Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X‐ray diffraction. Hollow γ‐Al2O3 particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α‐Al2O3 particles. Hollow spheres were obtained also for TiO2, ZrO2, and Y2O3 by ECM of TiCl4, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe2O3, CeO2, and MgO from aqueous solutions of their corresponding nitrates.
Alumina powders were synthesized by the emulsion combustion method, using w͞o (water in oil) type emulsions with different aqueous microsphere sizes. The effects of microsphere size on the size and shape of the synthesized powder were evaluated. The powders were spherical and hollow in shape with a very thin shell (from 10 to 20 nm in thickness) when synthesized from large aqueous microspheres (from 200 nm to 1 mm). The sizes and specific surface areas of the powders were consistent with those calculated. Large particles, which did not correspond to the microsphere size, were obtained from small aqueous microspheres (6 nm). The short distance (7 nm) between microspheres causes the adhesion of particles during the firing process. FIG. 1. Schematic of ECM process.
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.
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