Electrophoretic Deposition Layers Research Articles

A Direct Laser Sintering Approach for the Electrophoretic Deposition Overlay of Yttria-Stabilized Zirconia on the Surface of a Thermal Barrier Coating System

The laser sintering process and modification of yttria-stabilized zirconia (YSZ) coatings subjected to electrophoretic deposition (EPD) on YSZ air-plasma-sprayed (APS) thermal barrier coatings (TBCs) were investigated. A Ni-based superalloy was plasma-sprayed using yttria-stabilized zirconia (YSZ) to create a thermal barrier coating with a 400 μm thickness. The electrophoretic deposition (EPD) technique was used to deposit the nanopowder of YSZ on the surface of YSZ TBCs. In this study, a technology based on the direct sintering of a green EPD layer using a laser beam was employed. The best conditions for the deposition overlay of the YSZ coating using a DC current were obtained with an applied voltage of 40 V, deposition time of 5 min, and suspension concentration of 10 g/L. Iodine was added to the solutions as a stabilizing agent. To overcome the problems of high sintering temperatures, laser sintering was adopted as a new approach. The microstructures of all the specimens were studied using field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS) analysis. Surface roughness was investigated using atomic force microscopy (AFM) analysis and the central line average (CLA). The direct laser sintering (DLS) process for the EPD overlay on the surface of the TBCs caused a reduction in surface roughness and porosity, and improvements in the microstructural and mechanical properties of the surface coatings were observed.

Electrophoretic Deposition of Fluorine–Nitrogen Graphene Quantum Dots with Highly Luminescent Upconversion Properties for Solar Cell Applications

Nitrogen–fluorine codoped graphene quantum dots (N, F-GQDs) were synthesized through a one-pot hydrothermal method using glucose and ammonium fluoride (AF). The composition of nitrogen and fluorine with GQDs by AF was optimized to approach the highest light absorption edge in UV–visible spectroscopy and receive upconversion properties in photoluminescence (PL) analysis. Maximum absorption edge of the optimized N, F-GQDs was observed at 580 nm. Transmission electron microscopy analysis revealed the formation of the nanoparticles with an average size of 18 ± 0.9 nm. Raman analysis approved the formation of GQDs with graphitic carbon atom structures. X-ray photoelectron spectroscopy analysis indicated doping of F and N in the GQD structure and photoluminescence analysis revealed excitation-dependent emissions with upconversion properties for the best sample of the N,F GQD synthesized with an AF concentration of 0.07 gmol/dm3 in the primary synthesis solution. For the fabrication of solar cells, a uniform and stable layer of N, F-GQDs was deposited on the TiO2/FTO electrode, as the photoanode, by an additive-free electrophoretic deposition (EPD) method, confirmed by field-emission scanning electron microscopy analysis. Photovoltaic properties of the fabricated solar cells were studied under a simulated solar irradiation of AM 1.5 G. It was revealed that an appropriate ratio of N,F doped in GQDs in addition to the EPD layer formation highly improved the solar cell efficiency. The best cell with N, F-GQD0.07/TiO2/ FTO photoanode (size of 1 × 1 × 0.2 cm3) improved the efficiency, open circuit voltage, and short circuit current density, from 0.07 to 0.51, 370 to 699 mV, and 0.3 to 1.2 mA/cm2, respectively, compared to the cell fabricated by the blank TiO2/FTO photoanode.

Photocatalytic degradation of antibiotics under various conditions

Frequent detection of antibiotics in aquatic environment represents a global ecologic problem due to the fact, that these compounds are not fully biodegradable during conventional purification processes in wastewater treatment plants. The presence of antibiotics cause that the bacteria present in water and in animal or human bodies build resistance, which can be problematic for treatment of infections. However, heterogeneous photocatalysis is a promising method for the removal of harmful organic pollutants from wastewater. In this work, a reaction rate of photocatalytic degradation of sulfathiazole was determined, using TiO2 nanopowders and TiO2 EPD layers. In the next step, the effect of the additional antibiotic presence (ampicillin) and the use of greywater as a matrix on the photocatalytic reaction was evaluated. Sulfathiazole and ampicillin were photocatalytically degraded both separately and in mixture. For the photocatalytic reactions, nanoparticles of TiO2 P25 and pure anatase in two particle sizes (5 and 100 nm) were used. The photocatalysts were added into the reaction mixture both as a free powder and immobilized by electrophoretic deposition (EPD) on stainless steel plates. The degradation kinetics was determined by HPLC analysis with UV detection. The decrease in organic carbon was monitored using a TOC instrument. Theoretical degradation products were determined by DFT calculations. Firstly, the convenience of using EPD layers was evaluated. It is necessary to filtrate or centrifuge the samples after using TiO2 suspensions, which is time and money consuming. Thus, EDP layers have a more practical use for water purification purposes. The reaction rates were comparable with both suspension and EPD photocatalysts. When sulfathiazole (10-4 M) was degraded, the reaction rate was highest with P25, followed by anatase 5 nm and anatase 100 nm. The use of EPD layers instead of free powder photocatalyst had no significant effect on the reaction rate. Furthermore, the use of immobilized photocatalyst solves problems with separating the photocatalyst from the reaction mixture after the degradation is completed. The addition of ampicillin to the reaction did not have any influence on the rate of degradation of sulfathiazole when the molar concentration was kept constant. The use of greywater instead of demineralized water for the experiments had no decreasing effect on the photocatalytic degradation of both sulfathiazole and ampicillin. The mineralization of the reaction mixture determined as a decrease in total organic carbon correlated with the results of decrease in the concentration of studied analytes. When greywater was used instead of demineralized water, it had no observable effect. In this work, the photocatalytic degradation of sulfathiazole was performed using three different TiO2 forms. The photocatalytic activity of the particles in suspensions was compared with the activity of the particles deposited on the layers. Then, the photocatalytic reaction of the solution containing the mixture of two antibiotics in demineralized water and in greywater was carried out and the mineralization under the conditions mentioned above was compared.

Combination of electrophoretic and electroless depositions to fabricate Ni/TiC cladding

ABSTRACT A novel method is established that improves the shortcoming of embedding low volume fraction of reinforcements in Ni–P electroless coating. Experimental design of the present study is based on 5 steps: (1) electrophoretic deposition (EPD) of titanium carbide core inside the Ni–P shell particles (2) pre-sintering of as-EPD layer (3) electroless deposition of Ni–P top layer on as-EPD layer (4) heating the multilayer structure and (5) infiltration of the Ni–P melt phase through porous EPD layer. Anchoring TiC particles inside a Ni–P shell was done for catalyzing electroless Ni–P deposition on as-EPD layer and improving the high-temperature wettability of the EPD layer. By infiltration sintering on EPD layer (20 V for 2 min) a composite coating of Ni–P/TiC with a volume fraction of ∼49% TiC was successfully produced. According to wear test results, embedding TiC into Ni–P significantly increases hardness (972–1460 VHN) and reduces friction coefficient (0.45–0.23).

Wear Behavior and Mechanical Properties of TiO2 Coating Deposited Electrophoretically on 316 L Stainless Steel

In this work, the TiO2 coatings were synthesized by electrophoretic deposition (EPD) of nanosized powder in order to improve the tribological properties. Several characterization methods were applied to the coated substrates. The surface topography of the EPD layers, their morphology, composition, and mechanical properties were investigated. The influence of heat treatment, which results in calcination, on the wear performance of coated films was also examined. It was noticed that the effect of the normal force and sliding velocity on the coefficients of instantaneous and stabilized friction was not the same in treated coatings and untreated ones. Moreover, the treated and uncoated films showed a close relation between the dissipated accumulated energy and the worn volume. The energetic wear coefficients of fretting wear were also studied. As expected, the treated coating reduced the energetic wear coefficient, which enhanced the resistance to fretting wear.

Heat-resistant, thermally conductive coating of alumina on metal via electrophoretic deposition with added polydimethylsiloxane-based organic–inorganic hybrid materials

Electrophoretic deposition (EPD) of a suspension with added polydimethylsiloxane (PDMS)-based organic–inorganic hybrid materials can provide a heat-resistant, thermally conductive, and electrically insulating coating on an aluminum substrate. The addition of high-molecular-weight PDMS imparts flexibility to the resultant material, which is advantageous. However, the inclusion of PDMS with higher-molecular weight in the suspension can also affect the properties of the EPD suspension and the EPD kinetics. In this paper, the influence of the molecular weights of the starting materials of a PDMS-based hybrid (which is used as a binder) on the resultant material is investigated. These effects are examined in terms of the structure, thermal properties, thermal conductivity, and electrical insulating properties of the EPD layer, which is composed of Al2O3 and the PDMS-based hybrid materials. It is found that the weight ratio of the Al2O3 to the binder component is increased, but the addition of higher-molecular-weight PDMS reduces the density of the EPD film. Thus, Al2O3 coatings on metal substrates with good electrical insulation properties, heat conductivity, and thermal stability are fabricated via EPD, using an added PDMS-based organic–inorganic hybrid sol of appropriate molecular weight as a binding additive.

Effect of Deposition Parameters on Electrophoretically Deposited TiO2

In the current study, TiO2 coatings on stainless steel substrates were prepared by Electrophoretic Deposition (EPD) of colloidal dispersions of TiO2 nanoparticles in ethanol. The effects of deposition parameters on surface morphology, phase composition and mechanical properties were investigated. The surface morphology of the EPD layers was observed using Atomic Force Microscopy (AFM). The composition of the EPD layer was determined from the peak intensity using an X-ray Diffractometer (XRD) and mechanical properties of films were investigated by nanoindentation techniques. Characterization of the obtained films by atomic force microscope showed a relatively uniform microstructure. The coatings mainly consisted of anatase and rutile; anatase is the predominant phase with an average percentage of 71%. As a result of nanoindentation experiments, load–displacement curves were obtained and two mechanical characteristics of the substrate and investigated films – indentation hard-ness (HIT) and indentation modulus (EIT) – were calculated using Oliver & Pharr’s approximation methods. Mechanical properties show an improvement with the applied voltage. The results illustrate that Young's modulus and hardness of TiO2 thin films are increased with increasing voltage.

The Photogenerated Cathodic Protection of Steel Using the Thin Layers of Photoactive Nanocomposite Fabricated By Electrophoretic Deposition

The photogenerated cathodic protection of steel can be achieved by a photoactive coating layer. It is recently attracting attention because it can overcome the limitations of the sacrificial cathodic protection method. In theory, it can provide permanent cathodic protection because it used energy from solar light rather than to consume itself to protect against corrosion of steel. In the present work, a novel nano-structured layer for the photogenerated cathodic protection was coated on steel using electrophoretic deposition (EPD). Through EPD, thin photoactive composite films can effectively be fabricated on conductive substrates using the colloidal suspension of functional nanoparticles with the simple application of an electrical field. Firstly, crystalline TiO2 nanoparticles were deposited on a steel substrate by the EPD process for the photo-generated cathodic protection. To improve the cathodic protection ability of the photo-stimulated layer, graphene nanoplatelets were incorporated into the TiO2 composite layer by the simultaneous co-deposition of graphene and TiO2 nanoparticles using EPD. Despite the superior cathodic protection afforded by a photo-stimulated TiO2 EPD layer, the coating only works when exposed to solar irradiation during the daytime. However, steel suffers from corrosion at all times. There have been many attempts to overcome this drawback. The incorporation of various photo-electron storing materials into the coating layer is the most promising strategy for maintaining the efficacy of the cathodic protection that is provided by TiO2 in the absence of sunlight. WO3 nanoparticles were used in this study to impart photo-generated cathodic protection to the EPD layer at all times. Moreover, the graphene was exploited as a barrier to protect steel from corrosion because it forms a better barrier to molecules. A graphene film was prepared on steel using EPD with a suspension of graphene oxide in water. When graphene was used as an underlying film for the organic coating, the corrosion resistance of the coated steel improved significantly.

Photo-generated cathodic protection performance of electrophoretically Co-deposited layers of TiO2 nanoparticles and graphene nanoplatelets on steel substrate

In this work, electrophoretic deposition (EPD) was employed to deposit TiO2 nanoparticles and graphene nanoplatelets composite films onto stainless steel in order to fabricate a photo-generated cathodic protection layer. The colloidal suspension used for the EPD was characterized by the measurement of the zeta-potential of the solution using a dispersion optical analyzer. The surface morphology of the EPD layers was investigated using scanning electron microscopy (SEM), and the relative composition of the EPD layer was estimated from the peak intensities using an X-ray diffractometer (XRD) with the distinct peak at 2θ=26.5°. Moreover, the photo-generated cathodic protection abilities were characterized by measuring the open circuit potential (OCP) and the transient photo-generated current density response from the TiO2-graphene co-deposited samples with and without exposure to UV light. The TiO2-graphene EPD layer was found to be uniform, with no noticeable particle homo-aggregation. As a result of the OCP measurement, it was verified that the EPD layers efficiently provided photo-generated cathodic protection to the stainless steel because the potential of the photo-stimulated EPD layers was more negative than the corrosion potential of the stainless steel. When 10wt.% graphene (vs. TiO2 nanoparticles) was used in the EPD layer, the generated photo-current increased significantly from 0.08μA∙cm−2 to approximately 0.15mA∙cm−2 due to the efficient separation of the electron-hole pairs and the increased electron conductivity of the EPD film. However, it was found that the excessive incorporation of graphene nanoplatelets can impede the photocatalytic activation of the TiO2 by reducing its light absorption intensity in the UV range.

Electrophoretic deposition of graphene oxide on mild carbon steel for anti-corrosion application

In the present work, electrophoretic deposition (EPD) was used to deposit graphene oxide (GO) onto carbon steel from a GO water suspension. The GO coating was used as a barrier layer for the corrosion protection of carbon steel. The suspension of GO was characterized by measuring the zeta potential of the solution using a dispersion optical analyzer. The morphology of the GO and the surface morphology of the EPD layers were investigated using scanning electron microscopy (SEM), and Raman spectroscopy was performed to determine the effects of EPD on the electrochemical reduction of GO. GO was successfully synthesized using the modified Hummers method, and a GO layer was efficiently deposited onto mild steel using EPD. EPD and the partial reduction of the GO occurred simultaneously under the applied electrical fields. Moreover, the anti-corrosion performance of the GO–EPD layers was characterized using electrochemical impedance spectroscopy (EIS), the potentiodynamic polarization method, and a cyclic corrosion test (CCT). The applications of GO–EPD as an underlying layer improved the anti-corrosion performance of organic top-coated steel due to the superior barrier property of GO.

Electrophoretic deposition of nano-ceramics for the photo-generated cathodic corrosion protection of steel substrates

Electrophoretic deposition (EPD) was employed to deposit crystalline TiO2/WO3 nanoparticles onto stainless steel to fabricate a photo-generated cathodic protection layer. The electrophoretic mobility of the colloidal particles was determined by measuring the zeta-potential of the particles in the suspension. The surface morphology of the EPD layers was observed using scanning electron microscopy (SEM), and the composition of the EPD layer was determined from the peak intensity using an X-ray diffractometer (XRD). Furthermore, the open circuit potential (OCP) of the TiO2–WO3-deposited sample was measured under UV irradiation to evaluate the photo-generated cathodic protection ability of the EPD layers on stainless steel. Through the zeta-potential measurement, it was verified that the TiO2 particle was effectively charged by phosphoric acid di-butyl ester in iso-propanol, but the WO3 particle was slightly negatively charged because of the different zero point of charge. However, TiO2 and WO3 particles were deposited simultaneously via an EPD process at the same rate despite their different electrophoretic mobilities in the suspension. The TiO2–WO3 co-deposited layer was uniformly deposited, and no noticeable homo-aggregation of the same type of particle was observed. Using the OCP measurement, it was also found that stainless steel was cathodically protected from corrosion by UV light irradiation because the potential of the photo-stimulated EPD layers was more negative than the corrosion potential of stainless steel. Because the WO3 contents in the EPD layer were increased, the time of potential recovery was gradually delayed. Moreover, the addition of binders enhanced the adhesion strength between the metal and the layer that hindered the delamination and improved the cathodic protection performance. The potential recovery time of the EPD sample containing 40% TiO2–60% WO3 was approximately 6h after 3h of light irradiation, which implied that the steel was cathodically protected for 6h in dark conditions.

Application of the Multi-Step EPD Technique to Fabricate Thick TiO2 Layers: Effect of Organic Medium Viscosity on the Layer Microstructure

In the present study, electrophoretic deposition (EPD) was used to obtain dense layers of TiO(2) in four organic media-methanol, ethanol, 1-propanol, and butanol-with different TiO(2) nanoparticle concenterations of 1-8 g/L. Microstructural study of the obtained layers by scanning electron (SEM) and optical microscope (OM) revealed that the multistep EPD technique could effectively prevent crack formation across the layer compared with the single-step method and will consequently increase the critical cracking thickness (CCT). The quality of EPD layers was also affected by viscosity. According to SEM and atomic force microscope (AFM) results, as the viscosity of the medium increased, more compact layers were formed which can be attributed to the lower deposition rates in heavier alcohols. High deposition rate in methanol and ethanol was also confirmed by zeta potential results. Suspension viscosity was interestingly observed to control the threshold concentration above which crack formation would occur. These values were measured to be 3 and 5 g/L for methanol and ethanol, respectively. However, in suspensions based on more viscous alcohols, the threshold concentration increased to 8 g/L which implied the decisive role of medium on concentration limits. It indicates that by employing organic vehicles of higher viscosity it is possible to maintain the CCT values obtained in less viscous media with no need to decrease the colloidal concentration of the suspension.

Preparation of Thin and Dense Lanthanum Cobaltite Coating on Porous Tubular Alumina Supports by Electrophoretic Deposition

The electrophoretic deposition (EPD) process is one of several ceramic powder assembling technologies using a simultaneous colloidal process and electrochemical driving force. For the further development of the EPD technique, the possibility and the usefulness of preparing a thin and dense ceramic coating on non-electronically conductive porous tubular ceramics using the EPD technique was investigated. La 0.8 Sr 0.2 Co 0.8 Sr 0.2 O 3-δ (LSCF) was used as the deposition material and a porous alumina tube was used as the deposition substrate. Methanol (MeOH) was suitable as a dispersing medium for the LSCF powder. LSCF particles were positively charged in MeOH. For the fabrication of a uniform EPD layer, the cathode was placed in a porous alumina tube. The insides of the porous alumina tubes were filled with MeOH and the cathode did not make contact with the EPD bath. A 39μm (200 g/m 2 ) thick uniform LSCF powder coating was obtained by EPD at 100 V for 10 min. After sintering at 1500°C for 5 h, a 20 μm dense membrane was obtained.

Thermal cycling of siliconized-SiC at high temperatures

Thermal cycling (between 1340 °C and 1480 °C) experiments were conducted using two types of reaction-bonded (siliconized) silicon carbide. A commercial material (CrystarTM) and various silicon carbide pieces that had been joined together using electrophoretic deposition (EPD) followed by reaction bonding were evaluated. During the thermal cycling, residual “free” silicon metal rapidly vaporized from the CrystarTM and cracks developed within its large SiC grains. In contrast, the EPD/reaction-bonded silicon carbide joints did not lose an observable amount of their residual silicon nor develop cracks. The reduced loss was attributed to reduced silicon content with the silicon residing largely in closed pores of the EPD layer. Reduced vaporization of the silicon that resided in surface-connected pores was engineered by applying a thick SiC surface coating. The morphology of the resulting coating was microscopically evaluated and two sequential growth mechanisms were postulated. An implication of this research is that hermetic (gas-tight) joints could be formed using EPD-derived SiC as a filler material.

Al<sub>2</sub>O<sub>3</sub> Coating on Pt Wire by the Electrophoretic Deposition

The effect of powder characteristics (such as specific surface area and morphology) and iodine addition on the electrophoretic deposition (EPD) coating of alumina on Pt wire was investigated. Electrical conductivity of the bath solution was increased by adding iodine and depended upon specific surface area of alumina powder. Moreover, adding a suitable amount of iodine led to a remarkable improvement of stability of the bath solution, and uniform EPD layers resulted Round shaped alumina produced by chemical vapor deposition (CVD) method was more suitable than irregular shaped alumina made by sol-gel method for preparing thick and uniform layers. The difference of deposition behavior was explained in terms of electrical resistance of the formed alumina layer and the bubbling of H2 gas generated during deposition. Crack-free alumina -50μm thick layers could be formed on Pt wire by sintering at 1500°C.