Papers by Author: Tetsuo Uchikoshi

Abstract: The Mo₆ cluster which has the great optical properties and chemical activity because of their unique electronic structure have been attracted attention in many fields such as phosphor and photocatalyst. However, the Mo₆ cluster it’s hard to recycling which limited its industry application because of its such small nanoscale. Immobilizing the Mo₆ cluster on 2-D material has a great value to challenge it. In this research, we study on the sulfurization process of Mo₆Br₁₂ cluster to investigate the more possibility of the immobilization of Mo₆ cluster.

Abstract: Dual-phase membrane composed of oxide ion conductor and electron conductor was fabricated for application to oxygen separation membranes. 8 mol% yttria-stabilized zirconia (8YSZ) and carbon felt were used for the oxide ion conducting phase and the electron conductiing phase, respectively. Carbon felt was impregnated with YSZ aqueous suspension (40 wt%), dried, then sintered by a spark plasma sintering (SPS) process under the applied pressure of 80 MPa at 1200, 1400 and 1600 ° C for 10 min. When sintered at 1600 ° C, the XRD pattern showed small peaks indicating the formation of the zirconium carbide phase, but the microstructure observed by SEM showed that the YSZ was well densified and tightly bonded with carbon felt. This method has been demonstrated to be an effective process for the fabrication of YSZ-Carbon composites with both phases percolation structure.

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: Orientation technique based on the magneto-scientific crystal alignment phenomenon combined with electrophoretic deposition (EPD) technique was applied for the seeding process of zeolite L particles. Well-dispersed, ethanol-based zeolite L suspension was prepared and then consolidated on porous zirconia substrates by EPD. Conducting polypyrrole film synthesized on the zirconia substrate was used as an anodic substrate for the EPD process. The EPD was performed in a superconducting magnet with applying 12 T strong magnetic field to the suspension. The degree of orientation was characterized by XRD and compared with that of the zeolite L layer prepared by slip casting in a 12 T strong magnetic field using the same suspension.

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.

Abstract: The surface modification of Gd doped ceria (GDC) and Sr-and Mg-codoped lanthanum gallate (LSGM) powders with cationic and anionic polyelectrolytes, Poly (diallyldimethylammonium chloride) (PDDA) and poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), respevtively, was performed by the Layer by Layer (LbL) adsorption method to improve the surface-charging uniformity. The tri-layer of GDC/LSGM/GDC was deposited on a polypyrrole coated porous NiO-YSZ substrate by sequential EPD using the ethanol-based suspensions of the surface-modified powders. The topcoating of hydroxyl-propyl cellulose (HPC) on the deposited layers was conducted to control the drying rate with suppressing the cracking and peeling-off of the deposits. The advantage of the use of those polymers for the EPD process including the drying technique was demonstrated.

Abstract: The nano-porous Al2O3 layer was performed onto inner surface of micro- porous Al2O3 tube by using electrophoretic deposition (EPD). Initially, Polypyrrole (Ppy) was applied on inner wall of tube to make conductive surface. The Al2O3 deposition was carried out in Al2O3 suspension with 5 wt % solid content in ethanol medium system using various applied voltages. Thickness of the deposited layer depends on applied voltages, after sintering at 1400oC the morphology of the deposited layer was investigated by FE-SEM. The good deposited surface without cracks and peeling has been prepared under applied voltage condition of 10 V.

Abstract: Fabrication of textured hematite was achieved from paramagnetic goethite by electrophoretic deposition in a strong magnetic field followed by thermal treatment via topotactic phase transformation. The textured microstructure of the hematite was characterized by XRD and SEM observations. It was confirmed that the a,b-axes of the goethite were taken over the c-axis of the hematite through the topotactic phase transformation The magnetization vs magnetic field measurement using a VSM revealed that the textured hematite showed an anisotropic magnetic property depending on the direction of the crystalline orientation.

Abstract: We present a method for fabrication of textured MAX phase ceramics, particularly, Ti₃SiC₂; by EPD in a strong magnetic field (12T). Ti₃SiC₂ was dispersed in cationic polyelectrolyte-Polyethylenimine (PEI). Addition of 0.3-1dwb PEI resulted in high zeta potential values and suspension was found to be stable and of good fluidity. The optimized suspension parameters for EPD were determined as 10vol% Ti₃SiC₂ and 1dwb PEI in 50 % ethanolic water at pH ~ 7. X-ray diffraction analysis of the textured samples revealed that the preferred orientation of Ti₃SiC₂ grains parallel to the magnetic eld direction was along the a,b-axis. The Lotgering orientation factors on the textured top surface and textured side surface were determined as f _(hk0) = 0.35 and f _(00l) = 0.75, respectively.

Abstract: Grain-oriented Barium titanate (BaTiO₃) ceramics were prepared using an electrophoresis deposition (EPD) method under high magnetic field of 12 T and sintering at 1350 °C. It was found that BT03 and BTKK nanoparticles were necessary to synthesize the grain-oriented BT ceramics. The grain orientation was correlated with particles size and c/a ratio of lattice constants. The reason why the grain-oriented BT ceramics using the BT03 and BTKK were prepared was having the large values of the particles size and the c/a ration of lattice constants.