Materials Science Forum Vols. 534-536

Abstract: Magnetic characteristics observed in BiSrCaCuO superconductor were studied. In the measurement of differential conductance, it was cleared that the mechanism of magnetic memory effect couldn't be explained by using conventional flux flow model. By changing the density of external magnetic flux, changes in inductance of a coil in which a superconducting bar inserted were also measured. The results showed that the filament model was valid to explain the mechanism of the occurrence of a voltage in superconducting sample. It was concluded that the electromagnetic characteristics arose from the interaction between the trapped magnetic flux and weak link of the filament formed in the superconducting bulk.

Abstract: Using 6wt%Y2O3-2wt%Al2O3 as sintering additives and Si as a raw powder, the continuously porous in-situ Si2N2O-Si3N4 bodies were fabricated by multi-pass extrusion process and their microstructures were investigated depending on the addition of carbon (0-9wt %) in the mixture powder. The introduction of Si2N2O fibers observed in the unidirectional continuous pores as well as in the pore-frame regions of the nitrided bodies can be an effective method in increasing the filtration efficiency. In the case of no carbon addition, the network type Si2N2O fibers with high aspect ratio appeared in the continuous pores with diameters of 150-200nm. However, in the case of 9wt% C addition, the fibers were found without any network type and had diameters of 200-250nm.

Abstract: By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for hydroabrasive cutting were fabricated. The ceramics were obtained from pure alumina, as well as from alumina, doped by TiO2, MgO and AlMg. The ceramic properties of the channel surface and the nozzle volume were investigated. It was shown that the samples sintered from AlMg doped Al2O3 powder had the best desired mechanical properties and structural characteristics: relative density ~0.97, channel microhardness – 18-20 GPa, channel surface roughness ~0.7 /m, average crystallite size ~1 /m.

Abstract: The TiC-TiB2-SiC system was a ternary eutectic, whose eutectic composition was 34TiC-22TiB2-44SiC (mol%). A TiC-TiB2-SiC ternary eutectic composite were synthesized via the floating zone method using TiC, TiB2 and SiC powders as starting materials. The TiC-TiB2-SiC eutectic composite showed a lamellar texture. TiC(022), TiB2(010) and SiC(111) of the eutectic composite were perpendicular to the growth direction. The TiC-TiB2-SiC ternary eutectic composite had a specific relationship among the crystal planes: TiC[011]//TiB2[010]//SiC[112], TiC(200)// TiB2(001)//SiC( 402 ) and TiC(111)//TiB2(101)//SiC( 220 ).

Abstract: Polymer derived ceramic composites have been developed for SOFC seals. The formation and properties of the ceramic composite derived from a mixture with polysiloxane and filler were investigated. In the presence of filler materials such as ZrO2 and AlCo, the thermal properties of the ceramic composite could be controlled. The mixtures with polymethylsiloxane and fillers were prepared and their conversions to ceramic composites by annealing in N2 atmosphere were studied. The microcrystalline composites with filler embedded in a silicon-boron-oxycarbide glass matrix were formed. The thermal expansion behaviors were measured and discussed.

Abstract: The Powder characteristics and sintering behavior of SiO2 coated BaTiO3 were studied. BaTiO3 powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the BaTiO3 powders was ~35 nm and the thickness of the SiO2 coating layer was ~5 nm. As the SiO2 content increased, the SiO2 layers improved the powder dispersion by increasing electrostatic repulsion between the BaTiO3 particles. The Zeta potential of SiO2 coated BaTiO3 was getting close to that of pure silica with a more negative charge, compared with that of the uncoated BaTiO3. The onset temperature of shrinkage curves shifted to higher temperatures with increasing SiO2 contents.

Abstract: Lanthanide tantalite LnTaO4 (Ln= La, Nd, Sm, Dy, Er and Tm) was synthesized by a solid state reaction between mixed powders of Ln2O3 (Ln=La, Nd, Sm, Dy, Er and Tm) and Ta2O5. The single-phase LnTaO4 was prepared by sintering at temperatures of 1423-1673 K in air. The SEM observation showed that the particles were provided with the growth steps and the depeloped facets. The photocatalytic activity for water splitting of LnTaO4 prepared was measured under UV light irradiation. The activity obtained was higher than that previously reported. These results suggested the crystallinity of LnTaO4 photocatalysts correlates closely with the efficiency of water splitting.

Abstract: Silicon nitride - silicon carbide composite was developed by using an abrasive SiC powders as a raw material. The composites were prepared by mixing abrasive SiC powder with silicon, pressing and sintering at 1400°C under nitrogen atmosphere in atmosphere controlled vacuum furnace. The proportion of silicon in the initial mixtures varied from 20 to 50 wt%. After sintering, crystalline phases and microstructure were characterized. All composites consisted of α- Si3N4 and β-Si3N4 as the bonding phases in SiC matrix. Their physical and mechanical properties were also determined. It was found that the density of the obtained composites increased with an increase in the Si3N4 content formed in the reaction.

Abstract: Several boride sintered bodies such as TiB2, ZrB2, and SiB6 were previously reported. In the present study, the sinterability and physical properties of chromium boride (CrB2) containing chromium carbide (Cr3C2) sintered bodies were investigated in order to determine its new advanced material. The samples were sintered at desired temperature for 1 hour in vacuum under a pressure by hot pressing. The relative density of sintered bodies was measured by Archimedes’ method. The relative densities of CrB2 addition of 0, 5, 10, 15 and 20 mass % Cr3C2 composites were 92 to 95 %. The Vickers hardness of the CrB2 with 10 and 15 mass % Cr3C2 composites were about 14 and 15 GPa at room temperature, respectively. The Vickers hardness at high temperature of the CrB2 addition of 10 mass % Cr3C2 composite decreased with increasing measurement temperature. The Vickers hardness at 1273 K of the sample was 6 GPa. The Vickers hardness of CrB2 addition of Cr3C2 composites was higher than monolithic CrB2 sintered body. The powder X-ray diffraction analysis detected CrB and B4C phases in CrB2 containing Cr3C2 composites.

Abstract: The preparation of single-phase CuLaO2 with delafossite-type structure by means of the solid-state reaction method was investigated using X-ray diffraction. The results showed that notwhistanding the fact that there was a trace of metallic copper, nearly single-phase CuLaO2 was obtained by using La(OH)3 as a lanthanum source and by firing the mixed powder with nonstoichiometric composition ratio of La(OH)3:Cu2O =1:1.425 in a vacuum at 1273 K for 10 h. The measurement of electrical conductivity and Seebeck coefficient showed that CuLaO2 thus obtained was a p-type semiconductor and had a Seebeck coefficient of approximately 70 /V/K.