In order to establish a sustainable society, with practical material recycling, it is appropriate to focus on a range of guiding ``Earth principles,'' including the character and application of hydrothermal processes. In this paper, it is demonstrated how information obtained from the study of fundamental Earth principles can be used to inspire the development of new methods for material recycling, such as the following: 1) Hydrothermal hot-pressing processes, simulating the formation of sedimentary rock sequences, can be used for the solidification of toxic and hazardous materials. 2) Organic materials could be formed from CO₂ under hydrothermal conditions (using Fe and Ni metals, and low valence Fe oxides), at temperature and pressure conditions consistent with a subduction (tectonic) setting, such as (under Japan) where the Pacific Plate sinks beneath the (Eurasian) continental plate. 3) Diamond-structured carbon may be formed from toxic chlorinated hydrocarbon, in very high pressure regions of the Earth, and at high alkaline hydrothermal conditions, where magma formation may occur. 4) High temperature dry steam in rock fractures (at near critical conditions -i.e. below saturated vapor pressure, but relatively high pressure) is not only a source/carrier of noble metals, including gold, silver and copper, but also ceramic materials, silica and alumina. Its laboratory simulation may also be a guide for the formation of thin layer silicate ceramics on metal plates (e.g. SUS-304 nickel alloy). 5) To design an underground boiler in hot dry rock, non-equilibrium dissolution and deposition hydrothermal processes may be studied using a tube reactor, which simulates fluid flow and temperature gradients in fractured hot rock.

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Two key technologies were reviewed to propose effective approaches to functional glasses. One is combinatorial glass synthesis system. The combinatorial glass synthesis system consists of automatic batch preparation apparatus and two types of automatic apparatuses for melting of glass batches in crucibles. The combinatorial system was effective to search new glass forming systems and to speed up preparation of glass samples. The system was useful for the developments of bulk functional glasses based on doping of ions or compounds. The other is a new technique based on anodization of aluminum. The anodic oxidation of sputtered aluminum film on glass surfaces was applied to preparation of alumina nanostructures possessing nanopore arrays on glass surfaces. Oxides or metallic compounds could be introduced into nanopores using sol-gel technique or electro deposition technique. The introduction of TiO₂ by sol-gel process yielded high performance photo catalysis showing decomposition rate of acetaldehyde higher by about 13 times than that of P-25 commercial high performance TiO₂ powder catalysis. The impregnation of Ni metal into nanopores by electro deposition gave high density magnetic rod array of about 600G/inch², suggesting that the process would be applicable to the development of high density magnetic recording media. The new process based on anodic oxidation of sputtered aluminum was very effective to develop functional nanostructure layers on glass surfaces.

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The half-wave potentials of the reduction of Fe³⁺ in 16M₂O (M: Li, Na, K and Cs)·10M′O (M′: Mg, Ca, Sr and Ba)·74SiO₂ glass melts were examined by differential pulse voltammetry. In all melts, the half-wave potential shifted to the positive side with increasing temperature. The equilibrium of Fe³⁺/Fe²⁺ moved toward the reduced side with increasing temperature. The replacement of Li⁺ ions by larger alkali ions resulted in a positive shift of the half-wave potentials. On the other hand, the smaller the ionic radius of the alkaline-earth metal ion, the larger the half-wave potential. The Fe³⁺/Fe²⁺ equilibrium was mainly affected by the stability of the Fe³⁺-complex and the basicity of the melts. Variations in the kinds of alkali and alkaline-earth metal ions influenced the stability of the complex and the basicity of the melts, respectively. The half-wave potential moved toward the positive side (45mV at 1473K) when the atmosphere over the melts was changed from pure oxygen gas to air; thus, the reversibility of Pt: O₂ reference electrode was confirmed.

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Solid solutions of BaLaIn₂O_5.5 and BaLaInMO_5.5 that formed by partial replacement of In by Sc and Ga have a cubic perovskite structure. The Sc³⁺- and Ga³⁺-doped compounds, which had almost the same electrical conductivities, exhibited lower conductivities than the parent compound BaLaIn₂O_5.5 in the temperature range from 573 to 1273K. The Ga compound showed a transference number, t_i, of unity at both high and low oxygen partial pressures in the temperature range from 973 to 1273K. As for the Sc compound kept at 973-1273K, a t_i of nearly unity was observed at low oxygen partial pressure, while the t_i was slightly lower than unity at high oxygen partial pressures at higher temperatures. The In compound had a t_i of almost unity at high oxygen partial pressure, whereas the number decreased to a value less than 0.9 at low partial pressures of oxygen. The stepwise increase in the Sc content from 0.1 to 1.0 in BaLaIn_2-xSc_xO_5.5 caused a monotonic decrease in conductivity. The decrease in conductivity and the increase in activation energy caused by Sc³⁺ and Ga³⁺ doping were ascribed to the partial ordering of originally disordered oxygen vacancies and a decrease in the size of the triangle formed by two A-site cations and one B-site cation, through which the oxide ion proceeds, respectively.

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A new joining process assisted by centrifugal acceleration is proposed. The process requires no pressurizing media, and enables diffusion bonding of parts with complex shapes, as demonstrated in this paper. As an additional merit, contamination from media can be basically avoided. These features derive from an unique pressing method that uses high centrifugal force of up to -90km/s², enhancing the joining strength of interfaces. Trial results indicate a tensile strength for Al₂O₃/Al/stainless steel joints equivalent to that of conventional diffusion bonded joints and double the adhesion strength of Cu thick film on quartz glass as compared to conventional screen printing.

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Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e. bioactivity. The essential prerequisite for an artificial material to bond to bone is the formation of an apatite layer on its surface when implanted in a bony defect. This apatite layer can be, for example, formed in a simulated body fluid (Kokubo solution) with ion concentrations similar to those of human extracellular fluid. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with γ-methacryloxypropyltrimethoxysilane (MPS) and calcium chlorides. In this study, the effects of the kinds of calcium salts on apatite-forming ability were examined by exposure to Kokubo solution. PMMA powder (molecular weight of 100000 and 14μm in average particle size) was mixed with 20mass% of calcium salts consisting of calcium chloride (CaCl₂), calcium acetate (Ca(CH₃COO)₂), calcium hydroxide (Ca(OH)₂), calcium lactate (Ca(CH₃CHOHCOO)₂), calcium benzonate (Ca(C₆H₅COO)₂) and calcium methacrylate (Ca(CH₂=C(CH₃)COO)₂), while 20mass% of MPS was added in the MMA liquid. The appropriate setting time was obtained by the usage of calcium acetate or calcium lactate, although the modification with MPS and calcium salts leads to an elongation of the setting time of the cement. Apatite formation could be detected after soaking in Kokubo solution for 1d when the cements were modified with calcium chloride, calcium acetate, or calcium methacrylate. Apatite formation could be observed on the modified cement with calcium hydroxide after 7d of soaking in Kokubo solution. The higher solubility of calcium salts allows for a higher rate of apatite formation in Kokubo solution. Furthermore, changes in pH after exposure of the cement are related to the apatite-forming ability, because the addition of calcium hydroxide also gives the cement the ability of apatite formation, even if the cement releases a small amount of calcium ions into the surrounding fluid. Smaller dissolution of calcium salts results in less decrease in compressive strength after exposure to a body environment. The release of calcium ions, followed by changes in pH, must be controlled to achieve a successful design of bioactive PMMA bone cement by modification with MPS and calcium salts.

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The catalytic effect of chemically modified metal alkoxides on the hydrolysis and condensation reactions of methylethoxysilanes and phenylethoxysilanes was investigated by ²⁹Si nuclear magnetic resonance spectroscopy and gel permeation chromatography. Metal alkoxides such as Al(O-sec-C₄H₉)₃, Ti(O-iso-C₃H₇)₄ and Nb(OC₂H₅)₅ modified with ethyl acetoacetate accelerated not only the condensation reactions but also the hydrolysis reactions of methyl- and phenyl-alkoxysilanes. The catalytic effect of these metal alkoxides was found to be different between methyl- and phenyl-alkoxysilanes. The catalytic activity increases in the order of Nb<Al<Ti alkoxides in the case of methyl-ethoxysilanes, whereas in the case of phenyl-ethoxysilanes it increases in the order of Nb<Ti<Al alkoxides. The difference in catalytic activity was discussed on the basis of the partial charge of M in metal alkoxide, the difference in electronegativity between M and Si and the difference between the coordination number and valence of M.

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Each p- and n-type powder of Si_0.8Ge_0.2 for thermoelectric elements was prepared by gas atomization of the corresponding melts. Then, the relationship between the characteristics of Si-Ge powders and their sinterability was studied. Particular emphasis was placed upon understanding the effect of ball-milling on the sinterability of the as-prepared powders. The composition of the as-prepared powder was different from the batch composition due to melting and evaporation of the dopant above 1550K. Ball-milling made the particle size of the as-prepared powders small, presumably together with introducing distortion to the crystal lattice. Densification of as-prepared powders was abruptly promoted above 1500K by a pulse-current sintering; however, this densification temperature of the powders after ball-milling was lowered by approximately 100K. The grain size and elemental inhomogeneity of the dense body after sintering were also reduced by ball-milling process.

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Nd solubility is evaluated in SrS- and BaS-Ga₂S₃ glasses using a series of absorption measurements. The result reveals that Nd up to 2-3mol% can be dissolved in these glasses. Rare-earth solubility in sulfide glasses is discussed in terms of the ionicity of chemical bonds. Raman spectroscopy suggests that Nd ions play a role of modifiers to the networks of GaS₄ tetrahedra in a similar manner of the alkaline-earth ions. The limitation of Nd solubility is related to glass-forming ability during the cooling process of alkaline-earth gallium sulfide melts.

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Porous Si₃N₄ ceramics were fabricated by normal sintering of low-purity Si₃N₄ powder and 5mass%Y₂O₃ as sintering additive. Porous Si₃N₄ ceramics with >40% porosity were obtained at sintering temperatures in the range 1700-1800°C. The microstructural development, pore morphology, and mechanical properties of these porous ceramics were investigated. The strength of the porous Si₃N₄ ceramics was high for samples sintered at 1800°C. The high flexural strength was contributed by fine elongated β-Si₃N₄ grains and some large elongated grain. This paper outlines the use of low purity powder for the economical fabrication of porous Si₃N₄ ceramics.

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The in vitro bioactivity, in terms of apatite-forming ability, of calcium silicate glasses containing 10mol% fluoride ions in the NaF-CaO-SiO₂ system was examined by soaking in Kokubo's simulated body fluid (SBF) at 36.5°C for 7d. The surface structure of the glasses was examined by thin-film X-ray diffraction (TF-XRD) and Fourier transform infrared reflection spectroscopy (FT-IR) in order to confirm the apatite deposition. The structure of the calcium silicate glasses was examined by ²⁹Si magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Three calcium silicate glasses containing 10mol% fluoride ions had different apatite-forming abilities. In the case of CaO/SiO₂=1, the apatite-forming ability of 10NaF·45CaO·45SiO₂ was lower than that of 50CaO·50SiO₂. This indicated that the addition of fluoride ions suppressed the apatite-forming ability, irrespective of the structural similarity of the silicate network based on the ratio of CaO/SiO₂ between the glasses.

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Effects of superlattice ordering and ceramic microstructure on the microwave dielectric properties of complex perovskite-type oxide Ba(Zn_1/3Ta_2/3)O₃ polycrystalline ceramics are studied. The superlattice ordering ratio was controlled by the sintering time at 1350°C. The superlattice ordering of Zn and Ta ions on B sites increased with increasing sintering time until 80h and reached a saturated value of 80%. However, the microwave Q factor of the samples showed a large variation of the same magnitude of the superlattice ordering ratio. This result suggests that the microwave Q factor of Ba(Zn_1/3Ta_2/3)O₃ ceramics depends not only on the superlattice ordering but also on the ceramic microstructure.

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The residual stress and strength characteristics of partial stabilized zirconia induced by shot peening with soft aluminium particles were evaluated by the X-ray stress measurement method. It was confirmed that a compressive residual stresses ranging from 250 to 340MPa were induced on to the plates of partially stabilized zirconia by the soft shot peening treatment. It was also confirmed that the modilation of surface defects and surface roughness after shot peening with soft aluminium particles was insignificant. Furthermore, the bending strength and the Weibull modulus of the shot peened partially stabilized zirconia was improved by compressive residual stresses.

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The purpose of this paper is to interpret the enhancement of T_c and J_c by the replacement of cations and changing the excess oxygen content for a Bi-2223 system by the replacement of Bi and Ca by Pb and Y, respectively, to form Bi_1.76Pb_0.44Sr_1.86Ca_2.08-xY_xCu_2.86O_y. The relation between lattice constant, average valences of Bi+Pb and Cu, excess oxygen content and superconducting characteristics has been studied as a function of Y substitution content, and anneal treatment. The highest T_c was obtained at x=0.05. Oxygen doped and overdoped regions and highest T_c(zero), which were obtained upon adjusting the optimum excess oxygen content, existed at each Y content, x=0-0.30. Furthermore, in order to elucidate the effect of metal substitution and oxygen content on J_c of a Bi-2223 system, films were prepared, which have the same metal composition of bulk, on a MgO(100) single crystal substrate by the spin coating-pyrolysis method. The measurements of J_c and T_c were carried out on highly oriented films of Bi-2223 phase with changing Y content. The highest T_c(zero) was obtained at Y content, x=0.05. T_c(zero) decreased with increasing x in the region of x>0.05. On the other hand, the highest J_c was obtained at x=0.10. The Y content for optimum J_c was different from that for optimum T_c. J_c increased with increasing excess oxygen content, Δy, and after that increase or constant in the oxygen overdoped region. Consequently, the metal and oxygen contents were very important for obtaining the highest T_c and J_c.

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Alumina ceramics were densified at sintering temperatures of 1250-1550°C by pulse electric current sintering (PECS) using transition alumina powder of mixed phases of γ- and χ-alumina prepared from polyhydroxoaluminum (PHA) gel. The starting high-purity powder (HP) was obtained by grinding the alumina powder with a planetary ball mill using a high-purity alumina (purity: 99.9%) pot and balls to prevent contamination derived from the abrasion powder worn during the milling. The HP thus obtained realized full densification at sintering temperatures 50-100°C lower than those of the corresponding lower-purity powder (LP), which was obtained by grinding with a planetary ball mill using a 93%-pure alumina pot and 99.9%-pure alumina balls. The HP could also provide alumina ceramics with higher bending strengths (approximately 860MPa) than those obtained using LP.

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Stress analysis was carried out on two kinds of friction tests (pin-on-disk test and block-on-ring test). The test procedure of pin-on-disk test is standardized as JIS R 1613. If we follow the procedure as stated in this document, a tensile stress from several hundred MPa to 1GPa is generated on the test surface. This value equals the tensile strength of typical engineering ceramics, meaning that this test condition corresponds to severe wear conditions with possibility of mechanical fracture on the surface. In the block-on-ring test, the surface tensile stress is one-digit smaller compared to that of the pin-on-disk test, under the same testing force. It is thus assumed that the block-on-ring test can measure wear under mild conditions without the risk of mechanical fracture on the surface. It is important to use an appropriate friction test method that fits with the application of the investigated material, for properly discussing the friction property of ceramic materials.

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