Papers by Author: Kenichi Myoujin

Abstract: La-doped SrTiO₃ (LST) powders were synthesized by ultrasonic spray pyrolysis using an aqueous solution of a metal nitrate. SEM images showed that the as-prepared LST powders had a spherical morphology with a diameter of 1 μm. XRD patterns showed that the crystal phase of the as-prepared powders was amorphous and that the powders crystallized to the perovskite phase by calcination at 900 °C. The sintered LST body had the highest electrical conductivity at a La doping concentration (La_x) of 0.1 under a reducing atmosphere. A solid oxide fuel cell (SOFC) with La_0.1Sr_0.9TiO₃Sm-doped CeO₂ (1:9) as the anode exhibited a maximum power density of 137.8 mW/cm² and an open circuit voltage of 1.08 V at 880 °C.

Abstract: BaTiO₃ precursor powders were synthesized by two types of pulse jet spray pyrolysis1000 and 2000 kcal/h typesusing an aqueous solution of metal salt. All as-prepared powders crystallized to the cubic and other phases. However, the powders almost reached the tetragonal phase through calcination at 900 °C in air for 2 h. The crystallinity of the powders obtained from 2000 kcal/h type pyrolysis was higher than those obtained from the 1000 kcal/h type. When Ba (NO₃)₂ was used, nanoparticle formation at an average particle size of approximately 150 nm, with a narrow size distribution, was observed. The relative density of the sintered body was 87 %. The relative dielectric constant of the BaTiO₃ body was 1450, and its tanδ value was 0.017 at room temperature.

Abstract: BaTiO₃ nanopowders were prepared by salt-assisted spray pyrolysis using a flux of KNO₃ and NaNO₃. Compounds of metal sources are thermally decomposed in the melting flux. Some flux mixtures make a eutectic composition because of the reduced melting point of the flux. The optimum temperature for the preparation of BaTiO₃ nanoparticles was 700 °C. When both KNO₃ and NaNO₃ were used as the flux, the average particle size of the BaTiO₃ powders was 40 nm, and the particle distribution was broad. On the other hand, when only KNO₃ was used, the average size of BaTiO₃ powders was 60 nm, and the particle distribution was narrow. This suggested that the sodium ions in the BaTiO₃ nanoparticles led to a broad particle distribution. X-ray diffraction (XRD) revealed that all the diffraction peaks were in agreement with the crystal phase of BaTiO₃. The relative density of the sintered body of BaTiO₃ powders was 87 %. The relative dielectric constant of the sintered body was 1180, and the dielectric loss (tanδ) was 0.023 at room temperature. This suggested that the residual potassium ions in the BaTiO₃ nanoparticles led to a reduction in the relative density and dielectric constant.

Abstract: Ce_0.8Sm_0.2O_1.9 (Samaria-doped ceria: SDC) precursors were synthesized by carbon-assisted spray pyrolysis. SDC thin films were prepared by electrophoretic deposition using the SDC precursor particles. The as-prepared SDC thin films were sintered at 1600 °C for 10 h. Uniform films with a thickness of approximately 20 μm were obtained. A fuel cell using the prepared thin films showed a maximum power density of 60.6 mW/cm² and an open circuit voltage (OCV) of 0.63 V at 700 °C.

Abstract: Spherical samarium doped ceria (Ce_0.8Sm_0.2O_1.9, SDC) powders having high specific surface area (SSA) were successfully synthesized by carbon-assisted spray pyrolysis (CASP). Saccharides, such as monosaccharides and disaccharides, or organic acids were used as carbon sources. The physical and chemical properties of these powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Thermo gravimetry-Differential Thermal Analysis (TG-DTA), and BET. Decarbonized powders obtained by this method exhibit spherical morphologies and nano- and submicron-sizes. The SSA of SDC obtained from CASP was more than seven times higher than that obtained from conventional spray pyrolysis (CSP). The SSA of the decarbonized SDC powders obtained by calcination at 900 °C was estimated to be approximately 70 m²/g by using the BET method. The relative density of SDC obtained from CASP was higher than that obtained from CSP. The relative density of the SDC pellet was highest (96 %) when it was sintered at 1400 °C.

Abstract: La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) precursor particles were successfully prepared by ultrasonic spray pyrolysis. LSGM thin films were prepared by the electrophoretic deposition (EPD) technique using ethanol containing iodine. The LSGM films were obtained by sintering at 1300 °C for 10 h. The X-ray diffraction patterns revealed that the diffraction peak of LSGM thin films was in agreement with the perovskite structure. The LSGM films attained a uniform thickness of 10 μm.

Abstract: Spherical La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) precursor powders were synthesized by aerosol plasma pyrolysis using an aqueous solution of metal nitrate. As-prepared powders obtained by this method were found to have a spherical morphology with a bimodal size distribution of nanosized (primary) and submicron-sized (secondary) particles. The average size of the primary particles was less than 100 nm. X-ray diffraction (XRD) patterns showed that as-prepared powders crystallized to LSGM and other phases. XRD revealed that LSGM pellets were crystallized to a perovskite structure after sintering at 1300 °C for 10 h.

Abstract: Ag and Ni spherical fine powders were continuously produced by carrying out an aerosol process in a mass nanopowder production apparatus. The particles size, particle morphology, crystal phases and crystallinity of the as-prepared powders were characterized by a scanning electron microscope (SEM) and X-ray diffraction (XRD). The particles were nonaggregated and they exhibited a spherical morphology with a narrow size distribution. The average sizes of Ag and Ni particles were 500 nm and 700 nm, respectively. The crystallinity of the as-prepared powders was high. The XRD patterns showed that the crystal phases of the as-prepared powders were the same as those of their respective metals.

Abstract: Spherical Ce0.8Sm0.2O1.9 precursor powders were synthesized by Aerosol Plasma pyrolysis using aqueous solution of metal nitrate. As-prepared powders obtained by this method have a spherical morphology with a nano size and submicron size. They had bimodal size distribution. The average size of primary particles was less than 100 nm. The concentrations of starting solution influenced to average particle size. The relative density of SDC pellet was highest when it was sintered at 1623 K. The relative density was 86 %. XRD, SEM, DTA-TG and BET analysis were used for determination of the composition, morphology, particle size and surface area.

Abstract: LiNi1/3Co1/3Mn1/3O2 precursor powders were successfully prepared by internal combustion type spray pyrolysis. The production capacity of precursor powders was about 1 kg/h when the solution concentration was 0.5 mol/dm3. Particle size, morphology and crystal phase of LiNi1/3Co1/3Mn1/3O2 powders were characterized by XRD and SEM. XRD showed that a layered rock salt structure with a R3m space group was formed by calcination at 750 °C for 10 h. SEM showed that hollow powders with a particle size of 6 μm and irregular morphology were obtained. The discharge capacity of LiNi1/3Co1/3Mn1/3O2 was 130 mAh/g, which showed good cycle performance.