Solid-state kinetic analysis by the Johnson-Mehl-Avrami plot was introduced to understand the reaction mechanism of fine BaTiO₃ powders prepared under hydrothermal conditions. In the experiment reactants were dissolved and consumed to spherical particles of 50nm from aggregation of several nanometer-sized particles. The particulate formation of BaTiO₃ underwent 1st-order hydrolysis-condensation reaction with phase-boundary transition in the early stage of the reaction regardless of the initial concentration of the feedstock. However, as the concentration of nutrients reduced, dissolution followed by precipitation became dominant, and a diffusion-controlled reaction proceeded. When the concentration of nutrients reduced to an extent that was not high enough to sustain supersaturation, the reaction was controlled by solidification for encapsulation of aggregated particles, inside of which the diffusion-controlled reaction slowly proceeded.

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The influences of the sintering additive content of MgAl₂O₄-ZrO₂ (total 5-15mass% with a MgAl₂O₄/ZrO₂ ratio 1:1) on sintering behaviors, microstructure and mechanical properties of Si₃N₄ ceramics were investigated. Sintering was carried out in the temperature range of 1200 to 1900°C. Densification was enhanced with increasing sintering additive content due to an improved particle rearrangement; however, phase transformation and grain growth were significantly suppressed. The phase transformation and grain growth occurred through a solution-reprecipitation mechanism controlled by a diffusion process in this additive system. With the addition of a small amount of the above-mentioned additive mixture (5mass%), both high flexural strength and high fracture toughness could be obtained.

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Matrix algebra analysis of martensitic transformations has been employed for the determination of habit planes and shape deformations of Ca₂SiO₄ upon β-to-α′_L transformation during heating. The cell parameters of both the parent β and product α′_L-phases at the transformation temperature (710°C) have been found from extrapolation of the regression of their cell-parameter variations. The analysis indicates that one of the principal distortions (=c_α′L/3b_β) of the lattice deformation is equal to unity, and the other principal distortions are larger and smaller than unity. This satisfies the requirement for the formation of completely coherent interfaces between the two phases, which are almost parallel to either (100)_β or (001)_β. Because the transformation involves a very small volumetric expansion of 0.3%, the strain accommodation would be almost completed. Both the complete coherency at the interphase boundaries and the effective strain accommodation probably lead to the thermoelasticity of the transformation, in accord with a previous study for doped Ca₂SiO₄.

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A red clay body containing 7mass% Fe₂O₃ was fired at PO₂=0.1kPa and its bloating and blackening mechanisms were investigated.
Blackening started at around 1100°C and the Fe²⁺/total Fe ratio in the fired body was about 5%. The disappearance of open pores started at about 1200°C, and the sealed porosity began to increase above 1200°C. The Fe²⁺/total Fe ratio in the body fired at 1200°C was 16%, indicating that a considerable amount of oxygen had been released. Although the evolution of oxygen started at around 1100°C as judged from the results of chemical analysis of Fe, the evolution of oxygen was detected only at around 1080°C and at the soaking temperatures probably due to the high heating rate (5°C/min).
The results of thermodynamic calculations suggested that oxygen evolution was caused or at least assisted by the reaction of iron oxides with Al₂O₃ to form FeAl₂O₄, a stable spinel. It is, however, assumed that FeAl₂O₄ reacted with silicate compounds during sintering at high temperatures.

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When a powder mixture consisting of Al₂(SO₄)₃, SiO₂ and K₂SO₄ was heated in a closed alumina crucible, a reactant mass remained at the bottom of the crucible. Needlelike leucite crystals were obtained by treating this reactant mass with hot HCl. The effect of the mixing ratio of the raw materials, the heating temperature and the duration of heating at the selected temperature on the formation of needlelike leucite crystals was investigated. When a powder mixture, consisting of Al₂(SO₄)₃:SiO₂:K₂SO₄=1.0:2.8:1.9 (molar ratio), was heated at 1200°C for 3h, the obtained needlelike leucite crystals were 1-2μm in length and 0.1-0.3μm in width. Needlelike leucite crystals were formed by the crystallization of leucite on small mullite crystals obtained by heating, followed by growth of the leucite crystals in a liquid phase of the K₂SO₄ flux as the main component.

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HAp nucleation from SBF was investigated in this study on Si substrates on which various kinds of organosilane SAM were formed. Saturation of number densities of HAp particles was found in the early stage of HAp deposition process while particles continued to grow after saturation. Slight dependence of the kind of organosilane SAM was also observed on particle number density. Depletion of calcium and phosphate ions in the vicinity of a substrate should limit nucleation. The minimum ionic concentration for HAp nucleation depends on the kind of SAM.

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The alumina-zirconia-graphite (AZG) refractory is one of the most important refractory for AISI 304 stainless steel strip casting especially used as slide gates or nozzles. The AZG refractories were obtained through baking techniques using fused Al₂O₃, partially stabilized ZrO₂ and flake graphite as the starting materials with Al, Si and SiC powders as additives. A particle size distribution was designed by Andreasen model for coarse Al₂O₃ (250-1000μm)/medium Al₂O₃ (61-250μm)/fine Al₂O₃ (<61μm) in which the contents of fine, medium and coarse Al₂O₃ powders were variables on the basis of constancy of other fine particles in the matrix. At the same particle size, the accumulative mass percent finer increases when the N-value decreases. The highest bulk density (3.3g/cm³) and the lowest apparent porosity (5.70%) were obtained at N-value of 0.9 with 1000μm Al₂O₃ particle. The reheat linear change fraction about 0.4 to 0.8% indicates that these materials have an acceptable volume stability. The number of air exposure cycles of thermal shock resistance decreased gradually from 8 to 6 as N-value increased from 0.6 to 0.9. The erosion fraction tended to decrease with the N-value increasing.

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A low temperature direct synthesis (LTDS) method is useful for preparing nm-sized barium titanate crystallites. However, the precise characterization of impurities in barium titanate crystallites is difficult because barium carbonate is formed as a by-product. In this study, a normal LTDS method was modified to prepare barium titanate crystallites under a CO₂-free atmosphere, i.e., an N₂ atmosphere. The barium titanate single phase was first prepared using this modified LTDS method. In the characterization of as-prepared barium titanate crystallites, only a hydroxyl group was detected as an impurity for ca. 11mass%. A chemical analysis of the as-prepared barium titanate crystallites determined that the Ba/Ti atomic ratio was 0.635±0.005, which means that a lot of barium vacancies formed in the crystallites. The average crystal structure, determined by XRD, was assigned to a cubic m3m symmetry, while the local structure, determined by Raman scattering spectroscopy, was assigned to a tetragonal 4mm symmetry, which suggested that in the crystal structure of as-prepared barium titanate crystallites, there existed a disorder system. Crystallites were also characterized after annealing at various temperatures.

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The objective of this study is to clarify the grain growth behaviors of zinc-oxide varistor ceramics with Bi₂O₃ and TiO₂ additions. Zinc-oxide based ceramics have been widely used as transient surge suppressors for protecting electric equipments, because of their highly nonlinear voltage (V)-current (I) characteristics and excellent surge absorption capability. The nonohmic properties of these ceramics are highly affected by characteristics of the microstructures, such as ZnO grain size. A ZnO-6mass% Bi₂O₃-0.55mass% TiO₂ ceramic has been selected for investigating the ZnO grain growth behavior. The experimental results show that the samples consisted of equiaxed ZnO grains and a second phases with the Bi₂O₃ and spinel crystal structure. It also indicated that the grain growth behavior could be observed to follow a time law for grain size ω of the form ω=κ⋅tⁿ, where t is time and n is a kinetic exponent. The kinetic exponent for ZnO grain growth has been determined to be 1/2 for temperatures below 1303K, but 1/5 above 1379K. A convenient computer-aided system was developed for analyzing the grain growth behavior of sintered materials. It simulated the effects of heating rate and cooling rate on the ZnO grain growth in the ZnO-6mass% Bi₂O₃-0.55mass% TiO₂ ceramic during the sintering process. As a result, it was clarified that the effect of heating rate on the ZnO grain growth was not neglected in comparison with the cooling rate in the range of practical use.

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Red coloring of glaze by mixing three kinds of zircon-based pigments was studied. The zircon-based pigments used in the glaze have chemical and thermal stabilities in comparison with other ceramic pigments. Generally, the mixture of two kinds of zircon-based pigments produces an intermediate color. From a spectroscopic point of view, it seems to be able to obtain red color by mixing purple and yellow. Therefore, we attempted to synthesize a new type of Mn-zircon purple pigment using ZrO₂, SiO₂ and MnCO₃. The influence of ZrO₂ to SiO₂ ratio and the type of glaze on the color was analyzed spectroscopically. The color of the pigment (ZSM-50) prepared at the ratio of ZrO₂:SiO₂=1:1 was fairly purple. It was verified by X-ray diffraction (XRD) that the main phase of the ZSM-50 was zircon. However, the mixture of the ZSM-50 and the yellow Pr-zircon did not yield a fine red color. Hence, salmon pink Fe-zircon pigment was added as third pigment and the ratio of the three kinds of pigments on the color was examined. The reddish brown glaze, which was the most reddish color at present, could be obtained at the ratio of Mn-zircon:Pr-zircon:Fe-zircon=8:1:1.

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B₄C-TiB₂-C and TiB₂-TiC-C composites were synthesized by reactive spark plasma sintering of powder mixtures of Ti and B₄C, accompanied by their solid-state displacement reactions. When varying the mixing ratio of the starting materials Ti and B₄C, x, the following reactions were completed: when 0<x≤2, B₄C+xTi→xTiB₂+(1-x/2)B₄C+(x/2)C and when 2<x≤3, B₄C+xTi→2TiB₂+(x-2)TiC+(3-x)C. Carbon, which was precipitated in the product TiB₂ phases, increased pores and cracks in the TiB₂ phases and resulted in a decrease of the relative density and Young's modulus. For x=3, the composite contained no carbon and had the highest values for both the Young's modulus and fracture toughness. The Young's modulus of the composites prepared was represented by E/GPa=460V_B4C+600V_TiB2+488VTiC-1414V_C, where V_i is the molar volume of component i.

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Al₂O₃-coated graphite powder was prepared using ethyl acetoacetate aluminium diisopropoxide through the sol-gel method. The fluidity of the Al₂O₃-coated graphite powder slurry was studied. The apparent viscosity of a 2mass% Al₂O₃-coated graphite powder slurry was lower than that of a graphite powder slurry in the range of 25-40mass% solid loading. It is concluded that the fluidity of the Al₂O₃-coated graphite powder slurry depends on the fraction of free water of the slurry, the degree of dispersion and the wettability by water of the Al₂O₃-coated graphite powder.

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Surface coating of natural wollastonite fiber with colloidal rutile was performed in order to produce antibacterial inorganic filters for ventilators of buildings. The wollastonite surface in suspensions was made sufficiently negative to electric charge by adding chelating reagents, such as disodium salt of the ethylenediaminetetraacetic acid (EDTA) and sodium citrate for masking Ca²⁺ which dissolves from the raw materials acting as counter ion in the electric double layer. Rutile particles with positive charge adsorbed quantitatively onto the wollastonite surface by electrostatic force of attraction at pH6. Detaching of rutile particles from the wollastonite surface during filtration and drying processes due to aggregation by large surface tension of water was avoided by replacing water by acetone. As a result, wollastonite fibers were covered with a homogeneous layer of colloidal rutile, and the rutile particles firmly adhered on the surface by heating at 500°C for 2h.

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From the view point of a more valuable use of clay as an industrial material, clay-ceramic composite materials containing commercial alumina particles were fabricated by injection molding process. The mechanical property and quality of the mold parts were investigated by changing the ratio of alumina powder against the clay to obtain a fine composite material. The heat treatment to evaporate water (contained in the clay), the alumina content and the degreasing speed were specified by analyses of variance of the dimensional accuracy, hardness and bending strength of the parts. At the firing temperature of 1573K, the mechanical properties of the parts were improved drastically. In order to investigate the reason for the high hardness and strength obtained at 1573K, X-ray analyses of the fired parts were performed, and the added alumina was confirmed to remain unchanged. From these results, alumina powder is considered to produce a decrease in deformation of the fired parts, which is caused by partial melting of the clay and bloating of the part above a temperature of 1473K. The added alumina powder also plays the role of a reinforcement in the clay composite material.

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We evaluated the characteristics of Ni powder paste used for the fabrication of internal electrodes of multilayer ceramic chip capacitors (MLCs). Moreover the effect of the grain size of Ni powder on sintering characteristics was evaluated using the paste. High filling densities were obtained for Ni powder of two different grain sizes, 0.2 and 0.5μm. The experimental result reversed that pulverized Ni powder exhibits a high level of dispersion when it is used in paste form. From the measurements of sintering shrinkage rate, it has been observed that the 0.2μm Ni powder had a higher shrinkage rate than the 0.5μm Ni powder, indicated that the sintering shrinkage rate is closely related to grain diameter. A similar result has been obtained by observation of the surface structure of sintered bodies.

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Seven kinds of sodium rare-earth silicate glass, (Na₂O)_35.7(RE₂O₃)_7.2(SiO₂)_57.1 (RE=Sm, Gd, Dy, Y, Ho, Er and Yb), were synthesized by melting a mixture of Na₂CO₃, RE₂O₃ and SiO₂ and their electrical properties were investigated. The densities of glasses were in fairly good agreement with the theoretical densities predicated for Na₅RESi₄O₁₂ ceramics. The crystallization temperature and the crystal melting temperature linearly decreased with increasing the ionic radius of RE. The highest electrical conductivity at 200°C (1.55×10^-4S·cm^-1) was achieved for (Na₂O)_35.7(Yb₂O₃)_7.2(SiO₂)_57.1. The electrical conductivity slightly decreased with increasing the ionic radius of RE.

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Yttria-stabilized zirconia (YSZ) was deposited on hydrogen-terminated Si(001) by pulsed laser deposition (PLD) under various oxygen pressures (about 2-2×10^-4Pa) and laser energy densities (0.87-1.09J/cm²) at 800°C. The effects of O₂ pressure and laser energy density were found to be important to the formation of an epitaxial oxide thin film. With decreasing laser energy density, the O₂ pressure required to grow epitaxial YSZ films was shifted toward the lower region. Therefore, epitaxial growth of YSZ films could be achieved at a very low pressure of 2×10^-4Pa compared with the known O₂ pressure region used for epitaxial growth. The roughness of surfaces was very low, within 0.18-0.26nm.

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It can be said that this article took the lead in studying a bioceramic group called “calcium phosphate cement” or “apatite cement.” The active promotion of calcium phosphate cementing materials has been made since the Monma-Kanazawa paper appeared.
Many researchers have long believed that tricalcium phosphate is stable in water. However, the authors of this paper reported that α-tricalcium phosphate (α-TCP) converts to hydroxyapatite in hot water (80-100°C) and produces hardened porous products. The main results were as follows: bulk densities of 0.9-1.2g/cm³, compressive strengths of 15-16MPa and diametral strengths of 2-3MPa. The resulting products were composed of calcium-deficient hydroxyapatites. This phenomenon was very peculiar since some other calcium phosphate did not show such a hardening property even if a similar phase change occurred.
Generally, cement-type materials possess many advantages different from densely sintered ceramics. If calcium phosphate cementing materials were created, they would be a significantly new type of calcium phosphate material and also to be bioactive. Therefore, this paper concerning the hydration-hardening of α-TCP has attracted the attention of material researchers. At nearly the same time, the possibilities of various cementing calcium phosphate compositions were proposed by Brown and Chow based on thermodynamic considerations. The following two basic patents have been issued; H. Monma et al., “Production of porous apatite, ” Jpn. Pat. 1103653 (Jul. 16, 1982), Appl. 53-124025 (Oct. 7, 1978) and W. E. Brown et al., “Dental restorative cement pastes, ” U.S. Pat. 45185430 (May 21, 1985), Appl. No. 539740 (Oct. 6, 1983).
Subsequently, many studies on cementing calcium phosphate materials have increasingly appeared in technical and medical journals. Details of the hydration reaction of α-TCP were clarified. The hydration-hardening of α-TCP was made even at room temperature using various additives, and its possibility as a practical cementing material was significantly improved. A mixture of α-TCP and calcium hydrogenphosphate dihydrate was found to have good hydration-hardening properties (H. Monma et al., J. Ceram. Soc. Japan, 96, 878 (1988)). This combination gave the following results; about a 10-min setting time, 50-60% porosity and 15-20MPa wet compressive strength. Presently, the compressive strength has been improved to 50-90MPa.
After this author's paper, the following studies were made. The mixture of tetracalcium phosphate and calcium hydrogenphosphate dihydrate first proposed by Brown and Chow has been continuously investigated by many researchers, and its hardening properties were improved by using dilute phosphoric acid and adding synthetic hydroxyapatite powder. About 470 kinds of combinations using various calcium phosphates, calcium carbonate, calcium oxide, sodium fluoride, calcium sulfate hemihydrate, etc., were evaluated, and some available combinations for use as cementing materials were developed as follows: Lemaitre et al. in 1987, Mirtchi et al. in 1990, Bermudez et al. in 1993, and Driessens et al. in 1994. The glassy powder in the system of CaO-SiO₂-P₂O₅ was developed as a bioactive cementing material (Kokubo et al., 1991). Hardened porous materials prepared from these calcium phosphate cements also became important also as supports for drug delivery systems. At present, α-TCP-based cementing materials are being used a a dental pulp lining (Sankin Co. Ltd., 1986), root canal filling (Sankin Co., Ltd., 1987) and osteoporosis filling (Mitsubishi Materials Co., Ltd., 2000).

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