Papers by Keyword: Electrophoretic Deposition (EPD)

Abstract: The aim of this work was preparation of alumina laminates and fibre reinforced alumina containing zirconia micro-fibres inside the inter-layer interface. Electrophoretic deposition was performed from concentrated isopropanolic suspensions stabilised by monochloracetic acid containing mixture of alumina powder and certain amount of zirconia micro-fibres. A method for in-situ monitoring of deposited amount of mixture of particles and fibres mass was applied to control deposition kinetics. Two different approaches for composite deposition were applied: pre-milling of powders mixture prior electrophoretic deposition and milling of suspension containing stabilization aid. Applying the optimised procedure the alumina laminates were prepared consisting of fibres in the interlayer boundary affected dramatically fracture response of these materials.

Abstract: We report on the electrophoretic deposition (EPD) of metal nanoparticles (NPs) prepared in reverse micelles on semiconductor substrates with the aim to fabricate sensitive Schottky-based hydrogen sensors with fast response and high degree of selectivity. We discuss the mechanism of NP monolayer formation and show which parameters are essential for the transition from three-dimensional to two-dimensional growth.

Abstract: Nickel oxide/Ni foam composite was studied as an electrode for electrochemical capacitors. The material has been processed by a simple, green and cost-effective electrophoretic deposition (EPD) method directly from the post-reaction medium in an one-pot synthesis and its later heat treatment.NiO films were obtained after calcination (325 and 450ᵒC) of β-Ni(OH)₂ deposits. β-Ni(OH)₂ nanoplatelets were produced by chemical precipitation of Ni precursors and the aid of ultrasound, free of modifiers. The stabilization of the hydroxide powder in suspension in different mixtures of Ethanol:Water (4:1, 9:1 and 19:1) and the optimization of the EPD parameters allowed coating the commercial Ni foams via colloidal processing.Electrochemical properties of the electrodes were evaluated by cyclic voltammetry (CV) showing significant differences in terms of specific capacitance of 192 and 79 F/g for the electrodes calcined at 325 and 450ᵒC, respectively.

Abstract: In this work the stability of TiN and TiC nanopowders in isopropyl alcohol as well as the fabrication of dense and well adhered thin coatings based on TiN and TiC by electrophoretic deposition (EPD) have been evaluated in terms of zeta potential and mass deposited when hydrazine is added. The surface of TiN and TiC nanoparticles has been modified to improve the dispersion in isopropyl alcohol adding a cationic polymer (polyethylenimine) as dispersant with two different molecular weights. The influence of acidic/basic character of the solvent also has been evaluated in order to reach the most efficient EPD process. It was found that the adsorption of polyethylenimine with higher molecular weight can preserve the homogeneity of TiC coatings. The surface of TiN nanoparticles can be tuned in order to achieve a similar polyethylenimine adsorption which also improves the deposition in basic media.

Abstract: Processing of piezoelectric linear-array elements for high-frequency linear-array transducers by electrophoretic deposition (EPD) was investigated. Powders with the nominal composition Pb (Zr_0.53Ti_0.47)_0.98Nb_0.02O₃ (PZT Nb) and PbO were stabilised in ethanol by the addition of a polyelectrolyte and mixed together in a molar ratio 98:2. The suspensions of both powders consisted of particles with a median size of 0.2 μm and with a zeta potential of about-50 mV. They were deposited on alumina substrates with patterned gold electrodes at a constant current density. The deposits were sintered at 950°C in a PbO-rich atmosphere. The influence of the inter-electrode distance and the geometry of the counter electrode on the shape and dimensions of the thick films were studied. With the increasing inter-electrode distance the width of the elements decreased and the space between them (kerf) increased. A higher lateral resolution of the elements was obtained when using square-shaped counter-electrode compared to lined-shaped one. When depositing on a substrate with the electrode width of 1 mm and the kerf of 0.5 mm using an inter-electrode distance of 25 mm and a square counter electrode, 20 μm thick PZT Nb elements with a kerf of 360 μm and sharp edge were obtained. When the substrates with the electrode width and kerf of 150 μm were used, the 160 μm wide elements with a kerf of 144 μm were obtained at the same deposition conditions. The results demonstrated that EPD is a suitable technique to process aligned linear-array structures with an element width and a kerf in the order of a few tens of micrometres at optimised deposition conditions.

Abstract: An alginate (Alg) based coating containing nanoparticles of titania (nTiO₂) and bioactive glass 45S5 (nBG) was deposited on stainless steel substrates by electrophoretic deposition (EPD). The composite nTiO₂-nBG/Alg coating developed for potential biomedical applications, was produced from a stable ethanol/water suspension (ζ–potential of-53±13mV) using 7V of deposition potential and 1min of deposition time as optimal conditions. Morphology and composition of the coatings were studied by FTIR, EDX, SEM and XRD, showing that all components were successfully deposited on the final coating. According to TG analysis the coatings presents a 62.4wt% of ceramic phase and 37.6wt% polymer. The coating shows corrosion protection properties compared with the bare uncoated material when analyzed via polarization curves in Dulbecco ́s MEM.

Abstract: The processing of ceramic thick and thin films, nano- and micro-scaled ceramic structures as well as bulk ceramics of high quality and precise dimensions under electrophoretic boundary conditions requires a full understanding of the dynamics of relevant interfacial mechanisms and interactions of colloidal phases at the nano- and micro-scale. Recent findings and latest insights on the importance of electrokinetic and electrohydrodynamic interfacial processes for membrane electrophoretic depositon in aqueous media are summarised. In this context, the paper addresses the fundamental importance of surficial charge heterogeneities, electric double layer instabilities, electrokinetically induced micro-vortex dynamics, as well as lateral and medial effective electrical field gradients. These phenomena are evaluated in terms of reasonable correlations and mechanistic coincidences of general EPD deposition principles. The experimental results are based on potentiometry, in-situ videomicroscopy, high-resolution as well as secondary electron microscopy. A numerical method for the simulation of the electrophoretic deposition process is suggested based on a multiphysical Finite Element approach given by Nernst-Planck, Poisson- and Navier-Stokes equations. The results of the simulations provide adequate agreement with experimental findings.

Abstract: In this study, a non-commercial ceramic compound with high corrosion resistance based on Na₂O, Al₂O₃, SiO₂, K₂O, CaO, TiO₂, FeO and others, was developed and stabilized in an aqueous media. The enamel coatings were developed over stainless steel 316L at 7.5 V and 30, 60 and 90 secounds by electrophoretic deposition technique (EPE coatings). EPE coatings were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) techniques showing a compact and homogeneous enamel surface and a typical composition of the glass frit deposited. Surface micro hardness measurements of EPE coatings were 7.6 times harder than the steel base material using an automatic hardness tester equipped. As well as, surface roughness measurements of EPE coatings were 19 times and 15 times less rugged than the steel base material at about R_a and R_z, respectively using a confocal microscope. EPE coatings at 60 s and 90 s show a better behavior for reducing the corrosion process, evaluated using potentiodynamic polarization method in 3.5 wt. % NaCl solution.

Abstract: We found non-ionic polymer containing ester and sulfonyl group, poly (ester-sulfone), showed anode-selective electrophoresis under the electrophoretic deposition (EPD) condition. In this paper we investigated an electrophoretic behavior of vinyl porymer having sulfonyl group in the side chains and compared with the main chain type of poly (ester-sulfone). Herein, we synthesized new poly (methacrylate) containing pendent sulfone to investigate the electrophoretic behavior.

Abstract: Hydroxyapatite (HAP) and 58S Bioactive Glasses (BG) coatings are successfully synthesized by Electrophoretic Deposition (EPD) on Ti6Al4V alloy subjected to Surface Mechanical Attrition Treatment (SMAT). This process uses steel balls impacts on the Ti6Al4V surface to improve its mechanical properties. However when the Ti6Al4V substrate is treated by SMAT the industrial plasma spray technique is not efficient to obtain adherent HAP coatings. This problem is mainly related to the modifications of the Ti6Al4V surface topography due to the SMAT process. Therefore, in this work we demonstrate that EPD offers an efficient solution to solve this technical problem. Indeed we obtain a homogeneous and adherent HAP coating on the SMATed Ti6Al4V surface from a suspension of nanoparticles in ethanol. Moreover EPD is successfully employed to produce a 58S BG coating on the SMATed Ti6Al4V surface. Scanning Electron Microscopy (SEM) associated to Energy Dispersive X-Ray Spectroscopy (EDXS) reveals that the coatings obtained by EPD are adherent and compact without alteration of their chemical composition.