Norimasa Sakamoto

Dielectric Properties of Spherical Dielectric Oxide Powder and Its Ceramic-Polymer Composite

A spherical filler of Ca0.65Sr0.35TiO3 dielectric oxide was prepared by flame fusion to improve the fluidity of ceramic-polymer compounds. The dielectric permittivity of the powder decreased by about 20% after melting-spheroidization but recovered after being heat-treated above 1150°C for 4 h. Composite dielectrics made from the spherical powder and a thermosetting polymer exhibited lower viscosity before hardening, thus making it possible to increase the filler concentration by over 5 vol %. A dielectric permittivity between 12 and 19 was achieved by adjusting the filler concentration of the spherical powder in the range of 40–70 vol %.

Crystallization of Spherical Dielectric Oxide Particles in a Melting-Spheroidization Process Using Chemical Flame

BaNd2Ti4O12 dielectric oxide particles were spheroidized by melting them with a LPG-O2 flame to improve packing and fluidity of the powder. Changes in the particle morphology, structure and crystallinity during the process were investigated. It is revealed that most of the as-melted particles are dense, spherical and amorphous with smooth surfaces, which crystallize in the annealing process to form polycrystalline spherical particles with uneven surfaces. Annealing at above 1100°C is necessary for the spheroidized powder to recover its crystallinity and dielectric properties.

Synthesis of Barium Titanate Nanoparticles from Decomposition of Barium Titanyl Oxalate Tetrahydrate with Aid of Supercritical Water

A novel process of BaTiO3 manufacture was conducted by using supercritical water. Preparation of BaTiO3 nanoparticles was investigated from decomposition of BaTiO(C2O4)2•4H2O (BTOT) with aid of supercritical water for the first time. When BTOT was exposed to supercritical water around 673 K and 30 MPa, it decomposed quickly in 5-22 seconds. The products formed strongly reply on environmental conditions. BaCO3 and TiO2 were always observed as the products in the absence of alkaline additives. BaTiO3 nanoparticles with specific surface area as high as 12~14 m2/g were able to be obtained under strong alkaline conditions, such as NaOH/COSubscript text2=2/1. It was found that environment of supercritical water was better than sub-critical conditions to obtain high quality BaTiO3 particles with fewer defects. Employment of supercritical water significantly reduced the reaction time and temperature compared to other BaTiO3 manufacture processes utilizing BTOT as precursor.

Preparation and Formation Mechanism of Micrometer-Sized Spherical Single Crystal Particles of Perovskite Oxides by Flame Fusion

Micrometer-sized spherical single crystal particles of a perovskite oxide based on Ca0.40Sr0.60Ti0.95Zr0.05O3 were prepared from a pulverized powder by flame fusion method. The obtained particles are polyhedrons exhibiting 6 quadrate planes, 8 octagonal planes and 8 triangular planes. Semplice electron diffraction patterns corresponding to orthorhombic structure were obtained for the whole thin section of a particle from different radiation directions, indicating that the particle is single crystal. Changes of the morphology, structure and crystallinity of particles were observed by SEM and TEM to investigate the formation mechanism of the particles. It is revealed that a pulverized particle melts in the flame and solidifies to form an as-fused spherical particle which is composed of an amorphous shell and a crystal core. The crystal core acts as a crystal nucleus in the sequential heat-treating process and finally grows to a single crystal above 1150°C.

A Technique for Permittivity Measurement of Ceramic Powders at Microwave Frequencies

Details of a new technique for the permittivity measurement of ceramic powders at microwave frequencies are described. Permittivity of a powder is calculated from the permittivity of liquid medium and that of the slurry made from the liquid medium and the powder. Measured permittivities of BaNd2Ti4O12 ceramic powders vary by processing conditions of the powders. This result is consistent with permittivities of composite substrates made from these powders and a thermosetting resin.