Tomoyoshi Shoji

Thermoelectric Properties of Nb-Doped SrTiO3 / TiO2 Multiphase Composite

In this study, we fabricated and examined a series of multiphase type composites constructed of Nb-doped SrTiO3 / TiO2 fine particles. The composition of the composites and the sintering temperatures were selected in a two-phase region where a perovskite SrTiO3 and a rutile TiO2 phases coexist. The composites obtained here were found to commonly have a mosaic type texture constructed of TiO2 and SrTiO3 fine particles with a typical size of about 500 nm. In some samples we also found additive phases such as Sr6Ti7Nb9O42. The thermal conductivity values measured for the most samples with different contents are ranged between 2 and 5 Wm K. The values are apparently lower than the value for single crystal SrTiO3 samples presented in literature. A sample with rather low relative density of about 80% showed a quite low thermal conductivity, about 1 WmK. Taking account the other TE data, e.g. Seebeck coefficient and electrical conductivity, we calculated dimensionless figure of merit, ZT, to be at maximum 0.24 at 600°C.

Experimental discussion on the effect of carboxylic acid addition on the specific surface area of calcium hydroxide powder generated from calcium oxide.

The dioxin from the arbage incineration is one of the most serious environmental problems in recent years. There is a method using calcium hydroxide [Ca (OH) 2] as one of the dioxin preventive methods, reacting in the present garbage incineration and removing the chlorine in combustion exhaust gas. The formation mechanism of specific surface in the calcium hydroxide powder generated by reaction from quicklime is not sufficiently elucidated up to now.Calcium hydroxide was thought to decrease specific surface area until now in the case where carboxylic acid is used as an addition in calcium hydroxide reaction.In this paper, the applicability of carboxylic acid to calcium hydroxide reaction, and the morphology formation mechanism of the specific surface of calcium hydroxide is experimentally discussed. As a result, a new triple product factors of the alkyl chain length of the added carboxylic acid, the acidity and the interaction between carboxylic acid and water, were successfully introduced to be reasonably described the experimental result between specific surface area and amount of acid.And, the optimum alkyl chain ength was experimentally pointed out to exist at 5 showing the maximum specific surface area of calcium hydroxide. Also, the increment effect to specific surface area by carboxylic acid addition was shown to be maximum at 0.05 of the amount of carboxylic acid.

Thermophysical Discussions on the Powder Surface Improvement Effect of Initial Powder Packing

The powder materials are used in various field of industry as raw or intermediate materials. And many kinds of powder unit operation handle these powder materials, but various phenomena of powder have not yet been elucidated sufficiently. Fundamental relationship between powder surface properties and behavior is expected to be discussed as one of important subjects.In this paper, calcium carbonate is used as test packing powder and powder packing operation is fundamentally discussed. And the effects of powder surface improvement on initial bulk density distribution are experimentally and thermophsically discussed using X-ray radiograph system. As a results of it, the optimum conditions to generate the most homogeneity of powder density distribution is pointed out to exist.

Propagation of Powder Entropy and Thernophysical Structure of Granular Flow

If free energy is applied to a specified position in particulate medium, the energy is changed into entropy and propagates outward around the position and is dissipated completely. The problem is how the free energy propagates and dissipates in a particulate medium. In order to elucidate this problem, two fundamental points have to be discussed. First is the energy transmission property of the geometrical particle structure in a particulate medium. Second is experimental observations on the propagation behavior in particulate media, in which component particles make a random steady movement. In the former, the thermophysical understanding of the energy propagation property in a particulate medium is presented on the basis of thermophysical concepts of a particle system and introduces a new concept for a particulate original function1), and symmetry of particle structure. Next, the propagation behavior of powder bulk density in a particulate medium is experimentally observed by use of shear tests and a X-ray radiograph system. The propagation behavior of powder bulk density is thermophysically discussed. As a result of it, the mutual relationship among wave propagation properties in particulate media and the fundamental concepts of particle entropy and free energy are discussed, considering the symmetry of particle arrangement.

The Effect of Initial Bulk Density Distribution on The Homogeneities of Powder Compact and Sintered Powder Compact.

Recently, the ceramics are used in various fields. Especially, electro ceramics which have specific electric function are taken notice. Then, electro ceramics manufacturing process become more and more important in industry.The ceramics manufacturing process consists of various kinds of unit operations, and can be considered as combination of forming process and sintering one. However, basic relation between forming process and sintering one has not yet been elucidated. In other words, the effect of the homogeneity of initial bulk density distribution in the forming cell on the homogeneity of bulk density of powder compact or sintered powder one has not yet discussed.In this paper, the effects of initial bulk density distribution on the bulk density distributions of powder compact and sintered powder one are experimentally discussed by using the X-ray radiograph system. As the result, these bulk density distributions of powder compact and sintered one are greatly effected on the initial bulk density.

Thermophysical Discussions on The Homogeneity of Ceramics Thin Powder Layer.

In the ceramics production process composed of unit operations such as weighing, mixing, drying, crushing, granulation, forming, firing and so on, to control the homogeneity of materials is one of the most important problems because the properties of ceramics are strongly effected by the homogeneous degree.In this paper, thin powder layer forming process is selected to be discussed, and doctor blade method is used, which is one of the thin powder layer forming processings. This method will give a thin powder layer. However, the thermophysical mechanism of the forming process has not yet been discussed. Then, the bulk density distributions are observed by its X-ray radiograph using the image processing system, and are thermophysically discussed.The following findings are obtained. When electric field is applied to the powder layer, the homogeneity increases enormously. And the stronger electric field applies, the higher homogeneity of powder layer is obtained. Beacuse the electric field produces the corresponding negative free energy to the field in powder, it results in the increase of the entropy of powder laver.