Electrolyte Agitation Research Articles

Electrolytic galvanizing technology on internal surfaces of machined parts using computer numerical control (CNC)

In the present investigation, the study of the Zinc electrolytic galvanizing process on the interior surfaces for high-pressure pipe couplings is detailed, this through a statistical factorial analysis 23 that allowed to relate the 3 factors of the experimentation layout of parts, electrolyte agitation and immersion time; in this way, 8 types of possible iterations were determined in order to analyze the correlation and the incidence in the quality of the anticorrosive protection under the ISO 10289:2001 standard. The adequate levels of the electrolyte were determined using a Hull cell, and optimal working parameters were established at a temperature of 20 °C, a current density of 2.7 A/dm2 and a voltage of 5 V. After experimentation it was determined that the arrangement of the parts is the most determining factor for the coating to provide good anti-corrosion protection in combination with acid baths. The methodology used could serve as a basis for the collection of new results and possible comparisons.

The Effect of Ultrasonic Agitation on the Seedless Growth of Cu on Ru-W Thin Films.

Ru attracted considerable attention as a candidate to replace TaN as a diffusion barrier layer for Cu interconnect metallisation. The addition of W improves the diffusion barrier properties of Ru but appears to weaken the adhesion strength between the barrier and Cu and the direct (seedless) electroplatability behaviour. Although Cu can be directly electroplated on near equimolar Ru-W thin films, no complete substrate coverage is obtained. The understanding of Cu electrocrystallisation on Ru-W is essential to develop methods of fabricating thin, continuous, and well adherent films for advanced interconnect metallisation, where Ru-W thin films could be used as diffusion barriers. This work studies the effect of ultrasonic agitation on the growth of Cu films electroplated on Ru-W, namely on the impact on substrate coverage. Film structure, morphology and chemical composition were evaluated by digital and scanning and transmission electron microscopies, and X-ray diffraction. The results show that Cu particles decrease with increasing current density, but when no electrolyte agitation is applied, substrate coverage is incomplete in the central region, with openings around larger Cu particles, regardless of current density. Under ultrasonic agitation, substrate coverage is remarkably improved. An active particle detachment mechanism is proposed as responsible for attaining improved substrate coverage, only possible at intermediate current density. Lower current densities promote growth over nucleation, whereas higher currents result in extensive hydrogen reduction/formation. Ultrasonic agitation also enhances a preferential Cu growth along <111> direction.

Electrodeposited Co-P alloy and composite coatings: A review of progress towards replacement of conventional hard chromium deposits

Hard chromium coatings have attracted much attention due to their strong tribological and corrosion performance. There is a global need to replace such coatings in industrial applications owing to technical problems, environmental concerns and legislation. Co-P electrodeposits are a promising alternative to hard chromium in a variety of engineering applications due to their appreciable microhardness and high corrosion resistance . Attractive magnetic, tribomechanical and electrical properties are evident together with excellent thermal stability. Environmentally acceptable process conditions may be used which allow controlled deposition on diverse workpieces across a wide scale. This review provides an overview of the influence of operational parameters, including type of current control, electrolyte composition, pH, current density and electrolyte agitation on the physicochemical and mechanical characteristics of the deposits. The incorporation of ceramic particles into Co-P electrodeposits to produce tailored composite coatings is also considered. An insight is given into the development of next generation alloy and composite deposits to replace hard chromium deposits from acidic Cr(VI) baths. Diverse applications for Co-P electrodeposits are considered and topics deserving further R & D are highlighted. • A concise overview of Co-P alloy electrodeposits is provided. • The most common types of bath used for Co-P electrodeposition are considered. • The influence of operating conditions on properties of deposits is addressed. • Effects of included particles on deposit characteristics are comprehensively discussed. • Potential applications of Co-P films are highlighted.

Effects of cathode rotation and substrate materials on electrodeposited CoMnP thick films

In this study, rotating-cathode electrodeposition was performed to deposit 30 μm thick CoMnP films on various substrate materials at room temperature. The electrodeposition configuration and parameters realized a constant current efficiency of about 95%, which was under activation control rather than mass-transport control. Compositional analysis indicated that the deposited thick films were Co-rich with a Co content 92–95 wt.%, regardless of deposition parameters. X-ray diffraction revealed that cathode rotation physically altered the preferred orientation of Co crystallites. The texture of Co crystallites changed with the cathode rotational speed from distinct hexagonal close-packed (HCP) (002) to a heterogeneous phase mixture of HCP (110) and face-centered cubic (FCC) (220). The substrate materials physicochemically affected the relationship between rotational speed and microstructural evolution. The microstructural texture changed nonlinearly with the cathode rotational speed when the films were deposited on catalytic substrate materials, suggesting a substantial influence of the substrate activation nature. Due to magnetocrystalline anisotropy, the resultant films exhibited hard magnetic properties while depositing at the optimal cathode rotational speed. Stationary-cathode electrodeposition resulted in rough CoMnP films with Co grains of 8–18 nm and high Mn content. These films exhibited unique in-plane magnetic properties compared with the films deposited with electrolyte agitation. This study is the first to investigate the combined effects of cathode rotational speed and the activation nature of substrates on the growth behavior of electrodeposited Co-rich CoMnP thick films. The results can be extended to electrodeposition of other Co-based alloys, such as CoP, CoNiP, CoWP, CoPtP, and CoNiMnP.

On the comparison of the tribocorrosion behavior of passive and non-passivating materials and assessment of the influence of agitation

In this study, the tribocorrosion behavior of an AISI 316 stainless steel (passive) and a Low-Alloyed steel (non-passivating or active) was compared, evaluating also the influence of electrolyte agitation. Unidirectional ball-on-disc tests were performed in synthetic seawater with the Zero Resistant Ammeter technique. The differences on the currents registered for both materials evinced the high rate dissolution of the active steel even in the absence of sliding, while the AISI showed negligible electrochemical activity. The results showed little influence on the agitation for the passive material, but a considerable effect on the wear-accelerated corrosion in the unworn surface of the non-passivating steel.

Electrodeposition of Pd from a deep eutectic solvent system: effect of additives and hydrodynamic conditions

ABSTRACTElectrodeposition of palladium from a mixture of choline chloride/urea/palladium(II) chloride (deep eutectic solvent) has been carried out by direct and pulse current electrodeposition. The influence of five organic additives, current mode (direct current vs. pulsed current) and hydrodynamics on the surface morphology of the electrodeposited palladium films was investigated. The surface morphology and thickness of the palladium layers produced was determined by scanning electron microscope and energy dispersive X-ray fluorescence spectroscopy. The experimental results showed that the surface morphology of the palladium deposits could be affected significantly either by applying pulse current and/or addition of organic additives. Current mode, electrolyte agitation and surface effects of the selected additives mutually interfere with each other, causing changes in the microstructure of the deposits (coarse → nodular/smooth). It was possible to improve the palladium deposit quality and metal deposition rate by addition of appropriate additives and by applying pulsed current.

The effect of anodization conditions on the morphology of porous tungsten oxide layers formed in aqueous solution

Nanostructured WO3 layers were obtained by one-step anodic oxidation of tungsten in an aqueous solution containing fluoride ions. A detailed investigation of the growth of anodic films on metallic substrate was focused on the study of the influence of anodization conditions, such as anodization potential, duration of the process, electrolyte composition, applied temperature, and electrolyte agitation on morphological features of as-received materials. Such kind of comprehensive studies has been performed for the first time. It was found that the optimal conditions allowing synthesis of nanostructures with well-defined pores and the thickest possible oxide layer are: anodization potential of 50 V, anodization time of 4 h, the electrolyte containing 1 M ammonium sulfate and 75 mM ammonium fluoride, temperature of 20 °C, and agitation of electrolyte of 250 rpm. A post-treatment procedure was developed to effectively remove the precipitates formed on the surface of anodic layers during anodization. The obtained materials were also examined as photoanodes in photoelectrochemical (PEC) water splitting experiments. It was confirmed, that PEC performance of nanostructured WO3 photoanodes can be significantly improved (higher photocurrents by 24%) after ultrasonic treatment in a 20 wt% HF solution for 10 s and ethanol for 5 s.

A re-understanding of the breakdown theory from the study of the plasma electrolytic oxidation of a carbon steel — A non-valve metal

Plasma electrolytic oxidation (PEO) is normally not applicable to non-valve metals. However, in this study, PEO of Q345 carbon steel, a non-valve metal, has been carried out under pulsed unipolar regimes in aluminate based electrolytes with the addition of sodium dihydrogen phosphate to understand its coating formation and plasma generation mechanisms. Real time imaging, optical emission spectroscopy (OES), gas collection, scanning electron microscopy (SEM) assisted with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) have been adopted to characterize the PEO processes. It has been found that the cell potential-time responses and plasma initiation are affected by the surface roughness of the carbon steel and the electrolyte agitation, which are not encountered in PEO of valve metals. The addition of sodium dihydrogen phosphate is critical to the establishment of stable plasma discharges and formation of thick PEO coatings on carbon steel. It has been found that the formation of a thin layer of aluminum phosphates (AlPO4 and AlPO4·2H2O) or alumina aluminum phosphate (AAP) at the initial PEO stage plays an important role for the plasma generation and hence PEO coating formation on carbon steel. The variations in the cell potential-time responses are associated with the stability of the aluminum phosphates or AAP layer on the carbon steel. The findings in this paper indicate that the presence of a dielectric layer on the metal surface is a prerequisite for the occurrence of plasma breakdown. Hence, the previous models that dielectric breakdown in PEO is preceded by the breakdown of a bubble layer need to be reconsidered.

Research into effect of electrochemical etching conditions on the morphology of porous gallium arsenide

The method for the formation of porous gallium arsenide in a solution of hydrochloric acid was improved. The goal of present research was to establish correlation between conditions of electrochemical etching of gallium arsenide crystals and morphology of low-dimensional structures. Porous layers were formed by the method of electrochemical etching in a solution of hydrochloric acid. The mode of electrolyte agitation was applied. This makes it possible to avoid the formation of bubbles on the surface of the crystal during etching and leads to the formation of regular porous space. Basic regularities in the formation of porous spaces were studied. It was shown that morphological properties of por-GaAs depend on etching conditions. The effect was explored of current density on the thickness of a porous layer and diameter of pores. It was established that the composition and concentration of electrolyte correlate with surface porosity and affect the rate of crystal dissolution reaction. Etching time determines thickness of a porous layer and surface porosity. Chemical composition of por-GaAs was explored. An oxide layer was not formed on the surface of the examined samples; oxygen was present only in small concentrations. Stoichiometry of the samples was disrupted towards an excess of gallium atoms

Formation of ZnO nanowires during anodic oxidation of zinc in bicarbonate electrolytes

Dense arrays of ZnO nanowires were obtained by one-step anodic oxidation of metallic Zn in bicarbonate electrolytes followed by 2h of annealing in air at 200°C. A detailed inspection of the anode morphology at the initial stages of anodizations was performed. It was confirmed that nanowire bundles are initially formed both inside and outside the pits created during the anodic dissolution of the metallic substrate. In consequence, root-like structures are formed inside the cavities. However, no roots are observed for nanowire bundles formed outside the pits, directly on the surface of Zn. The effect of anodizing conditions on the growth of nanowires was studied. It was found that applying higher anodizing potentials and more concentrated electrolytes result in not only the significantly faster nanowires growth, but also the formation of denser NW films. In addition, the electrolyte agitation can also increase the rate of nanowires formation. Finally, we proved for the first time that the previous usage of electrolyte and the orientation of electrodes, can significantly affect the morphology of as-formed anodic films. Thermal treatment of as-anodized samples resulted in the successful conversion of the carbonate-containing precursor to crystalline wurtzite ZnO without the loss of nanowire morphology.

Characterization and corrosion behavior of graphene oxide-hydroxyapatite composite coating applied by ultrasound-assisted pulse electrodeposition

Abstract Hydroxyapatite (HA) coating reinforced with graphene oxide (GO) had been developed for getting rid of restrictions associated with its brittleness. This study introduced a promising method of ultrasound-assisted pulse electrodeposition to fabricate the GO-HA coating on the anodized heat-treated surface of titanium. The SEM images indicated that the combined effect of employing ultrasonic waves and GO as a second mechanically resistant phase resulted in the formation of a fine and compact microstructure for the HA-based coating. The EDS elemental maps and micro-Raman spectra showed that the ultrasonic power of 60 W was more effective to incorporate the GO sheets into the coating. However, aggressive agitation of electrolyte with increasing the power to 100 W limited the electrocrystallization of HA crystals in some regions of the surface. The results of nanoindentation test demonstrated the highest nano-hardness (3.08 Gpa) and elastic modulus (41.26 Gpa) for the GO-HA coating prepared by the ultrasound-assisted method. The EDS and FTIR analyses revealed that both the GO sheets and highly reactive OH · radicals produced during the water sonolysis had a positive influence on the mineralization of HA phase. In addition, the pore size distribution diagrams calculated from the N 2 adsorption-desorption isotherms indicated a decrease in the pore size of HA crystals for the electro-co-deposited GO-HA sample. Finally, anodizing/heat-treatment process and the incorporation of GO sheets into the coating led to a significant improvement in the corrosion protection of titanium.

Pulse frequency and duty cycle effects on the electrodeposited Ni–Co reinforced with micro and nano-sized ZnO

Ni–Co/ZnO nano and micro composite coating were prepared by PC electrodeposition methods on the pure copper substrate. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, EDAX mapping and atomic force microscopy were employed for investigating of phase structure, surface morphology, elemental analysis, elemental distribution and surface roughness of coatings, respectively. The effects of pulse frequency and duty cycle on the microhardness of coating were investigated. Microhardness of nanocomposite coating was more than that of the microcomposite coating. There were optimum values for pulse frequency and duty cycle (20 Hz, 40% and 10 Hz, 60% for nanocomposite and microcomposite, respectively). Any detour from those optimum values led the microhardness to reduce. Actually pulse frequency and duty cycle influenced the TON (electrical current on time) and TOFF (electrical current off time) values. Optimum TON is required to prepare enough electrical attraction force between the particles (surrounded by cationic cloud) and cathode surface. Optimum TOFF prepared sufficient conditions for particles which be surrounded by cationic cloud and then reach to the cathode surface (using agitation of electrolyte) and reduce there. ZnO microparticles are so greater than ZnO nanoparticles, so more electrical attraction force (lower pulse frequency and higher duty cycle) is required to make them adhere to the cathode surface and prevent from dislodging them from cathode surface by hydrodynamic forces in the electrolyte. Corrosion and wear behaviors of nanocomposite were better than those of microcomposite.

Electrochemical investigation of electrolyte composition and electrolysis parameters during zinc electrowinning

The effect of different Mn2+ and Pb2+ concentrations added to the zinc sulfate acid electrolyte during zinc electrowinning process was investigated. Operating parameters such as zinc ion concentration, acid concentration, current density, electrolyte agitation, and temperature were investigated in the presence of Mn2+ and Pb2+. Galvanostatic polarization, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy studies were performed to examine the cathodic behavior. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the surface of the zinc deposit. The addition of lead ions to the zinc electrolyte led to an increase in the cathodic potential and current efficiencies of the zinc deposition. The addition of Mn2+ to the zinc electrolyte resulted in a decrease in the cathodic potential and current efficiency of zinc deposition. An increase in the current density from 45 to 60 mA cm−2 and in electrolyte agitation from 60 to 412 rpm resulted in an increase in the cathodic potential and decrease in current efficiencies. A temperature increase from 35 to 45 °C led to a decrease in the cathodic potential. After a short initial electrodeposition (2–4 h) using a Pb–0.7%Ag anode, the lead content in the zinc deposit was higher than that obtained with a Pt anode (0.15 mg L−1 Pb2+). A long deposition period of more than 72 h was also considered, and Pb content was almost the same in the zinc deposit for Pb2+ quantities (0.15 or 0.2 mg L−1).

Effect of pH on the properties of electrochemically prepared ZnO thin films

Zinc Oxide (ZnO) thin films have been electrochemically deposited on fluorine doped tin oxide (FTO) coated glass substrates from an aqueous electrolyte. Deposition potential −0.96V was optimized by cyclic voltammetry experiment for slow scan rate 5mV/s with moderate agitation of electrolyte. The effect of pH on the electrodeposition of ZnO is studied by cyclic voltammetry, X-ray diffraction (XRD), scanning electron microscopy (SEM), optical spectroscopy and photoelectrochemical I-t transient characteristics. It is revealed that the pH of the electrolyte has significant influence on the surface morphology and structural properties. Highly crystalline ZnO layers with hexagonal crystal structure deposited for all pH of the solutions. A systematic shift observed in the reflections (002) and (101) is correlated with an effective tensile strain developed in the crystal lattice. A remarkable improvement in the crystallinity was noticed in the as-deposited ZnO samples with increasing pH and upon heat treatment. Optical direct band gap ~ 3.26–3.33eV and transmittance ~70 −80% was measured by optical spectroscopy. PL measurement showed the band edge emission at 375–382nm and a visible light emission at 410–550nm. The intensities of emission peaks are found to be affected by the pH of bath. The compact, densely packed and well adherent thin films of ZnO electrodeposited in zinc nitrate bath for pH 2.0, 3.5 and 6.0. The surface morphology has been changed from granular to disc shaped and finally a large hexagonal sheets were obtained with an increase in the pH of bath. Nearly stoichiometric ZnO thin films are electrodeposited at −0.96V versus Ag/AgCl reference electrode for pH 6.0. The photoelectrochemical (PEC) measurement (I-t transient curve) shows the enhancement in photocurrent with increasing the pH of zinc nitrate solution. After heat treatment the photocurrent is increased by 54%, 98% and 130% in the samples deposited from 2.0, 3.5 and 6.0pH of the bath. I-V measurements were further confirmed the current enhancement in all samples after heat treatment.

Electrochemical deposition of Ni–TiN nanocomposite coatings and the effect of sodium dodecyl sulphate surfactant on the coating properties

Ni–TiN nanocomposite coatings were prepared by using electrochemical deposition in a Watt’s bath containing TiN particles to increase the hardness of Ni. The effects of deposition current density, electrolyte agitation speed and the number of particles in the solution on the amount of incorporated particles in the coating process were investigated. The optimum deposition current density of 4 A dm−2 and agitation speed of 450 rpm were obtained. The effect of sodium dodecyl sulphate (SDS) anionic surfactant on the amount of particles in the coatings was investigated. It was observed that the maximum amount of incorporated particles, with a value of 7.5% by volume, was created in the current density of 4 A dm−2, stirring rate of 450 rpm, 30 g l−1 TiN particles and in the presence of 0.6 g l−1 SDS anionic surfactant.

Anomalous Al–Mg Electrodeposition Using an Organometallic-Based Electrolyte

The Al–Mg electrodeposition is investigated using the organometallic–based electrolyte: Na[AlEt4]+2Na[Et3Al–H–AlEt3]+2.5AlEt3+6toluene (Et =-C2H5), employing Mg anode. With an increase of Mg in the deposit the predominant morphology and its composition changes from ground (90–95 atom% Al) to smooth globules (75–80 atom% Al) to rough globules (15–45 atom% Al). The ground and smooth globules possessed face centered cubic (fcc) Al(+Mg) phase and the rough globules possess hexagonal close packed (hcp) Mg(+Al) phase. The overall composition (atom% Al-the more noble metal) of the deposits is less than that of the electrolyte, and increases steeply with a slight change in the latter. This indicates the absence of preferred deposition of the more noble metal suggesting the anomalous electrodeposition of Al-Mg. A critical ratio of Al/Mg exists in the electrolyte beyond which the anomalousness is enhanced. This critical ratio is identified by the onset of hcp Mg(+Al) phase formation in the deposits. A lack of trend in the overall deposit composition with electrolyte agitation affirms the anomalous electrodeposition of Al–Mg system under present experimental conditions.

Effect of electrolyte agitation on anodic titanium dioxide (ATO) growth and its photoelectrochemical properties

Nanoporous anodic titanium dioxide (ATO) layers were synthesized at 20°C by a three-step anodization carried out at the constant voltage of 30V in the electrolyte based on an ethylene glycol containing fluoride ions. The effect of stirring speed on the growth of anodic TiO2 layers was investigated in the range of 0–500rpm. It was found that the thickness of grown oxide layer, and consequently, the rate of oxide formation depend directly on the stirring speed. The morphological characterizations – porosity, cell density, cell size, oxide thickness, percentage of defective cells and their arrangement in ATO layers were correlated with different electrolyte stirring speeds. The influence of ultrasound irradiation during ATO formation and extended time of third anodization on photoelectrochemical response of ATO electrodes was studied. Photoelectrochemical properties of received anodic oxide layers were measured in a 0.1M KNO3 aqueous solution under the applied potentials of 0–1000mV vs. SCE. The generated photocurrents were studied at the wavelength range of 300–400nm. The highest values of generated photocurrents were observed at 350nm. For all studied stirring speeds, photoconversion efficiencies, determined as incident photon-to-current efficiency (IPCE), were calculated.

An investigation of ruthenium coating from LiCl–KCl eutectic melt

In this study, electrodeposition of ruthenium (Ru) from LiCl–KCl eutectic melt was investigated in a systematic manner and the effects of process parameters namely current density, time and agitation of electrolyte on the thickness and morphology of Ru layer were explored. The presence of Ru on graphite substrates was confirmed by thin film X-ray diffraction method. The Ru coatings formed at all electrodeposition conditions appeared as a white/gray deposit. The typical “faceted structure” was observed on the surface of Ru deposited at 3 and 7mA/cm2. Fracture cross-section examinations revealed the columnar morphology of Ru which was twinned with boundaries. The smooth appearance of Ru coating became uneven and rough with coarse nodules at 12mA/cm2. The thickness of Ru increased with increasing both current density and time at stationary electrodeposition conditions. A dense and 7.5μm thick Ru coating was possible to grow on graphite without any agitation at 3mA/cm2 for 2h. The highest cathodic current efficiency (η), 99.68%, was achieved at 3mA/cm2 after 2h of electrodeposition time with the rotating cathode speed of 50rpm. The cross sectional micro-indentation studies indicated that the Ru layer has hardness as high as 450±10HV.

Sonochemical assisted synthesis of nano-structured titanium oxide by anodic oxidation

This work describes the effect of electrolyte agitation conditions on the anodic growth of nano-structured titanium oxide on titanium samples of size 20mm×10mm (thickness 2mm) in an electrolyte containing 0.02M calcium glycerophosphate (Ca-GP) and 0.15M calcium acetate (CA). Magnetic stirring and different intensities of ultrasonic waves were applied during anodization. The application of ultrasonic waves during anodization was found to increase the reaction rates; the higher the ultrasonic irradiation power, the faster the growth rate of nano-structured titania. The diameters of the pores created under ultrasonic wave conditions were found to be larger than those of the pores created under magnetic stirring conditions in the corresponding nano-structured titania. An increase in the sonication power to 180, 250, and 350W resulted in an increase in the density, uniformity and diameters of the pores, respectively. The surface roughness and Ca/P ratio also increased with an increase in the sonication power. It was found that the applied ultrasonic wave could determine the surface morphology, properties and compositions of the anodic oxide films. We believe that sonoelectrochemistry is a simple method to design and synthesize nanostructured titanium oxide for implant applications.

Synthesis and characterization of Ni–Co/SiC nanocomposite coatings using sediment co-deposition technique

SiC nano-particle reinforced Ni–Co alloy matrix nanocomposite coatings were electrodeposited in a modified Watt’s bath using sediment co-deposition (SCD) technique. The SiC nano-particle content and the microhardness of the Ni–Co/SiC nanocomposite coatings were investigated as a function of the electrodeposition parameters; such as the deposition current density (id), concentrations of the Co (CCo) and the SiC nano-particles (CSiC) in the bath and the electrolyte agitation rate (ar). The deposited coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and microhardness testing. CCo=50g/L and the CSiC=5g/L, id=3A/dm2 and ar=350rpm were determined as the optimum electrodeposition conditions to achieve the maximum microhardness. The highest microhardness was obtained for a coating containing 8.1vol.% SiC nano-particles and 55wt.% Co. Effects of the electrodeposition parameters on co-deposition behavior of the SiC nano-particles were discussed based on a co-deposition kinetic model. The variations in the microhardness of the coatings were explained based on the nano-structural details.