Si₃N₄ ceramics were sintered at 1873-2023 K (1600-1750°C) with additives from the SiO₂-MgO-Y₂O₃ system. The degree of densification, α-β transformation, mass loss and microstructure were measured as a function of additives composition, sintering temperature, nitrogen gas pressure, and with/without packing powder. Specimen prepared from 3 mass% SiO₂, 3 mass% MgO, and 5 mass% Y₂O₃ as the sintering additive could be sintered to almost full density at relatively low temperature as 1923 K for 2 h under ambient pressure of nitrogen atmosphere without using packing powder. The α-β transformation was not completed at this condition. The mass loss was relatively high due to the evaporation of SiO₂ and MgO. However, the resulted materials have high bending strength as 980 MPa, with fracture toughness of 6.6 MPa•m^1/2, Vickers hardness of 18.4 GPa, and thermal conductivity of 34 Wm^-1K^-1.

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For the purpose of carbon dioxide (CO₂) capture at high temperatures, Toshiba developed a novel CO₂ absorbent, a lithium silicate (Li₄SiO₄). It shows an immediate CO₂ absorption and emission properties, which results in an obvious weight change of up to 36%. Since, in the case of Li₄SiO₄, CO₂ emission occurs at a considerably lower temperature than for a calcium oxide (CaO) absorbent, the reaction between Li₄SiO₄ and CO₂ is very reversible. The emission temperature in 101 kPa of pure CO₂ is ca. 800°C, whereas CaO absorbent requires a temperature of 950°C. Considering the practical use of this material as a CO₂ absorbent for power plants, a pellet-type absorbent is thought to be more realistic than a powder-type absorbent. Moreover, regarding the application to the system, the characterization of a reactor using Li₄SiO₄ pellets is required. This paper describes the removal efficiencies of a packed bed reactor using cylindrical pellets of Li₄SiO₄. In a gas flowing condition of 20 vol% CO₂, the reactor achieved 100% CO₂ removal at 500°C. Temperature dependence was also investigated. It is noteworthy that the reactor and gas stream were obviously heated during the CO₂ removal because of the exothermic reaction between the Li₄SiO₄ and CO₂. We believe that this phenomenon is one of the important findings to improve the energy penalty for CO₂ recovery.

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Biodegradable inorganic-organic composite hollow spheres, consisting of poly(L-lactic acid), calcium carbonate, β-tricalcium phosphate and siloxane, were prepared by an oil-in-water emulsion evaporation method to develop an injectable bone substitutes incorporated with cells. The spheres had an almost flat diameter of about 1.0 mm and an open channel of 500-600 μm in diameter on the shell. After soaking the spheres in a simulated body fluid, the silicon and calcium ion-species were gradually released from the spheres. Osteoblast-like cells, marrow stromal cells (MSCs) and osteoblasts migrated into the spheres through the open channel and attached to the inside surface of the sphere shell. The MSCs expressed a high level of alkaline phosphatase on the spheres. Some bone nodules formed on the spheres after the culture of osteoblasts.

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Heteropolyacid containing phosphosilicate glasses were prepared by the sol-gel technique and were studied in relation to their structural, thermal, and textural properties. These glasses are mechanically, thermally, chemically stable and have proton conductivity. It was found to be a suitable potential electrolyte for H₂/O₂ fuel cells. The average pore size of up to 3 nm was observed from a N₂ adsorption-desorption analysis. The electrical conductivity was measured under humidity and temperature conditions. The glasses showed the proton conductivity values in the order of 10^-3-10^-2 S cm^-1, especially, 9.8×10^-2 S cm^-1 at 90°C and 70% RH. The cell performance is mainly determined by the higher conductivity characteristics of the electrolyte. We have successfully achieved a high power density value of 17.2 mW/cm² using P₂O₅-SiO₂-PMA (7-89-4 mol%) glasses as an electrolyte and 0.1 mg/cm² of Pt/C loaded on the electrode at 30°C and RH 30%.

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Crystallographic properties such as polymorphs and crystal orientations of calcium carbonate formed in biological systems can be controlled by interactions between organic matrices and inorganic substances. We have attempted to reveal such control mechanisms, using a polymerized Langmuir-Blodgett film of 10,12-pentacosadiynoic acid (PDA) as an organic matrix with highly regulated molecular alignment. Only calcite crystals were precipitated on the polymerized PDA film, even though in presence of Mg²⁺ ions which were reported to enhance aragonite formation in previous works. The calcite precipitates were aligned on the PDA film with their a-axes in parallel to the polymerization direction. Calcite structure does not give a reasonable match over the molecular alignment of the PDA film along its a-axis. A concerted mechanism of geometric matching and stereochemical effect should determine the polymorphs and directions of calcium carbonate crystals on the organic matrices.

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Hydroxyapatite (HAp) materials with different morphology, size and crystallinity were prepared and were implanted into a male rat tibia. Each of the HAp materials showed a high biocompatiblity and osteoconductivity. The morphology and size of the implanted HAp affected the intrusion of bone marrow derived cells among HAp materials, and this cell intrusion was important for regulating the newly formed bone mass. High crystalline sintered HAp was stable and remained in its initial shape for long periods. However, low crystalline HAp was absorbed and disappeared during bone remodeling. This study indicates that choosing suitable HAp materials in morphology, size and crystallinity is important for a treatment plan (e.g. reconstruction or regeneration; large region or small region etc.) and for achieving a desired prognosis.

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The sintering behavior of 7.8 mol% Yttria-stabilized cubic stabilized zirconia (Y-CSZ) powders was investigated, with emphasis on the effect of Al₂O₃ addition at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact with 0.25 mass% Al₂O₃ enhanced the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact with Al₂O₃ was lower than that of powder compact without Al₂O₃. The diffusion mechanisms at the initial sintering stage were determined by the new analytical method applied to the CRH data. This analysis exhibited that the diffusion mechanism changed from grain boundary to volume diffusions (VD) by Al₂O₃ addition. It is therefore concluded that the Al₂O₃ addition enhances the densification rate because of decreasing the activation energy of VD at the initial sintering stage.

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Silica-hybridized hydroxyapatite powder was prepared from a calcium hydroxide and phosphoric acid together with a tetra-n-butyl orthosilicate as the silica source in order to apply it as a gas adsorbent. According to the X-ray diffraction patterns, all peaks were assigned to the hydroxyapatite. No secondary phases, such as calcium hydroxide and silicon oxides, were observed. Moreover, the transmission electron microscope observations indicated that the crystallite size hardly changed by increasing the silicon oxide content. However, the adsorption areas of nitrogen, water and benzene were remarkably dependent on the silicon oxide content. In this paper, in order to explain the change in the adsorption areas, the lattice structure of the silica-hybridized hydroxyapatite is discussed based on the results obtained by the ²⁹Si and ³¹P magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR).

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The dielectric properties vary significantly with the B-site cations in ABO₃ perovskite-type oxides. In this study, we tried to understand the difference in the dielectric properties between SrTiO₃ (STO, ε_r=290, Qf=3000 GHz) and SrZrO₃ (SZO, ε_r=30, Qf=13700 GHz) by measuring the dielectric spectroscopy of their solid solutions in a wide frequency range. The dielectric permittivity and the loss tangent (tan δ) of SrZr_xTi_1-xO₃ (STZ, 0.0≦x≦1.0) ceramics were evaluated up to a GHz region using the planer electrode method and ring resonator method. The four-parameter-semi-quantum (FPSQ) model was employed to analyze the Infrared-reflectivity (IR-reflectivity) data of the STZ ceramics. Both dielectric properties up to the GHz region and IR reflectivity in the THz region were incorporated in the analysis to accurately determine the optical phonon parameters. Ultra wide band dielectric spectra of the SZT ceramics and the STO single crystal were presented. The ionic polarization dominantly determined the dielectric permittivity of the SZT ceramics and the STO single crystal. High permittivity of STO was due to the Slater mode. The decrease of dielectric permittivity and the Q-factor (=1/tan δ) with an increasing Zr content (x) in STZ ceramics was attributed to the depression of the Slater mode. The effect of the optical phonon parameters on the permittivity and tan δ in the microwave region was simulated to generalize the results obtained for the STZ ceramics.

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Recently inorganic/organic composites, such as calcium carbonate and water-soluble organic polymer with fine and complex structures have been actively advancing. Therefore, it is necessary to develop a novel analytical method for these materials. In order to solve the problem, a comprehensive non-destructive methodology for the simultaneous quantitative analysis of the calcium carbonate crystal phases in their binary mixtures and organic polymers was developed, based on the use of a Raman microscope. In this method, relative error of aragonite was on a level of X-ray diffraction, while that of organic polymers was 30%.

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The dependence of fracture toughness estimated by indentation fracture technique on measuring method was studied using several Si₃N₄ samples with various microstructures. The crack length at the indentation load of 19.6 N was measured by optical microscopy and SEM and fracture toughness was calculated for each case. The consistency of results between the two methods was obtained within the accuracy of the data for any microstructure. It was revealed that in the case of silicon nitrides indented at low load, the IF technique was not so equipment sensitive, indicating that the accuracy of IF method by OM is not necessarily inferior to one by the SEM. It was considered that the IF method with optical microscopy would become useful test for fracture toughness if the testing procedure is properly controlled to minimize the source of the measuring error.

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The absorption and emission spectra of Ni-doped glasses and transparent glass-ceramics are discussed in relation to its coordination number. The results evidenced that the color changed drastically to deep pink from yellow for the lithium metasilicate crystal based transparent glass-ceramics and to blue from brown for the spinel crystal based transparent glass-ceramics after crystallization, respectively. The absorption spectra of lithium metasilicate and Spinel glasses suggest the existence of a tetrahedral Ni²⁺ ion and a trigonal bipyramid Ni²⁺ ion. On the contrary, tetrahedral Ni²⁺ ions in the lithium metasilicate transparent glass-ceramics and the octahedral Ni²⁺ ion in Spinel transparent glass-ceramics are dominant. The emission at around 580 nm was observed in Spinel transparent glass-ceramics under the excitation of 380 nm, however, a very weak or no emission was observed in the lithium metasilicate glass, lithium metasilicate transparent glass-ceramics and Spinel glass under the excitation of 430 nm. This emission might be due to a ¹T₁(D)→³A₂(F) transition after the excitation from ³A₂(F) to ³T₁(P) of the octahedral Ni²⁺ ions. In addition, only Spinel transparent glass-ceramics exhibits a broad NIR emission at around 1220 nm under the excitation of a 974 nm laser diode. This emission may be due to ³T₂(F)→³A₂(F) transition. It is considered that the tetrahedral Ni²⁺ ion is located between the chains in the lithium metasilicate crystal.

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Crystal structure of a layered perovskite, KCa₂Nb₃O₁₀, was determined by the Rietveld refinement method for a powder neutron diffraction pattern. The compound crystallizes a monoclinic system with a space group P2₁/m (No. 11) and lattice parameters of a=0.77418(6) nm, b=0.77073(6) nm, c=1.4859(1) nm, β=97.51(1)°.

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