Fourier transform infrared (FT-IR) transmission spectra of six commercially available α-alumina powders produced by two different production methods, i.e., in-situ chemical vapor deposition and hydrolysis of aluminum alkoxide are measured in the 400-1000cm^-1 of infrared wavenumber region. Distinctive peaks are detected at 473, 626 and 703cm^-1 wavenumbers in the spectra of the powders produced by in-situ chemical vapor deposition. Scanning electron microscope (SEM) observation of the powders shows a significant shape difference between the powders, where the powders produced by in-situ chemical vapor deposition seem to have more regular and nearer to spherical shape than the others. The differences in spectra are explained by the generalized theory of average dielectric constant considering influence of the spherical shape of the powder particles on the FT-IR transmission spectra.

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The stability during sintering of SiO₂, Y₂O₃ and Al₂O₃, well known as sintering aids of Si₃N₄ ceramics, was examined from both thermodynamical and experimental aspects. Both the heat treatment of SiO₂-Y₂O₃-Al₂O₃ glass and the sintering of Si₃N₄ ceramics were carried out. In the thermodynamical considerations, the stability of the glass composition was discussed on the basis of known volatility diagrams for SiO₂, Al₂O₃ and MgO and the thermodynamic data of Y₂O₃ available in the literature. The results suggest that Y₂O₃ is the most stable among all materials in the sintering temperature range usually selected for Si₃N₄ ceramics. SiO₂-Y₂O₃-Al₂O₃ (equi-mass%) glass was heat-treated in a BN sagger at 2023K for 2h in N₂ gas of 0.1 MPa. Si₃N₄ with addition of 5 mass% Y₂O₃ and 3 mass% Al₂O₃ was sintered in the BN sagger at 2023K for 0 to 16h in N₂ gas of 0.1MPa. The elemental contents in the glass and ceramics before and after heat treatment and sintering were determined by chemical analysis. As a result, it was found that only SiO₂ in the glass and SiO₂ and Si₃N₄ in the Si₃N₄ ceramics vaporized. On the other hand, the Y₂O₃ and Al₂O₃ contents in both the glass and Si₃N₄ ceramics did not decrease under the selected temperature.

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Ultrafine Mn-Zn ferrite powders were synthesized under mild hydrothermal conditions by precipitation from metal nitrates with an aqueous ammonia. R value (alkalinity) was introduced to adjust the amount of added ammonia. A method of controlling the desired compositions and crystallite sizes of synthesized powders was proposed in this paper. In addition, the effect of R value and hydrothermal time on powder characterization, such as the Mn/Zn ratio in spinel structure of synthesized powders, variation of X-ray diffraction angle of spinel ferrites, crystallite size and the loss ratio of Zn²⁺ for different starting suspensions during hydrothermal process, was also investigated. Powders upon hydrothermal treatment exhibited superior sinterability as compared to powders which were not subjected to hydrothermal treatment. High densities, 99.4-99.8% of theoretical densities, were obtained upon sintering green ferrite powders at relatively low temperature (900-950°C) in N₂ atmosphere without any sintering aids.

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Indium tin oxide films were deposited on acrylics by reactive magnetron sputtering at a low substrate temperature for their application to pilot windows. The effects of oxygen flow on the microstructure and chemical composition of films were explored. The deposition rate of ITO films invariably increased with the cathode current and decreased with the bias voltage. In addition, it initially decreased significantly with increasing oxygen flow rate but this decrease slowed down as the oxygen flow rate exceeded a certain critical value. The composition of ITO films is considerably different from the stoichiometric composition. However the O/(In+Sn) ratio approached the stoichiometric composition with the increase in the oxygen flow rate. No obvious crystalline phases were detected in ITO films at an oxygen flow rate of 1sccm. However crystalline phases were observed as the oxygen flow rate increased. The lattice parameters of ITO films increased with the oxygen flow rate and were greater than that of In₂O₃. This was attributed to the decrease in oxygen vacancies at high flow rates. Low-energy (110) planes grow preferentially in ITO films with no bias voltage. Non-close-packed preferential planes of (111) predominated, however, as the bias voltage was increased.

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Relationships among in-plane residual stress and some dielectric properties (remanent polarization, coercive field, dielectric permittivity, etc.) were investigated on ferroelectric thin films. Epitaxial PbTiO₃ thin films were deposited on Pt/(100) SrTiO₃ substrate by MOCVD. Residual stresses of the films were determined by a modified sin²ψ method. The external stress in this study could be varied from +2.0GPa up to +6.0GPa. We first observed the change of the dielectric properties together with the tensile stress application in actual experiments; decrease of the remanent polarization from 11μC·cm^-2 down to 3μC·cm^-2 and of the coercive field from 115kV·cm^-1 down to 95kV·cm^-1. The Curie temperature of the film was decreased from 450°C to 437°C with increasing the residual stress, while the dielectric permittivity at room temperature was measured to be approximately 210, irrespectively of the residual stress. Further, the tensile stress caused deformation of PbTiO₃ crystal lattice, which was described as the decrease of the c/a ratio. We conclude that the residual stress varied the dielectric properties by deforming the crystal lattice.

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Various cubic Cs-leucite compounds with the space group Ia3d were synthesized by a solid-state reaction method, and thermal expansion properties for the synthetic powders were studied in the temperature range from 123 to 1273K using high-temperature X-ray diffraction (HTXRD) and low-temperature X-ray diffraction (LTXRD). The thermal expansion rates of both the synthetic cubic CsB_0.2Al_0.8Si₂O₆ and cubic Cs₂MSi₅O₁₂ (M=Cd, Mg, Ni, Zn) were lower than that of the synthetic cubic CsMSi₂O₆ (M=Al, Fe), and the thermal expansion rate of the synthetic cubic Cs_0.9Al_0.9Si_2.1O₆ was lower than that of CsAlSi₂O₆. Consequently, decreasing the average ionic radius of cations in the M site, or increasing the Si/M molar ratio of the (Si, M)O₄ tetrahedra was found to be effective for decreasing the thermal expansion rate. Furthermore, it was suggested that the increase of the space for Cs sites in the unit cell decreases the thermal expansion rate of the cubic Cs-leucite compounds with the space group Ia3d.

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New carbon thin films were prepared using radio frequency magnetron sputtering of a woodceramic disk in argon plasma and their mechanical and electrical properties were measured. A film series was deposited varying the substrate temperature between 50 and 500°C. The film's mechanical and electrical properties depended on the substrate temperature. Films deposited at 50°C had a density of 1.9-2.2g/cm³, comparable to that of typical diamond-like carbon films, but the Vickers hardness of the film experienced a value as low as ≈1/50. Adhesion was between 120 and 200MPa for substrate temperatures below 300°C and decreases rapidly for temperatures higher than 400°C. Films deposited below 300°C were insulative, i.e., ρ>10¹⁰Ω·cm. For deposition below 100°C, the films showed good frequency characteristics terms of both relative permittivity and loss coefficient, which were almost constant over the range between 1kHz and 5MHz.

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Solid solutions of (1-X) Ba_3.75Y_0.83Nb₁₀O₃₀-XBa_3.75Sm_0.83Nb₁₀O₃₀ were synthesized and examined with regard to their ferroelectric properties. No abnormal changes of lattice parameters were found over the investigated range of solid solution. Hysteresis curve measurement indicated that the polarization property could be improved by employing different rare earth cations. The coercive field (E_c) decreased as the composition approached Ba_3.75Sm_0.83Nb₁₀O₃₀. The remanent polarization (P_r) of the solid solution was higher than those of end members, and maximum values were observed at X=0.4-0.6. Variation of Curie temperature and cell distortion showed the same tendency as that of E_c. Atomic displacement calculated from refined structural parameters agreed with the abnormal change of P_r. The contribution of larger macroscopic polarization for X=0.4-0.6 region could be apparently attributed to the larger displacement of Nb⁵⁺ ions.

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When a powder mixture of K₂SO₄, Al₂(SO₄)₃, and SiO₂ is heated at 1000°C in an alumina crucible covered with a lid, a solid phase remains at the bottom of the crucible. Spherical leucite crystals are obtained by treating this solid phase with hot HCl. The effects of the mixing ratio of the raw materials, heating temperature, and duration of heating at the fixed temperature on the formation of spherical leucite crystals obtained by the above procedure are investigated. When the powder mixture of K₂SO₄:Al₂(SO₄)₃:SiO₂=5.9:1.0:1.1 (mol%) is heated at 1000°C for 3h, spherical leucite crystals of diameter 70-110μm (average diameter: 34μm) form. Upon increasing the duration of heating at 1000°C, the average diameter of the spherical leucite crystals increases, reaching 115μm after 12h.

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Preparation of highly proton-conductive and thermoplastic composites was successfully pursued from H₃PO₄-doped silica gel and organic polymers with sulfo groups. The sulfo groups and polystyrene blocks in the organic polymers were found to improve the proton conductivity and molding characteristics of the resultant composite, respectively. The composite composed of H₃PO₄-doped silica gel with a molar ratio=0.5 of H₃PO₄/SiO₂ in 80mass% and sulfonated styrene-isoprene-styrene (SIS-SO₃H) block copolymer in 20 mass% showed a high electrical conductivity of 10^-4S·cm^-1 at 25°C in dry N₂ atmosphere and good molding characteristics. The temperature dependence of the electrical conductivity of the composite was of the Vogel-Tamman-Fulcher type, indicating that proton transferred through a liquid-like phase present in the composites consisting of silica gel and organic polymer. The elastic modulus of the composite was larger by one to two orders of magnitude than that of the SIS-SO₃H elastomer. The thermoplastically deforming temperature of the composite was around 130°C, which was higher by 50°C than that of the SIS elastomer itself. The capacitance of a totally solid state electric double-layer capacitor, which was fabricated using the composite as a solid electrolyte, was comparable to those of the conventional capacitors with liquid electrolytes.

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The suppressing effect of Zn²⁺ and Co²⁺ ions on stress corrosion of a glass surface was investigated in 10^-3mol/dm³ Zn(NO₃)₂ and Co(NO₃)₂ aqueous solutions at various pHs. The mechanism behind this effect was clarified by measuring the stress corrosion limit (K_scc), the pH of the solution, concentration of ions, and by surface analysis of glass using X-ray Photoelectron Spectroscopy (XPS). The suppression of stress corrosion in Zn(NO₃)₂ solution increases to some extent with increase in the amount of Zn²⁺ reacted with glass surface, which suggests that the amount of zinc hydroxide precipitated on the glass surface is associated with the extent of corrosion. However, in Co(NO₃)₂ solution a suppressing effect of corrosion was not as large as that in Zn(NO₃)₂ solution. Since XPS results showed that the amounts of cobalt hydroxide precipitated on the glass surface was almost the same as that of zinc hydroxide, the difference of the suppression of stress corrosion (K_scc) may be caused by the difference of population of Si-O^- site existing in surface of the glass due to a higher pH used for the precipitation of Co²⁺ as compared with Zn²⁺ precipitation.

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The temperature distribution in large sized ceramic substrates at 1600°C sintered by vertical type furnace was simulated by using a model of heat conduction and radiation heat transfer. The temperature distribution at the center of each ceramic substrate is larger than that in each ceramic substrate at steady state in the case of 3 substrates were fired. The temperature distribution becomes narrow by using a high thermal conductivity material setter or inserting heat insulating material between the bottom setter and the furnace floor. The temperature distribution in each ceramic substrate is closely related to the distance between the surface of the ceramic substrate and the bottom of the upper setter.

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The concentration of sintering aids, Y₂O₃ and Al₂O₃, appearing on the fracture surface of sintered Si₃N₄ on which either dynamic or cyclic stress is applied, was determined by X-ray Photoelectron Spectroscopy (XPS). The concentration ratio, (Y+Al)/Si, can be used as a correlational index that is useful to study the fracture behavior. According to our results, there is a direct correlation between larger (Y+Al)/Si concentration ratios on the fracture surface and the tendency of sintered Si₃N₄ to suffer fracture by cyclic fatigue, namely, intercrystalline cracking is dominant when fracture by cyclic fatigue occurs.

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The effect of forming pressure on the internal structure and the sintering behavior of green compacts made from ceramic granules was investigated with the aim of describing those by a constitutive model. Alumina granules were compacted by cold isostatic pressing (CIP) at three different pressures of 98, 196 and 294MPa. Examined were the initial pore structure, shrinkage and densification of the granular compacts during sintering at four temperatures in the range between 1100 and 1400°C. Three distinct regions in the microstructure with fractured, unfractured granules and crack-like cavities were identified as the three peaks observed in the pore size distribution. The ratio of the respective pore volumes in these three regions was independent of the forming pressure within the range under examination, while the pore size decreased as the pressure increased. The sintering rate of the compacts formed at 98MPa was similar to that at higher pressures, because the dominant process responsible for the densification during sintering is the shrinkage of small pores in a dense region. However, the final density after sintering of the compacts formed at 98MPa was somewhat lower than that of the compacts formed at higher pressures. This stems from large crack-like pores around the unfractured granules remained even at 1400°C. The shrinkage behavior was modelled with a set of constitutive equations by taking account of the pore size distribution of granular compacts. The sintering behavior related to the forming pressure could be well described by the present model.

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Spectroscopic measurement has been carried out for identification of chemical species in inductively coupled Ar plasma. In addition, the excitation temperature has been calculated for each condition by the Boltzmann plot, using relative intensities of spectra for neutral Ar. Only ionized Ar⁺ lines were observed at 133Pa in the low pressure range, while only neutral Ar lines were observed at 8.0×10³Pa in high pressure range. At 667Pa and 8.0×10³Pa in high pressure range, the plasma is reached an almost local thermodynamic equilibrium (LTE) and excitation temperatures for these pressure conditions could be calculated. The results indicated temperatures were about 7800K and 6400K, respectively.

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The influences of various types of inorganic salts on the fluidity of CaCO₃ suspensions with comb-type macromolecules containing polyethyleneoxide graft-chains have been investigated. The fluidity of suspension with polymer and the amounts of polymer adsorbed on CaCO₃ are remarkably decreased by the addition of inorganic electrolytes. The decrease for fluidity of suspension is related to the reduction of such adsorbed amounts of polymer. This may be due to the change of polymer conformation by addition of inorganic salts. The fluidity of suspension with K₂CO₃ or K₂HPO₄ is lower than that of suspension with KCl or K₂SO₄. Inorganic electrolytes seem to be in a following order for the reduction effect of fluidity of suspension with polymer; K₂HPO₄≅K₂CO₃>K₂SO₄>KCl. This may be related to the affinity of anions for water. The fluidity of suspension with polymer and K₂CO₃ is improved by the addition of CaO. This is based on the removal of CO₃^2- by the reaction of CaO and CO₃^2-.

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Durability of 3-D woven Si-Ti-C-O fiber/Si-Ti-C-O matrix composites with and without glass sealant was evaluated by an arc jet facility (arc wind tunnel). The surface temperature of the composite during arc jet test was far lower than the temperature predicted by a numerical calculation. This was due to high temperature gas flow through large pores arising from the 3-D fabric configuration. Rapid temperature rise was observed around large pores in the composite without glass sealant under high heat flux condition. On the other hand, the phenomenon was not observed in the glass sealed composite. Thus, the glass sealant was effective for the stable aerodynamic heating on the composite surface. The surface of glass sealed composite was uniformly covered by a silica layer formed by crystallization of the glass sealant material during arc jet test. The silica layer might prevent the composite surface from oxidation. Surface recession was hardly recognized bellow 1450°C at surface temperature and above 5kPa in oxygen partial pressure at the stagnation point, because passive oxidation was dominant under the heating condition. Passive/active oxidation boundary of the composite agreed with the Balat's theory for silicon carbide under the present experimental condition. Mass loss was observed just above 1500°C, which was due to decomposition of Si-Ti-C-O fiber and matrix.

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The effect of metal oxide additives; Al₂O₃, MgO and SiO₂ to ZnO ceramics was investigated from the point of view of both the electrical resistivity and the sintering property. Doping of Al₂O₃ to ZnO ceramics with 5.0-20.0mol% caused on increase of the electrical resistivity with increasing the concentration of Al₂O₃, but also caused deterioration of density after sintering. Temperature coefficient of resistivity of ZnO ceramics doped with over 5.0mol% MgO changed from a negative to a positive value. Sintering density of ZnO ceramics was improved by small doping of SiO₂. ZnO ceramics including above 3 kinds of additives: Al₂O₃, MgO and SiO₂ with suitable controlled concentration respectively, showed good electrical performance (resistivity, linearity, temperature coefficient) as a linear resistor. The microstructure of this ZnO ceramics were mainly formed by ZnO, Zn-Al-O complex oxides and pores.

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Effect of impurities in kaolin materials on the sintering behavior of the cordierite ceramics was studied. Three kinds of kaolins were used, that is, Georgia kaolin, Chinese kaolin and New Zealand kaolin. Georgia kaolin without α-quartz and cristobalite only gave a dense sintered body. α-quartz contained in both Chinese kaolin and New Zealand kaolin would retard the densification of sintered bodies. In the case of Chinese kaolin, chemical components except for MgO, Al₂O₃ and SiO₂ in mixture accelerated the generation of liquid phase at above 1300°C and apparent porosity in sintered body decreased by liquid phase sintering. In the case of New Zealand kaolin, cristobalite and α-cordierite crystallized at higher temperature than that of Georgia kaolin and Chinese kaolin.

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Control of the microstructure and pore characteristics of porous hydroxyapatite was examined. Porous hydroxyapatites were prepared with using different starting hydroxyapatite powders and sintering at various temperatures by pressureless-sintering method. The overall microstructure porosity characteristics, such as the fraction of open porosity and the pore size distribution, of porous hydroxy-apatites were evaluated. The pore volume and size distribution greatly depended on sintering temperature and the morphology of the starting hydroxyapatite powders. The fraction of open porosity of whisker hydroxyapatite powder sintered at 900 and 1000°C was 100 and 96%, respectively. The pore diameter and pore volume of porous hydroxyapatites prepared from whisker-like hydroxyapatite powder were larger than that from spherical and rod-like powders. Furthermore, the pore size distribution of the porous hydroxy-apatites body from whisker-like powder was very narrow. According to these results, various porous microstructure hydroxyapatite can be designed and the porosity characteristics reliably controlled.

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The use of polycrystalline silicon thin-film on inexpensive ceramic substrates for solar cells is one of the most promising approaches to realize both their high performance and cost reduction. Mullite-based ceramics prepared from kaolin-alumina are appropriate for cost-effective substrates for the polycrystalline silicon thin-film solar cells. They fulfill requirements such as thermal and mechanical stability up to 1200°C and no thermal expansion mismatch with silicon.

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Fine hollow microspheres with mean particle size less than 15μm were prepared from seven kinds of pulverized vitric volcanic materials (Shinjo-Shirasu, Kakuto-Shirasu, Yoshida-Shirasu, Biei-Hakudo, Nakano-Hakudo, Pitchstone and Obsidian) using a fluidized bed furnace. The whiteness of the prepared fine hollow microspheres increases as the content of Fe³⁺ decreases and the expansion ratio of the pulverized particles after foaming was found to increases.

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The Journal of the Ceramic Society of Japan (JCerSJ), as a journal reporting about ceramic science and technology, has now achieved over 100 years of history. As shown in the figure below, JCerSJ has published more than six thousand reports in 107 volumes since its first issue in 1892. As one of the CSJ Millennium Projects, the Editorial Board of JCerSJ plans to select, from all the papers published in JCerSJ, the most important papers in the 20^th century which have had great influence on science and technology and especially those which have opened new phases of research in this field. With that object in mind, 43 papers (48 entries) were recommended by thoughtful members of CSJ. We express our heartfelt thanks to them. After careful judging, 12 papers were selected as “Leading Papers on Ceramics in the 20^th Century: the Best of JCerSJ”. Here, we offer the papers and their authors praise and honor by reprinting the papers in sequential issues of JCerSJ during the final year of the 20^th century. In this issue “the Prospectus” in JCerSJ, Vol. 1 No. 1 (1892) appears again.

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