Abstract: Non-aqueous solvents have been popularly used as suspending medium in Electrophoretic deposition (EPD) for several applications. The drawbacks of these solvents are that they cause environmental concerns and are expensive. Therefore, there is a great interest for the development aqueous EPD, which is low-cost and environmental friendly. There are several problems when using water as the suspending medium in EPD. First, there is gas evolution at the electrodes on application of the electric field. Hydrogen is generated at cathode and oxygen at anode. This results in incorporation of bubbles in deposits and the quality of deposit suffers. Several approaches, such as the use of pulse DC, asymmetric AC, and palladium electrode have been reported in the literature to overcome this problem.However, the biggest problem concerning aqueous EPD is reproducibility of deposition. As an example, in batch EPD of Al2O3 from aqueous suspension, we observed the best quality of deposition from the first deposit. Invariably, the amount and quality of deposit decreased progressively with increased number of deposition from the same suspension. For prolonged first deposition, the deterioration became severe and no deposition occurred from the second deposition onwards. This occurred even for cases when only a small fraction of the powder suspension is depleted in the first deposit. A closer look showed destabilized suspension and significant change in bulk pH of the suspension. Here, we measured the change in bulk pH as a function of time, and starting pH during water electrolysis as well as during aqueous EPD of Al2O3. The bulk pH of suspension increased with increasing time of deposition and with increasing applied voltages, resulting in progressive destabilization of suspension and decrease in deposit yield and quality. Use of suitable dosages of cationic dispersant polyethyleneimine (PEI) in the suspension decreased the extent of bulk pH variation during aqueous EPD.
Abstract: Classical EPD has typically been conducted in organic solvent media. Many suitable solvents are volatile and highly flammable and this limits the industrial application of the technique on the basis of safety alone. Aqueous EPD may be seen as a safer method, but issues relating to electrolysis and surface energy phenomena become prominent and can create interferences and variability unless the substrate type and its preparation are compatible with the aqueous EPD chemistry and its deposition method. As EPD layers become thinner, factors such as substrate surface structure and wettability become more critical. Industrial processes utilising some principles of EPD for applying paint from water-based preparations are well established in the metal finishing sector. Consequently there is a significant body of practical experience available from this sector that can be of use in translating classical EPD from a solvent to an aqueous technique while avoiding interferences inherent in the use of water as the deposition medium. In this paper, substrate selection is discussed in relation to the electrolyte content of the system where phenomena such as dissolution and micro-arcing can occur. The initial wetting of the substrate must be considered prior to applying voltage. Surface preparation techniques and the methods of introducing the substrate into the EPD dispersion all can have an impact on the final result. Note: This paper is based on the authors’ personal and practical experience of industrial electrophoretic painting over more than 40 years. Only metal substrates are discussed because these have been almost exclusive in this sector during that time. Non-metal substrates such as conductive plastics, graphite and carbon fibre have also been coated with electrophoretic paints but this is not yet at any significant scale and so no general principles have been established
Abstract: The interaction between bioactive glass particles and polymers with different functional groups has been established in this work to better understand and control the colloidal processing of the bioactive glass phase. Cationic polyvinylpyrrolidone (PVP), anionic polyacrylic acid (PAA) and neutral polyvinyl alcohol (PVA) were selected and the surface reactions in alcoholic media and between bioactive glass particles and polymers were considered. All three polymers were successfully employed to obtain soft composite coatings incorporating bioactive glass particles.
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: The mathematical model of hydrodynamic mathematical modeling of copper electrodeposition on rotating cylinder electrode are presented. Mass transfer of electrolyte ions is described by diffusion-convection equation. Reynolds-averaged Navier–Stokes equations with Low Reynolds k-e model are used to describe turbulent flow of electrolyte. The results of mathematical modeling are in good agreement with the published experimental data
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: Processing of piezoelectric linear-array elements for high-frequency linear-array transducers by electrophoretic deposition (EPD) was investigated. Powders with the nominal composition Pb (Zr0.53Ti0.47)0.98Nb0.02O3 (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: The preparation of a ZSM-5 zeolite membrane on porous stainless steel disk by hydrothermal synthesis with electrophoretic deposition (EPD) as a seeding method was investigated. Micron size ZSM-5 crystal powder was seeded by EPD on the support disk by using ZSM-5 powder dispersed in ethanol. The seeded amounts were easily controlled by the deposition time during EPD. The membrane after secondary growth had a low amount of zeolite in comparison with the in situ seeding method and the permeance of single gas such as He, N2 and CO2 was also low in comparison with that of the in situ seeding method.
Abstract: Recently it was possible to prepare tailored laminates with perfect and strong interface of layers with precise thickness management. Tailoring of ceramic laminates to obtain optimal mechanical properties with enhanced fracture resistance is possible when predictions based on numerical calculations are employed. Extraordinary mechanical properties were achieved via high internal stresses development during material processing. The aim of this investigation can be seen in two directions. The enhanced crack free green bodies through incorporating small volume fraction of micro-fibres to the powders were prepared. Additionally, control of the crack propagation by incorporated directionally oriented micro-fibres both in the volume and in individual layers. In this contribution both alumina and zirconia micro-fibres were used to help eliminate drying defects in the green body stage before sintering. The co-deposition of ceramic micro-fibres and powder led to the preparation of microstructures having unique orthogonal fracture properties. Developed laminate with thin layers created by zirconia micro-fibres in the alumina matrix seems to be the most promising. This type of material exhibited potential of the crack trapping and deflection even when very small amount of micro-fibres was used.