Electrophoretic deposition (EPD) is gaining increasing interest as a processing technique for production of novel inorganic nanostructured and nanoscale materials, including the use of nanoparticles, nanotubes, nanorods and related nanomaterials. Recent advances in the electrophoretic deposition of a great variety of ceramic and metallic nanoparticles, carbon nanotubes and other inorganic nanoscaled materials are discussed in this review. The purpose of the paper is to demonstrate the utility of an applied electric field to manipulate and control the deposition of electrically charged nanoscaled particles and other nanostructures on solid surfaces from liquid suspensions. A wide range of applications has been reviewed, demonstrating the high versatility and suitability of the EPD technique as a convenient nanotechnology processing tool. Nano-enamels and structural coatings, electrodes and films for fuel cells, capacitors, sensors and other microelectronic devices, fibre-reinforced and graded ceramic composites, nanostructured films and coatings for electronic, biomedical, optical, catalytic and electrochemical applications are some of the examples discussed. The combination of sol-gel methods and EPD for production of a variety of nanomaterials is also reviewed.

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The properties of piezoelectric ceramics are enhanced by the development of crystallographic texture. One of the most convenient preparation methods for textured ceramics is the sintering of green compacts containing aligned anisometric particles. This review deals with the mechanisms of texture development by examining microstructure development in the compacts. The characteristics of microstructure development are summarized separately, depending on the preparation methods, which are divided into four groups: oriented consolidation of anisometric particles, templated grain growth, reactive-templated grain growth, and heterotemplated grain growth.

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This review paper is focused on the area of titania nanocoatings prepared from sol-gel derived films by hot-water treatment under external reaction fields to design their functionality through the control of their surface morphology and crystallinity at low processing temperatures. First, the formation of titania nanocrystalline coatings at low temperatures by wet chemical procedures is briefly reviewed. Second, a concept of material design based on an external-field hot-water treatment for sol-gel derived films and the effects of the external fields on the formation of titania nanocrystals from the sol-gel derived films are discussed. Finally, promising characteristics of the resultant titania nanocrystal-dispersed coatings with unique morphology are described. External fileds of vibrations and electric voltages affect the nanostructure of titania crystallites formed on SiO₂-TiO₂ gel coatings during hot-water treatment. Without the external fields granular anatase nanocrystals of 30-50 nm in size are formed on the coatings during the hot-water treatment, whereas the shape of the precipitates becomes sheetlike by applying a vibration to the substrate during hot-water treatment. Similar changes in shape of the precipitates on the coatings are also observed, and ramiform (branchlike) crystallites are formed at the negative electrode by applying an electric field between the substrates. The sheetlike and ramiform crystallites are mainly composed of a hydrated titania, m(TiO₂)•nH₂O, with the lepidocrocite-like layered structure with a d-spacing of 0.6-0.8 nm. Titania nanosheets are characterized by a large surface-to-volume ratio, which gives rise to the excellent wettability for water and antifogging properties. Processing temperatures for the preparation of the coatings are lower than 100°C under atmospheric pressure, so that the coatings have a great potential for applications to various substrates including organic polymers with poor heat resistance.

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The electrophoretic deposition (EPD) process is one of several ceramic powder assembling technologies using a simultaneous colloidal process and electrochemical driving force. For the further development of the EPD technique, the possibility and the usefulness of preparing a thin and dense ceramic coating on non-electronically conductive porous tubular ceramics using the EPD technique was investigated. La_0.8Sr_0.2Co_0.8Sr_0.2O_3-δ (LSCF) was used as the deposition material and a porous alumina tube was used as the deposition substrate. Methanol (MeOH) was suitable as a dispersing medium for the LSCF powder. LSCF particles were positively charged in MeOH. For the fabrication of a uniform EPD layer, the cathode was placed in a porous alumina tube. The insides of the porous alumina tubes were filled with MeOH and the cathode did not make contact with the EPD bath. A 30 μm (200 g/m²) thick uniform LSCF powder coating was obtained by EPD at 100 V for 10 min. After sintering at 1500°C for 5 h, a 20 μm dense membrane was obtained.

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A novel process to immobilize oxide particles with electrolytically deposited metals as binders was proposed. Commercial TiO₂ photocatalyst particles, P25, were successfully immobilized on the surface of stainless steel substrates with Pd and Cu by this process. The effects of the conditions of electrolysis and the composition of the source solutions on the amount and the morphology of the particles accumulated on the surface were investigated. Addition of another particle with superior dispersibility, NanoTek, and sonication during electrodeposition were important to inhibit agglomeration of the particles and to achieve uniform and dense immobilization. Photocatalytic activity, which was evaluated by photobleaching of methylene blue solution, of the immobilized particles was as high as 50% of the particles suspended in the solution.

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In this paper, the synthesis of TiO₂ films and simultaneous P ion-doping for them were attempted by the anodic oxidation of titanium in phosphoric acid solution under various conditions (several concentrations of phosphoric acid solution and applied voltages on the anodic oxidation etc). Products obtained by this anodic oxidation of titanium were thin films and attached firmly to the surface of titanium. Although the surface of the oxide film obtained by an anodic oxidation in 0.25 M phosphoric acid at 350 V was flat, their oxide films were consisted of fine particles of 20-50 nm in diameter and had the unidirectional pores with the pore of about 200 nm to 1 μm in diameter. From XPS results, P⁵⁺ ions were mainly doped near the surface of the oxide film, although P ions were existed as P³⁺ inside the TiO₂ films, suggesting the successful doping of P ions, such as P⁵⁺ and P³⁺ into the TiO₂ films. Therefore, this anodic oxidation processing is useful for synthesis of TiO₂ films and simultaneous doping of P ions, leading to the development of a useful vector processing from an electro-chemical vector effect.

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A macroporous hydroxyapatite ceramic coating was fabricated on a titanium substrate by an electrophoretic deposition (EPD) process followed by a heat treatment in order to obtain high performance bioactive porous hydroxyapatite. The key of this EPD process is a formation of composite particles by using a heterocoaguration reaction, consisting of hydroxyapatite ceramic nanoparticles for the ceramic frame material and monodisperse polystyrene polymer microspheres for template component, in a suspension. Microstructure of the porous ceramic coating layer depends on electrophoretic deposition parameters, and on heat treatment conditions. Under the optimized fabrication conditions, the hydroxyapatite ceramic coating layer with well-controlled macroporous structure was obtained. In vitro examination using a simulated body fluid revealed a good biocompatibility of the macroporous specimen.

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The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.

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Magnetic susceptibility is very small in feeble magnetic ceramics such as alumina, consequently, it had been very difficult to develop a textured microstructure in these ceramics by using a magnetic field. We have demonstrated, however, that textured microstructures in alumina, titania, zinc oxide can be prepared by colloidal processing in a high magnetic field followed by sintering. We applied this processing technique to alumina based composites. The degree of crystallographic texture was small in specimen sintered at the low temperature. The degree of orientation increased rapidly with increasing sintering temperature and depended on the grain size of alumina matrix. The grain size can be controlled by the content of YTZ particle as a second phase, the kind of dopant, sintering temperature, annealing temperature and annealing time.

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Bone-like hydroxyapatite (b-HA) formation abilities of β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) after autoclaving were evaluated by immersion tests using simulated body fluid (SBF). The b-HA formation was observed on an autoclaved β-TCP, while no deposition was observed on the non-autoclaved one. The b-HA formation on HA was observed to be enhanced after autoclaving. Decrease of surface potentials by autoclaving may enhance the b-HA formation abilities.

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Glass-ceramics of Na₂O-R₂O₃-P₂O₅-SiO₂ (Narpsio) consist of a skeleton structure of 12-tetrahedra-membered rings and exhibit a super Na⁺ conductivity. Glass-ceramic Narpsio was proved to be electrically polarized through highly mobile sodium ions. Narpsio also shows relatively higher solubility in water. Taking into account of the water solubility and the chemical composition, the reactivity of polarized and non-polarized glass-ceramic Narpsio in the stimulated body fluid (SBF) were investigated in relation to bioactivity. After the 6 days' immersion of SBF, hydroxyapatite microcrystals aggregated semispherically were grown on the glass-ceramic Narpsio surfaces. Although the acceleration effects were under study, the growth rate was recognized to be higher in both of the negatively and positively charged surfaces. In analogy with polarized bioglasses, we confirmed the chemico-vector effects of glass-ceramic Narpsio for biomedical purpose. Additionally, glass-ceramic Narpsio, prepared by the locally biasing crystallization method, showed unreported microstructural changes of surfaces during chemical polishing with water, depending upon the direction of a biasing field. The phenomenon was interpreted as a mechanochemico-vector effect.

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γ-Methacryloxypropyltrimethoxysilane (γ-MPS) was grafted on a silicone elastomer by emulsion polymerization in order to improve cytocompatibility. The wettability of the grafted surface was evaluated with a contact angle toward distilled water. By grafting within 30 min at 60°C, the contact angle was reduced from 110° to about 70° while it remained almost constant for longer grafting. A larger number of osteoblastic cells (MC3T3-E1) and fibroblast cells (L929) proliferated on the surface modified with γ-MPS compared with the original silicone surface. After culturing for 7 d, the cells completely covered the grafted surface and even formed a cell layer.

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Polyethylene (PE) and polyethylene terephthalate (PET) substrates were irradiated by the simultaneous use of oxygen (O₂) cluster and monomer ion beams to improve their hydrophilic property. The hydrophilic groups such as COOH and C-OH groups were formed at the PE and PET surfaces by the irradiation. The contact angles of PE and PET substrates were decreased remarkably by the irradiation. Bioactive calcium silicate (CS) gel layer was successfully formed on the irradiated PE and PET substrates, and the irradiated and CS-coated PE and PET substrates formed uniform bonelike apatite layer on their surfaces in SBF within 4 d.

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Control of the surface reactivity of bioactive materials to surrounding body fluids is essential in the design of novel bone-repairing materials, because apatite formation on bioactive materials is governed by the dissolution of constituents from the materials and the nucleation of hydroxyapatite on the resultant surface. These bioactive materials are therefore recognized as “chemicovector ceramics”, as described by Yamashita et al. Glass-based bioactive materials have the benefit of easy control of their bioactivity and bioresorbability, as their surface reactivity in body environments can be easily controlled by varying their composition. Consequently, glass-derived biomaterials are attractive for use in the fabrication of porous glass-ceramics as bone substitute and scaffold materials for bone regeneration. We anticipated that a glass-ceramic containing tricalcium phosphate (TCP; 3CaO•P₂O₅) and diopside (CaO•MgO•2SiO₂) would show high bioactivity and high mechanical strength, as well as bioresorbability. In this study, glass-ceramics were prepared with compositions of x(3CaO•P₂O₅)•(100-x)(CaO•MgO•2SiO₂), where x=0, 38, 50, or 60 mass%, and their bioactivity evaluated by examining in vitro apatite formation in a simulated body fluid (SBF). Pulverized glasses of each composition were compacted and heated to obtain the bulk glass-ceramics. When the compacted materials were sintered at 1200°C, whitlockite (β-TCP) and diopside precipitated from the glasses with compositions where x=38, 50, 60 mass%, and diopside alone precipitated when x=0. The prepared glass-ceramics containing β-TCP and diopside formed apatite on their surfaces within 7 d in SBF. This result indicates that these glass-ceramics have the potential to show bioactivity. Porous glass-ceramics with continuous pores of about 500 μm were successfully prepared with the above compositions. These porous glass-ceramics containing β-TCP and diopside are expected to be useful as scaffold materials for bone repair.

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Several kinds of ceramics called bioactive ceramics have attractive features such as direct bone-bonding in living body. However, they are much more brittle and much less flexible than natural bone. Previous studies reported that the essential condition for materials to show bone-bonding property, i.e., bioactivity, is formation of biologically active apatite on their surfaces after exposure to the body fluid. The same type of apatite formation can be observed even in a simulated body fluid (SBF, Kokubo solution) with inorganic ion concentrations similar to those of human extracellular fluid. Several functional groups such as Si-OH and Ti-OH are known to trigger nucleation of the apatite in body environment. This is significantly enhanced by the release of Ca²⁺ from the materials. These findings suggest that organic modification of bioactive inorganic components would provide bioactive materials with mechanical performances analogous to those of natural bone. We previously synthesized bioactive organic-inorganic hybrids from alkoxysilane that provides Si-OH groups and calcium salts that release Ca²⁺ by organic modification with hydroxyethylmethacrylate (HEMA). If another type of functional group can be incorporated into the hybrids, useful guideline for designing bioactive materials with different biological and mechanical properties would be obtained. In this study, we synthesized organic-inorganic hybrids from HEMA by addition of tetraisopropyl titanate (TiPT) and CaCl₂. Their apatite-forming ability was examined in SBF. The obtained hybrids formed the apatite in SBF within 7 d, when they were added with appropriate amount of CaCl₂. It was speculated that the apatite deposition was induced by Ti-OH groups formed on the hybrids and the release of Ca²⁺. The chemicovectors including the ion release govern the apatite formation on the hybrids. Mechanical properties of the hybrids were also evaluated by tensile test. They showed Young's modulus analogous to human articular cartilage.

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When zinc metaphosphate glass powders were mixed with water, their hydration immediately started with an exothermic reaction; the mixture of the glass powders and water was completely converted into a translucent hydrogel (ZP gel) after 2 d. No hydrogelation occurred when water was mixed with beryllium metaphosphate, strontium metaphosphate, or barium metaphosphate glass powders. The long-chain phosphate structures in beryllium metaphosphate glass powders were almost not broken after mixing water, while those in strontium metaphosphate and barium metaphosphate glass powders were easily broken as shown in our earlier work. This result suggested that hydrogelation occurs after mixing water and the metaphosphate glasses with adequate bonding strength between bivalent metal ion and non-bridging oxygen in the phosphate chain structure. The phosphate chains in the ZP gel were gradually broken, resulting in an increase of orthophosphate amount. Crystalline phases were observed in the ZP gel after 12 d of mixing with water the glass powders. The proton conductivity of the ZP gel, which showed 5.7 mS/cm at 30°C, was not influenced by the precipitation of the crystalline phases.

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We report high-quality and high-density Bi_3.25La_0.75Ti₃O₁₂ ceramics prepared by sintering at a low temperature of 900°C from the nanosized powder with a diameter around 100 nm synthesized by the flash creation method. The densification at 900°C, which was 300°C lower sintering temperature compared with conventional solid-state reaction, enables us to obtain the ceramics showing a remanent polarization of 14.5 μC/cm², a coercive field of 50 kV/cm and a leakage current of ~10^-9 A/cm². The superior properties are indicated to originate from lower defect concentration achieved by the low temperature sintering.

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We investigated thermoelectric properties of 20-%-Nb-doped SrTiO₃ at high-temperature (300-1000 K) using single-crystalline epitaxial film, polycrystalline film (average grain size ~200 nm) and ceramic (average grain size ~20 μm) samples to clarify the effect of grain boundaries on the thermoelectric performance. Although carrier concentration and Seebeck coefficient of all samples showed no significant differences, Hall mobility of the polycrystalline film was extremely small («10^-1 cm²V^-1s^-1 at 300 K) as compared to those of the epitaxial film and the ceramic sample (~3 cm²V^-1s^-1). However, it drastically increased with increasing temperature and exhibited the value similar to those of the epitaxial film and the ceramic sample above 700 K. The thermoelectric figure of merit for 20%-Nb-doped SrTiO₃ was found to reach 0.35 at 1000 K irrespective of the grain size.

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The microwave-assisted self-heating profile and sinterability of porous NiO-(Ce, Sm)O₂ composites with 25, 50 and 75 mass% NiO, which were prepared by heating at 800-1200°C for solid oxide fuel cell applications, were investigated. The porous NiO-(Ce, Sm)O₂ composites were heated to ca. 1300°C within 5 min in a microwave field. The sinterability of the self-heating NiO-(Ce, Sm)O₂ composites in a microwave field was dependent upon the mixing ratio of NiO and the pre-heating temperature. A large shrinkage of over 20% was achieved for the 25 mass% NiO-containing composites microwave-heated at 1300°C for 2 h after the pre-heating at 800°C. The sinterability was comparable to that by conventional sintering at 1400°C for 2 h.

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Second-harmonic generation (SHG) has been observed in optically poled 15Nb₂O₅•85TeO₂ glasses doped with V₂O₅ and Tb₂O₃. The SH intensity of optically poled V₂O₅-Tb₂O₃-codoped glass is approximately 4-fold that of optically poled V₂O₅-doped glass, whereas the SH intensity of the optically poled Tb₂O₃-doped sample is approximately one-fifth that of the V₂O₅-doped sample, which means that the terbium ions contribute to the enhancement of χ⁽²⁾ only when the vanadium ions coexist.

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The organosilxane-based organic/inorganic hybrid was synthesized by adding 3-glycidoxypropyltrimethoxysilane (GPTMS) to an aqueous solution of tungstic acid and gelling it at 70-150°C. The FT-Raman and ¹³C NMR studies revealed that the alkoxy and epoxy groups of GPTMS were subject to hydrolysis and ring-opening reaction, respectively. The ²⁹Si NMR study revealed that the inorganic component derived from tungstic acid appeared to have Si-O-W bonds with the GPTMS-derived siloxane network. The GPTMS-derived organic/inorganic hybrid containing the inorganic component derived from tungstic acid was transparent and colorless. In addition, it showed the photochromism that resulted from the incorporation of the inorganic component derived from tungstic acid into the GPTMS-derived organic/inorganic hybrid. A broad peak around 880 nm with a shoulder peak around 650 nm was observed in the spectra after the UV-irradiation, meaning two kinds of d-d bond intervalence transition states exist in the organic/inorganic hybrid. Assuming that the photochromism was the first-order reaction, the reaction rate constant was estimated to be 1.9×10^-1 min^-1.

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The mechanism of “top-gathering” pillars and the controllability of top-gathering pattern formation were investigated. Two-dimensional pillar arrays with micrometer repetitions have been fabricated from a hybrid organic-inorganic material by photolithography. The type of array structure formed depending on the distance between neighboring pillars. From in situ observation during drying, it was found that capillary force is affected by the distance between the pillars. Such pillars of 16 μm height were gathering, and top-gathering units could be obtained when the distance between neighboring pillars is less than 8 μm. Gathering units composed of four pillars can be formed periodically by controlling the arrangement of the pillars.

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Inorganic-organic hybrid films with a maximum thickness of about 40 μm were prepared from vinyltriethoxysilane (VTES) through a sol-gel process. UV light from a high-pressure mercury lamp was irradiated through a photomask on the hybrid films from VTES. IR and ²⁹Si NMR spectra of the coating films showed that C=C bonds in VTES were polymerized by UV irradiation. Micropatterns with a maximum height of about 40 μm were formed by the etching of unirradiated area of the films.

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PZT thick films were prepared using electrophoretic deposition (EPD) process with special emphasis placed on the powder packing behavior on silicon substrates. The suspending medium used was an ethanol solution containing an appropriate amount of HCl to introduce surface charges to the Pb(Zr, Ti)O₃ particles, which were deposited on Pt/Ti/SiO₂/Si substrates under a constant electrical field. It was found that the deposited microstructure gradually changed across the film thickness: large particles were initially deposited, followed by the deposition of small particles. Such a phenomenon was explained by using the Derjauin-Landau-Verwey-Overbeek (DLVO) theory which considers a particle size effect on the surface charge responsible for the EPD process.

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In this study, highly oriented collagen structures were successfully synthesized using a conventional superconducting magnet with magnetic field intensities of 2.5 to 8 T. The relationship between the orientation order parameters f_2D of osteoblasts cells (that is, the orientation of collagens) and the magnetic field intensity was mainly investigated. As a result, it was clarified that collagens highly oriented perpendicular to the magnetic field direction were obtained by exposure to a magnetic field intensity of 3.0 T.

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In this study, magnetic activated carbons (MACs) were synthesized by a chemical processing, adding iron (II and III) sulfates and alkali (aqueous NaOH solution) to the suspension of activated carbons at room temperature. Fine magnetite particles with some tens nanometer in diameter were precipitated on the surface of activated carbons. MACs prepared by this chemical precipitation processing could rapidly adsorb several pollutants such as bisphenol A and nonylphenol. In addition, MACs were easily collected with a permanent magnet and may be suitable for collection in a simple magnetic separation system.

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Dense translucent mullite-amorphous composite was fabricated from the metakaoline powder by spark plasma sintering, which was synthesized from halloysite powder mined in Algeria by annealing process. The dense sintered body with translucent could be formed by heating to 1300°C at heating rate of 100°C/min under applied pressure of 40 MPa and reducing atmosphere. The characterization was performed by X-ray diffraction analysis, TEM observation and ultraviolet spectroscopy. The result of X-ray diffraction analysis indicated that the mullite with crystallite size of 20-30 nm was precipitated into the dense sintered body during spark plasma sintering, which corresponded to the result of TEM observation. The result of ultraviolet spectroscopy indicated that this sample had translucence of 70-80% under wave length 1000 to 2500 nm.

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