Tetsuo Uchikoshi

Preparation of porous materials with controlled pore size and porosity

Well-defined porous ceramics with controllable pore size and porosity were fabricated via a hetero-coagulation of template/ceramic particle colloidal processing. Monodispersed polymer spheres were used as template and ceramic nanoparticles as inorganic building blocks to create porous structures. The preparation of well-dispersed suspensions of polymers and ceramics is essential for the fabrication of uniformly porous materials. Core-shell composites of polymer/ceramic could be obtained by mixing the oppositely charged two suspensions via electrostatic attraction following by filtration and calcination to produce macroporous ceramic materials. SEM images and pore size distribution results revealed that various materials, such as Al2O3, TiO2 and ZrO2, with ordered and uniform macropores have been obtained by this simple procedure. The pore size could be controlled readily by varying the polymer size and the porosity could be manipulated by modifying the volume ratio of polymer/ceramic particles

Control of texture in alumina by colloidal processing in a strong magnetic field

Abstract Electrical, mechanical and other properties of ceramic materials can be controlled by designing their microstructures. It had generally been difficult to utilize a magnetic field for tailoring the microstructure in feeble magnetic ceramics, such as Al2O3; however, the possibility of controlling the microstructure by a magnetic field occurred with the development of superconducting magnets. In this review paper, we introduce a novel processing for the microstructual design in ceramics by colloidal processing in a strong magnetic field and an electric field. We demonstrate that the textured alumina can be fabricated by slip casting in a strong magnetic field and the production of alumina/alumina laminar composites with different crystalline-oriented layers can be achieved by electrophoretic deposition in a strong magnetic field. In order to control the texture using a magnetic field, a good dispersion of powder in a suspension is necessarybecause a strong attractive force between the agglomerated particles prevents each particle in a suspension from rotating in the magnetic field. The degree of orientation depends on the processing factors, such as heating temperature, viscosityof suspension, etc. And the grain growth in Al2O3 matrix enhances crystallographic texture development. The bending strength of the laminar composite depended on the direction of the multilayered microstructure with alternate crystalline-oriented layers. Crack propagation and fracture mode depend on the direction of microstructure in the laminar composite with controlled crystalline orientation.

Dense, bubble-free ceramic deposits from aqueous suspensions by electrophoretic deposition

The characteristics of electrophoretic deposition (EPD) of positively charged particles onto a cathode were investigated using aqueous alumina and zirconia suspensions. The deposition was performed using several kinds of metal substrates at different current densities. For most substrate materials, a large number of macropores appeared in the deposit, and their size increased with the current density due to gas bubble formation. However, no macropores were formed in the deposit on a palladium substrate, regardless of the current density. The green density and sintering properties of the EPD deposits on a palladium substrate from aqueous suspensions were the same as from slip casting. Bubble-free zirconia/alumina laminate composites were also fabricated by EPD from aqueous suspensions.

Electrophoretic deposition of aqueous nano-γ-Al2O3 suspensions

The deposits of nano-sized gamma-Al2O3 powders were fabricated via a simple electrophoretic deposition process in aqueous suspensions. Bubble-free deposits of nano-gamma-Al2O3 powders with a uniform microstructure and high green density up to 56.8% were successfully obtained. Some factors that contribute to the deposition characteristics of the EPD in an aqueous suspension are discussed

Electrophoretic deposition of aqueous nano-sized zinc oxide suspensions on a zinc electrode

Electrophoretic deposition (EPD) was used to form ZnO deposits. ZnO with an average particle size of 40 nm was dispersed in water with the addition of an appropriate amount of anionic polyelectrolyte. Uniform and bubble-free ZnO deposits have been obtained via EPD on a zinc anode in an aqueous suspension. The obtained deposits showed good sinterability.

Fabrication of porous ceramics with controlled pore size by colloidal processing

Abstract Well-defined macroporous ceramics consisting of TiO2 and ZrO2 have been fabricated by two methods. One is via a template-assisted colloidal processing technique and the other is via a hetero-coagulation of template/ceramic particle colloidal processing. The former technique is as follows. Close-packed polymer spheres were first prepared asa template using centrifugation or gravitational sedimentation, followed by infiltration with alkoxide precursors. Then the removal of the template beads was achieved by calcination of the organic–inorganic hybrids at appropriate temperatures, yielding well-ordered macroporous ceramics. The latter technique is as follows. Core–shell composites of polymer/ceramic were obtained by mixing the oppositely charged two suspensions via electrostatic attraction following by filtration and calcination to produce macroporous ceramic materials. SEM images revealed that macroporous TiO2 and ZrO2 with ordered and uniform macropores have been obtained by both procedures.

Electrophoretic deposition of lead zirconate titanate (PZT) powder from ethanol suspension prepared with phosphate ester

Abstract The formation of thick PZT films via electrophoretic deposition (EPD) was studied. The colloidal suspension of a nano-sized PZT powder dispersed in ethanol was prepared using a phosphate ester (PE) as a dispersant. The amount of PE addition on the stability of the PZT suspension has been investigated by measuring the pH and conductivity of the suspension, deposition weight and the relative density of the PZT green compacts. The effect of the applied voltage on the relative green density was also determined as a function of the wt% PE. The composition and microstructure of the sintered PZT ceramics were characterized by XRD and SEM. The electrical properties of the PZT ceramics were also investigated.

Tri-axial Grain Orientation of Y2Ba4Cu7Oy Achieved by the Magneto-science Method

Tri-axial orientation of orthorhombic and twin-free Y2Ba4Cu7Oy (Y247) powders was attempted using a rotating magnetic field with modulated rate. Although magnetic anisotropy of paramagnetic Y247 originated only from the two-dimensional CuO2 and one-dimensional Cu–O chain structures are small, strong tri-axial grain orientation with misorientation angles below 1.5° was successfully achieved during the solidification process of epoxy resin. Our present results indicate the possibility of fabrication of tri- or bi-axial grain-oriented bulk and thick films without applying epitaxial methods, such as melt-solidification or thin film deposition, and that the modulated-rotation magnetic field is applicable not only to RE247 compounds but also to orthorhombic high critical temperature cuprate superconductors, including practical REBa2Cu3Oy, in principle.

Electrophoretic deposition of α-alumina particles in a strong magnetic field

The electrophoretic deposition of single-crystalline α-alumina particles dispersed in aqueous media was performed in a strong magnetic field of 10 T. The α-alumina particles in the stable suspension were aligned due to their anisotropic diamagnetic susceptibility and then deposited on a cathodic substrate. The orientation of the α-alumina crystallites was confirmed by x-ray diffraction of the sintered specimen.

Fabrication of multilayered oxide thermoelectric modules by electrophoretic deposition under high magnetic fields

The authors report the fabrication of grain-aligned [Ca2CoO3−δ]0.62CoO2 (Ca349) thick films and a multilayered thermoelectric unicouple of Ca349 and Ca0.9La0.1MnO3−δ (Mn113) using electrophoretic deposition (EPD) and magnetic alignment methods. Strongly c-axis-oriented Ca349 thick films were obtained by EPD performed under magnetic fields. In addition, the c axis of grains was found to always align parallel to the direction of field, independently of the EPD cell configuration. The required conditions for magnetic grain alignment of fine Ca349 powders were quantitatively discussed based on magnetization anisotropy. An α-Al2O3∕Mn113∕α-Al2O3∕Ca349∕α-Al2O3 multilayered thick film was successfully developed.