The particle-packing structure of Al₂O₃ slurry was evaluated by using constant pressure filtration. The influences of initial solid concentration and dispersant amount on the cake forming behavior were discussed. It was shown that the packing fraction of formed cake is almost independent of filtration pressure under 10 vol% of initial solid concentration. However at a relatively high solid concentration (20 and 35 vol%), the packing fraction of cake increased with filtration pressure. The cake forming behavior was classified into four patterns by plotting the resistance of the formed cake as a function of particle volume in the formed cake; the plots were (a) a straight line, (b) a convex curve, (c) a concave curve, and (d) a combination of a concave curve and a flat line. The particle dispersion and flocculate degree were discussed on the basis of the results obtained by constant-pressure filtration.

View full abstract

New preparation routes have been investigated for enhancing mechanical properties of a biomaterial composite consisting of with high-density polyethylene (HDPE) reinforced with hydroxyapatite (HA). HA was used as fine particles to coat each coarse particle of HDPE with an elliptical-rotor-type mixer and with a high-speed rotational impact blending machine. The effect of particle size of HDPE and mixing conditions were studied on mechanical properties of the composite material, such as rotor speed, total treatment time, number of preparation steps and total volume fraction of HA. In comparison, it was found that the embedment besides uniform coating and dispersion of HA fine particles onto the surface of HDPE core particle was easily achieved by rotational impact blending, due to high impact energy. This yielded relatively high properties. However, multi-coating steps or layers were required due to a high percentage of powder loss during operation. In contrast, uniform and tight coating of core particles was performed without particle loss by elliptical-rotor-type mixing. Nevertheless, due to a slight embedment of fine particles by gentle shear and compressive stress, HA could not disperse uniformly due to aggregates generated by the molten HDPE of core particles escaped through the thick and loose coating layer during material formation. This resulted in a weak bonding among coated particles to yield lower mechanical properties.

View full abstract

Si₃N₄ powder, produced by the fluidized-bed direct nitridation of silicon, was blended with water, compacted by pressure slip casting, and sintered under a pressurized nitrogen atmosphere. Compacts made from the powder showed roughly the same sinterability as those made from commercially available imide-process powder, yielding a hardness of H_v 1570, a fracture toughness of 7.2 MPa√m, and a three-point bending strength of 1062 MPa, highest values attainable with Si₃N₄. The powder produced by the fluidized-bed direct nitridation may replace the Si₃N₄ powder from the other process, when water is used for preparing slips. A processing rout is proposed, which may realize a substantial reduction of total cost for producing sintered Si₃N₄ parts.

View full abstract

Silica-pillared clays with mesopores were prepared from fluorohectorite, aminopropyltriethoxysilane (APS) and tetraethoxysilane (TEOS) affected using polyvinyl alcohol (PVA). The presence of PVA was important in this synthesis and was effective on the porosity of the obtained silica-pillared clays. Based on the X-ray diffraction measurements, the basal spacings of the silica-pillared clays increased from 1.7 to 5.6 nm with an increase in the PVA concentration. As with the basal spacings, the peaks of the pore size distribution and the average pore diameter shifted up to approximately 3 nm. The pore volumes corresponded to the basal spacings expanded by cointercalation of PVA and polysiloxane. The pore properties and structures of the pillared clays were investigated and the results indicated the relation between the layer structure and pore structure.

View full abstract

Nanocrystalline, monophasic Ba(Sn_xTi_1-x)O₃ [BST] have been prepared by a simple, new low-temperature, direct-precipitation method. The crystalline phase, particle size and compositional homogeneity of the BST powders thus synthesized are examined by XRD, SEM and ICP-OES. The dielectric properties of the solid solutions prepared by this new method are reported. Formation mechanism of the crystalline BST and the effect of Sn content on successive phase transitions, in this solid solution system, are also reported.

View full abstract

Oxygen adsorbed to Hydroxyapatite (HAp) after firing at 1200°C in oxygen atmosphere has been measured by Thermal Desorption Spectrometer (TDS). The quantity of adsorption oxygen has been determined by weight change of HAp at firing. HAp adsorbs oxygen in two different states. These two states correspond to HAp coloring phenomenon (HAp crystal structure). In case of the reddish-brown type HAp (Hexagonal HAp), it adsorbs oxygen as ionized molecule which weight is 0.2 mass% of HAp. As for the red type HAp (Monoclinic HAp), it adsorbs 0.4 mass% oxygen of the weight. In addition, with firing in argon atmosphere, it is measured 0.4 mass% weight change at white type HAp (Monoclinic HAp). In sintering high density HAp pellet, oxygen atmosphere accelerated densification. This pellet appeared transparent and its density was 99.69%.

View full abstract

The mass production process of Ce_0.9Gd_0.1O_1.95 (CGO) nanopowder with high-sintering characteristics has been studied. Although CGO powders were fabricated using a large scale coprecipitation bath with a capacity of 65 kg/batch, particle size distribution curve of this powder showed two peaks for the agglomeration and this powder showed lower sintering characteristics, compared to the CGO nanopowder by a small scale bath with a capacity of 0.1 kg/batch. It was found that when the impurity of NO₃ ^- in the powder was removed by water using the rate of 50 L/kg, the formation of oval shape particles was observed and it is easy to crush the agglomerations in the powder by hammer-type mill. The sintering characteristics of this powder are almost same to those of the powder synthesized by the small scale bath.

View full abstract

The objective of this study was to form a crystalline oxide film on a titanium substrate using the micro-arc oxidation (MAO) method. The study demonstrated that this was possible by controlling the type of electrolytic aqueous solution and pH value. Phosphoric acid radical in the electrolytic aqueous solution was indispensable. In principle, the crystalline oxide film was anatase, but the film made from electrolytic aqueous solution having a pH exceeding 12 or including poly-phosphoric acid was rutile. Below pH 12, the film was unstable and dissolved in the electrolytic aqueous solution considerably. The crystalline oxide film had a double-layer structure, and anions in the electrolytic aqueous solution entered the side layer of the electrolytic aqueous solution. As a result, the O^2- concentration rose and much more rutile was formed. Anatase contained little holes and the surface was smooth, whereas rutile contained columnar grains at the hole edges and the grains were oriented.

View full abstract

When 10-20 mass% of asbestos (chrysotile: Mg₃Si₂O₅(OH)₄)-containing cement board of 5 mm thickness was heated at 600°C for 2 h, the asbestos lost the crystal structure due to its dehydration reaction in the cement board, changing to an amorphous phase. Further, the heated cement board could be easily ground to grains with several μm size using a mortar. Then the asbestos seemed to be ground to below the size at the same time, because the fiber shape of original asbestos was not found in the sample.

View full abstract

A simple process for fabricating a “nano-laminar” ceramic composite was examined. Glass flakes with a thickness of 0.7 μm coated with silver were used as model materials, and were consolidated by pulsed current sintering with a uniaxial press of 7.1 MPa. The sintering temperature was varied in the range of 873-973 K. The consolidated samples sintered at 943 K were fairly dense, and the flakes were aligned by uniaxial pressing. The silver coating remained on the flakes through the sintering, and became an interface layer between the flakes. The indentation test demonstrated its high resistance to crack propagation through the transverse direction of the aligned flakes; this result was attributed to crack deflection at the interface and the accumulation of microfractures around the indent. The potential for a nano-laminar composite with high toughness were shown.

View full abstract

Mesostructured materials using a colloidal solution prepared from K₂NbO₃F and hexadecyltrimethylammonium were synthesized stirring at room temperature for 30 s. It was found that the Nb-containing colloidal solution was reactive to alkyltrimethylammonium. Furthermore, we synthesized porous Si-Nb oxides using the colloidal solution as a Nb source and tetraethoxysilane (TEOS) as a Si source. Microporous material was obtained by stirring at room temperature for 30 s, and mesoporous material was obtained by stirring at 323 K for 3 h. It was discovered that pore size depends on the condensation behavior of the silica network.

View full abstract

Highly c-axis-oriented aluminum nitride (AlN) thin film sensor elements were prepared on silicon single crystal substrate by rf magnetron sputtering technique. The sensor characteristics were evaluated under pressures of 0.4 to 8.0 MPa and frequencies of 0.1 to 40 Hz at room temperature. The deviation from the linearity of charges with pressures for the AlN sensor was within 0.90% of a full scale at 8.0 MPa, which indicates a good linearity between 0.4 and 8.0 MPa. The frequency response of AlN sensor showed the similar frequency characteristics as an electric model of connecting a capacitance to a resistance in parallel. It became clear that an electric model is effective in predicting the electric constant which determines the sensor characteristics.

View full abstract