Bi-based superconducting shapes were fabricated by extrusion of ceramic-polymer mixture involving a solgel derived superconductor and in situ polymerized polymethylmethacrylate as binder. The powder was intimately mixed with methylmethacrylate monomer and polymerized in the presence of other organic additives such as butylbenzyl phthalate, phosphate ester and benzoyl peroxide. The viscous mass was then extruded to wires 3mm in diameter and 25mm in length. They were heat-treated at controlled rates for binder burn out and sintering at 840°C for 20h. Zone melting refining was carried out on the sintered samples in a three-zone furnace at a controlled speed of 30mm per hour for introducing texture. The surface morphology of starting powder and microstructure of fractured surface of sintered and textured wires are presented and compared.

抄録全体を表示

Preparation of Pb(Ni_1/3Nb_2/3)O₃ (abbreviated as PNN) perovskite powder and thin film by sol-gel method was studied. The precursor of PNN was synthesized in 2-methoxyethanol using Pb(OAc)₂, Ni(OEt)₂ and Nb(OEt)₅. It was hydrolyzed, dried at 120°C and calcined at 900°C for 3h in air to obtain the perovskite powder. The films were deposited on various substrates by spin coating from the precursor solution, dried at 350°C for 5min and then calcined at temperatures between 400 and 1000°C for 3h to yield PNN thin films. Using BaPbO₃ ceramics substrate, which has a high electric conductivity, perovskite PNN films were produced by calcining at 700°C for 3h, which is rather low compared to the conventional method of powder synthesis.

抄録全体を表示

This paper reports the experimental results on PZT/polymer 1-3 connectivity composites for solid ultrasonic applications, especially for an AE transducer in nondestructive inspection. A high sensitivity and wideband AE transducer employing the PZT/polymer 1-3 composite has been developed. The 1-3 composite was fabricated based on the “dispersion of resonance” design: A large number of small rods with different heights were carved in a poled solid PZT disk with an ultrasonic cutter and were then back-filled with urethane rubber. Evaluation of piezoelectric characteristics indicated that the composite had g₃₃ value three times larger than that of solid PZT. It was found that the resonance frequency of rods was not intervened each other due to polymer matrix. The AE transducer had higher sensitivity and a wider resonance frequency than a conventional type AE transducer.

抄録全体を表示

p-type semiconducting ceramics of iron disilicide with high thermoelectric figures of merit were fabricated from composite powders composed of Fe_0.99Cr_0.01Si_2.00/5.38 mass% Cr(OH)₃ or Fe_0.92Mn_0.08Si_2.00/5.38 mass% Mn(OH)₂ that had been prepared by the precipitation method. The figures of merit were 0.52×10^-4/K(673K) and 1.23×10^-4/K(873K) for Cr-doped and Mndoped iron disilicide, respectively. Increase in the figure of merit through metal hydroxide addition was considered to be due to the optimization of the acceptor concentration which was caused by the simultaneous dissolution of dopant metals and oxygen into the iron disilicide phase.

抄録全体を表示

Si₃N₄/SiC composite ceramics containing 20mass% dispersed SiC particles were fabricated by hot-pressing at 1800°C under 35MPa for 2h. SiC powders with average particle sizes of 0.03, 0.27, 0.60 and 1.20μm were used, and the influence of the SiC particle size on the microstructure and mechanical properties (3-point bending strength and fracture toughness values) was investigated. As a result, grain growth and α-β transformation in Si₃N₄ matrix were prevented by the dispersed SiC particles. The Si₃N₄ matrix grain size decreased with decreasing SiC particle size, and in Si₃N₄/SiC (0.03μm) and Si₃N₄/SiC (0.27μm), α-phase remained. The fracture toughness decreased with decreasing Si₃N₄ matrix grain size. Accordingly, the fracture toughness was not improved by the dispersed SiC particles. In Si₃N₄/SiC (0.03μm), the bending strength showed a maximum value of 1161MPa at room temperature and 950MPa at 1400°C. It is considered that the remarkable improvement in the strength of Si₃N₄/SiC (0.03μm) is attributed to fine grains of Si₃N₄ matrix. On the other hand, other composites showed almost the same strengths as monolithic Si₃N₄.

抄録全体を表示

Reaction behavior of joining interface of zirconia-SUS304 by active metal brazing using Ti was studied by means of EPMA, XRD, IMA, XPS and AES. The results show that O was diffused from the zirconia, reacting with the Ti active metal zone to produce TiO. The amount of O in the denaturizing layer was found to dicrease compared with original zone of zirconia. The bonding state of Zr in the denaturizing layer changed from Zr⁴⁺ to Zr²⁺. At the same time, the diffusion of Ti were found in the zirconia near the interface of zirconia-Ti.

抄録全体を表示

Ba₂Ti₉O₂₀ with GeO₂ and B₂O₃ was synthesized by an ordinary sintering method. Fired densities, dielectric constants and dielectric losses were measured. Ba₂Ti₉O₂₀ containing B₂O₃ sintered at lower temperatures and Ba₂Ti₉O₂₀ containing GeO₂ showed more excellent dielectric properties than a single phase of Ba₂Ti₉O₂₀. However, Ba₂Ti₉O₂₀ containing GeO₂ and B₂O₃ showed no improvement in the sinterability and dielectric properties by low temperature firing. A two-step addition process, i.e., separate addition of GeO₂ and B₂O₃ before and after the calcination, respectively, was effective in reducing the firing temperature without affecting the dielectric properties. XRD (X-ray diffraction) analysis and SEM (scanning electron microscope) observation were carried out on those samples. The sintering mechanism of Ba₂Ti₉O₂₀ containing GeO₂ and/or B₂O₃ was proposed and the relationship between the microstructures and dielectric characteristics was discussed.

抄録全体を表示

A SiO₂-TiO₂-C precursor fiber, which was prepared from phenolic resin fiber (Kynol) impregnated with a mixed solution of ethylsilicate and titanium tetraisopropoxide, was heat-treated in N₂ at 1873K. The heat-treated fiber was examined by X-ray diffraction, SEM observation and chemical analysis, and compared with the fiber heat-treated in Ar. The heat treatment produced carbon fiber coated with a mixture of SiC and Ti(C, N). The solid-solubility of carbon in TiN increased with increasing carbon content in the precursor fiber. Carbothermal reduction and nitridation of TiO₂ to Ti(C, N) preceded carbothermal reduction of SiO₂ to SiC. While the fiber heat-treated in Ar was roughened by coarsening of the carbide crystals, the fiber heat-treated in N₂ was uniform and smooth in appearance. However, on heat treating the precursor fiber with a high concentration of SiO₂ and a low concentration of TiO₂, the hexagonal crystals of Si₃N₄ grew coarsely on the smooth surface.

抄録全体を表示

The R-curve and fatigue behavior were investigated for two kinds of silicon nitride with different microstructures. In these materials the toughening exponents determined by the indentation-strength-in-bending method are almost zero. Moreover, the values of fracture toughness obtained by the indentation crack size measurement and the single-edge-precracked-beam method are the same. Therefore, it is concluded that these materials show flat R-curves. On the other hand, it is found that a considerable cyclic-fatigue effect, distinct from static fatigue, exists in these materials. Cyclic-fatigue crack growth rates are higher in small grained silicon nitride than in large grained one. When the crack growth behavior is represented by a power law relationship including two terms of the stress intensity range ΔK and the maximum stress intensity K_max; i.e. da/dN=C(K_max)^p(ΔK)^q, significant differences in the values of the exponent p and q between these materials are not recognized. On the basis of the above results and other data available, the factors affecting the cyclic-fatigue behavior and cyclic fatigue mechanisms are discussed.

抄録全体を表示

Properties of diopside, CaMgSi₂O₆, powder prepared from metal alkoxides were investigated examine for its application as a biomaterial. Gel powder was synthesized by hydrolysis of mixed alkoxides, i.e. Ca(OEt)₂, Mg(OC₂H₄OEt)₂ and Si(OEt)₄. The hydrolyzed product was characterized by SEM, DTA, XRD, ICP and so on. The dry gel powder was X-ray amorphous and crystallized into diopside at 840°C. This amorphous powder showed better sinterability than that of the crystallized powder. The calcined powder could be coated on Ti metal by a thermal treatment at 800°C for 2h. The diopside coated Ti metal composite was expected to be useful for biomaterials as artificial bone and dental root.

抄録全体を表示

Beta (β)-Si₃N₄ powder containing 1mol% equimolar Y₂O₃-Nd₂O₃ was gas-pressure-sintered under three combined conditions of temperature, N₂ gas pressure and time. Cyclic fatigue testing of these materials was performed using smooth specimens in ambient air. The fatigue crack growth diagram (K_{I max}-da/dN diagram) was calculated from the fatigue lifetime distribution data by using the statistical method proposed by Fett and Munz. These materials had a microstructure of “in-situ composites” as a result of exaggerated grain growth of some β-Si₃N₄ grains during firing, and showed high fracture toughness. The crack growth rates of the materials were retarded by high fracture toughness. The threshold K_{I max} value of crack growth was recognized in crack growth rate diagrams of these materials. It was deduced that the characteristic fatigue behavior of Si₃N₄ materials prepared from β-phase powder was due to high fracture toughness caused by in-situ composite microstructure.

抄録全体を表示

New simultaneous toughening and strengthening method for Al₂O₃ composites has been investigated. The study on flake-forming process of refractory metal powders such as Mo, Ta and Nb was carried out using high purity Al₂O₃ (AKP-30) and easy-sintering Al₂O₃ (AES-11) matrices applying the wet ball milling. Three-point flexural strength and fracture toughness by means of SEVNB method of Al₂O₃/Mo, Al₂O₃/Ta and Al₂O₃/Nb composites fabricated by hot pressing were evaluated. The micro-dispersion of flaky particles of Mo, Ta and Nb in Al₂O₃ matrices contributes remarkably to increase of the flexural strength and fracture toughness. The mechanism of improvement in strength and toughness can be induced from SEM observation of the fracture surface and TEM observation of the microstructure. These properties are closely related to the fracture manner of flaky particles and the distribution of nano particles of refractory metals.

抄録全体を表示

Low-cost and low-purity β-Si₃N₄ powder was sintered at 1900°C for 8h in 1 MPa nitrogen gas with 2mol% Y₂O₃-2mol%Al₂O₃ additives. Fully densified bodies were obtained by the gas-pressured-sintering. This material had a strength of 689 MPa and a fracture toughness of 6.4 MPa·m^1/2. Furthermore, the high temperature strength, oxidation resistance, fatigue parameter were measured. The degradation of strength at elevated temperature was less than 5% up to 900°C. No fatal defect was created in 100h-oxidation in 900°C-air. The fatigue parameter was on a level with general material produced from α-rich powder. These properties are adequate for structural material application.

抄録全体を表示

SiC coating on stainless steel by reaction with SiH₄ and CH₄ was studied using plasma-assisted CVD in a triode bell jar reactor, in which a third electrode was used as the sample holder and rf bias potential was applied. Generally, it is thought that if an ionic species is introduced on coating surface, ablation of fragile parts may result; however when the bias potential was increased to -380V, the growth rate again increased. The breakdown voltage of coated films increased in the order of applied bias potential of -200, -300, -100, 0 and -380V, and the order was the same results of the chemical anti-corrosive test. It was found that the optical band gap and residual carbon content are increased with increasing methane feed rate. Applicaton of rf bias potential also leads to monotonic increase of the optical band gap except for 0 and -100V. It was found that there is good correlation between the applied rf potential and the breakdown voltage and the results of the anti-corrosive test except for applied bias potential of 0 and -100V.

抄録全体を表示

We attempted application of the simultaneous loading system previously proposed by us on dielectric ceramics. Electrical conduction was introduced by means of a conductive coating which does not affect the strength distribution. For fracture determination, a stepwise conduction profile was monitored. In this way, the simultaneous loading system was applied to dielectric ceramics and it demonstrated the same strength distribution as that obtained from conventional measurement. Therefore, this method can be applied to dielectric ceramics as well as to electroconductive materials. It is expected to be advantageous for measurements of strength distribution under extreme conditions of high temperature and pressure.

抄録全体を表示

Rare-earth alumino-silicate glasses were prepared from Shirasu (volcanic ash) and yttria concentrate as the main starting materials. Specific heats and elastic constants of these glasses were measured at room temperature. Using these values and previously measured values of thermal expansion coefficients and densities, Grüneisen constants were calculated from the Grüneisen relation. There is a good linear relation between specific heat and chemical composition of these glasses containing about 20 oxides. Observed values of specific heat coincide with calculated values within 3% error. Observed bulk moduli were quite high (about 80 GPa). Values of the Grüneisen constant mainly depend on SiO₂ content.

抄録全体を表示

The coating of thin films of various oxide compositions using alkoxide solutions was tried to confirm whether the control of pore characteristics of Vycor type porous glass is possible or not. Judging from the pore diameter distribution diagrams before and after the coating, apparently larger pores decreased and the pore diameter distribution became narrower and more symmetric by the coating.

抄録全体を表示

Silicon carbide ceramics which 5 mass% Al₂O₃ and 2 mass% Y₂O₃ were added to were prepared by the spark plasma sintering (SPS) method under the conditions of 30 MPa and 5 min. Mechanical properties at room temperature were eximined. The SPS brought dense silicon carbide ceramics at a sintering temperature of 1800°C, which was about 200°C lower than that of the hot-pressing process. The silicon carbide obtained by SPS had higher strength and fracture toughness than those obtained by hot-pressing. The results suggest that the inside temperature of the sintered bodies during spark plasma sintering was higher than the measured temperature.

抄録全体を表示

Thick silica films prepared on a stainless steel sheet by the electrophoretic sol-gel deposition in the presence of sodium dodecyl sulfate (SDS) as a surfactant were found to be an agglomerate of fine silica particles. The size and the dispersity of the silica particles on the sheet were dependent on the concentrations of both tetraethoxysilane (TEOS) and SDS. The particle size increased with an increase in the content of SDS. Monodispersed particles were obtained at relatively low concentrations of TEOS, whereas bimodal particles were deposited at higher concentrations of TEOS.

抄録全体を表示

The present work evaluates Si₃N₄ powder surfaces by transmission electron microscopy (TEM). Si₃N₄ particles are covered by oxidized layer. The surface impurity oxide phases of powders play important roles for good performance of structural Si₃N₄ ceramics. The Si₃N₄ powder surface was modified by heat treatment in air and washing treatment in Soxhlet extractor. The surface oxygen content increased by the heat treatment, or decreased by the aqueous washing process. The oxygen content was measured by a combustion type oxygen analyzer. The powder surface conditions were analyzed by high resolution TEM (HREM) images. X-ray diffraction analysis was carried out to identify the structure of the surface modified Si₃N₄ powders. HREM and X-ray diffraction analysis showed that the surface oxidized impurity layer on Si₃N₄ particle was thin amorphus layer. The surface oxidized impurity layer increased with increasing heat treatment time in air, and decreased by washing treatment. The thickness of the surface oxidized layer of the asreceived powder (1.42 mass% O) was about 1.0nm, and that of the surface oxidized powders was 1.5nm for 4h heat treatment (1.91mass% O), and 2.0nm for 8h heat treatment (2.46mass% O). On the other hand, the thickness was about 0.5nm for the washed powder (0.57mass% O). Assuming that the silicon oxide layer is uniform in thickness on the particle surfaces, and using the specific surface area of the raw powder and the density of silica glass, the surface oxidized layer can be calculated. The estimated values agreed well with the HREM observation. The surface oxidation occurs uniformly on the particle surfaces.

抄録全体を表示