Abstract: Natural hydroxyapatite has been electrophoretically deposited on medical grade 316L stainless steel. Stable suspensions were prepared by mixing 40 g/L milled natural hydroxyapatite powder in isopropyl alcohol and stabilized by polyethylenimine as dispersing agent and binder. The stability of suspensions was investigated by measuring zeta potential. It was found here that the suspension which was stabilized with 4 g/L polyethylenimine revealed a high value of zeta potential and stability. Deposition was achieved on the cathode at constant voltages of 30, 60, and 90 V for 1 to 5 minutes. After deposition, the samples were dried at room temperature for 24 hours and deposition weight, roughness, and thickness of the coatings were measured. The surface morphology of the coated samples was studied by a scanning electron microscope. The results of the electrophoretic deposition process showed that the sample coated at 60 V and 3 minutes led to an adherent, continuous, and crack-free coating. The coating efficiency and thickness increased with increasing deposition time and yielded to saturation at the constant applied voltage. Also, the current density decreased and yielded to saturation at the constant applied voltage during electrophoretic deposition.
Abstract: The electrophoretic deposition (EPD) technique was developed for depositing TiO2 films on stainless steel (SS) and titanium substrates. Titania coatings were obtained in conditions of optimal solution stability using acetylacetone suspensions of TiO2 nanoparticles and I2 at pH≈ 5. Deposition tests were carried out at 10V for varying times. The deposit thickness was seen to increase with EPD time, revealing that the deposits grew quickly for times <120 s, reaching a saturation value at longer times. The substrates were treated by physical and chemical methods before EPD in order to improve the adhesion of the films. The EPD coatings were sintered at 700, 800 and 900 °C under controlled argon atmosphere or in vacuum to study the influence of sintering atmosphere on crystalline phase transformation. The TiO2 coatings were characterized by XRD using Rietveld analysis. The results showed that TiO2 films on Ti substrates (chemically leached before deposition) had better adherence, homogeneity and density than those on SS. The coatings sintered al 700°C in vacuum resulted in a major proportion of anatasa phase. The porosity of the titania coatings sintered at 700°C (2 hr) in vacuum was calculated to be 19% .
Abstract: Layered clay has been of great interest because of their nano-sized layer structure and hence intercalation and ion-exchange capacity to be used as a host material of composite with polymers and/or metals. In this study, smectite as a silicate-layered clay was easily exfoliated and dispersed into purified water, and was deposited onto a cupper plate for which dc voltage ranging from + 1.0 V to + 6.0 V was applied with respect to a counter platinum plate electrode. The cupper plate was pre-treated by chemical and chemical mechanical polishing (CP and CMP) prior to the electrophoretic deposition (EPD). The surface roughness of the substrate as well as the smectite film formed was characterized by an atomic force microscope (AFM). The thickness of smectite layer was estimated using an X-ray fluorescence (XRF) analysis as well as a scanning electron microscope (SEM) observation. The layer thickness can be described as a function of operational parameters such as applied voltage and operating time. Smooth smectite film with thickness ranging from 100 nm to 10 μm has been successfully fabricated onto the CMP cupper plate by the EPD method in this study.
Abstract: Fly ash cenospheres coatings are a promising material in improving the oxidation and corrosion resistance of SiC. In this work, fly ash cenospheres coatings were deposited on SiC substrates by electrophoretic deposition process at 500 V during 30 seconds, 1, 2 and 3 minutes. These coatings were characterized by SEM to observe the surface morphology. The coatings were sintered at 1000, 1100 and 1200°C during 3 hours by microwave heating. After sintering, the coatings were characterized by XRD. Cross sections of the substrate/coating samples were analyzed by SEM/EDS. The coatings with the best deposition and sintering conditions were evaluated by oxidation and hot corrosion resistance tests. The oxidation test was performed in air at temperatures from 1000 to 1300°C during 100 hours. In addition, fly ash cenospheres coatings on SiC and uncoated SiC substrates were subjected to a hot corrosion test at 1000°C during 100 hours in Na2SO4. The coatings showed good adhesion after sintering; the main phases of the coating were mullite and SiO2. The uncoated substrates were found to gain weight due to the formation of SiO2 at the surface. In contrast, SiC samples coated with fly ash cenospheres showed no weight gain and exhibited no signs of cracking or spallation following the oxidation tests. After the high temperature corrosion test in Na2SO4, the uncoated SiC showed signs of oxidation and corrosion while the coated remained unreacted in the presence of molten Na2SO4, indicating that the electrophoretic deposition fly ash cenospheres acted as a hot corrosion barrier for SiC substrates.
Abstract: In this study we present the preparation of SOFC half cells by electrophoretic deposition. The cathode is deposited from a methyl ethyl ketone (MEK) suspension on dense apatite type lanthanum silicate (ATLS) pellets using a constant voltage. ATLS are a new class of electrolytes, which provides good oxygen permeability even at temperatures below 800°C. As cathode materials we used La2Ni0.8Cu0.2O4+δ (LNC) and La0.8Sr0.2Ni0.6Fe0.4O3 (LSNF). A conductive layer on the ATLS material was used to provide the necessary conductivity for electrophoretic deposition (EPD) process. For the preparation of suitable suspensions the charging behaviour and particle size of the different powders were investigated by means of zeta-potential and laser scattering measurements. When the electrophoretic mobility of the suspended particles was not sufficient iodine was added. Deposition kinetics were determined prior to preparation of the half cells. EPD parameters as well as sintering conditions were optimized in order to gain well adhering porous cathode layers.
Abstract: : In this study a thin dense YSZ film has been fabricated from stable non-aqueous suspensions by Electrophoretic Deposition (EPD) method on a porous pre-sintered NiO-YSZ substrate. Thin film of YSZ and NiO-YSZ composite were used as electrolyte and anode, respectively, in SOFCs that should have certain characteristics. Process parameters like porosity, pre-sintering temperature, voltage and time of deposition have been considered and optimized for obtaining a controlled thickness. After depositing a conductive layer, EPD has been performed on NiO-YSZ composites. These layers were sintered and a crack-free dense thin film of 8 mol % YSZ was obtained on porous NiO-YSZ anode. The interface and adhesion between the two layers was investigated by Scanning Electron Microscope and microstructural observations.
Abstract: Electrophoretic deposition of Al2O3 and ZrO2 powders from isopropanol suspension in the presence of monochloroacetic acid under constant-current conditions was studied. The similar charge and electrophoretic mobility of Al2O3 and ZrO2 in the suspensions was found. Adjusting to properly controlled kinetics of deposition deposits were prepared of pre-defined thicknesses. In view of the negative charge of Al2O3 and ZrO2 particles in the isopropanol suspensions used, the prepared layers were deposited on the anode and thus they were not affected by possible solvent electrolysis, which contributed to their defect-free and low-porosity structure.
Abstract: Laminated materials are used for special applications where combination of properties of two components is needed. Ceramics is inherently brittle and above all superior properties (wear resistance, temperature durability, stiffness, low density and others) the brittleness is limiting factor for massive implementation in wide range applications. The laminated structure can be capable to overcome this handicap. Electrophoretic deposition (EPD) is the technique able to prepare ceramic laminated structures having strong interface between layers . It is possible to prepare dense and crack free materials with tailored residual stresses controlled by layer thickness and deposition conditions by this technique. Crack propagation through layered composites based on Al2O3 and ZrO2 was studied. Cracks, produced by an indentation technique, propagated in direction to layer interfaces deflected towards the interface in the compressed layers and away from the interface in the layers containing tension stress [2,3]. Changes in the direction of crack propagation for the whole range of angles of incidence (0° - 90°) were described. The biggest change in the crack propagation was observed for the angle of incidence 45° for A/Z systems and was ca. 15°. The change in the crack propagation was independent on the level of residual stresses in the layers. Behaviour of indentation cracks observed in laminates under investigation was compared with the results obtained on standard SEVNB specimens having inclined the fracture plane with respect to the composite lamellar structure. This model condition helps to understand crack propagation in bulk material. All experimental work was supported by fractographical techniques enabling explanation of fracture micromechanism.
Abstract: The mechanical properties of ceramics materials can be tailored by designing their microstructures. Residual stress is one of the important factors for controlling the crack propagation and consequently improving the mechanical properties. On the other hand, development of the crystallographic orientation even in a diamagnetic ceramic can be controlled by colloidal processing in a strong magnetic field. In this study, alumina/alumina laminar composites with different crystalline-oriented layers were fabricated by EPD in a strong magnetic field in order to control the residual stress using the difference in the thermal expansion of each layer.
Abstract: Electrophoretic deposition (EPD) was used to infiltrate 2D and 3D SiC fabrics with SiC submicron particles with the aim to verify the potential of the technique for the fabrication of dense SiC/SiC composites. Bulk SiC deposits were first prepared from aqueous suspensions with different dispersants using cathodic and anodic deposition. The most suitable composition of the suspensions and the conditions for the infiltration were determined on the basis of the analysis of green parts formed. Using a specially designed EPD cell a relatively high packing density of SiC particles in infiltrated 2D and 3D SiC-fiber fabrics was achieved.