The heat resistance of shock-compacted polycrystalline diamond (PCD) was investigated and compared with that of commercially available PCD. Shock treatment of PCD with and without silicon was performed by impacting an iron flyer plate 3.2mm thick, at a velocity of 2.3km/s. Neither significant graphitization nor cracking was observed after heat treatment of the obtained PCD with silicon at temperatures of 1000 and 1200°C for 30min in vacuum. Vickers hardness of the compacted PCD decreased slightly with increasing temperature up to 1200°C, while the hardness remained unchanged after this treatment at 1000°C for the PCD with silicon. On the shock-compacted pure PCD, no crack formation was observed after heat treatment at temperatures of 1000 and 1200°C, but increasing heat treatment temperature caused an increase in the amount of graphite, and thus the hardness decreased. Therefore, the addition of silicon contributes to the improvement of the thermal stability of shock-compacted PCD.

抄録全体を表示

β-dicalcium silicate was stabilized at room temperature and synthesized from reagent grade chemicals using B₂O₃, K₂O or SO₃ as stabilizers. B₂O₃ acts as the most effective stabilizer for dicalcium silicate. Phase transformation from β- to γ-dicalcium silicate depends on the start temperature of quenching. Hydration heat of β-C₂S shows that SO₃ delayed hydration at an early hydration time, but higher heat liberation rate at a later hydration time than the other stabilizers. ²⁹Si MAS NMR analysis shows that the hydrate of dicalcium silicate stabilized by B₂O₃ is polymerized more than those of dicalcium silicates stabilized by K₂O and SO₃. Dicalcium silicate presents different shapes of calcium silicate hydrate according to stabilizers: dicalcium silicate stabilized by B₂O₃ shows crumbled foil shape and K₂O needle shape of C-S-H.

抄録全体を表示

Oxygen was incorporated into Fe-Si alloys sintered bodies by thermal oxidation of FeSi₂, Fe_0.95Mn_0.05Si₂ and Fe_0.95Co_0.05Si₂ powders at 550°C and 650°C, in air. The Seebeck coefficient and electrical conductivity were measured in the range of 100-600°C and the effect of oxygen on thermoelectricity was clarified. Oxygen gave rise to an increase of the fraction of a residual metallic ε-phase, lowering the Seebeck coefficient. Addition of oxygen to FeSi₂ prevented both densification during sintering and transformation from metallic phases to semiconducting β-phase during annealing treatment. Electrical conductivity of FeSi₂ was dependent on the quantity of residual ε-phase, SiO₂ and porosity in the sintered specimens. In an intermediate temperature range, polaron model could be applied to explain the variation of the Seebeck coefficient with temperature.

抄録全体を表示

Recently, novel gel techniques such as the metal-chelate gel method, in situ polymerized complex method and polymer precursor method have been utilized to prepare many kinds of ceramics. These techniques offer the potential advantage of achieving compositionally homogeneous and fine powders with a narrow size distribution. Since the hydration activity of calcium silicates is affected by phase changes and the surface area, it is of vital importance to take into account both polymorphic forms and particle size. In this study, a metal-chelate gel route based on gelation of the aqueous solution of citric acid has been successfully applied to the synthesis of calcium silicates (Ca₂SiO₄ and Ca₃SiO₅) for the first time. In addition, their phase transformations and particle size are discussed in comparison to the conventional solid-state reaction route. The novel citrate gel route and the conventional solid-state reaction route were found to produce β-Ca₂SiO₄ (high-temperature phase) and γ-Ca₂SiO₄ (low-temperature phase), respectively. This result can be explained in terms of the particle size effect and the energy barrier. The nucleation and propagation of microcracks were responsible for overcoming a comparatively high-energy barrier, ΔG*_β→γ. The particle size effect governs both the statistic of martensitic nucleation and the propagation of the β→γ transformation. In contrast to Ca₂SiO₄, triclinic Ca₃SiO₅ (low-temperature phase) was obtained by both the citrate gel route and the conventional solid-state reaction route. The nucleation and propagation are not responsible for the transformation, thus the energy barrier of the monoclinic (M) to the triclinic (T) transformation, ΔG*_M-T, are considered to be small.

抄録全体を表示

Si₃N₄ sintered body was obtained by pressureless sintering and then post-HIPing with addition of small amount of TiO₂ (3mass%). Sintering additives were 5mass% Y₂O₃, 3mass% Al₂O₃ and 3mass% AlN. It was found that round-shaped particles with diameter 0.2-0.5μm were distributed within the grain-boundary phase. The particles contained high density crystalline imperfections. They contained Ti and N, and were identified as TiN by energy-dispersive-type X-ray microanalysis and X-ray diffractometry. The grain-boundary phase was mainly an amorphous phase containing Si, Y, Al and O, but it did not contain Ti. Formation of TiN from TiO₂ by reduction and nitridation was suggested based on thermodynamic calculations and crystal chemical considerations. High density crystalline imperfections may be introduced during reduction of TiO₂ particles. It is believed that the grain-boundary distribution of round-shaped TiN particles contributes to the improvement of wear resistance of Si₃N₄ ceramics.

抄録全体を表示

(1) Direct precipitation of ceria-zirconia solid solutions containing more than 66.3mol% ZrO₂ was successfully achieved under hydrothermal conditions by co-hydrolysis of acidic aqueous solutions of ZrOCl₂ and Ce(SO₄)₂⋅2(NH₄)₂SO₄.
(2) The morphology of ceria-zirconia solid solutions obtained was spherical to some extent due to agglomeration of nanometer-sized primary particles.
(3) The crystallite size, lattice parameter, and lattice strain of ceria-zirconia solid solutions also changed depending on the composition in the system. The morphology and crystalline phase of the precipitates were greatly influenced by the nature of anion constituent of cerium and zirconium salts.

抄録全体を表示

Several gelatin-siloxane hybrids incorporating Ca²⁺ ions were synthesized through a sol-gel process starting with gelatin, 3-(glycidoxypropyl) trimethoxysilane (GPSM), and Ca(NO₃)₂. Amino acid analysis, ²⁹Si NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and dynamic mechanical thermal analysis were used to assess the hybrid structure. It has been indicated that the grafting degree of epoxy groups of GPSM to gelatin and the extent of polymerization of methoxysilane end groups of GPSM strongly depended on the fraction of GPSM (f_G) in the hybrids, but not on incorporation of Ca²⁺ ions. Hence, the hybrids with the same f_G value, independent of incorporation of Ca²⁺ ions, had a similar cross-link density. However, the glass transition temperature (T_g) and storage modulus (E′) around T_g decreased with incorporation of Ca²⁺ ions. Through the deconvolution of amide I bands of FT-IR spectra, flexibility may be interpreted by that the percentage of gelatin having a random structure increased with incorporation of Ca²⁺ ions. The Ca²⁺-containing hybrids can spontaneously deposit apatite when they were soaked in a simulated body fluid of the Kokubo recipe, showing their bioactivity.

抄録全体を表示

Nucleation and crystal growth mechanism of apatite formation on porous silica gel derived by a sol-gel procedure was investigated by the use of several simulated body fluids (SBF's) that had different concentrations of Ca(II), P(V), and OH^- but had the same degree of supersaturation for hydroxyapatite. Induction time of apatite crystallization in SBF's was evaluated by thin film X-ray diffractometry. The effect of each ion on the induction time increased in the order: Ca(II)-rich SBF<P(V)-rich SBF <<OH^--rich SBF, while that for the rate of initial crystal growth of apatite increased in the order: P(V)-rich SBF<Ca(II)-rich SBF<OH^--rich SBF. It suggested that amorphous calcium phosphate (ACP) deposited as the precursor of apatite and ACP transformed into apatite nuclei by the incorporation of OH^-. Moreover, the transformation was accelerated by large amount of ACP and was assisted by the rearrangement of silicate units in the gel surface. Ca (II) was richer in ACP deposited in Ca(II) -rich SBF and OH^--rich SBF than that deposited in P (V)-rich SBF. Ca(II)-rich ACP was favorable for crystal growth.

抄録全体を表示

The thermally decomposed products of the CuRE(dhbaen)(NO₃)(dmso)_m(H₂O)_n complex were investigated by differential thermal analysis (TGA), X-ray diffraction patterns (XRD), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). A mixed phase of RE₂O₂SO₄ and CuO was formed at a low temperature. The particle size of CuO in the mixed phase was estimated to be 30-90nm by XRD. When the ionic radius of RE³⁺ ion is small, the RE₂O₂SO₄ phase decomposed and formed a heterometallic RE₂Cu₂O₅ at 850-1100°C. It appears that one dmso directly interacted with the RE ion (RE-O=S(-CH₃)₂) for the complex and the RE-O=S bond remained as RE₂O₂SO₄ after the decomposition. CuO in the mixed phase did not interact with -SO₄ which was confirmed by XPS.

抄録全体を表示

A ceramic matrix composite (CMC) containing Si-Zr-C-O fibers with a surface carbon layer formed by heat treatment in CO atmosphere was studied. The thickness of surface carbon layer on Si-Zr-C-O fiber increased by adding 0.1% CO₂ in CO atmosphere, compared with that formed in pure CO atmosphere. The flexural strength of the CMC containing the Si-Zr-C-O fibers with carbon layer increased with increasing the thickness of the carbon layer. This result indicated that the formation of a carbon layer by heat treatment on the Si-Zr-C-O fibers is a suitable way for modifying the interface structure of CMC.

抄録全体を表示

The effect of polymeric flocculant on the uniformity of centrifugally formed green compacts was investigated. The compacts were obtained from heterogeneous ceramic powder slurries with different compositions and particle size distributions. When the content of cationic polymer, C_P, was >10^-3 (g/g-powder) in well-dispersed slurries containing aplite, alumina, and kaolin (with particle sizes in the range of 10^-1-10¹μm in diameter), these powders flocculated but the particle dispersion in the green compacts became uniform. This flocculation process in heterogeneous slurries added with a polymeric flocculant was effective in order to prevent segregation in the green compacts for mixtures of powders with different particle size.

抄録全体を表示

AlON-SiAl₇O₂N₇ composites were prepared in order to improve the oxidation characteristics of AlON ceramics. Composites with different ratios of AlON/SiAl₇O₂N₇ were obtained by heating mixtures with different Al₂O₃/AlN/Si₃N₄ ratios at 1750°C in 0.5MPa N₂ for 2h. Since sintering of SiAl₇O₂N₇ progresses by an evaporation-condensation mechanism accompanied by evolution of SiO gas, densification of AlON-SiAl₇O₂N₇ composites is hard to achieve. The oxidation behavior of the obtained composies was investigated in air at 1300°C. Compared with a monolithic-AlON material, the AlON-SiAl₇O₂N₇ composites showed higher oxidation resistance because the formed surface layer with glass phase inhibited inward diffusion of oxygen.

抄録全体を表示

Preceramic polymer of Si-N(-C), perhydro-polysilazane (PHS), polyborosilazane (PBS) and methyl-hydropolysilazane (MHS), were synthesized by a pyridine-adduct method. The properties of polysilazanes were examined in relation to their potential application to the precursors of ceramic composites. PBS had too high viscosity to be impregnated in a fibrous preform. Accordingly, a mixture of PBS and PHS with the mass ratio of PBS/PHS=1/10 (PHS-B) was studied as the alternative of PBS. The char-yield of the respective raw polymers ranged from 60 to 80mass%, while that of the cured polymers was by 10-20mass% higher than the raw polymers. The polymers pyrolyzed below 1400K were amorphous. However, α-Si₃N₄ crystallites were observed at higher temperatures exceeding 1473K for PHS, 1673K for PHS-B and 1723K for MHS. The crystallization increased the density from 2.4Mg/m³ to 3.1Mg/m³ at the maximum. The MHS pyrolyzed at 1723K, being nearly amorphous, the heat-resistance of which was examined in nitrogen atmosphere for the exposing time span of 360ks. The heat-resistance test at 1723K significantly enhanced the crystallization, the test at 1623K resulted in a subtle change in crystallization, and the test at 1523K caused no microstructural change. It was concluded from these heat-resistance test results that the amorphous Si-N-C via MHS may be usable as a matrix of ceramic composites at temperatures below 1623K.

抄録全体を表示

We evaluated the characteristics of Ni paste used for internal electrodes of multilayer ceramic chip capacitors (MLCs). The effects of dispensability of BaTiO₃ powder in Ni paste and Ni powder properties on sintering characteristics of electrode films were studied. The experimental results revealed that an improvement of dispensability of BaTiO₃ suppressed shrinkage of the films. It was observed that properties of Ni powder influenced on the shrinkage of electrode films, i.e., Ni powder prepared by the WCP method showed a higher shrinkage than that of the powder made by the CVD method. The similar results were observed on the surface microstructure of sintered electrode films by SEM measurements.

抄録全体を表示

Silicon nitride containing Yb₂O₃ as a sintering additive was gas-pressure sintered. A dilatometric study indicates that the liquid formation temperature of this additive is higher than that of commonly used additives. The material containing 3.6mol% of additive densified up to 99% of the theoretical density by sintering at 1950°C for 4h. The grain boundary phase of this material crystallized as Yb₄Si₂O₇N₂. The bending strength of this material was 460MPa at room temperature. This value is rather low because of voids formed during gas pressure sintering in the specimens. However, strength degradation at high temperature was limited because of the highly refractory Yb₄Si₂O₇N₂ grain boundary phase.

抄録全体を表示

The humidity conditioning ability of various ceramic powders was evaluated by the B-value method using a newly developed acrylic-resin container. The powders were filled in a container 1cm in thickness and the opening area of the container was evaluated as the exposed surface area of the compacted powders. The area to volume ratios (A/V, m^-1) were fixed at 0.25, 0.5, 0.75 and 1.0 for a desiccator with 0.0152m³ volume. The B-values increased with increasing of A/V, but the differences of the B-values among the samples decreased. The B-values of the samples were classified into two groups, i.e. high-B (diatomaceous shale, sepiolite, selectively leached kaolin) and low-B groups (zeolite, charcoal, Ishikawa diatomite). The difference between the samples belonging to each group was difficult to evaluated merely by their B-values, whereas it was easily distinguished by the increase of amount of water vapor adsorption between 60 and 70%RH of in-water vapor adsorption isotherms. This is interpreted by considering the ratio of the amount of water vapor in the desiccator to the absorbable water vapor in the material. If the ratio is low, the humidity in the desiccator changes near the initial humidity range. Therefore, it is difficult that the characterization of humidity conditioning property of high performance humidity controlled material by B-value. In that case, the amount of water vapor adsorption is a good indicator of the humidity conditioning ability of high B-value materials.

抄録全体を表示

An uniform layer of apatite was formed on ceramic and metal substrates by placing them on CaO-SiO₂-based glass particles soaked in a simulated body fluid (SBF) at 36.5°C, and then soaking the substrates in an aqueous solution with ion concentration 1.5 times those of SBF at 36.5°C. During the first treatment, the induction period required for apatite nucleation on the surface was considerably affected by the kind of substrate. The induction period was shortened with increasing silicon content in substrates. For silicon single crystal, it was 0d. This indicates that silicon single crystal has the ability to induce apatite nucleation by itself. The uniform apatite layer was also formed on ceramics and metals with various shapes including cloths, fibers, and beads as well as rectangular substrates.

抄録全体を表示

Crystallization behavior of BaO-Ln₂O₃-TeO₂ glasses (Ln=La, Pr, Sm, Eu, Er) was examined to prepare transparent crystallized glasses consisting of lanthanide tellurite crystals (Te⁴⁺ crystalline compounds) with low phonon energies. Transparent crystallized glasses with fluorite-type Ln₂Te₆O₁₅ or Ln₂Te₅O₁₃ nanocrystals (-50nm sizes) were successfully prepared for the first time. The crystallization mechanism depends strongly on the lanthanide species: surface crystallization (-15μm) is dominant in La³⁺ and Pr³⁺ containing glasses, but homogeneous nucleation occurs easily in Sm³⁺, Eu³⁺ and Er³⁺ containing glasses, giving transparent bulk crystallized glasses. These transparent nano-crystallized glasses are applicable to fabrication of optical amplified waveguides or Bragg grating fibers.

抄録全体を表示

Al₂O₃-coated graphite powder was prepared using ethyl acetoacetate aluminium diisopropoxide, aluminium tri-sec-butoxide and aluminium hydroxide lactate according to the sol-gel method. The effect of Al₂O₃ raw materials on fluidity of the Al₂O₃-coated graphite powder slurry was studied. The apparent viscosity of the Al₂O₃-coated graphite powder slurry depended on the selected Al₂O₃ raw material. The apparent viscosity of the Al₂O₃-coated graphite powder slurry prepared using aluminium hydroxide lactate was lower than that of other Al₂O₃-coated graphite powder slurries.

抄録全体を表示

Crystalline slab optical waveguides of a calcium aluminosilicate (Ca₂Al₂SiO₇) were prepared by surface crystallization of a glass with close composition, upon heat treatment after an ultrasonic surface treatment (UST). Singlemode and multimode waveguides were obtained, by controlling the depth of the waveguides with both varying heat treatment temperature and time. The refractive index and optical propagation loss of the slab waveguides was also characterized.

抄録全体を表示

Silver ion, as an antibacterial component, was introduced on the surface of glass lining layers by an ion exchange treatment and the antibacterial activity was examined. Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were selected as microorganisms. The antibacterial activity was examined by two kinds of cover-coat glass (A and B). 100% of death rate was obtained except the case of Staphyliococcus aureus on glass A. Possibility of improvement on antibacterial activity was also shown by adding KCl or CeO₂ with mill additives because of an increasing the content of silver ion.

抄録全体を表示

Ceramic materials/nanomaterials have received considerable interests and attention in materials science due to their potential applications such as to electronics, optics, catalysis, and magnetic storage. From the viewpoint of applications, it is very important to process ceramic materials with well-defined shapes, sizes, and form. However, most ceramic materials processing methods such as solid state reactions, CVD, MOCVD, and PVD involved using higher temperatures, or toxic organometallic precursors, or complicated reaction and post-treatment systems. Exploration of novel, convenient, lower temperature, and environmentally friendly solution processing routes for synthesis of advanced ceramic materials with desired shapes and sizes has been challenged in materials science. This review focuses on the latest development of hydrothermal process, its integration with other activation methods such as electrochemistry, microwave, and its counterpart solvothermal process for fabrication of ceramic thin films, nanoparticles, and single crystals. Especially, as a new emerging process and one complement for conventional hydrothermal process, solvothermal process has proved to play a significant role in synthesis of advanced non-oxide ceramic materials by using reactions in non-aqueous solutions, which will be an exciting and promising field for preparation of ceramic materials. Shapes, sizes, and phases of the synthesized ceramics are expected to be well controlled by employing different solution processes, which will play a key role in tailoring the properties of ceramic materials. These new innovations in hydrothermal/solvothermal processing may find wide applications in rational design of advanced ceramic materials in future.

抄録全体を表示

Piezoelectric thin films are attractive for applications in MicroElectroMechanical Systems (MEMS) due to the combination of high energy density and low power requirements relative to other on-chip actuation mechanisms. As such, they can be utilized for applications as diverse as the pumping systems in miniature analytical instrumentation, high sensitivity accelerometers and hydrophones, miniature motors, and high frequency biomedical ultrasound, for example. Critical in all of these applications is the magnitude of the electromechanical response that can be generated. This paper will focus on the factors which affect the measured piezoelectric response of ferroelectric thin films. Particular emphasis will be placed on the effects of substrate clamping, clamping of the extrinsic contributions to the properties, and the role of preferred polarization directions in increasing the long-term reliability of ferroelectric films for piezoelectric applications.

抄録全体を表示