The effect of preparation method on the chemical stability of sinterable (La, Ca)CrO_3-δ powder was investigated. The ceramic method (powder mixing method) resulted in inhomogeneous distributions of the calcium content (x) in the perovskite phase (La_1-xCa_xCrO_3-δ) after calcining at a temperature from 1223 to 1373K. More homogeneous powder was obtained by the liquid mixing method. The distribution of calcium content caused a large amount of second phases such as calcium oxychromates (Ca_m(CrO₄)_n) in a powder prepared by the ceramic method, and an excess amount of the second phase remained as Ca₅(CrO₄)₃OH on the surface of the ceramics after sintering at 1573K. During a treatment in an H₂+H₂O gaseous mixture at 1273K for 627h, Ca_m(CrO₄)_n decomposed to CaO and α-CaCr₂O₄, and the decomposition was enhanced by the existence of silicon-containing impurities. The liquid mixing method minimized the amount of Ca_m(CrO₄)_n, and resulted in sufficient chemical stability in H₂+H₂O.

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(1) Sodium germanate glass of the nominal composition of 20Na₂O⋅80GeO₂ in mol% (analyzed composition of 21.8Na₂O⋅78.2GeO₂), which was particulate and somewhat porous, was made by heating the gel obtained from Ge(O⋅C₄H₉ⁿ)₄ and NaOCH₃ by the sol-gel method.
(2) The fraction of 6-fold coordinated Ge⁴⁺ ions in the sol-gel-derived glass, which was evaluated on the basis of X-ray radial distribution analysis, was about 40%, much larger than in the melt-derived glass (N₆=25%). The IR absorption data was consistent with X-ray data.
(3) In the sol-gel-derived glass, major crystalline species precipitated on heating was Na₄Ge₉O₂₀ crystal, while metastable wadeite type Na₂Ge₄O₉ crystal was precipitated preferentially to Na₄Ge₉O₂₀ in the melt-derived glass.
(4) The large N₆ and crystallization behavior of the sol-gel-derived glass was interpreted in terms of the glass network consisting of edge-shared GeO₆ octahedra linked to GeO₄ tetrahedra, while melt-derived glass is made up y GeO₆ octahedra linked to GeO₄ tetrahedra at all six corners.

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To investigate the validity of a hypothesis “Crystal embryos exist in melt at temperatures above the liquidus (T_L) and their amount decreases with the increase in melting temperature”, crystallization behavior of Li₂O⋅2SiO₂ glass was studied. It has been known that homogeneous nucleation takes place in Li₂O⋅2SiO₂ glass on heating. The glass samples were prepared by melting the Li₂O⋅2SiO₂ composition at various temperatures above T_L (up to 1300°C) for 3h and were quenched in water. Crystal-particles were not detected in the quenched glass, but after a heat-treatment at 600°C for 30-60min crystal-particles were observed with an optical microscope. The number density and the particle size of precipitated crystals were measured. The number density of crystals decreased with increasing melting temperatures after a 30min-heat-treatment. Moreover, the particle size was largest at low melting temperature and decreased with increasing melting temperatures. It was proved that this result can ba explained by the above mentioned hypothesis. After prolonged heat-treatment (-60min), however, the nucleation rate and growth rate were found to increase remarkably as the melting temperature increase. This behavior implies a change of melt structure equilibrated at melting temperatures or a possibility of microscale phase seperation near the miscibility gap at 600°C.

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The problems of the Thomson-Freundlich equation in the solid state sintering are pointed out, which has been used as the relationship concerned with the chemical potential difference, surface curvature and vacancy concentration gradient. Based on the view point of the variation in total system energy as the driving force of the solid state sintering, the new concept of the reduction in local surface energy is introduced, and with the new introduced concept of the reduction in local surface energy, the change of surface configuration by surface diffusion is two dimensionally discussed.

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A high-density mullite which can be used as an oxygen sensor at high temperatures, did not show enough thermal shock fracture resistance in the melts of steel. The thermal stress distribution in a mullite tube after immersing into steel melts was calculated by the finite element method in order to prevent thermal spalling. Based on the calculated results, the resin-coated mullite tubes and the porous mullite tubes with excellent thermal shock fracture resistance were developed.

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A Weibull space is defined by three coordinates of failure probability, effective volume and strength. The two-parameter Weibull distribution function is presented by a plane (Weibull plane) in the Weibull space. The Weibull modulus can be obtained from the gradient of the Weibull plane. Therefore, the Weibull modulus can be evaluated by the method of least squares from the strength data obtained by various tests of different effective volume specimens. The Weibull modulus estimated by this method is more accurate than that by the conventional Weibull plot method. The Weibull modulus estimated by this method is expected to be twice as accurate as that by the conventional method, particularly when the strength data are obtained from two different volumes whose ratio is more than 100.

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The scintillator elements in X-ray CT equipment of the third generation type require high uniformity of distribution of light output as well as quality response characteristic. Parameters responsible for the distribution of light output were studied using the Monte Carlo method. Although the scattering coefficient was neglected, close agreement was obtained between calculated and experimental results. Calculated results indicated that relative output drop at both ends decreased with increasing optical absorption coefficient and was constant for X-ray absorption factor.

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The structure of NiO particles in the NiO/SiO₂ agglomerates prepared by CVD was investigated by XRD, TEM, XPS and TPR. TEM observation and XRD analysis indicated that the NiO particles obtained were in the aggregated state, and that the size of them became large, while that of primary particles became small, with increasing preparation temperature. TPR and XPS analyses indicated that a trace amount of nickel silicate coexisted with the NiO/SiO₂ particles, most likely at the outer region of the NiO aggregates near the interface with the SiO₂ deposited on them. From these results and the hydrogen reduction experiments, we proposed the following structure model of the NiO/SiO₂ agglomeration; at high preparation temperature small primary NiO particles grow into large secondary particles, followed by coating with thin SiO₂ layers, while at low temperature large primary NiO particles grow and are surrounded by SiO₂ matrix.

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Packing of monosized fine spheres in the presence of monosized coarse spheres is examined both experimentally and analytically. By modeling the extra pore volume generated from the interaction of fine and coarse particles as a linear function of the size of the fine particles and the surface area of the coarse particles, good agreements between model and experimental data from the present study and those from literature were found. Good agreement was also obtained when the model was applied and compared with trimodal packing data. From these agreements, it can be concluded that the development of coarse/coarse particle contacts does not dramatically change the amount of extra pore volume. As a consequence, extra pore volume in dense packing of mixtures of narrowly distributed particles can be treated as dependent on the surface area of the desrupting media and the size of the particle.

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β-Si₃N₄ powders containing 0.5mol% Y₂O₃ and 0.5mol% Nd₂O₃ were gas-pressure sintered at 2000°C for 2, 4, and 8h. The obtained materials presented the microstructure of self-reinforced composites consisting of some large rod-like grains in a fine matrix, as it was observed by scanning electron microscopy of plasma-etched surfaces. Two-dimensional distributions of grain diameter, grain length, and cross-sectional area were quantitatively analyzed using an image analyzer. The distribution curve of grain number and grain cross-sectional area did not reflect the presence of large grains, and therefore this method is not suitable for evaluation of self-reinforced materials. The volume fractions of large grains and fine matrix grains were estimated from the relation between the grain size and the two-dimentional distribution curve of grain cross-sectional area.

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The effective strength of the socket part (threaded hole at both end of pole) at the joint constructed by two poles and one nipple of artificial graphite electrodes was evaluated by using finite element method (FEM) and measured under the uniaxial tension loading. The stress distribution at the socket was analyzed as a function of length of nipple using FEM. The stress at supposed fracture point of the socket was lower as longer the nipple was. The experiment by bending fracture showed that the socket with a long nipple gave higher effective strength than that with the nipple of the JIS size. The results of FEM analysis agreed with those of experiment. The socket with longer nipple is expected to have higher effective strength in electric arc furnace for steel making.

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A strongly acidic ion exchange resin, H-R, is a novel dissolution agent for sparingly soluble inorganic materials in aqueous media. The dissolution proceeds by cation exchange reaction between H-R and dissolved ion of minute quantities, which promotes further dissociation tendency of the material to achieve complete dissolution. In this study, the dissolution processes of the fully and the immature hydration products of C₃S in the presence of H-R were followed by the methods of the ion exchange titration, chemical analysis and calorimetric measurement. The fully and the immature hydration products were obtained by stirring C₃S aqueous suspensions at 80°C for 3 days and 25°C for one night, respectively. The obtained restults are summarized as follows; (1) Complete hydration is achieved by stirring C₃S suspension (W/S=10) at 80°C for only few hours giving a mixture of Ca(OH)₂ and afwillite (C₃S₂H₃). Addition of H-R into an aqueous suspension containing the mixture results in consecutive dissolution of both compounds accompanying distinct variations in pH, specific conductivity and calorimetric thermogram. Preferential reaction between Ca(OH)₂ and H-R is due to higher solubility in H₂O remaining afwillite, which is dissolved by further addition of H-R. The heat of dissolution of afwillite in H-R suspension at 25°C is measured to be 273.7kJ/mol. (2) The degree of hydration and the amount of formed Ca(OH)₂ of C₃S suspension hydrated for one night are estimated to be about 60% and 0.75mol/C₃S-mol, respectively, by analyzing the results obtained by the ion exchange titration and the calorimetric measurement carried out by a small addition of H-R.

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Synthesis and CO₂ adsorption ability of calcium-deficient tobermorite were investigated. The calcium-deficient tobermorites with Ca/(Al+Si) atomic ratios lower than that of the theoretical composition, 0.83, were prepared by the reaction in the system CaCl₂-Na₂SiO₃-AlCl₃-H₂O under atmospheric pressure. The calcium-deficient tobermorites were characterized by means of X-ray diffraction, thermal analysis (TG-DTA), infrared spectroscopy and chemical analysis. The calcium-deficient tobermorite was formed from starting solutions with Ca/(Al+Si) atomic ratios lower than 0.95. Most Ca²⁺ ions existing in interlayers of the tobermorite, 20% of total Ca²⁺, were removed successively by decreasing the initial Ca/(Al+Si) atomic ratio from 0.95 to 0.70, and then the basal spacing of the calcium-deficient tobermorite expanded by replacing one Ca²⁺ ion site with two Na⁺ ions until the atomic ratio of 0.7. However, the layer structure of the tobermorite was destroyed at the atomic ratios below 0.7. The amount of Na⁺ ions to compensate for charge deficiency in calcium-deficient tobermorites obtained at an initial Ca/(Al+Si) atomic ratio of 0.7 and initial Al/(Al+Si) atomic ratio of 0.10 was changeable by number of washings with pure water. The composition after washing was expressed by the formulas of Ca₄Na_0.4[(Al+Si)₆O₁₁H₂]⋅4H₂O including ion defects after ten times washings (5g/dm³ H₂O) and Ca₄Na_2.1[(Al+Si)₆O₂₂H₂]⋅4H₂O after one time washing (5g/100cm³ H₂O). The maximum exchange capacity for Na⁺→K⁺ of Na⁺ present in the calcium-deficient tobermorite was 95meq/100g irrespective of the amount of Na⁺. The adsorption capacity of CO₂ at 60°C in the tobermorite increased with increasing Na/(Al+Si) atomic ratio and reached a maximum value of 3.0mmol/g at the atomic ratio of 0.36. The desorption of CO₂ and adsorption of Na⁺ progressed simultaneously on washing the tobermorite which adsorbed CO₂ with 1N NaCl solution. Accordingly the tobermorite washed with NaCl solution was available as CO₂ adsorbent. when the adsorption and desorption were repeated many times, the formation of CaCO₃ originated from partial carbonation in the tobermorite was unavoidable, and consequently, the adsorption capacity of CO₂ decreased successively with increasing recycle number. On the other hand, when the calcium-deficient tobermorite after desorption of CO₂ was heated at 200°C, its adsorption capacity was kept at 2.0mmol/g even after using five times.

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The Vickers hardness (H_v), Young's modules (E), fracture toughness (K_IC) and bending strength (σ_f) of a glass and an α-type polycrystalline cordierite with the cordierite composition (2MgO⋅2Al₂O₃⋅5SiO₂) were measured using Vickers indentation, resonance method, various indentation techniques and 3-point bending test. The polycrystalline cordierite was fabricated by densification and subsequent crystallization of compacted cordierite glass powder. The H_v, E and K_IC of a polycrystalline cordierite were 7.5GPa, 127.5GPa and 2MPa⋅m^1/2, while those of cordierite glass were 5.9GPa, 98.7GPa and 1.0MPa⋅m^1/2, respectively. On the other hand, the σ_f (113MPa) of a polycrystalline cordierite was smaller than that (149MPa) of a cordierite glass.

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Fatigue crack propagation under cyclic loading was observed in CT specimens of silicon nitride by employing an electrical resistance technique with crack gage made of platinum film. The crack growth rate was not uniform even if the fatigue condition was constant. The crack growth behavior in maximum stress intensity factor K_Imax-increasing condition was different from that in K_Imax-decreasing condition. The effect of stress ratio R(=σ_min/σ_max) was not significant when the minimum stress intensity factor (K_Imin) was greater than crack opening stress intensity factor (K_open). Fracture toughness measured by CT specimens after fatigue testing was smaller than that by SEPB method. The experimental results, indicated that the unloading may cause fretting and/or crashing of the asperities between the crack faces in silicon nitride, where toughening is achieved by grain bridging. Therefore, the cyclic loading may accelerate the static fatigue crack propagation caused by stress corrosion cracking.

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In relation to the synthesis of the reinforced ceramic matrix composites, the pyrolysis mechanism of Si-C-O fiber (Nicalon NL202) in alumina powder has been studied. The pyrolytic rate has been measured with a thermobalance in an argon atmosphere at temperatures from 1773 to 1973K. The heat-treated fibers were examined with X-ray diffraction, SEM observation and tensile test. In alumina powder, the pyrolysis of the fiber was suppressed. The pyrolytic rate decreased with decreasing size of alumina powder particles, and with increasing compactness and thickness of the alumina layer. It is considered that the pyrolysis of the fiber is controlled by the growth of β-SiC crystallites and the gaseous diffusion through the interparticle pores within the powder. The high temperature strength of the fiber in alumina was appreciably retained. The equation similar to Hall-Petch's law held between the tensile strength of the fiber and the size of β-SiC crystallites.

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The mechanical and thermal properties of SiC-AlN ceramics were examined in terms of the development of the modulated texture. The SiC-AlN solid solution ceramics with the addition of Y₂O₃ and Al₂O₃ were prepared by hot-pressing method, which were followed by the subsequent heat treatment to develop the modulated texture in the miscibility gap at the temperatures of 1600°C or 1800°C. It was found that the flexural strength and Weibull modulus of the ceramics (nominal composition: 70mol% SiC/30mol% AlN) increase from 589 to 674MPa and from 7.6 to 10.5 with the phase separation treatment at 1600°C for 8h. Thermal shock resistance is also enhanced by the phase separation. The addition of AlN to SiC causes a decrease in thermal conductivity. The phase separation does not influence the thermal conductivity of the SiC-AlN solid solution ceramics. The mass gain of the SiC-AlN ceramics due to the oxidation under 1400°C in air is lower than that of SiC ceramics.

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Diamond was deposited by microwave plasma CVD of the CO-H₂ reactant system onto the wire substrates of various transition metals, which were mounted vertically on a pyrophyllite susceptor. Effects of microflawing pretreatment, microwave power, pressure and wire height on the distribution and morphology of diamond were investigated under constant conditions of total flow rate (200ml/min) and CO concentration (5vol%). Euhedral microcrystals of diamond were deposited at lower positions of microflawed wire substrates of Mo, W, Ti with the microwave power of 750W. Nucleation density tended to increase with decreasing total pressure, which resulted in the formation of fine-grained diamond coating on wire substrate at the pressure of 15 Torr.

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Mullite-ZrO₂ and mullite-ZrO₂-Al₂O₃ composite ceramics were prepared by in-situ reaction between alumina and synthetic zircon powders. The mechanical properties of these composites were investigated as a function of Al₂O₃/SiO₂ weight ratio in the matrix. Three-point bending strength at room temperature and fracture toughness increased with increasing content of Al₂O₃ over the entire range of the Al₂O₃/SiO₂ ratio from 70/30 to 90/10. In particular, the mean bending strength was 650MPa in the vicinity of the composition ratio of 90/10. As judged by the crystalline phases and observation of the fine structure, a strengthening mechanism which acts significantly on the mechanical properties of the composite sintered bodies was indicated by the following: (1) grain size reduction of the mullite matrix by dispersion of the Al₂O₃ phase, (2) nano-structure in which Al₂O₃ and ZrO₂ particles were finely dispersed in the mullite grains and (3) dispersion-effect of the Al₂O₃ and ZrO₂ crystalline phase with a larger thermal expansion coefficient than that of the matrix.

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The effects of the impact angles of an abrasive water jet (AWJ) stream on the depth of groove and the worn volume of Si₃N₄ ceramics have been studied. Two kinds of Si₃N₄ ceramics, β-Si₃N₄ and α′/β′-Sialon, were eroded by AWJs using two kinds of particles, Al₂O₃ (WA) and SiC. The angles of the jet stream, which correspond with the angle of an abrasive nozzle, to the specimen were 45°, 60°, 90°, 120° and 135°. The effects of the jet stream angles were very different according to the particle. It was suggested that this difference was caused by the difference in fracture strength between the particles. The groove depth and the worn volume were strongly affected by secondary wear, when the particle was SiC. Considering the uniformity of groove depth and width, the best angle of the abrasive nozzle to cut Si₃N₄ ceramics was thougth to be 90°.

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The effect of addition of CaO, SrO BaO and ZnO on the crystallization, thermal expansion, and surface roughness of alkali-free porcelain enamel in the MgO-ZrO₂-P₂O₅-SiO₂-B₂O₃ system was investigated by means of DTA, XRD, SEM observations, thermal expansion measurements, and surface roughness observations. The addition of CaO, SrO and BaO in frit affected the temperature of crystallization in DTA, while the addition of ZnO did not affect the temperature. CaO and BaO raised the thermal expansion coefficient, while ZnO lowered it. The surface of porcelain enamel was smoother in the frit containing CaO than in the frit containing BaO.

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Sintering behavior and formation of mullite in kyanite-borosilicate glass (pyrex glass) system were examined. Kyanite decomposed to mullite and cristobalite from around 1300°C. Due to this decomposition, kyanite powder compact expanded about 20vol%, but the volume expansion of the compact decreased from 1500°C. In kyanite-glass system, the volume expansion of the specimen decreased with increasing glass content. The decompositon temperature of kyanite did not change with the addition of glass. The content of mullite formed from kyanite was 71wt% at 1550°C. In the case of kyanite-glass-alumina system, the content of mullite increased by the reaction between alumina and cristobalite formed from kyanite. Mullite formed in kyanite-glass-alumina system, was columnar and about 10μm long. The lattice constants of mullite were close to those of references. The bending strength in kyanite 70wt%-glass 30wt% specimen was 135MPa, and that in kyanite-glass-alumina system increased with sintering temperature and the value was 155MPa at 1550°C. On heating kyanite compact contacted with glass plate, needle-like mullite with an average length of 50μm grew into glass phase at the boundary between the compact and glass plate, but in dense part infiltrated by glass, the mullite was about 10μm long. It was suggested that the size of glass phase contacted to kyanite particle affected the growth of needle-like mullite crystal.

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This paper shows a simple analysis method for the contents of polytypes in the polycrystalline SiC. Theoretical diffraction intensities of single crystals of 2H, 3C, 4H, 6H and 15R were calculated by the crystallographic data. It was assumed that the polycrystalline SiC is a mixture of these polytype grains, and X-ray diffraction intensities of polycrystalline SiC were obtained by the sum of the theoretical intensities from these polytypes. The most probable contents of polytypes could be determined by fitting the observed X-ray diffraction intensities to the theoretical ones by the multiple regression method.

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Lithium ion conducting glasses were prepared in the system (0.6Li₂S⋅0.4SiS₂)-Li₃PO₄ by twin-roller rapid quenching. The temperatures of glass transition (T_g) and crystallization (T_c) were determined for the glassy samples with 0-40mol% Li₃PO₄. The conductivity values at 25°C (σ₂₅) were maximized and the activation energies (E_a) for conduction were minimized at the composition with 5mol% Li₃PO₄; the maximum σ₂₅ value was as high as 9×10^-4S⋅cm^-1. Since the difference between T_g and T_c was also maximized at the same composition, it was concluded that the doping of small amounts of Li₃PO₄ improved both the glass stability against crystallization and the lithium ion conductivities.

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