Papers by Author: Satoshi Tanaka

Abstract: Recently, we have developed crystal-oriented sheet forming (COSF) process from green sheet process and high-magnetic-field method. We formed c-axis-oriented (Sr,Ca)2NaNb5O15 (SCNN) sheets by the COSF process, and succeeded in realizing c-axis-oriented single-plate type piezoelectric ceramics (O-SP) and c-axis-oriented multilayered type piezoelectric ceramics (O-MLPC) for SCNN. From the measurement results of displacement induced by electric field, it was clarified that effective d33 of the O-SP was 210~240 pm/V. This value was about 3 times larger than that of the randomly oriented single-plate type, which was 70% of that of single crystal. Moreover, it was confirmed that O-MLPC indicated displacements 2.5 times as large as that of the conventional multilayer piezoelectric ceramics. In this study, we clarified that piezoelectric properties in bulk and multilayer structure can be drastically enhanced using the COSF process.

Abstract: Thermoelectric properties of zinc oxide ceramics are largely influenced by the mobility variation because of the formation of double Schottky barrier at grain boundary. It was demonstrated that magnetic texturing enabled to fabricate highly c-axis oriented ceramics with orientation degree of 100 MRD. This high orientation of grains resulted in periodic grain boundary structures along ab -plane, which was confirmed by edge-on HRTEM images. Hall measurement revealed that the mobility was enhanced at 80% by the magnetic texturing. Furthermore, it was estimated that the effect of magnetic texturing was equivalent to the reduction in the density of trap by 5.9×1012 cm-2.

Abstract: Machining damage and its influence on strength was examined for alumina ceramics with various grain sizes, which were prepared by dry-pressing method with spray-dried granules, followed by sintering at 1350-1550°C for 2-27 hours. Grain sizes of the sintered bodies were 1-6μm. After machining at the same grinding force, specimens were placed in an alcohol solution of fluorescent dye and dried. The fracture strength was measured by 4 point bending. The machining flaws in the specimens were observed with a confocal scanning laser fluorescence microscope. Machining flaws appeared continuous, wide and deep in the specimen with small grain size, and discontinuous with large size. On ground surfaces, intra-grain fracture appeared on the surface, whereas inter-grain fracture dominates. The continuous, wide and deep flaws were attributed to the dissipation of stored energy associated with the cracks propagation. The result suggested that the stored energy on the machining process increased with decreasing grain size. The strength of the specimen with 1 μm grain size reduced from 500MPa to 250 MPa with machining damage. The strength depended remarkably on the depth of the machining damage.

Abstract: This paper shows a very promising approach for developing the structure of grain orientation through weak magnetic interaction of ceramics particles in a high magnetic field. Grain oriented bismuth titanate ceramics was successfully developed through a processing in a high magnetic field. XRD and SEM show that c-axes of particles were oriented perpendicular to the applied magnetic field. The orientation structure developed by sintering, and the orientation factor achieved 0.85 as determined using the Lotgering method.

Abstract: A high magnetic field of H = 10 T was applied to 30BaO-15TiO2-55GeO2 glass through its crystallization process. It was found that the c-axis of Ba2TiGe2O8 optical nonlinear/ferroelectric crystals oriented along the magnetic field. The second harmonic intensity of crystallized glass which the high magnetic field was applied perpendicular to the surface of glass was enhanced compared with a conventional crystallization in no magnetic field. Transparencies, photorefractive indices and thicknesses were also measured. As a result, crystal orientation of Ba2TiGe2O8 in glass matrix induced by a high magnetic field causes improvement of transparency and low value of photorefractive index.

Abstract: Supercritical water (SCW) has both the solvent power approximate to liquids and the transport properties common to gases. It is therefore expected as an excellent solvent for industrial waste treatment. In this study, various building materials were treated with SCW, and their morphological changes after treatment were observed. The effects of SCW treatment on the pore structure and compressive strength of cement concrete and mortar were also investigated. In the range of this study, after SCW treatment, inorganic materials and organic materials can be recovered as solids and liquids, respectively. Under sub-critical and super-critical temperature and pressure conditions, compressive strength of mortar decreases, while the effective pore volume increases.