imatinib, nilotinib and dasatinib, were 601.4nM (R2=0.99), 32.3nM (R2=0.99) and 1.3nM (R2=0.98), respectively. These results were consistent with literature data. To the best of our knowledge this is the first time a LC–InPED method has been used to monitor an enzyme reaction.

The Pulse Electrolysis Treatment of Waste Emulsion Orthogonal Experimental Study

This mechanical processing waste emulsion for the study, handled by pulse electrolysis. Arrangements by orthogonal testing, experimental study on plate distance (d), current density (i), the pH value and the pulse width (tP) impact on COD removal efficiency, very poor analysis of test data to determine various factors affecting the COD removal efficiency of primary and secondary sort: pH value > current density > pulse width > plate distance, optimal operating conditions. Orthogonal experimental data derived from regression analysis, determination of cross of quadratic polynomial regression equations, mathematical model. Tests confirmed that pulse electrochemical method for treatment of waste emulsion with low energy consumption, short response time, and other advantages, strong applicability of wastewater, building mathematical models, providing theoretical basis for subsequent design.

Heavy metal removal from water by magnetite nanorods

In this paper, a new effective adsorbent for removal of some heavy metal ions such as Fe, Pb, Zn, Ni, Cd and Cu from aqueous solution is synthesized by pulsed current electrochemical method. Scanning Electron Microscopy (SEM) imaging and X-ray diffraction shows the synthesized sample including pure magnetite nanorods (MNR) with 60nm average diameters and 1000nm average lengths. The adsorbed ions can easily eluted by small volume of nitric acid solution. The adsorption equilibrium study exhibited that the heavy metal ions adsorption of magnetite nanorods followed a Langmuir isotherm model. The experimental kinetic data for adsorption of heavy metal ions on the surface of the synthesized nanorods were described by a pseudo-second-order equation. From the Langmuir isotherms, the maximum adsorption capacities of magnetite nano-adsorbents towards Fe2+, Pb2+, Zn2+, Ni2+, Cd2+ and Cu2+ were 127.01, 112.86, 107.27, 95.42, 88.39 and 79.10mgg−1, respectively. The experimental data shows the synthesized MNRs can quantitatively remove heavy metal ions from water.

Electrochemically controlled growth of silver nanocrystals on graphene thin film and applications for efficient nonenzymatic H2O2 biosensor

We report a double pulse electrochemical method to controllably prepare silver nanocrystals (AgNCs) on graphene thin film electrode for fabricating a high performance H2O2 biosensor. The approach relies on two potential pulses that can independently control the nucleation and subsequent growth processes of AgNCs on graphene substrate. This method also allows the observation of AgNCs growing from a particle shape to a nanoplate form by increasing the growth time with the maximum lateral scale up to micrometer scale range. A proposed mechanism for these silver nanoplates (AgNPLs) formation was the oriented growth of small AgNCs and two-dimensional graphene template inducing effect. Such obtained graphene–AgNPLs hybrid thin films exhibit remarkable electrocatalytical activity toward H2O2 electrochemical reduction. Further fabricated nonenzymatic H2O2 biosensor displays a fast amperometric response time of less than 2s and a good linear range from 2×10−5M to 1×10−2M with an estimated detection limit of 3×10−6M. This biosensor also exhibits good stability (RSD, 1.3%), and high sensitivity of 183.5μAcm−2mM−1 as well as high selectivity. The results show that this powerful double pulse potential electrochemical method could enable new opportunities in controllable preparation of multifarious nanomaterials on graphene substrate for their future applications.

The role of pulse time Toff on porous silicon as template for Au nanoparticles by using the integrated electrochemical technique

Gold nanoparticles (AuNPs) having variety of sizes and shape were prepared using the template synthesis approach. Porous silicon (PSi) was fabricated using the pulsed electrochemical anodization method at different pause times, T off as template for gold deposition. Choosing suitable pulse parameter produces PSi with higher porosity and smaller crystallite size. SEM showed that the variation of T off affects the pores formation and the growth of gold nanoparticles while EDX suggested the presence of Au inside the pores structure. Photoluminescence spectra showed emission enhancement and a blue shifted relative to porous silicon before deposited with AuNPs. XRD shows a high degree crystallinity of the samples and the presence of cubic gold with crystalline sizes was around 42 nm.

Fabrication of Silicon Carbide Thin Film as a Stabilizing Layer for Improving the Stability of Porous Silicon Photodiodes

This paper investigates the effect of silicon carbide (SiC) thin film as a stabilizing layer on porous silicon (PS) in metal–semiconductor–metal (MSM) photodiodes. Photo-assisted pulsed electrochemical etching method was used to produce the PS layers with large pore density and small crystallite size. As–prepared PS surface was modified with acetylene gas flow in a thermal process (750°C) in order to replace the hydrogen termination by Si–C bonds which is more stable. During the thermal carbonization, carbon atoms penetrated into the silicon lattice forming a thin (~4 nm) SiC layer. Because of high inertness of silicon carbide thin film, thermally carbonized porous silicon layer (TC-PS) was found to be more stable than the freshly prepared PS surfaces. A small reduction in specific surface area was found after carbonization which is due to the small size of acetylene molecules. The FTIR measurements confirmed the presence of SiC bonds in the TC-PS sample. The photocurrent of the fabricated photodiodes based on as-grown PS was lowered under prolonged green laser radiation (532nm, 5mW), but devices based on TC-PS showed more stable I-V characteristics under the same condition even for 120 min of laser exposure.

Pulsed electrodeposition of Bi 2Te 3 and Bi 2Te 3/Te nanowire arrays from a DMSO solution

Dense, continuous and polycrystalline bismuth telluride (Bi 2Te 3) nanowire arrays have been deposited from a DMSO solution containing Bi(NO 3) 3·5H 2O and TeCl 4 in porous alumina templates by a pulse electrochemical method. The composition of the nanowire is dependent on the applied potential, and the composition distribution along a single nanowire becomes more uniform as the potential-off time becomes longer. The Bi 2Te 3 nanowire arrays have a highly preferential orientation along the [1 1 0] direction. Bi 2Te 3/Te multilayered nanowire arrays have also been deposited from the same DMSO solution. A clear interface between segments of different composition can be distinguished by TEM analysis. The elemental analysis shows the atomic percentage of Te in Te segments to be more than 95 atom%. Bi-rich regions were obtained in the Bi 2Te 3 segments.

Pulsed Current Electrochemical Synthesis of Nickel Nanoclusters and Application as Catalyst for Hydrogen and Oxygen Revolution

The main objective of this research is to prepare nickel nanoparticles with more porous structure by the pulsed current electrochemical method. A nickel optimized nanopowder was synthesized by using nickel chloride (0.005 M) as precursor, silver nitrate as a nucleation agent (at 0.5% mole of nickel salt in the starting solution), polyvinyl pyrrolidone (PVP) as structure director (with PVP/Ni = 1.7 g/g), ammonia (2 M), and hydrazine as reduction agent (with Hydrazine/Ni = 16 g/g) by pulsed current of 58 mA cm−2 with a frequency of 12 Hz. The morphology and particle size of each synthesized sample was studied by scanning electron microscopy (SEM). The obtained results showed that temperature has no considerable effect on the morphology and particle size of nickel nanopowder. The nickel nanopowder synthesized in optimum conditions has excellent uniform and a more porous structure including nanoclusters with a particle size of approximately 10–20 nm. The obtained results indicate that the pulsed current electrochemical method can be used as a confident and controllable method for the preparation of nickel nanoparticles. Optimized nickel nanoclusters were used as catalyst for hydrogen and oxygen revolutions. Cyclic Voltammetry results showed that the synthesized nanoclusters can facilitate hydrogen reduction and increase hydrogen and oxygen revolution rates.

Electrodeposition of silver particles from alkaline aqueous solutions and their electrocatalytic activity for the reduction of nitrate, bromate and chlorite ions

A pulsed electrochemical method was used for the preparation of silver deposit onto glassy carbon surfaces from an alkaline medium containing ammonia ligand. The morphology of the silver deposit, obtained under pulsed and cyclic conditions was examined and compared using the scanning electron microscopy (SEM) technique. From the experimental evidences, it can be inferred that pulsed method induces a favourable dendritic growth of silver particles, while deposited films obtained under cyclic voltammetry appear formed of globular particles with well regular and defined surface geometry. The electroanalytical performance of the deposited silver, towards the electroreduction of NO 3 −, BrO 3 − and ClO 2 − ions, using cyclic voltammetry and chronoamperometry technique, was evaluated. Interesting analytical results, in terms of sensitivity and temporal reproducibility, in alkaline medium and under constant applied potentials (i.e., −1.45 and −0.6 V vs. SCE), were obtained.

Synthesis of Iron Nanoclusters by Pulsed Current Method

The main objective of this research is to prepare iron nanoclusters with more porous structure by the pulsed current electrochemical method. In this method, there are some effective parameters including; pulse amplitude (current amount), pulse frequency, iron salt concentration, sulfuric acid concentration and synthesis temperature, which were optimized by the “one at a time method”. An iron optimized nanopowder was synthesized by using iron sulfate (0.005 M) as precursor and silver nitrate as a nucleation agent (at 0.5% mole of iron sulfate in the starting solution) by pulsed current of 20 mA cm−2 with a frequency of 14 Hz. The relative gravimetrical density was used as an optimizing parameter for iron nanoparticles synthesis. The morphology and particle size of each synthesized sample was studied by SEM, TEM and XRD. The iron nanopowder synthesized in the optimum conditions has excellent uniform and a more porous structure including nanoclusters with a particle size of approximately 20–40 nm. The obtained results indicate that the pulsed current electrochemical method can be used as a confident and controllable method for the preparation of iron nanoparticles. XRD, EDX and ICP-AES results showed that the iron nanoclusters can be synthesized with high purity by the proposed method.

Investigation of organic expanders effects on the electrochemical behaviors of new synthesized nanostructured lead dioxide and commercial positive plates of lead-acid batteries

Positive electrode with uniform lead dioxide nanostructures was directly synthesized by pulsed current electrochemical method on the lead substrate in 4.8 M sulfuric acid solution. The effect of synthesis parameters were studied by the “one at a time” method on the morphology and particle size of lead dioxide. The composition, morphology and structure were investigated using energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM) and X-ray diffraction techniques (XRD). The effect of conventional organic expanders including humic acid, 1,2-acid (α-hydroxy β-naphtoic acid) and Vanillex was studied on the electrochemical behaviors of the prepared positive electrodes by cyclic voltammetry and on the discharge capacity and cyclelife of commercial positive plates. The used organic expanders improve the performance of negative plates but, they have not positive effects on the performance of positive electrodes of lead-acid batteries.

Pulse electrochemical method for porosification of silicon and preparation of porSi powder with controllable particles size distribution

AbstractWe have proposed to use a special electrochemical regime to introduce a preferable grain size into the entirely porosified Si material. This periodic pulse electrochemical regime permits layering of the entire porosified film and defines its preferable partition in the post anodization mechanical treatment. Thus, a preferable grain size is “hidden” in the grown porSi film and is revealed only under additional mechanical treatment like milling. The pore dimension and total porosity are controlled by applied current density at the work pulse and prefabricated (hidden) grain size is introduced during an application of the cut or/and relaxation pulses. We have applied a described procedure to produce a sub‐micrometric grain porSi powder and report results on SEM analysis of the material fabricated in different pulse regimes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of Co–Ag films by direct and pulse electrochemical methods

A new electrolytic bath containing sodium perchlorate, thiourea, sodium gluconate, boric acid and silver and cobalt salts, able to favour simultaneous electrodeposition of silver and cobalt, has been developed. A systematic analysis of the effect of cobalt(II) concentration, applied deposition potential, hydrodynamic conditions and electrochemical techniques was made. From this bath, Co–Ag deposits of different composition have been prepared and characterized. Granular deposits were obtained from all the electrochemical deposition procedures tested; more compactness and uniformity were attained when the deposits were obtained by pulse plating method. Electrochemical and compositional characterizations indicated that heterogeneous cobalt–silver deposits were prepared containing some oxi- and/or hydroxylated cobalt species.

Fabrication of wedge-shape tool via electrochemical micromachining with diamond-like carbon coating

Abstract A wedge-shaped micro cutting tool with an edge radius of 0.6 μm is fabricated from stainless steel using pulse electrochemical machining method (PECM). This tool is then coated with Ti-containing diamond-like hydrocarbon (Ti-DLC) to enhance its surface roughness and hardness. Surface roughness and edge sharpness of the ECMed tool face are shown to improve with decreasing pulse width of the ECM supply voltage. The Ti-DLC coatings on the electrochemical fabricated stainless steel tools have been synthesized by unbalanced magnetron sputtering process. The microstructures and mechanical properties of Ti-DLC coating are characterized by Raman spectroscopy and nano-indentation techniques. The results show that the sp 2 bonding increases with decreasing Ti composition. Therefore, as Ti composition decreases, the hardness of Ti-DLC coatings increases. On the other hand, the elastic modulus of the coating is found to decrease with decreasing Ti composition. For improved wear resistance, the high ratio of hardness to elastic modulus is achieved at 7.2% of Ti composition. The fabricated tool is tested successfully in a scribing experiment and compared with a single crystal diamond cutter. Due to its higher surface roughness and the consequent higher rubbing resistance, the specific cutting energy of the fabricated tool is found to be greater than that of the single crystal diamond cutter.

Developing Concepts of Chromium Functions in the Passivation and Pitting of Fe–Cr Alloys

The passivability and pitting resistance of Fe–(0–100)Cr alloys in deaerated acidic sulfate environments (at a concentration of sulfate ions of 0.1 to 1.0 mol/l and pH from 0.5 to 1.8) and neutral borate buffer solutions with a chloride concentration of 0.003 mol/l and pH 7.3 are studied with the use of steady-state and pulse electrochemical methods. Four critical alloy compositions corresponding to the sharp changes in the passivability, repassivability, and pitting resistance of the alloys are discussed: ∼6.5; ∼11; ∼17; and ∼27% Cr. Based on considering the alloys as purely “mechanical” mixtures with no sign of any order so that a chromium atom can occupy any lattice point with a probability proportional to the bulk chromium content, the following hypothesis is put forward. It is the crystallographic and electronic structure of Fe–Cr alloys that forms the main reason for the existence of the mentioned critical concentrations. Upon reaching certain critical compositions, chromium atoms either occupy positions in each coordination sphere (∼6.5% Cr), each elementary cell of an scc lattice (∼11% Cr), or each quasirhombohedral pore (∼17% Cr); or a superlattice compound appears (∼27% Cr).

An electrochemical study of enzymatic oligonucleotide digestion

This paper describes the synthesis and application of a novel ferrocene (Fc) label that can be efficiently attached to oligonucleotides. We demonstrate how pulse electrochemical methods can be used to measure very low concentrations of ferrocene label and, importantly, show good electroanalytical discrimination between a labelled oligonucleotide and an enzyme digested labelled oligonucleotide, in which the ferrocene label nucleotide conjugate has been released. Real time in situ analysis gives a much greater understanding of the process. Potential applications include the detection of specific nucleic acid sequences and measurement of nuclease activity.

Narrow-line light emission from porous silicon multilayers and microcavities

Porous silicon multilayers and microcavities, prepared by the pulsed electrochemical etching method, exhibit a variety of reflectivity and photoluminescence spectra. A comparison of the measured results with those calculated based on the transfer matrix method and quantum-box model reveals that the variation of the spectra can be attributed to the change in wavelength position of the stop-band of distributed Bragg reflectors and the maximum of the broad light emission of porous silicon. Different confined electric field modes appear in three different cases of porous silicon microcavities. Their different characteristics are summarized and considered as criteria to distinguish species of the porous silicon microcavities from their photoluminescence spectra.