Naoyoshi Watanabe

Preparation and Characterization of Nano-structured Ceramic Powders Synthesized by Emulsion Combustion Method

The emulsion combustion method (ECM), a novel powder production process, was originally developed to synthesize nano-structured metal-oxide powders. Metal ions in the aqueous droplets were rapidly oxidized by the combustion of the surrounding flammable liquid. The ECM achieved a small reaction field and a short reaction period to fabricate the submicron-sized hollow ceramic particles with extremely thin wall and chemically homogeneous ceramic powder. Alumina, zirconia, zirconia–ceria solid solutions and barium titanate were synthesized by the ECM process. Alumina and zirconia powders were characterized to be metastable in crystalline phase and hollow structure. The wall thickness of alumina was about 10 nm. The zirconia–ceria powders were found to be single-phase solid solutions for a wide composition range. These powders were characterized as equiaxed-shape, submicron-sized chemically homogeneous materials. The powder formation mechanism was investigated through the synthesis of barium titanate powder with different metal sources.

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO2 and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO2 sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO2 sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 μm). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each others particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO2 occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO2 sol and ZA, creating a ZnO and SiO2 mixture. The reaction of ZnO with SiO2 was likely to be enhanced by ECM of the SiO2 sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, β-willemite and Zn1.7SiO4 mixed phase.

Piezoelectric and Dielectric Properties for Doped Lead Zirconate Titanate Ceramics under Strong Electric Field

Piezoelectric and dielectric responses were investigated for doped lead zirconate titanate (PZT) ceramics under strong electric field (1.6 MV/m). Displacements and polarization changes were measured and the effects of dopants were discussed. Doping of 2% Nb significantly increased the displacement of (Pb0.875Sr0.125)(Zr0.55Ti0.45)O3 ceramics. Doping of 2% Fe suppressed 90° domain rotation and decreased displacement. Results were discussed by dividing displacement and polarization change into two components, i.e., a piezoelectric or dielectric contribution and a 90° domain rotation contribution.