Plasma Electrolysis Research Articles

Favorable deposition of γ-Al2O3 coatings by cathode plasma electrolysis for high-temperature application of Ti-45Al-8.5Nb alloys

Cathode plasma electrolysis deposition (CPED) has been used to prepare γ-Al2O3 coatings on Ti-45Al-8.5Nb alloys for high-temperature application. The effect of deposition voltage and duty cycle on microstructure and high-temperature oxidation resistance of the coatings has been studied. The surface and cross-section morphologies before and after high-temperature oxidation test, chemical composition and phase identification of the coatings have been investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the thickness and high-temperature oxidation kinetics of as-prepared Al2O3 coatings initially increase and then decrease, with the increase of deposition voltage from 110V to 150V and duty cycle from 40% to 80%. The minimum weight gain of only 0.495mg/cm2 after oxidation duration of 100h at 900°C can be achieved for the coatings formed with deposition voltage of 130V and duty cycle of 60%. The deposition mechanism of the coatings and effect of CPED parameters are also explained in this work.

Microstructural, corrosion and mechanical behavior of two-step plasma electrolyte oxidation ceramic coatings

Abstract Plasma electrolytic oxidation (PEO) is considered as a cost effective and environmentally friendly surface treatment process for improving surface properties of light alloys. The formation of ceramic coatings on Ti6Al4V alloy was reported by two-step PEO process and its structural, electrochemical and mechanical properties with the coated samples were compared by one-step PEO process in an alkaline electrolyte. The structural properties were studied using field-emission scanning microscope (FESEM) and X-ray diffraction (XRD). Electrochemical studies were carried out using linear polarization method and in addition mechanical behaviors were investigated by means of Knoop microhardness and nanoindentation method. Results showed that the second step process resulted in an increase of both porosity percentage and average pore diameter on the surface. The two-step process resulted in a small increase of thickness from about 12.5 to 13.0 µm. Electrochemical test results showed that applying the second step resulted in the decrease of both polarization resistance from 1800.2 to 412.5 kΩ/cm2 and protection efficiency from 97.8% to 90.5%. Finally, the nanoindentation results indicated that the PEO coatings became softer but more ductile after applying the second processing step in acidic electrolyte.

Electrolytic plasma processing of complex products from aluminum alloy D16

The study analyzed scientific resources, collected statistics on composition of electrolytic solutions for electrolytic plasma processing of aluminum alloy D16. Moreover, a procedure for determining the potential components of the electrolytic solution has been found and there has been developed an electrolytic solution that excludes surface etching and provides the required quality of the surface layer. Finally, rational technological regimes have been determined

Electron-Donor and -Acceptor Agents Responsible for Surface Modification Optimizing Electrochemical Performance.

The electrochemical roles of electron-donor and -acceptor agents in surface reforming of magnesium alloy were investigated via plasma electrolysis. The surface modification was performed in an aluminate-based electrolyte, having urea and hydrazine with inherent molecular structures, which might act as electron acceptor and donor during plasma-assisted electrochemical reaction. The presence of hydrazine working as donor would promote the formation of magnesium aluminates in the oxide layer, resulting in superior compactness of the oxide layer to that when urea was used as the working as acceptor since the precipitation of MgCO3 was favored in the electrolyte with urea. The thickness of the oxide layer formed by a combination of urea and hydrazine was higher than urea, while the porosity was higher than hydrazine. The electrochemical performance was enhanced in the order of hydrazine, urea and hydrazine combined, and urea, which was discussed on the basis of impedance interpretation.

Strong saturable absorption of black titanium oxide nanoparticle films

Nonlinear optical materials with strong saturable absorption (SA) properties play an essential role in passive mode-locking generation of ultrafast lasers. Here we report black TiO2-x nanoparticles are promising candidate for such an application. Black TiO2-x nanoparticles are synthesized by using cathodic plasma electrolysis, and nanoparticle films are deposited on optical glass plates via natural sedimentation and post annealing. Characterization of the samples with TEM, SEM, XRD and XPS reveal that nanoparticles have diameters of 8–70nm, and are in polycrystalline structure and co-existence of anatase, rutile and abundant oxygen-deficient phases. Optical transmittance and reflectance measurements with a UV/VIS/NIR spectrophotometer evidence an excellent wide-spectral optical absorption property. The nonlinear optical properties of the samples were measured by using open-aperture Z-scan technique with picosecond 532-nm laser, and verified by direct transmission measurements using nanosecond 1064-nm laser. Strong SA behavior was detected, and the nonlinear absorption coefficient is as high as β=−4.9×10−8m/W, at least two orders larger than most previous reports on ordinary TiO2. The strong SA behaviors are ascribed to the existence of plenty surface states and defect states within bandgap, and the relaxation rates of electrons from upper energy levels to lower ones are much slower than excitation rates.

Dual Electrolytic Plasma Processing for Steel Surface Cleaning and Passivation

To remove the rust on rebars and passivate the fresh surfaces, electrodes reversing electrolytic plasma processing (EPP) was proposed and conducted in a 10 wt.% Na2CO3 aqueous solution. The morphology and the composition of the surface were investigated by SEM and XPS. Experimental results show that the rust on the surface was removed effectively by cathode EPP, and a passive film containing Cr2O3 was achieved by the succeeding anode EPP treatment, by a simple operation of reversing the bias. The corrosion resistance was evaluated in a 3.5 wt.% NaCl aqueous solution using an electrochemical workstation. In comparison, the corrosion resistance was improved by the succeeding anode EPP treatment, which is evidenced by a positive shift of the open-circuit potential, an increase in the electrochemical impedance representing the inner layer by 76.8% and the decrease in the corrosion current density by 49.6%. This is an effective and environment-friendly technique to clean and passivate rebars and similar steel materials.

Cathodic plasma electrolysis for preparation of diamond-like carbon particles in glycerol solution

We extracted diamond-like carbon particles from glycerol solution by cathodic plasma electrolysis process under atmospheric pressure. The electron temperature in plasma discharge region was calculated. The morphology and composition of diamond-like carbon particles, as well as the decomposition mechanism of electrolyte were analyzed. The results showed that the electron temperature during cathodic plasma electrolysis process was about 11000 K. The high electron temperature provided the formation environment for diamond-like component. The carbon particles were less than 100 nm in diameter with the sp3 content about 28.7%. Glycerol molecules were decomposed into C, H, O reactive species during the intense plasma discharge process. Some carbon species were accelerated by electric field towards cathode forming a hardened layer on the surface, while others were polymerized into suspended diamond-like carbon particles in the solution.

Aluminum Treatment in the Electrolytic Plasma During the Anodic Process

Aluminum Treatment in the Electrolytic Plasma During the Anodic Process

One-step preparation of hydrogenated ZrO2 microspheres by cathode plasma electrolysis

Hydrogenated ZrO2 microspheres were directly prepared by cathode plasma electrolysis (CPE) in an aqueous solution of Zr(NO3)4•5H2O. Owing to the energy of plasma and the cathodic hydrogen evolution reactions, the CPE method combined the preparation of ZrO2 ceramic and the hydrogen treatment into only one step. The results showed regular microspheres consisting of tetragonal-ZrO2 and monoclinic-ZrO2 with 1–10 µm in diameter were formed at relatively high concentration of Zr(NO3)3•5H2O. These ZrO2 microspheres contained about 52.54 µg g−1 hydrogen which caused a narrow band gap (3.10 eV). Thus, the microspheres showed good photocatalytic activity under simulated sunlight, and the degradation of RhB dye reached nearly 58% for 3 h of irradiation, much better than the ZrO2 microspheres after dehydrogenation treatment.

Effect of power supply on the deposition of Zn on a steel substrate using cathodic plasma electrolysis

Cathodic plasma electrolysis (CPE) has been used as an environmentally-friendly process to deposit metal coating on metal substrate. In this work, a coating of zinc was deposited via CPE on a low carbon steel wire using direct current (DC) and square wave pulsed current (SWPC) power. The experimental results showed that application of continuous DC power did not produce zinc deposition, but a dense coating of zinc was easily applied to the substrate with the application of SWPC power at 120V, 4000Hz and an 80% duty cycle. The resulting coating was porous with some imperfections on the surface, but the morphology and quality of the coating could be controlled by adjusting the parameters of the SWPC power. Increasing both the duty cycle and frequency of the power resulted in a lower deposition rate, but the coating was denser. The steel wire surface was cleaned using plasma generated in the CPE process and the Zn coating was found to accumulate during the rise in the power pulse. A linear regression model was established to describe the relationship between coating thickness and power parameters.

Preparation of Continuous Al<sub>2</sub>O<sub>3</sub>/Y<sub>2</sub>O<sub>3</sub> Coating on Carbon Fiber by a Novel Aqueous Plasma Electrolysis

A novel aqueous plasma electrolysis applied for depositing a uniform and continuous Al2O3/Y2O3 ceramic coating on each fiber within a carbon fiber bundle are reported in this study. All equally spaced tungsten wires generated plasma arc, where the plasma was overlapped, excluded and extruded each other, finally a cylindrical plasma arc zone was formed, promoting the full coverage of the coating on each fiber. The Al2O3/Y2O3 coating protected the carbon fiber from oxidation above 850oC. Similarly, the coating significantly improved the oxidation resistance of the carbon fiber with the mass loss of ~5% after isothermal oxidation in N2 atmosphere at 800°C for 30 min, compared to ~14% of bare carbon fiber. By the movement of the T300 carbon fiber bundle, 1500 m coated carbon fiber bundle with the high-quality Al2O3/Y2O3 coating deposited on each fiber was successfully realized. It is believed that the novel aqueous plasma electrolysis will find a wide range of applications in modifying the interface of the carbon fiber reinforced composites. The present investigation will also open up a new horizon for preparing a protective coating on each fiber within two/three-dimensional carbon fiber fabric.

키토산 기반 미세다공성 고분자의 Pd2+에 대한 선택적 흡착성 및 재사용성

A green and simple glow-discharge electrolysis plasma (GDEP) technique was used to synthesize the chitosan/attapulgite/poly(acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (CS/ATP/P(AA-co-AMPS)) microporous polymer. The results showed that the optimum pH for the adsorption of PbSUP2+/SUP, CdSUP2+/SUP, CoSUP2+/SUP, and CuSUP2+/SUP is 4.8, and time of adsorption equilibrium is 60 min. Adsorption kinetics fits well to the pseudo-second-order model. The maximum adsorption capacities for PbSUP2+/SUP, CdSUP2+/SUP, CuSUP2+/SUP and CoSUP2+/SUP are 500.0, 301.7, 180.0 and 151.7 mg gSUP-1/SUP, respectively. The microporous polymer has higher adsorption selectivity toward PbSUP2+/SUP with the coexistence of CdSUP2+/SUP, CoSUP2+/SUP, and CuSUP2+/SUP. The CS/ATP/P(AAco-AMPS) possesses promising regeneration and reusability using 2.0 g L–1 ethylenediamine tetraacetic acid tetrasodium salt (EDTA-4Na) solution as eluent. CS/ATP/P(AA-co-AMPS) can be used as a very promising absorbent for the separation purification and selective recovery of PbSUP2+/SUP in aqueous solution containing CdSUP2+/SUP, CoSUP2+/SUP, and CuSUP2+/SUP ions.

Room-temperature aqueous plasma electrolyzing Al2O3 nano-coating on carbon fiber

A novel room-temperature aqueous plasma electrolysis technique has been developed in order to prepared Al2O3 nano-coating on each fiber within a carbon fiber bundle. The microstructure and formation mechanism of the Al2O3 nano-coating were systematically investigated. The oxidation resistance and tensile strength of the Al2O3-coated carbon fiber was measured at elevated temperatures. It showed that the dense Al2O3 nano-coating was relatively uniformly deposited with 80–120nm in thickness. The Al2O3 nano-coating effectively protected the carbon fiber, evidenced by the slower oxidation rate and significant increase of the burn-out temperature from 800°C to 950°C. Although the bare carbon fiber remained ∼25wt.% after oxidation at 700°C for 20min, a full destruction was observed, evidenced by the ∼0GPa of the tensile strength, compared to ∼1.3GPa of the Al2O3-coated carbon fiber due to the effective protection from the Al2O3 nano-coating. The formation mechanism of the Al2O3 nano-coating on carbon fiber was schematically established mainly based on the physic-chemical effect in the cathodic plasma arc zone.

The determination of micro-arc plasma composition and properties of nanoparticles formed during cathodic plasma electrolysis of 304 stainless steel

This paper presents the research focused on the determination of micro-arc plasma composition during cathodic plasma electrolysis of AISI304 stainless steel in water solution of sodium hydroxide. The complex line shape of several Fe I spectral lines was observed and, by means of a dedicated fitting procedure based on the spectral line broadening theory and H2O thermal decomposition data, the mole fraction of micro-arc plasma constituents (H2, Fe, O, H, H2O, and OH) was determined. Subsequent characterization of the cathodic plasma electrolysis product formed during the process revealed that it consists of Fe-nanoparticles with median diameter of approximately 60 nm.

Investigation of the effect of a low-temperature plasma of vapor–gas discharges with the use of electrolytic electrodes at lower pressure on products of complex shape

The effects of mechanical, electrochemical, laser, and electrolytic plasma treatment on the morphology and grade of finish of the outside and face surfaces of stator rings made of electrical steel are investigated with the use of X-ray diffraction analysis.

Raising the Corrosion Resistance of Low-Carbon Steels by Electrolytic-Plasma Saturation with Nitrogen and Carbon

Structural features of the external oxide layer and internal nitrided, carbonitrided and carburized layers in steels 10, 20 and St3 produced by the method of electrolytic plasma treatment are studied. Specimens of the steels are tested for corrosion in a naturally aerated 1-N solution of sodium chloride. The condition of the metal/sodium chloride solution interface is studied by the method of electrochemical impedance spectroscopy. It is shown that the corrosion resistance of low-carbon steels can be raised by anode electrolytic-plasma saturation with nitrogen and carbon. Recommendations are given on the choice of carbonitriding modes for structural steels.

(Invited) Electrolysis with Plasma Cathodes: Modeling and Experiments to Understand the Electrochemical Interface

In the conventional picture of electrolysis, two metal electrodes are submerged into an electrolyte solution and an applied voltage drives redox reactions at the cathode and anode, respectively. Plasma electrolysis, also called glow discharge electrolysis, changes this convention by replacing one or both of the solid electrodes with a plasma or gas discharge. Reduction and/or oxidation reactions, therefore, are no longer mediated by a solid/liquid interface but by a gaseous/liquid interface, requiring that free charges traverse from the gas to liquid and vice versa. The plasma cathode configuration replaces the typical metal cathode with a plasma, such that free gaseous electrons in the plasma must be injected into the solution phase to initiate reduction reactions at the “cathode”. Recently, this approach to electrolysis has received significant attention for nanomaterials synthesis and emerging applications include the ‘catalyst-free’ electrochemical processing of carbon dioxide (CO2) into useful chemicals. However, there are significant questions that persist about the nature of the electron reactions at the plasma-liquid interface. Recent studies have confirmed that the plasma electrons solvate in the solution before reacting with other dissolved species, and interfacial measurements of the absorption spectrum show that it is similar to, but different from, the standard solvated electron spectrum measured using radiolysis techniques. This anomaly suggests that the plasma-liquid interface is a wholly different environment for solvated electrons from that they experience in bulk radiolysis. To understand this interface, a model of the interfacial electrostatic Debye layer was constructed by considering both the electrostatic potential variation on the plasma side and the liquid side along with electron injection across the liquid interface. This analytical model predicts a non-linear scaling relationship between the plasma current density and electrolyte conductivity, and experimental measurements confirm the model. Extracted values from the model, including the interfacial electric field (~105 V/m) and the electrolyte cation concentration, offer insight into the electrochemical interface, but do not fully resolve questions regarding the anomalous absorption spectrum of plasma-injected solvated electrons.

Changes in mechanical properties and structure of electrolytic plasma treated × 12 CrNi 18 10 Ti stainless steel

Abstract The paper addresses findings regarding the influence of electrolytic plasma treatment on the mechanical properties as well as structural and phase states of × 12 CrNi 18 10 Ti steel. Electrolytic plasma treatment is based on carburizing of stainless steel heated in electrolytes. Treatment of steel samples has been performed as follows: the samples were heated up to a temperature between 850 and 950 °C and then they were cured for 7 minutes in an electrolyte of an aqueous solution containing 10 % glycerol (C3H8O3) and 15 % sodium carbonate (Na2CO3). It is found that, after plasma electrolytic treatment, the surface of × 12 CrNi 18 10 Ti steel had a modified structure and high hardness. Increasing wear resistance of × 12 CrNi 18 10 Ti steel has been observed after carburizing and the coefficient of friction has been reduced. X-ray analysis showed that retained austenite γ-Fe is a main phase, and there are some diffraction lines of orthorhombic Fe3C phase as well as Fe3O4 cubic phase. It has been de...

Effect of process parameters on coating composition of cathodic-plasma-electrolysis-treated copper

Cathodic plasma electrolysis is a novel technique to form nanostructured layers on metallic surfaces by application of high voltage in a suitable aqueous electrolyte. In the present study, copper is treated by plasma electrolysis in 50 vol% ethanol electrolyte and coatings comprising carbon nanostructure and copper oxide are formed on the copper. The effect of some process parameters such as electrical conductivity, volume and temperature of electrolyte and ratio of anode to cathode surface area on current–voltage behaviour and subsequently coating compositions are investigated at 150 V deposition voltage. The composition and morphology of these coatings are characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Different current–voltage behaviours, temperatures of substrate and the contents and energies of radicals and ions around the substrate by changes in the mentioned parameters cause different compositions from 100 vol% copper oxide to different ratios of copper oxide to carbon, the structure changing from amorphous to graphitic structure in carbon and amorphous to cubic morphology in copper oxide on the substrate. Therefore, the understanding of cathodic plasma electrolysis can be developed.

Electrolytic plasma processing-an innovative treatment for surface modification of 304 stainless steel

There is widespread attention to surface profile and modification of 304 stainless steel for research development and application. Here, a successful electrolytic plasma processing (EPP) technique has been developed for both surface pretreatment and coating deposition of 304 stainless steel. Representative images confirm that the number of the pits increases and the ravines gradually disappear on the steel pretreated by EPP with the increase of processing time and applied voltage. Moreover, there is an obvious enhancement in surface roughness of 304 stainless steel after EPP pretreatment. In the case of coating deposition, the further EPP modification conducted on the pretreated sample offers a simple and effective technique for the production of zinc coatings having the features of full coverage and homogeneous distribution. The results show that a zinc coating with a thickness of approximately 0.5 μm can be obtained on the 304 stainless steel by means of EPP for only 60 s.