Zenji Kato

Sintering deformation caused by particle orientation in uniaxially and isostatically pressed alumina compacts

Effect of particle orientation on deformation during sintering is reported for model systems; one made with industrial grade low soda alumina, which has an elongated particle shape, and the other a special alumina with a spherical particle shape. To ensure the homogeneous packing density of particles, compacts were made by uniaxial pressing followed by cold isostatic pressing. The particle orientation was examined with a polarized light microscope and was found to be an important cause of sintering deformation. In a green body, for elongated shape of particles, the particle orientation occurred during uniaxial pressing, causing the anisotropic sintering shrinkage during sintering and thus the sintering deformation. No particle orientation nor shrinkage anisotropy was noted in the system made with the powder of spherical particle shape.

Chemical effects of DCCA to the sol-gel reaction process

The effects of drying control chemical additives (DCCA) on the growth of silica particles, gelation time and physical properties of the dry gel were examined in a two-step silica sol-gel process.N,N-dimethylformamide,N,N-dimethylacetamide and ethylene glycol (EG) were applied as DCCAs. The shapes of growing silica particles were distorted spheres on addition of DCCA. EG accelerated the gelation process. Despite the use of DCCA, crack-free, dry gels were obtained only under limited conditions.

Preparation and Thermoelectric Property of Highly Oriented Al-Doped ZnO Ceramics by a High Magnetic Field

Highly oriented Al-doped ZnO ceramics were prepared by a high magnetic field method and their anisotropic thermoelectric properties were examined. The c-axis oriented specimen along the ab-plane showed a higher electrical conductivity compared to the a-axis and non-oriented specimens as a result of high electron mobility. On the other hand, the differences in the Seebeck coefficients and thermal conductivities between oriented and non-oriented specimens were a small. Consequently, the dimensionless figure of merit of the c-axis oriented specimen increased by about 30% compared to the other specimens.

Fabrication of c-axis oriented higher manganese silicide by a high-magnetic-field and its thermoelectric properties

Fabrication of c-axis oriented higher manganese silicide by a high-magnetic-field and its thermoelectric properties

Direct observation of aggregates and agglomerates in alumina granules

Abstract Aggregates and agglomerates in granules prepared from milled alumina powder were studied with new confocal laser scanning fluorescence microscopy (CLSFM) using the liquid immersion method. Two kinds of ground powders were prepared by agitation bead milling and conventional ball milling and spray drying. The observation by CLSFM was very effective for detecting aggregates and agglomerates of very low amounts in alumina granules. Aggregates and agglomerates were absent in the granule made from powder milled by agitation bead milling, whereas they remained in the granule made from powder milled by ball milling. The volume fractions of these particles were about 2.0 vol.% and under 0.1 vol.% for the granules made from ball-milled and bead-milled powders, respectively.

Direct observation of internal structure in spray-dried yttria-doped zirconia granule

Spray-dried yttria-doped zirconia granules were made transparent by immersion in a liquid and the internal structure was characterized using an optical microscope. This unique technique was found to be applicable for this system by using an immersion liquid with appropriate refractive index, and it enabled observation of the internal structure to be made over the entire volume of granules, in clear contrast to conventional SEM observation. Distinct features, which were considered to be agglomerates, were found in the granules. This was supported by SEM observation.

Wetting of aqueous solutions of organic binder (PVA) on sapphire and fused quartz

Wetting by PVA aqueous solution of sapphire and fused quartz was studied by measuring the contact angle of a sessile drop placed on them. At a given temperature, the contact angle increased with increasing concentration of solution up to 2% and became rather constant for further increase in concentration. The contact angle also increased with increasing temperature. At temperatures over 70° C, the contact angle for sapphire exceeded 90° for PVA aqueous solutions of concentration over 2%. The effects of temperature and concentration on wetting for fused quartz were similar to those found for sapphire. These results are discussed in terms of bulk thermodynamics.

Fabrication of a- and c-axis oriented Zn0.98Al0.02O by a high magnetic field via gelcasting

Highly a- and c-axis oriented Zn0.98Al0.02O ceramics were prepared by a combination of the high magnetic field and gelcasting techniques, and their thermoelectric properties were examined. The gelcasting made it possible to align the particles preferentially along the a- and c-axis within a short exposure time in the high magnetic field. The particle orientation was not degraded and disturbed by the gelation and subsequent processing. The c-axis oriented specimen along the ab-plane showed a higher electrical conductivity compared with the a-axis and non-oriented specimens as a result of high electron mobility. The differences in the Seebeck coefficients between oriented and non-oriented specimens were a very small. This study indicated that applying the magnetic alignment via gelcasting method provides effective and versatile techniques to fabricate the grain oriented materials without hindering the thermoelectric properties

Particle sedimentation monitoring in high-concentration slurries

In this study, the sedimentation states of particles in high-concentration slurries were elucidated by monitoring their internal states. We prepared transparent high-concentration silica slurries by adjusting the refractive index of the aqueous glycerol liquid in which the particles were dispersed to match that of the silica particles. In addition, a fluorescent dye was dissolved in the liquid. Then, we directly observed the individual and flocculated particles in the slurries during sedimentation by confocal laser scanning fluorescent microscopy. The particles were found to sediment very slowly while exhibiting fluctuating motion. The particle sedimentation rate in the high-concentration slurry with the aqueous glycerol solution (η=0.068Pa·s) and a particle volume fraction on the order of 0.3 was determined to be 1.58 ± 0.66 μm·min−1 on the basis of the obtained image sequences for 24.9 h. In-situ observation provides a large amount of information about the sedimentation behavior of particles in condense...

Direct Observation of Alumina Particles Orientation in High Magnetic Field

Introduction Recently, super-conducting magnets were applied for the fabrication of ceramics with unique structures and properties. In a high magnetic field (10T), there is an appreciable interaction between materials and the field even for “non-magnetic” materials such as alumina. Recent study shows that alumina has anisotropic diamagnetic susceptibility as shown in Fig.1, and orients with their c-axis parallel to the magnetic field as shown in Fig. 2. It is interesting to observe directly the process of orientation in the magnetic field. Recently, a new optical method was developed to determine the degree of grains orientation in an alumina compact with a crossed polarized light microscope (ref.1). It has a very high sensitivity even for a very weak orientation, which can not evaluated by the X-ray diffraction analysis. It is very promising to apply this method for directly observing the orientation process of particles in a high magnetic field. However, a microscope made of non-magnetic materials is needed to observe the process of particle orientation in a high magnetic field. In this study, we develop a new crossed polarized light microscope with non-magnetic materials for in-situ observation of particle orientation of alumina grains in a high magnetic field.