Fabrication of aluminum nitride coatings by electrophoretic deposition: Effect of particle size on deposition and drying behavior

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss measurements revealed higher drying rates for micro-layer as compared to nano-cover. This seemed owing to the larger pore sizes and lower specific surfaces of the former. Stress inducement by lateral drying of small capillaries led to crack initiation from the edges and its propagation across the surfaces. This resulted in fragmentation of the samples due to their delamination. Effect of deposition rate on particles packability was also investigated.     

Fabrication of c-axis oriented zinc oxide by electrophoretic deposition in a rotating magnetic field

The fabrication of c-axis oriented zinc oxide was attempted by electrophoretic deposition (EPD) in a rotating magnetic field. The EPD was conducted in a small container which was placed on a turntable arranged in a superconducting magnet. The suspension was rotated at 0–90 rpm in a 12 T magnetic field during the deposition. The deposits were dried and then sintered at 1400 °C for 2 h. The degree of the c-axis orientation was evaluated by the Lotgering factor calculated from the X-ray diffraction data.     

Critical particle concentration in electrophoretic deposition

The role of particle concentration in electrophoretic deposition (EPD) was investigated with two different suspension systems. The first system consisted of positively charged TiO₂ nanoparticles dispersed in isopropanol with 1 vol% water. The second system consisted of negatively charged polystyrene (PS) microbeads dispersed in isopropanol. Constant voltage EPD was performed using suspensions with variable particle concentration (0.013–0.43 vol% TiO₂ and 0.06–11.4 vol% PS). Threshold concentration values were identified for both systems after EPD at 100 V (250 V cm^?1) for 1 min. Below these values the deposited mass deviated from the trend dictated by Hamaker's equation. Higher applied voltages and longer deposition times were tested and the results suggested that the threshold concentration did not depend on those parameters. A phenomenological model of particle deposition was proposed, which accounts for the local electrochemical conditions close to the substrate in relation to particle size.     

Fabrication of CNT-SiC/SiC composites by electrophoretic deposition

Due to the outstanding mechanical and thermal properties of carbon nanotubes (CNTs), they are considered suitable reinforcement for structural materials. In this study, for the first time, electrophoretic deposition (EPD) was used to deposit (multi-walled) CNTs onto SiC fibres (SiC_f) to form an effective CNT interphase layer for SiC_f/SiC composites. This deposition was followed by electrophoretic infiltration of the CNT-coated SiC fibre mats with SiC powder to fabricate a new CNT-SiC-fibre-reinforced SiC-matrix (SiC_f/SiC) composite for fusion applications. In these EPD experiments, a commercial aqueous suspension of negatively charged CNTs and an optimized aqueous suspension of negatively charged SiC particles were used. The CNT-coatings on the SiC fibres were firm and homogenous, and uniformly distributed nanotubes were observed on the fibre surfaces. In a following step of EPD, a thick SiC layer was formed on the fibre mat when the CNT-coated SiC fibres were in contact with the positive electrode of the EPD cell; however, spaces between the fibres were not fully filled with SiC. Conversely, when CNT-coated SiC fibres were isolated from the electrode, the SiC particles were able to gradually fill the fibre mat resulting in relatively high infiltration, which leads to dense composites.     

Fabrication of titania dense layers by electrophoretic deposition in aqueous media

Fabrication of titania dense layers by electrophoresis in aqueous media has been studied according to the suspension formulation. Stable titania suspensions with negatively charged particles are obtained by adding either the strong basis (C₂H₅)₄NOH, or the Tiron molecule or a salt of polymethacrylic acid. To prevent water electrolysis at the anode which is the collecting electrode, ethanol is added as cosolvent. A concentration of 10 vol% is sufficient to avoid gaseous emission at the anode and to keep a stable suspension suitable for electrophoretic deposition (EPD). The parameters influencing the deposit kinetic of particles are studied, such as the concentration of ethanol, of solid and of dispersant, and the current intensity applied. Finally, it is possible to fabricate layers with a relative density of 60% with a very narrow size distribution of pores.     

Fabrication of SiC/diamond composite coatings by electrophoretic deposition and chemical vapor deposition

In this research, SiC/diamond composite coatings were fabricated by a novel procedure that consisted of the electrophoretic deposition (EPD) of diamond particles onto graphite substrates followed by chemical vapor deposition (CVD) of SiC. Various concentrations of MgCl₂ were employed to increase the deposition rate and uniformity of the deposits during the EPD process by giving a positive charge to diamond particles. The CVD of SiC was found to have a tightly connected diamond‐graphite interface and spherical texture. With higher weight fraction of diamond particles deposits, the wear of steel ball increased, while the wear of SiC coating decreased.     

Fabrication of ceramic membranes on porous ceramic supports by electrophoretic deposition

Abstract

Nanoporous alumina membrane and continuous zeolite L membrane were fabricated on the inner surface of microporous alumina tubes. In the former case, an electrophoretic deposition (EPD) technique was used for the deposition of bimodal alumina particles for the subsequent low temperature sintering. In the latter case, the EPD was used for the seeding process of zeolite L particles for the subsequent hydrothermal synthesis. A thin layer of polypyrrole was synthesised on the inside wall of the porous tubes by the chemical polymerisation of pyrrole to give the wall electric conduction for the EPD electrode. The thickness of the coating layers was controlled by altering the applied voltage and deposition time. The interfacial connection of the alumina or zeolite coated layer and the substrate was evaluated by SEM observations before and after the thermal treatment. The nanoporous structure of the alumina membrane was also characterised by a pore size analyser.     

Fabrication of alumina parts by electrophoretic deposition from ethanol and aqueous suspensions

This paper discusses the effect of the properties of alumina suspensions in ethanol and in water, on green and sintered ceramic parts formed by electrophoretic deposition. The results of the study demonstrate that a small amount of water present in ethanol suspensions as a hidden additive due to the hygroscopicity of alumina powder and ethanol can detrimentally affect the behaviour of the suspension, thus lowering the reliability of the process. Electrophoretic deposition from aqueous suspensions appears to be advantageous over ethanol, from a reliability standpoint, and due to higher achievable green and sintered densities of the deposits and higher deposition rates. Dolapix CE64 appears to be superior surfactant in water as it results in deposits with the lowest green and sintered porosities.     

Fabrication of textured alumina by orienting template particles during electrophoretic deposition

(0 0 1)-Textured α-alumina has been processed by electrophoretic deposition (EPD) and templated grain growth. The mechanism of platelet template orientation during EPD was examined with respect to the impact of the electric field force, gravity and hydrodynamic force in two different deposition cells with vertically or horizontally positioned deposition electrodes. A sharp (0 0 1) ‘fibre texture’ was obtained after templated grain growth during sintering of a deposit formed from a stirred 5 vol% platelet containing suspension in a vertical deposition cell. The texture was characterized by means of the Lotgering factor, texture index and electron backscattering diffraction (EBSD).     

Fabrication of yttria-stabilized-zirconia coatings using electrophoretic deposition: Effects of agglomerate size distribution on particle packing

Yttria-stabilized-zirconia (YSZ) particles with various size distributions have been electrophoretically deposited (EPD) on Fecralloy substrate to investigate the particle size effect on EPD coatings. The deposition rates, as-deposited particle packing densities, green densities and sintered (for 2 h at 1250 °C in air) coating hardnesses are dependent on particle size. The particle packing arrangement in EPD coatings can be affected by further electric field densification (EFD) of the as-deposited coating in which the wet EPD coating is immersed in pure solvent (acetylacetone) with the application of a constant electric field. The effect of EFD was found to be most effective on small particles (<0.5 μm) when they are co-deposited with large particles (>1 μm). The improvements are reflected in increased mechanical hardness of sintered coatings.     

Characterization of polyetheretherketone particle suspensions for electrophoretic deposition

Suspensions of polyetheretherketone (PEEK) using mixture of ethanol and isopropanol as solvent were prepared to carry out PEEK electrophoretic deposition (EPD). The rheological behavior and suspension structure of PEEK particles dispersed in co‐solvents were investigated over a range of pH values (1–10) and shear rates (γ = 10¹?3 × 10² s^?1). These PEEK suspensions generally exhibited a pseudoplastic flow behavior, indicating the occurrence of particle aggregation in the liquid medium. The maximum solids fraction (?_m) showed an estimated value of  ?_m = 2.9 wt %. Using a suspension with 3 wt % PEEK concentration, PEEK coatings on stainless steel substrates were obtained by EPD at constant voltage condition. The influence of the electrolyte conductivity on PEEK EPD from ethanol–isopropanol suspensions was studied. Experimental results showed that high‐conductivity ethanol‐based suspensions yield non‐uniform deposits, while low‐conductivity suspensions resulted in uniform coatings. The difference in the deposition behavior is due to the different pH of the suspensions and the relationship of pH with suspension conductivity. pH = 8 was the optimal value for this system in terms of deposition results. The surfaces of EPD PEEK coatings were homogenous and a qualitatively good adhesion between the PEEK deposits and the substrate was confirmed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40953.     

Thermal residual stress gradients in an alumina–zirconia composite obtained by electrophoretic deposition

In order to understand the mechanical behavior of layered composites with compositional gradient, it is necessary to determine their state of residual stresses. Compositionally graded materials can offer the advantage of eliminating abrupt changes in composition between layers having different thermal expansion coefficient. The existence of a compositional gradient can reduce discontinuities in thermal residual stresses, something beneficial from the point of view of the mechanical properties.We present here a study of the microstructure and state of residual stressses in a layered material made of homogeneous layers of alumina and alumina–zirconia separated by thin (less than 300 μm) intermediate compositionally graded layers. The composite was obtained by controlled deposition of powders from solution using an electrophoretic deposition (EPD) method. The phase distribution and compositional gradient in the sintered composite were investigated using scanning electron microscopy (SEM). Thermal residual stresses generated during cooling after sintering were measured by using fluorescence ruby luminiscence piezo-spectroscopy and the profile of hydrostatic stress on alumina was determined at steps of about 300 μm along the direction of the compositional gradient, and at steps of about 30 μm in the compositionally graded layers. The obtained profile of hydrostatic stresses on alumina grains follows closely the profile of compositional changes along the layered composite. The presence of thin intermediate graded layers reduce significantly changes in stress in the layered composite.     

Fabrication and characterization of carbon-based counter electrodes prepared by electrophoretic deposition for dye-sensitized solar cells

Three different carbon-based counter electrodes are investigated in light of catalytic activities such as electrochemical frequencies and interface impedances. We fabricated carbon-based counter electrodes of dye-sensitized solar cells [DSSCs] using graphene, single-walled carbon nanotubes [SWNTs], and graphene-SWNT composites by electrophoretic deposition method. We observed the optical and electrochemical properties of the carbon-based counter electrodes. The DSSC with the graphene-deposited counter electrode demonstrated the best conversion efficiency of 5.87% under AM 1.5 and 1 sun condition. It could be utilized for a low-cost and high-throughput process for DSSCs.     

Fabrication of BSCF-based mixed oxide ionic-electronic conducting multi-layered membrane by sequential electrophoretic deposition process

The Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF)-based multi-layered oxygen separation membrane was fabricated by the sequential electrophoretic deposition (EPD) process. A thin porous/dense bi-layer of BSCF was formed on a thick porous support of BSCF. The porous support prepared by a sacrificial template method using BSCF powder mixed with wheat starch (30 wt%) as a pore-forming agent, followed by uniaxial pressing and low-temperature sintering, was directly used as an EPD electrode. A thin BSCF layer was first formed on the porous support, and then a thin BSCF + PMMA (polymethyl methacrylate) layer was sequentially formed on the thin BSCF layer using a bimodal suspension of BSCF and PMMA. A 30-μm thin porous/dense bi-layer of BSCF of which the total thickness was obtained by optimizing the processes of EPD and subsequent co-sintering. The oxygen separation performance of 3.7 ml (STP) min^?1 cm^?2 at 860 °C was achieved for the BSCF-based multi-layered oxygen separation membrane.     

Fabrication of BSCF-based mixed ionic-electronic conducting membrane by electrophoretic deposition for oxygen separation application

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), which exhibits a high mixed oxide ionic-electronic conduction, was used for the fabrication of an oxygen separation membrane. An asymmetric structure, which was a thin and dense BSCF membrane layer supported on a porous BSCF substrate, was fabricated by the electrophoretic deposition method (EPD). Porous BSCF supports were prepared by the uniaxial pressing method using a powder mixture with BSCF and starch as the pore-forming agent (0–50 wt.%). The sintering behaviors of the porous support and the thin layer were separately characterized by dilatometry to determine the co-fired temperature at which cracking did not occur. A crack-free and thin dense membrane layer, which had about a 15 μm thickness and >95% relative density, was obtained after optimizing the processes of EPD and sintering. The dense/porous interface was well-bonded and the oxygen permeation flux was 2.5 ml (STP) min⁻¹ cm^-2 at 850 °C.     

Fabrication of cylindrical SiCf/Si/SiC-based composite by electrophoretic deposition and liquid silicon infiltration

Cylindrical SiC-based composites composed of inner Si/SiC reticulated foam and outer Si-infiltrated SiC fiber-reinforced SiC (SiC_f/Si/SiC) skin were fabricated by the electrophoretic deposition of matrix particles into SiC fabrics followed by Si-infiltration for high temperature heat exchanger applications. An electrophoretic deposition combined with ultrasonication was used to fabricate a tubular SiC_f/SiC skin layer, which infiltrated SiC and carbon particles effectively into the voids of SiC fabrics by minimizing the surface sealing effect. After liquid silicon infiltration at 1550 °C, the composite revealed a density of 2.75 g/cm³ along with a well-joined interface between the inside Si/SiC foam and outer SiC_f/Si/SiC skin layer. The results also showed that the skin layer, which was composed of 81.4 wt% β-SiC, 17.2 wt% Si and 1.4 wt% SiO₂, exhibited a gastight dense microstructure and the flexural strength of 192.3 MPa.     

Magnetic effects in particle adhesion. Part II. The influence of particle composition and size on deposition in a magnetic field

The effects of a magnetic field on the deposition of particles of various compositions, sizes, shapes (spherical and rod-like) on steel beads of different kinds and sizes in an aqueous environment are described. In the systems studied, the particles and the collector bear a negative charge. If both interacting bodies have a sufficiently high magnetic moment, the magnetic force causes an enhancement in the particle attachment. The process is very sensitive to the size of the depositing solids; larger particles adhere much faster. Interpretation of the results is based on the shape of the total interaction energy function consisting of electrostatic, dispersion, and magnetic contributions. The major influence of the magnetic field is in the formation of a deep secondary minimum in which the particles, moving toward the surface, are accumulated. The magnetic force enhances the flux of these particles and deepens the minimum, causing an increase in the retention efficiency.     

Fabrication of tubular SiCf/SiC using different preform architectures by electrophoretic deposition and hot pressing

This paper reports the processing feasibility of electrophoretic deposition combined with hot pressing in the fabrication of dense tubular SiC_f/SiC composites using a cylindrical mold. A simulation of pressure distribution using ANSYS software was performed by varying the angular inclinations in a cylindrical mold with an ‘out → in’ configuration so as to ensure a maximum and uniform conversion of vertical hot press force to the lateral side of a centrally-located preform through graphite powder. The simulation revealed an inhomogeneous pressure distribution along the height of the preform, which could be minimized by mold optimization to achieve a more uniform tube density. To verify this, two different preform architectures such as 0/90° woven 2-D fabric rolled in a jelly state and filament winding with two plies having an inter-ply angle of 55° were hot-pressed using a mold fabricated based on the simulation after infiltrating the matrix phase by electrophoretic deposition. The density of the tube could be increased with more uniform microstructures. Although the tube using a filament winding preform exhibited a lower flexural strength (105 MPa) and relative density (90%) than those with the preform rolled in a jelly state (221 MPa, 95%), the results revealed a high degree of fiber pull-out due to the PyC coating on the SiC fiber.     

Fabrication of patterned carbon nanotube thin films using electrophoretic deposition and ultrasonic radiation

A simple wet-deposition method for preparing patterned carbon nanotube (CNT) thin films is reported. Using electrophoretic deposition (EPD), CNTs were deposited over indium tin oxide (ITO) plates that had been patterned with a photoresist; consequently, CNTs covered not only the exposed ITO areas but also the photoresist areas because thinness of the photoresists could not prevent the transverse deposition of CNTs over the photoresist areas. The ultrasonic treatment for the samples removed only CNTs on the photoresist areas, resulting in the formation of patterned CNT thin films, because Ni metal formed during EPD connects CNTs to ITO plates.     

Beta-sialon phosphor deposits fabricated by electrophoretic deposition (EPD) process in a magnetic field

Phosphor deposits of β-sialon:Eu²⁺ were prepared by electrophoretic deposition (EPD) process within a magnetic field. Under the action of the magnetic force, which was parallel to the direction of the electric field of the EPD, the β-sialon:Eu²⁺ crystals were aligned along the c-axis of the hexagonal cell unit to form an oriented deposit via the EPD fabrication. Higher orientation degree was obtained at longer depositing time (300 s) and stronger applied magnetic field (12 T). The oriented deposit aligned along the c-axis obtained higher relative deposit density than the randomly fabricated deposit. Due to the improved relative density, the oriented deposit prepared within the magnetic field possessed an enhanced external quantum efficiency (η_ex). Also, because of different relative densities of the deposits prepared within and without the magnetic field, they presented different chromaticity coordinates.