Papers by Keyword: Electrophoretic Deposition (EPD)

Abstract: This study presents experimental results on the electrophoretic deposition (EPD) of chitosan/halloysite nanotube/titanium dioxide composite coatings based on the Taguchi design of experiments (DOE) approach. Taguchi array of L₁₈ type with mixed levels of the control factor was used to study the influence of EPD parameters, including halloysite nanotubes concentration, electric voltage and deposition time, on deposition yield. For identifying the significant factors that affected the deposition yield, multivariate analysis of variance (MANOVA) and regression analysis based on partial least-square method were used. The coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses, respectively. It was found that the deposition time has significantly influenced the deposition rate but the halloysite nanotube concentration and the applied voltage have the smallest effect on the deposition. The optimum condition for high yield of deposition with low standard deviation is achieved when the concentration of halloysite nanotubes is 0.3 g/L and the applied voltage is 40 volt with 300 sec. as a deposition time. The predicted EPD conditions were verified by experiments and qualitative agreement was obtained.

Abstract: Te-based compounds are promising dielectric candidates for Base-Metal Electrode Multilayer Ceramic Capacitors (BME-MLCCs) and Low-Temperature Co-fired Ceramics (LTCCs) applications due to their low sintering temperature and good dielectric properties. In spite of the possible compatibility with Cu electrodes for microelectronics, data on compounds of the CuO-TeO₂ system are scarce. Recently, we have reported the phase formation process of Cu₃TeO₆ and the first dielectric data for Cu₃TeO₆ ceramics. Due to the interest for some applications in thick films, in this work Cu₃TeO₆ thick films were fabricated by electrophoretic deposition (EPD) on platinized silicon substrates under different processing conditions. The relation between processing and film’s quality was established. ~ 50 μm Cu₃TeO₆ thick films sintered at 860 oC for 5 h exhibit a permittivity of ~2 and dielectric loss of 0.01 at room temperature and the temperature coefficient of the dielectric permittivity is 9.5×10³ ppm°C^-1 at 1 MHz from 40 °C to 120 °C. It is expected that this dielectric performance, when compared with the one of Cu₃TeO₆ ceramic counterparts, improves if the density of the films is increased.

Abstract: Electrophoretic deposition (EPD) has traditionally been viewed as a thin film deposition technique for coating conductive surfaces. Recently, there have been reports of producing functional parts with EPD to near net shape, often containing gradients in material properties normal to the conductive deposition surface. By using reconfigurable electrode systems, a few researchers have gone beyond purely out-of-plane gradients and demonstrated gradients in material properties in the plane of the deposition electrode, a necessary condition for 3D additive manufacturing. In this work, we build upon a previously published technique called light directed electrophoretic deposition (LD-EPD) in which the deposition electrode is photoconductive and can be activated with light, leading to a patterned deposit. Here, we demonstrate that the LD-EPD technique can also lead to patterned deposits on any conductive surface by utilizing the photoconductive electrode as the counter electrode. This eliminates several issues with standard LD-EPD by allowing the potentially expensive photoconductive electrode to be reused, as well as mitigates post-processing material compatibility issues by allowing deposition on any conductive surface. We also detail the results of a finite element simulation of the deposition process in LD-EPD systems that captures key features seen experimentally in the final deposit.

Abstract: Nanoparticles synthesized in various ionic liquids (ILs) were immobilized by electrophoretic deposition (EPD) at the surface of a gas sensor made of thin polyaniline (PAni) film. We used pulsed DC voltage to overcome electrochemical treatment in IL-based electrolytes. In spite that EPD is commonly used for synthesis of nanoparticle films or coatings, here we just functionalized the surface of PAni by scattered nanoparticles. Immobilized nanoparticles were observed by SEM imaging and dynamic responses of gas sensors functionalized by different nanoparticles (Ni, Ni-Fe and Ag-Cu) were compared. Using the EPD technique, sensitivity or selectivity of a gas sensor based on PAni can be improved easily.

Abstract: Zirconia-based ceramics have gained considerable interest for several applications (e.g. solid electrolytes in fuel cells and in oxygen sensors, thermal barrier coatings and biomaterials for dental and orthopaedic applications) due to their high mechanical strength, improved fracture toughness and easy affordability. Zirconia occurs in three crystal modifications at low-pressure conditions: monoclinic, tetragonal and cubic. The monoclinic phase is the natural room temperature stable phase, while the tetragonal and the cubic phase can be stabilized at room temperature by doping with the right amount of some oxide dopants (e.g. CaO, MgO, CeO₂ and Y₂O₃). The stabilization of the tetragonal phase results in a remarkable increase in mechanical toughness, whereas the stabilization of the cubic phase results in an increase of the ionic conductivity to values significantly higher than for other ceramics. In order to optimize the properties of the final ceramic by combining the high mechanical toughness of the tetragonal phase of zirconia together with the high ionic conductivity of its cubic phase, we established an EPD layering process with nanometric sized powders of Y-TZP with different mol percentages of yttrium oxide (3 % and 8 %) and produced multilayers of alternating tetragonal and cubic phases with a clearly defined interface. The crack propagation through this interface was studied by means of micro-indentation

Abstract: In this work, we present a facile technique based on electrophoretic deposition (EPD) to produce transition metal hydroxide decorated carbon nanotubes (CNT) for electrochemical applications. We specifically explore the performance of nickel-cobalt hydroxides given their high activity, conductivity and stability as compared to the individual hydroxides. We exploit the high local pH at the negative electrodes during water-based EPD to form nanoparticles of nickel-cobalt hydroxides in situ on the CNT surface. We focus our work here on obtaining functional and conductive deposits on CNTs. The hydrophilic binderless deposits of Ni-Co double hydroxide decorated CNTs obtained here are used for non-enzymatic glucose detection. XPS data and electrochemical testing reveal difference in the deposited double hydroxide based on chronology of charging salt addition even at the same ratio. When cobalt and nickel salts are sequentially added at a ratio of 1:1, the deposited double hydroxides show excellent glucose sensitivity of ~3300μA/mM.cm² at applied potential of 0.55V vs. Ag/AgCl reference electrode.

Abstract: Electrophoretic deposition (EPD) with controlled gas evolution by electrolysis was used for producing ceramic green bodies with unidirectional pore channels. The method was applied to alumina, alumina-toughened zirconia, and mullite. It requires stable aqueous suspensions with sufficiently high particle charge for the electrophoresis and appropriate amounts of electrolyte for the gas bubble formation. An anionic polyelectrolyte and ammonia were shown to be a suitable additive combination for all three oxide powders. The amount of polyelectrolyte was chosen for each of the powders on the basis of electroacoustic measurements of the zeta potential. The addition of ammonia solution was necessary in order to obtain the desired porous structures.

Abstract: Bilayer thick films of sacrificial titanium dioxide and Nb-doped lead zirconate titanate (PZTN) have been deposited on bare silicon wafers using electrophoretic deposition (EPD) technique. Deposition of such ceramic particles, dispersed ethanol-based suspensions, on semiconductor substrate has been made possible after preparation of alloyed junctions Al/Si characterized by ohmic behaviour. Sintering of green TiO₂/PZTN films was performed at 900 °C for 1 h. The composition of the films, the thickness and relative density of the deposited materials have been analysed by EDS-SEM analysis. The lead diffusion through the silicon wafer has been reduced.

Abstract: Biodegradable polymers and bioactive ceramics are being combined in a variety of novel materials for tissue engineering scaffolds. These composite systems, which combine the useful mechanical properties of polymers with the bioactivity of ceramics, seem to be a promising choice for bone tissue engineering. In recent years, the use of biopolymers that gelate on cooling has received a lot of attention with regards to the production of laminates and coatings. In this work, we report the incorporation of hydroxyapatite (HA) into a gelatin coating on stainless steel substrate using colloidal processing technology. A titania (Ti) buffer layer prepared by dip coating was inserted to improve the bonding strength between the HA/gelatin layer and stainless steel substrate. The suspensions, composed of 1 vol% of HA and three different additions of gelatin, were formulated with a focus on rheological properties for codeposition of both phases by electrophoretic deposition (EPD). The composite coatings performed by EPD were investigated in terms of deposition efficiency and kinetics over different deposition times. The EPD process was performed at both ambient temperature and the gelling temperature of the suspension. While at room temperature no electrophoretic growth of the layers was observed, the thermal gelation of gelatin promotes the growth of a homogeneous, well-adherent coating.

Abstract: Beta-sialon:Eu²⁺ phosphor deposits were fabricated by electrophoretic deposition (EPD) process within a strong magnetic field (12 T). The direction of the magnetic field was adjusted to be parallel or perpendicular to that of the electric field, that is, vertical-or horizontal setup. The oriented deposits were fabricated by aligning the β-sialon:Eu²⁺ particles along the higher magnetic-susceptibility c-crystal axis (a, b-crystal plane). For the case of vertically-setup magnetic field, the oriented deposit aligned along the c-axis possessed higher relative deposit density than the randomly fabricated deposit, as a result, varying the intensity ratio of emission and transmitted excitation, and therefore, presenting different chromaticity coordinates; for the case of horizontally-setup magnetic field, photoluminescence (PL) intensities of the deposits oriented along c-axis were significantly improved by comparing with those of the randomly-oriented ones.