TAILORED MICROSTRUCTURE OF CERAMICS BY USING ELECTRIC AND MAGNETIC FIELDS

The mechanical and functional properties of ceramics can be improved by designing their microstructures, such as grain size, grain geometry, crystallographic orientation, second phase and so on. Tailoring the crystallographic orientation in ceramics is one of effective ways for improving their properties. Layered structure with different crystalline orientation layer by layer has been proposed as an alternative for the design of structural ceramics. Grain sliding during the high temperature deformation depends on the grain boundary structure and misorientation angle between grains. The energy release mechanisms during the crack propagation such as crack deflection and crack bifurcation can improve the crack growth resistance in the laminar ceramics. The residual stress generated in each layer during cooling down from the sintering temperature has an influence on the crack deflection and crack bifurcation, hence the control of the residual stress is important for the crack growth resistance in order to improve the mechanical properties. There are some reports about the laminate composite materials with different components for controlling the thermal expansion coefficients in order to generate the residual stress. Our concept is that the crystalline axis depending on the thermal expansion coefficients aligns for controlling the residual stress in the monolithic ceramics. We controlled the layered structure in the monolithic ceramics, such as alumina and silicon carbide for control the crack deflection. The starting materials were spherical a-Al2O3 powder and a-SiC powder with trigonal and hexagonal crystal structure, respectively. These powders were dispersed in ethanol using an ultrasonic homogenizer and a magnetic stirrer. The suspension was placed in a superconducting magnet with a room temperature bore of 100mm, and then a strong magnetic field of 12T was applied to the suspension to rotate each particle due to the magnetic torque. The magnetic field was maintained in the suspension during the electrophoretic deposition (EPD) at room temperature. The crystalline-oriented laminate ceramics were produced by alternately changing the angle between the vectors E and B, jB-E, layer by layer during EPD in the 12 T magnetic field. Please click Additional Files below to see the full abstract

Spontaneously formed gradient chemical compositional structures of niobium doped titanium dioxide nanoparticles enhance ultravioletand visible‑light photocatalytic performance

Semiconductor photocatalysts showing excellent performance under irradiation of both ultraviolet (UV)- and visible (VIS)-light are highly demanded towards realization of sustainable energy systems. TiO2 is one of the most common photocatalysts and has been widely investigated as candidate showing UV/VIS responsive performance. In this study, we report synthesis of Nb doped TiO2 by environmentally benign mechanochemical reaction. Nb atoms were successfully incorporated into TiO2 lattice by applying mechanical energy. As synthesized Nb doped TiO2 were metastable phase and formed chemical compositional gradient structure of poorly Nb doped TiO2 core and highly Nb doped TiO2 surface after high temperature heat treatment. It was found that formed gradient chemical compositional heterojunctions effectively enhanced photocatalytic performance of Nb doped TiO2 under both of UV- and VIS-light irradiation, which is different trend compared with Nb doped TiO2 prepared through conventional methods. The approach shown here will be employed for versatile systems because of simple and environmentally benign process.The present work is partially supported by JSPS KAKENHI Grant Number JP20K15368, JSPS Core-to-Core Program, Foundation for the Promotion of Ion Engineering, Izumi Science and Technology Foundation (2019-J-112), International Network on Polyoxometalate Science at Hiroshima University, Leading Initiative for Excellent Young Researchers from the Ministry of Education, Culture Sports, Science and Technology (MEXT) of Japan, and the Strategic Research Foundation at Private Universities from MEXT of Japan

Bending strength of multi‐layered alumina with controlled residual stress

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FABRICATION OF POROUS, CRYSTALLINE-ORIENTED TITANIA LAYER ON TRANSPARENT ELECTRODE BY MAGNETIC FIELD-ASSISTED EPD

Dye-sensitized solar cells (DSSCs) are the most extensively investigated systems for the conversion of solar energy into electricity, since it can convert light at longer wavelengths into electricity and can be manufactured using less energy compared to the bulk semiconductor-type cells with a p-n junction. Despite these advantages, DSSC commercialization is still limited because of its low conversion efficiency and low reliability of the liquid electrolyte. The low conversion efficiency is due to the non-uniformity of the electrode components with respect to the packing density of TiO2 particles and film thickness of the electrode. Therefore the research on DSSC in general has been directed toward improving the photo-current and photo-potential. In order to significantly enhance the cell performance, it is important to optimize the photo-anode structure of the DSSC on the basis of its fundamental properties. In this study, crystalline-oriented porous TiO2 thin films were fabricated on indium-tin oxide (ITO) or fluorine-doped tin oxide (FTO) glass substrates by electrophoretic deposition (EPD) in a superconducting magnet. Please click Additional Files below to see the full abstract

Rapid fabrication of colloidal crystal assisted by electrophoretic deposition technique

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Investigation of affecting parameters of Electrophoretic deposition (EPD) method in (Bi0.5Na0.5)TiO3-Hexagonal BaTiO3 and their properties

Nowadays, eco-friendly materials have been attracting attention worldwide since the legislation of RoHS/WEEE directives in Europe. (Bi0.5Na0.5)TiO3-BaTiO3 (BNT-BT) systems are well known candidate of lead-free piezoelectric materials. However, BNT-BT systems have relatively low piezoelectric constant (d33 ~ 140 pC/N) which is difficult to apply in commercial products. In spite of this problem, BNT-BT systems have good potential because it is easy to apply mass production. Electrophoretic deposition method (EPD) has good advantage in mass production because size and shape of green ceramics is easily controlled by control of electrode. Moreover, it is reported that EPD method can be fabricated textured ceramics using high magnetic field and texture technique is important in enhancing piezoelectric properties. Our final goal is making [111] oriented BNT-BT ceramics which have enhanced piezoelectric properties and appreciate for mass production. Please click Additional Files below to see the full abstract

EPD FOR COMPOSITE CATHODE LAYER IN ALL-SOLID-STATE LITHIUM ION BATTERY BASED ON SULFIDE ELECTROLYTE

All-solid-state lithium ion batteries (LIBs), in which liquid-organic electrolytes are replaced with solid state inorganic electrolytes, are expected to be the optimal rechargeable batteries in the next generation because of their higher energy density, cycle stability and ignition safety. In order to develop all-solid-state LIBs with practical performance, controlling architecture in electrode layer consisting of active materials and solid electrolyte, to obtain good contact of the solids interfaces, with high packing ratio is necessary. However, there are few studies on controlled fabrication of macrostructure. We would like to propose a novel method which is employs electrophoretic deposition (EPD) for preparing composite cathode layer, with LiNi1/3Mn1/3Co1/3O2 (NMC) and 75Li2S-25P2S5 (LPS) used as the cathodic active material and solid electrolyte, respectively. The EPD technique can be used to prepare a cathodic layer with a desired structure because its equipment set up is simple but can be used to obtain complex composite structures. Please click Additional Files below to see the full abstract