This paper discusses phase relations between α′- and β′-Sialons in the Si₃N₄(-SiO₂)-AlN-Y₂O₃ system. The total amount of AlN and Y₂O₃ was varied from 5 to 11wt%, and the molar ratio of AlN/Y₂O₃ was 0 to 11. Specimens were prepared by hot-pressing. In specimens with a small amount of AlN, compounds including SiO₂, that was contained in the Si₃N₄ powder, were detected. The solubility of α′-Sialon increased remarkably with increasing amount of additives and increasing molar ratio of AlN/Y₂O₃. On the other hand, those of β′-Sialon increased slightly.

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The microstructure of iron nitride-titanium nitride binary films prepared by CVD was investigated by electron microscopy in comparison with those of iron nitride and titanium nitride films. Their microstructures varied from that similar to that of iron nitride film to that of titanium nitride film depending on Ti/(Fe+Ti). These films were made up of columnar particles grown normal to the substrate in the upper region near the surface and finer particles in the lower region near the substrate. Two different composition regions with 0.6μm in size existed in this lower region near the substrate. Two regions with different composition existed at the initial stage of the deposition.

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The electrochemical deposition of calcium-deficient apatite on a stainless steel substrate was conducted by electrolyzing 0.02-0.21mol/dm³ Ca(H₂PO₄)₂⋅H₂O [MCP] solutions added with and without NaNO₃ and NaF at a cathode current of 6mA/cm² at 20-90°C. The formation of apatite from F^--free MCP solutions was limited in a dilute MCP concentration region. At relatively high MCP concentrations brushite (CaHP₄⋅2H₂O) or monetite (CaHP₄) was deposited. The addition of NaNO₃ and/or NaF was effective for the formation of apatite. Deposited apatite layers were composed of ellipsoidal grains, needles or very fine granules depending on electrolysis conditions. Apatites deposited from F^--added MCP solutions were calciumdeficient apatites with Ca/P molar ratios near 1.50, and contained F^-, HPO₄^2- and Na⁺ ions.

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The decomposition of Mg(OH)₂-MgCl₂⋅6H₂O (4wt%) was observed in situ by TEM. The decomposition of Mg(OH)₂ started with gnawing holes through the (0001) plane. The detached pieces became round MgO particles. HCl chemisorbed on the (0001) plane of Mg(OH)₂ formed nuclei for the decomposition and enhanced the formation of Mg(OH)_xCl_y phase locally in the particle of Mg(OH)₂, which decomposed to form round MgO particles. Such round particles were also obtained by the calcination of Mg(OH)₂ in 10vol% HCl atmosphere. The calcined powder was densified up to 99% of the theoretical density by sintering at 1673K in air.

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Two titled compounds which have different structures have been synthesized by heating mixtures of hydrates of copper (II) nitrate and copper (II) chloride, or indium nitrate. Their crystal structures have been refined by the Rietveld method using neutron powder diffraction data. Cu₆O₈InCl is a stoichiometric compound and has a murdochite-like structure (E. Dubler, 1983). The obtained crystallographic data are: space group Fm3m, a=9.1555 (2) Å, d₀=5.69g/cm³ and Z=4. Final S (=R_wp/R_e) was 1.04. A [Cu₆O₈] block, a 3-dimensional network of 26-sided polyhedra, is composed of [CuO₄] planes sharing oxygen atoms (Cu-O: 1.908Å). Another block is a network of [InO₈] cubes sharing corner oxygens with the 26-sided polyhedra (In-O: 2.257Å). The centers of each block are occupied by Cl and In, respectively. Oxygen (32f) and chlorine sites (4b) were found to be fully occupied. This compound has been concluded to have a ordered structure with a chemical composition of Cu₆O₈InCl. In Cu₆O₈Cu₂Cl, Cl sites were found to be partly substituted by NO₃^-. Its crystallographic data are: space group Fm3m, a=9.381 (1) Å, d₀=4.95g/cm³ and Z=4. S was 1.15. The crystal structure of Cu₆O₈Cu₂Cl is essentially the same as that of Cu₆O₈InCl except Cu sites corresponding to the In sites. The Cu atoms are not located at the In site (2b) in the cube, but distributed among 6 equivalent sites (24e) around the center of the oxygen cube with an occupation factor of about 0.29. A Cu atom in the cube is coordinated to 4 oxygens to form a distorted [CuO₄] plane with a Cu-O distance of 1.916Å, and [CuO₄] planes form a 3-dimensional network. Therefore, this type of compounds can be expressed as Cu_6-mO₈⋅Cu_2-nCl_0.7(NO₃)_0.3 where m+n are 0.4. For the sample used in this work, m was 0.1. Cu₆O₈Cu₂Cl has a larger unit cell than Cu₆O₈InCl, which is explained in terms of the fact that the former contains large NO₃^- instead of Cl^-.

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The change in total surface area, namely fracture surface area, of a carbon fiber-reinforced silicon nitride composite (unnotched specimens) was measured by the BET adsorption technique during loading/unloading tests in three-point bending. The actual fracture energy of unnotched specimens, which had been defined as the ratio of the work done during one cycle of loading/unloading to the fracture surface area, was compared with that of notched specimens reported previously. Changes in fracture surface area and actual fracture energy corresponded to the transition of fracture mechanism during failure, and obviously reflected the difference in the damage process of the specimens with and without notch. The actual fracture energy had a physical meanings close to the effective fracture energy ordinary reported when the main fracture mechanism was the macroscopic crack extension. It was considered that the evaluation of fracture surface area and actual fracture energy was an effective method to investigate fracture behavior of fiber-reinforced ceramic composites.

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The thermal stability of amorphous SiN_xC_y films prepared by the plasma CVD method was described. The compositions of the films prepared were SiN_1.34(-Si₃N₄), SiN_0.75C_0.43(SiNC) and SiC_0.92(-SiC). The films were analyzed by infrared absorption spectroscopy (IR), thermal analysis (DTA/TG), X-ray diffraction, TEM, SEM and Auger electron spectroscopy to investigate the effect of annealing on the structure, bonding, crystallization temperature and crystalline phases. Hydrogen in films was desorbed on annealing from room temperature to 1173K. The loss of hydrogen, which was affected by the ambient atmosphere, was larger in vacuum than in N₂. The crystallization temperatures of Si₃N₄, SiNC and SiC films were above 1673K, 1673K and 1373K when annealed in N₂, and above 1373K, 1573K and 1273K when annealed in vacuum, respectively. The crystalline phases formed during annealing in vacuum were α, β-Si₃N₄ for Si₃N₄ films, α, β-Si₃N₄ and α, β-SiC for SiNC films, and β-SiC (α-SiC above 1673K) for SiC films. It was revealed that the SiNC film, a mixed composition of Si₃N₄ and SiC, had the highest crystallization temperature and thermal stability among them in spite of the absence of stable phases between Si₃N₄ and SiC. As for the thermal stability in morphological change (the occurrence of peelings and cracks on annealing) for Si₃N₄, SiNC and SiC films on the several kinds of substrates (stainless steel, carbon steel, Si, Si₃N₄, Al₂O₃), the Si₃N₄ film on stainless steel was superior to the other films on each substrate.

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The purpose of the present work is to toughen the weak gain boundary phase in Si₃N₄ ceramics by forming a nano-composite gain boundary phase of SiC particles. The SiC particles are formed by a reaction between carbon and silicon oxide impurity phase on Si₃N₄ powder surfaces. The carbon is coated on Si₃N₄ powder surfaces by thermal decomposition of CH₄ gas. The sintered bodies are obtained by hot-pressing under 30MPa applied pressure at 1800°C for 60min in N₂ atmosphere. Results of mechanical property measurements show that the bending strength increases to 1250MPa for the 0.29wt% carbon coated Si₃N₄ from 990MPa for the non-coated one, and the fracture toughness shows a similar tendency, i.e., from 5.2MN/m^3/2 to 6.3MN/m^3/2. The crystalline phases of the hot-pressed bodies are determined by X-ray diffraction, and the existence of β-SiC is confirmed. The fractured surfaces are observed by SEM, and the fracture mode is observed to change from intergranular to transgranular fracture by applying the carbon coating. The generated SiC particles toughen the grain boundary phase, and improve mechanical properties by eventually producing a nano-composite phase of the grain boundary phase and nano-size SiC particles.

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Thermal expansion characteristics of A-site deficient Sr-doped lanthanum chromites, La_1-xSr_xCr_1.01O_3-δ (x=0.02, 0.03, 0.05, 0.10, 0.13, 0.15), have been studied in air and in a reducing atmosphere (log P_O2=-16) from room temperature to 1000°C. The phase transition from orthorhombic to rhombohedral, accompanying linear contraction, was respectively observed for samples with x=0.02 to 0.10 both in air and in the reducing atmosphere. The phase transition temperature was found to shift downwards with increase in Sr content. Samples with x=0.10 to 0.15 in air and a sample with x=0.13 in the reducing atmosphere gave expansion coefficients comparable to that of 8mol% Y₂O₃-stabilized ZrO₂ (YSZ). In the reducing atmosphere, the thermal expansion coefficients of the samples with x=0.10 to 0.15 remarkably increased in the vicinity of 1000°C due to generation of oxygen vacancies.

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Alumina hydrate-coated SiC whisker, a starting powder for fabrication of SiC whisker reinforced alumina ceramics, was prepared from SiC whisker and aluminum sulfate by homogeneous precipitation method using urea. Effects of reaction conditions on the coalescence of coated bodies and formation of independent alumina hydrate particles were studied. Observation of coated bodies during reaction showed that coalescence of coated bodies occurs by collision and agglomeration followed by deposition of alumina hydrate on the collided specimens. Coalescence of coated bodies was suppressed by intensive stirring, use of a flow reactor, high [SiC]/[Al₂(SO₄)₃] ratio, low hydrolysis rate of urea, and high urea concentration. Generation of independent alumina hydrate particles was suppressed at a high SiC whisker concentration, a low aluminum sulfate concentration, and a low hydrolysis rate of urea. When the deposition rate of alumina hydrate was very low, coating was not uniform.

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A new technique for preparing Zn_xFe_3-xO₄ fine powders from α-Fe₂O₃ and Zn in Ar using a spontaneous completion reaction in the thermite method has been proposed. Preparation conditions for the Zn_xFe_3-xO₄ fine powders were investigated by varying Zn/α-Fe₂O₃ molar ratio and heating conditions under an Ar gas flow. The Zn_xFe_3-xO₄ fine powders of single phase were successfully prepared by firing the powder mixture of Zn/α-Fe₂O₃=0.35 (molar ratio) at 500°C for 1-10h in Ar (200cm³/min). The particle size of Zn_xFe_3-xO₄ powder prepared at 500°C for 3h was 0.3-0.6μm, and the powders showed nearly spherical in shape and little aggregation. The saturation magnetization and coercive force of the Zn_xFe_3-xO₄ powders were 97emu/g and 0.11kOe, respectively.

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Three-point bending, 4-point bending and tensile fatigue tests were carried out on sintered silicon nitride at room temperature and 1000°C, and size effect on the fatigue behavior was discussed. The difference in room temperature fatigue behavior estimated by different testing methods was explained by effective volume of the surface layer with a depth of 100μm. At high temperature, the difference was explained substantially by the effective volume of the whole specimen, but, the tensile fatigue data did not agree with the bending one in a low stress region in spite of the data correction by effective volume. The different cavitation effects on crack growth properties under bending and tensile loading conditions were considered to be responsible for the disagreement.

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To determine the thermal shock resistance in ceramics quantitatively with water quenching test, the heat transfer coefficient between water and surface of the specimen is known to be the most important factor and is closely related with the critical temperature difference. In this study, changes of temperatures at two different positions in the specimen were measured after the water quenching. The Biot number and heat transfer coefficient were estimated by comparing these data with the analytic or numerical solutions of thermal conduction equation. Based on this method, the heat transfer coefficients at different quenching temperatures and valuable information concerning the thermal shock test were obtained.

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The microstructure and mechanical properties of SiC-AlN solid solution ceramics and the ceramics after phase separation treatment were evaluated in relation to the temperature and time of annealing. The SiC-AlN (SiC/AlN=70/30) solid solution ceramics with the addition of Y₂O₃ and Al₂O₃ were prepared by hot-pressing at 2200°C under 22MPa for 8h in Ar, which were followed by a subsequent heat-treatment in the miscibility gap at a temperature of 1600°C or 1800°C up to 120h in Ar. The modulated structure characteristic of the spinodal decomposition was developed within crystalline grains by the phase separation treatment. The fracture toughness was enhanced by the phase separation at both 1600°C and 1800°C for 8h. The hardness also increased with the phase separation treatment. The changes of these properties are considered to be dependent on the introduction of a modulated structure in the crystalline grains. Both the solid solution ceramics and the ceramics with phase separation exhibited an increase in crack resistance with crack extension. This phenomenon suggests that the crystalline structure of solid solution or the modulated structure contributes effectively to the shielding of crack extension. Although the modulated structures which consist of phases with different Young's modulus and linear thermal expansion coefficient were introduced to the crystalline grains by the phase separation treatment, these two properties of the ceramics were independent of the phase separation.

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A humidity effects on impedance were examined for the Ruddlesdon-Popper type oxides series of SrLaScO₄ (n=1), SrLa₂Sc₂O₇ (n=2), and LaScO₃ (n=∞) with the general chemical formula SrO (LaScO₃)_n. The influence of adsorbed water in these samples on electrical properties has been characterized by the complex impedance analysis. These compounds showed the humidity sensing characteristics nearly the same as the well known ceramic humidity sensor materials, with the high sensitivities and the fast response time. In these layered oxide compounds, the humidity sensing characteristics showed a strong dependence on the structural parameter n.

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In order to investigate dynamic crack propagation processes in thermally tempered glass, observation of shadow spots and evalution of the dynamic stress intensity factor K_1D have been attempted using the method of caustics. Changes of the shadow spot diameter were studied at crack bifurcation in glass plates of 10mm thickness as a function of propagation distance before and after bifurcation, and also of the angle of bifurcation. It has been shown that values of K_1D could be reduced to one half at the bifurcation.

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The ceramization mechanism of electron-irradiation cured and incompletely heat-treated polycarbosilane fibers has been investigated. The pyrolysis rate was measured with a thermobalance in N₂ at temperatures from 1173 to 1373K. The pyrolyzed fiber was examined by X-ray diffraction, scanning electron microscope, specific resistance measurement and tensile test. The properties of the fiber changed abruptly at the early stage of pyrolysis, and changed gradually during subsequent pyrolysis. Because of ceramization of the fiber, the specific resistance decreased and the tensile strength increased. The pyrolysis rate was described by the first order rate equation. The activation energy was 148kJ/mol.

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Beta-SiC powder was synthesized by carbothermal reduction of silica contained in rice hull ash, and porous ceramics were fabricated by conventional sintering. Electrical conductivity and Seebeck coefficient were measured as functions of temperature under Ar atmosphere to evaluate their applicability to thermoelectric energy conversion. Thermoelectric properties of β-SiC ceramics fabricated from rice hull ash were comparable to those fabricated from a commercial high-purity powder.

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Ball milling is an important technique in powder processing of ceramics. Although small balls as grinding medium in ball milling give fine powder, the grinding performance depends on many other milling conditions, such as combination of ball size, rotation speed and packing volume of balls. In this paper, particlesize reduction rate of alumina was studied with respect to the combination of TZP (Tetragonal Zirconia Polycrystals) ball size and rotation speed. The TZP balls with a geometrical standard deviation of 1.7 in log-normal ball size distribution gave the highest relative density and the highest particle-size reduction rate. The particle-size reduction rate increased with increasing rotation speed under the conditions studied.

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Cordierite ceramics were prepared by sol-gel process using metal salts and a metal alkoxide as the starting materials, and their electrical and thermal properties were studied. Best starting materials were aluminium nitrate, magnesium acetate and tetraethoxysilane. Any other salts did not give a homogeneous solution and deposited after gelation. The solvent effect was very drastic. A highly homogeneous solution was obtained by using dihydric alcohols as a solvent, such as ethylene glycol. DTA and XRD were measured to identify the crystal phases of sintered specimens. IR spectra and NMR spectra were measured to study the solvent effects on the amorphous structure. DTA and XRD revealed that μ-cordierite single phase was obtained at 900°C and α-cordierite single phase at 1100°C using ethylene glycol as a solvent. However other phases, such as spinel and cristobalite, were obtained using ethanol as a solvent. IR and NMR data suggested that aluminium ions were mainly six-coordinated ([Al(H₂O)₆]³⁺ etc.) in wet gels, but the amount of four-coordinated aluminium ions ([AlO₄]) increased at the expense of six-coordinated aluminium ions with increasing heating temperature. It was considered that almost all aluminium ions were present as hydrated ions in wet gels and incorporated into four-coordinated silica network by heating. It was found from NMR measurements that five-coordinated aluminium ions exist in amorphous samples. Dense α-cordierite ceramics were obtained by calcining the gel powder at 700°C for 3h and by sintering at 1300°C. The thermal expansion coefficient and relative dielectric constants were evaluated as 1.5×10^-6K^-1 (r.t.-800°C) and 5.0 (<1MHz), respectively.

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The wear mechanism of ceramics by abrasive water jet (AWJ) has been studied. Two kinds of Si₃N₄ ceramics, β-Si₃N₄ and α′/β′-Sialon, were eroded by AWJ using four kinds of particles, garnet, Al₂O₃ (WA), Al₂O₃ (SA) and SiC. The water pressure was 147, 221 and 343MPa. The results indicate that the wear rate depends on the hardness ratio H_vt/H_vp of the specimen to the particle. When H_vt/H_vp<1, the wear rate was in the order of 10^-3cm³/cm³. When H_vt/H_vp>1, on the other hand, the wear rate was in the order of 10^-5cm³/cm³. The dependence of the wear rate (V) on the velocity (v) of the particles was expressed by the equation, V∝vⁿ, with n equal to 2-3. The wear rate of α′/β′-Sialon was always smaller than that of β-Si₃N₄ under the same AWJ conditions. This was related to the fact that the hardness of α′/β′-Sialon is higher than that of β-Si₃N₄. These phenomena have a tendency similar to that of sand erosion. Under water pressure of 147MPa and at a SiC abrasive particle feeding rate of 170g/min, β-Si₃N₄ and α′/β′-Sialon plates having a thickness of 5mm were cut at a speed of 80mm/min and 20mm/min, respectively.

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Thin films of PbTiO₃ and Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ were prepared by an alternate evaporation method. Ingredient metals of the thin films were repeatedly deposited on SnO₂-coated substrates by using electronbeam evaporation sources, then the deposited films were heated in air. Dependence of oxidation and crystallization process on the temperature and period of time for heat treatment was studied by X-ray diffraction analysis. When the thickness of each layer of the films was limited, films with a perovskite-type structure were obtained. By electron probe micro analysis, the compositions of the prepared thin films were confirmed to be nearly equal to the stoichiometric compositions.

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Superconducting Sr-Ca-Cu-O samples were prepared by using a high-pressure technique. (Sr_0.7Ca_0.3)_0.9CuO_y powders with KClO₃ (0.00-6.00wt%) were sintered at 930°C for 20min. under 5GPa. The sample made from the powder containing 4.00wt% KClO₃ showed a diamagnetic signal of -6% full Meissner at 5K. However, the sample contained little “infinite-layer” phase. This result suggested the presence of a new superconducting phase in the Sr-Ca-Cu-O system.

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This is the first study of slip cast continuous FGM. The material system used here is Al₂O₃, W, Ni, and Cr. For preliminary investigation and evaluation of sample properties, several tests were conducted. These analyses yielded the following results:
(1) Samples produced in this study contain three distinguishable zones: the filtrated low metal content zone, the sedimented high metal content zone, and the sedimented low metal content zone.
(2) Since a continuous compositional gradient exists in the sedimented zones, FGM having a gradually increasing Al₂O₃ content and a gradually decreasing metal content can be obtained by eliminating the filtrated low metal content zone either during green finishing or during final finish ing.
(3) The thermal expansion characteristic of these samples is similar to that of pure Al₂O₃ because these samples contain Al₂O₃ rich matrix throughout their bodies. Other properties such as fracture toughness, hardness, and electrical resistance of this material vary along the sample length in the forming direction.

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