An extended model of turbostratic stacking faults in hexagonal boron nitride crystals has been presented. In addition to the current state, the proposed model considers tilting in the layers of hexagonal boron nitride paracrystals. Besides reducing the velocity of phonons due to low periodicity in the turbostratic solid, the tilting causes an increase in hardness to 50% higher than that in crystalline material.
In sites of BN crystals where the interlayer distance is shorter than that in perfect hexagonal crystals, a secondary hybridization (sp^x), to which sp² was the main contributor but already resembling that in metastable BN (sp³), is suggested for explaining higher hardness of turbostratic materials. The symmetry of four sp^x orbitals is that of a trigonal pyramid with three basal and one vertex bond.
To verify the proposed turbostratic model, extensive research work must be carried out on detail study of the effect of the crystallinity of layered boron nitride on the phase composition of products of high-pressure phase transformation, especially from the aspect of topology. Moreover, theoretical calculations are desirable to establish the hypothetical secondary hybridization proposed here.

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The present study involves the fabrication of three-layered ceramics with an interior layer of SiC/Si₃N₄ which has a greater thermal expansion coefficient than the two outer surface layers formed of monolithic Si₃N₄. Surface compressive stress develops upon cooling owing to the higher thermal expansion coefficient of the inner layer. The bending strength and toughness of layered Si₃N₄ composites are substantially greater than those of monolithic Si₃N₄ because of the surface compressive stress on the outer layer and crack deflection by the interfaces. The residual stress increases with the addition of SiC in the inner layer and with the inner layer thickness. Crack behavior in layered samples is affected by the residual stresses, interfaces and free sample surfaces. Theoretical stress calculated based on beam theory is compared with the experimentally determined residual stress.

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Titanium nitride (TiN) whiskers were formed on the outer surface of a graphite tube by heating potassium fluorotitanate (IV) (K₂TiF₆) above 1300°C in a stream of nitrogen. It is found that the addition of reduced metals has remarkable effects on the deposition temperature, shape, and yield of TiN. By addition of calcium, aluminium, and silicon, TiN whiskers were formed at 1100-1400°C on the outer surface of the graphite tube. By addition of magnesium, TiN whiskers were formed at 1200°C on the outer surface of the graphite tube. When aluminium and silicon were added, TiN whiskers were formed on the surface of residual additive. It is speculated that the reduced metals accelerated the reduction of titanium fluoride. The shape of the whiskers was observed by SEM. The cross section of whiskers on the graphite tube was mostly square, and that of whiskers on residual additive was mostly octagonal. It was suggested that the whiskers with a square cross section formed on the graphite tube grew in the ‹100› direction, and those with an octagonal cross section obtained on residual additive grew in the ‹112› direction.

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A chemically durable glass containing a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to β-emitter with 14.3d half-life by neutron bombardment. Microspheres of the activated glass injected to the tumors can irradiate β-ray directly to the tumors without giving radiation to neighboring normal tissues. In order to examine possibility for obtaining such a glass by ion implantation, P⁺ ion was implanted into a pure silica glass in a plate form under 50keV to different doses. This implantation energy is estimated to give the maximum concentration of P⁺ ion at 48.6nm in depth from the surface. Structural damage was produced near the surface of the glass by the ion implantation for all the doses in the range from 5×10¹⁶ to 1×10¹⁸cm^-2. The phosphorus was localized only in the regions deeper than 1.2nm from the surface, taking a form of phosphorus colloids, for a dose of 5×10¹⁶cm^-2, whereas it was distributed up to the glass surface and a part of it near the surface was oxidized for doses above 1×10¹⁷cm^-2. The former glass little released both P and Si into water at 95°C even after 7d, whereas the latter glasses released appreciable amounts of these elements. At implantation energy of 20keV, even a dose of 5×10¹⁶cm^-2 formed an oxidized phosphorus at the glass surface and gave appreciable releases of P and Si from the glass into water. This indicates that a chemically durable glass containing a larger amount of phosphorus could be obtained if P⁺ ion is implanted at higher energies and localized in a deeper region, even if the surface structure of the glass is damaged by the ion implantation.

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A peroxo titanic acid (PTA) solution has been prepared by mixing titanic acid wet gel and hydrogen peroxide solution. The PTA solution was a neutral, transparent, stable liquid. The PTA crystallized to form an anatase phase after calcination at a temperature above 250°C. When the PTA solution was autoclaved at a temperature above 100°C for 6h, it changed to a sol containing anatase crystals less than 20nm in diameter. Aggregation occurred after autoclaving at a temperature above 120°C. When the PTA solution was heated to 100°C, it was translucent and stable in spite of containing ultrafine anatase crystals (9nm in diameter). It was deduced that the surfaces of anatase crystals are modified by the peroxo groups.

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For use in a microelectronic circuit, as-sintered and polished aluminium nitride substrates have imperfections of surface roughness with pores and open porosity, respectively. The use of a thin coating of silicon oxide was studied for forming 10-μm-wide patterns on the surface of the aluminium nitride substrate. When polished substrates were used and the thickness of silicon oxide was held at less than 1200nm, the minimum surface roughness of coated substrates had R_a of 20nm and R_max of 200nm, and a functional 10-μm electric circuit pattern could be made. Thermal conductivity of coated substrates decreased from 186 to 179W/m·K with increasing thickness of silicon oxide up to 1200nm. The thermal conductivity of coated substrates decreased following the value calculated by an expression for a multilayer board.

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The thermal expansion ratio of baked MgO-C bricks under an applied load (TEAL) of 4MPa decreased in the temperature range of 400-700°C and became negative at room temperature (RT) after heating and cooling, due to volatile matter in the resin binder. The thermal expansion ratio under free load (TEFL) was almost constant in the temperature range of 400-700°C and became positive at RT after heating and cooling. The TEAL could not be correlated with the TEFL and both exhibited nonelastic characteristics. For MgO-C bricks after heat treated twice at 1000°C, the effect of the volatile matter in the resin could not be confirmed, and the TEFL at 1000°C was lower than that at the same temperature for the baked samples. The TEAL remained unchanged at temperatures ranging from RT to 400°C and became negative at RT after heating and cooling, due to the irreversible effect of thermal expansion absorption caused by the free carbon in the resin. The TEAL could be correlated with the TEFL by assuming an elastic-like modulus for the free carbon. When the effect of the free carbon ended, the TEAL changed linearly and was close to the estimated thermal expansion ratio based on those of the raw materials. For MgO-C bricks containing 3% Al, the elastic modulus at temperatures above 700°C was higher than that of the samples without Al because of the formation of metal reaction products. Furthermore, the TEAL in the former case was higher than that in the latter case, when the effects of volatile matter in the resin and the free carbon could be neglected.

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H-R represents a strongly acidic ion exchange resin with hydrogen form. Dissolution mechanism of two modifications of Ca₃(PO₄)₂, α- and β-TCP, in the presence of H-R was studied to compare their reactivities. Chemical analysis of liquid phase, simultaneous measurement of calorimetry and conductimetry, XRD and SEM observation were carried out to discuss the dissolution process. Hydroxyapatite (HAp) and brushite (DCPD) were also used for reference. The results obtained are summarized as follows; (1) The heat of dissolution (exothermal in kJ/mol) at 25°C measured by introducing a sample into aqueous suspension containing an excess amount of H-R was estimated as follows; β-TCP: 122.8, α-TCP: 137.1, HAp: 310.8, DCPD: 2.4. Consequently, the heat of transition from α- to β-TCP was calculated to be 14.3kJ/mol. (2) The dissolution of β-TCP proceeds by the following two-stage reactions; Ca₃(PO₄)₂+4(H-R)→2(Ca-R₂)+Ca(H₂PO₄)₂ (aq)……(1), Ca(H₂PO₄)₂(aq)+2(H-R)→Ca-R₂+2H₃PO₄(aq)……(2). (3) In contrast with the β-phase, the dissolution of metastable α-phase proceeds by the three-stage reactions of Eqs. (1), (3) and (4). An initial addition of H-R gives Ca(H₂PO₄)₂ solution (Eq. (1)), which was soon followed by crystallization of intermediate DCPD according to the Eq. (3). Two distinct thermal flows due to the dissolution (Eq. (1)) and crystallization (Eq. (3)) processes are accompanied by the corresponding variations of specific conductivity. Ca₃(PO₄)₂+Ca(H₂PO₄)₂(aq)+8H₂O→4[CaHPO₄⋅2H₂O]……(3). Finally, the dissolution of DCPD is completed to give phosphoric acid and Ca-absorbed resin (Eq. (4)). CaHPO₄⋅2H₂O+2(H-R)→Ca-R₂+H₃PO₄+2H₂O……(4).

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Dried boehmite gel was preheated at various temperatures below 800°C and they were pressed and formed into bars. Then they were sintered in the temperature range of 1500-1650°C. The porosity and the bending strength of these sintered bodies were affected by the preheat-treatment temperature of the boehmite gel. There was no change in the structure of the sintered bodies which were preheated at temperatures below 200°C. A sintered body at 1650°C gave a porosity of 40% and a high bending strength of 80MPa. The relation, σ=ãρⁿ was established between the bending strength (σ) and the density (ρ) of the sintered bodies. The exponent n in the above relation is the same and the factor ã is different between these two starting samples, boehmite and intermediate alumina. The factor ã is affected by the fractal structure of sintering body.

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The oxidation behavior of porous high-purity SiC was studied at 1600 and 1700K for 15h in Ar-O₂ (P_O2: 0.02-97kPa) by measuring the oxidation rate. In oxidation at 1600K, only the weight gain of the SiC was observed after the oxidation, and the amount of cristobalite on the oxidized surface increased with increasing P_O2. In oxidation at 1700K, the weight loss was observed at the oxygen partial pressure of 0.02kPa while the weight gains were observed at an oxygen partial pressures of 2 and 97kPa. The oxidation rate was determined by measuring the evolved gases throughout the oxidation reaction using a mass spectrometer. The oxidation kinetics obeyed the parabolic law under 0.02-97kPa at 1600K and under 2-97kPa at 1700K, indicating that. the passive oxidation occurred. The transition oxygen partial pressure below which the oxidation mechanism changes from passive to the active one, is presumed to be approximately 0.1kPa in the case of the oxidation at 1700K.

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An accurate evaluation of transient heat transfer coefficients during quenching is quite important to estimate the thermal shock resistance of ceramics, especially for the quenching medium which makes phase change. In this paper, transient heat transfer coefficients for typical quenching media are obtained from experiments and calculations, and then Biot's numbers are estimated under various quench conditions. Thermal shock stresses in specimens during quench tests are also analyzed numerically by a finite element method. Results show that Biot's numbers vary with the initial temperature of the specimen and the variations of thermal stress with time in the case of cooling by boiling heat transfer differ from those of cooling by convection heat transfer. It is also mentioned that thermal shock stresses do not always increase in spite of the increase in the quenching temperature difference under the heat transfer of the transition boiling and the film boiling regions.

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Silicon nitride with anisotropic microstructure was fabricated by tape-casting of raw powder slurries with 0-10vol% seed particles of morphologically regulated β-Si₃N₄ single crystal, followed by gas pressure sintering of stacked sheets. The effect of orientation degree and area fraction of large elongated grains on mechanical properties was studied. Fracture toughness (K_IC) and bending strength (σ_f) measured in the direction perpendicular to grain alignment increased with an increase in seeds amount, which was associated with the fact that both orientation degree and area fraction of large elongated grains increased with increasing amount of seeds. The specimen with 5vol% seeds, in which large elongated grains occupy a cross-sectional area of about 46%, exhibited a dominant orientation parallel to the casting direction. The specimen showed high K_IC of 11.7MPa·m^1/2 and high σ_f of 1200MPa. Further addition of seeds resulted in a slight decrease in K_IC and σ_f owing to pore generation and coalescense of large elongated grains. On the contrray, K_IC and σ_f measured in the direction parallel to the grain alignment decreased monotonously with an increase in seeds amount.

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Vickers hardness distributions in disk shaped and hollow-disk shaped compacts with SiC granules, which showed typical elasto-plastic behavior, and their sintering shrinkage were measured to investigate the influence of the CIP Compaction method on the density distribution. The reduction of raw density toward the center in the radial direction was indicated indirectly from Vickers hardness measurements for the disk shaped compact. For the hollow-disk shaped compact prepared with mandrel, however, the density near the interface to mandrel increased extremely, while little or no density gradient was observed in other part. In the hollow-disk shaped compact, the result that the shrinkage of inner diameter was smaller than that of outer diameter was qualitatively compatible with the density distribution provided by hardness measurements. The density distribution in the disk shaped compact from hardness measurements qualitatively agreed with the density distribution predicted by finite element method (FEM) analysis with assumption of nonlinearity for the powder material, but the density distribution in the hollow-disk shaped compact did not completely agree with that predicted by FEM. For the hollow-disk shaped compact, it was thought that the differences in results between measurements and FEM analysis were influenced by the reduction of applied pressure near the center and the stress concentration near the interface to mandrel.

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Powder and film of amorphous antimonic acid (Sb₂O₅⋅nH₂O) are prepared by a direct reaction of Sb(O-n-C₃H₇)₃ with H₂O₂ aqueous solution at 0°C. Thermal decomposition behavior of the powder in air almost coincides with that of the previouly reported one which was prepared by hydrolysis of SbCl₅. Electrical conductivity measurement of the film is carried out by using an alternating current complex impedance method. The conductivities at 20°C in the relative humidity range of 0.1 to 1.0 are in the range of 3×10^-6 to 1×10^-3Ω^-1·cm^-1, whose values increase with increasing the relative humidity.

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Sialon/SiC whisker composites with 5 and 10mass% SiC(w) were prepared by hot-isostatic-pressing. The fatigue behavior of composites at room temperature in air was investigated. Dynamic, static and cyclic fatigue tests were carried out on smooth specimens by the 3-point bending method. The microstructure, bending strength and fracture toughness of composites were similar to those of monolithic sialon. The addition of SiC(w) inhibited the slow crack growth attributable to the stress corrosion by humidity in air observed in monolithic sialon. The dynamic fatigue parameter “n” was 26 in monolithic material, 108 in composite with 5mass% SiC(w) and 90 in 10mass% SiC(w). In static fatigue tests, the observed lifetime of each sample was in agreement with that predicted from dynamic fatigue properties. The acceleration of fatigue was observed in monolithic sialon and composite with 5mass% SiC(w), but the addition of 10mass% SiC(w) reduced the accelerative effects on cyclic fatigue.

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Dioctahedral mica ceramics containing fluorine muscovite and amorphous phase were prepared by solid state reaction in air with using kaolinite and K₂SiF₆ as raw materials. The appropriate molar ratio for obtaining high contents of fluorine muscovite was 0.6K₂SiF₆: 1.5 kaolinite. Fluorine muscovite crystallites were precipitated at 600-700°C for shorter sintering times of 3-6h, developing house of cards microstructure with remaining relatively high porosity of 18-28%. The porosity depended on the heating rate. The lattice constant b of precipitated fluorine muscovite slightly increased with increasing temperature from 600°C to 700°C, coinciding with that of fluorine muscovite synthesized as a single phase in the closed system by using γ-Al₂O₃ as a raw material. This indicates that tetrahedral aluminium substitution slightly increases with increasing temperature and that fluorine muscovite having an ideal composition is formed at 700°C. However, topaz crystallized as a stable high temperature phase at higher temperatures over 750°C.

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β-sialon (z=1)-SiC (50mass%) composite was fabricated by hot-pressing a spray-dried mixture of α-Si₃N₄, SiC and aluminum-iso-propoxide solution. The bending strength and fracture toughness (K_IC) of sinterd bodies were investigated by comparing with β-sialon (z=1) without SiC. Both strength and K_IC were increased from 1000 to 1560MPa and 3.5 to 4.5MPa·m^1/2 by SiC addition, respectively. About a half of tested specimens fractured from internal defects and the other fractured from surface flaws. The strength of the specimens which fractured from internal defects increased from 1180 to 1580MPa. This value coincided with that derived from the equation K_IC=σ_fY√c, due to the same size of defects as fracture origins (c). In case of the specimens which fractured from surface flaws, the strength increased from 900 to 1540MPa. The increase in K_IC presumably resulted in decreasing the size of machining flaws as fracture origins. It was considered that as the transgranular fracture occurred in the β-sialon matrix of this composite, homogeneously dispersed SiC particles immediately brought small crack deflection. This might be a reason for increase in both strength and K_IC.

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Synthesis of CdCr₂Se₄ spinel for optical spectra measurements has been carried out by the dry technique at 773, 873 and 973K. Although nearly single phase was obtained at 873 and 973K after extremely long period of heating, say 47d, of presintered materials at 773K, 100d heating at 773K did not yield single phase due to firm association of accessory phases of CdSe and Cr₂Se₃. EPMA mapping analysis for such samples showed the independent presence of massive grains of CdSe among the spinel grains and disseminated presence of Cr₂Se₃ in the spinel grains as inclusions. This isolate presence of CdSe and Cr₂Se₃ is probably the main cause of preventing the formation of the spinel single phase in a short period of time. Unit-cell parameters, spinel u-parameters and band gaps as measured by XRD and optical spectroscopy were 1.0744-1.0749nm, 0.388-0.389 and 1.27-1.30eV, respectively, depending on synthetic conditions.

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Amorphous Bi₂O₃-TiO₂ and Nb₂O₅-TiO₂ transparent films were successfully prepared by dip coating method, using Bi-Ti complex alkoxide and corresponding metal alkoxide solutions, respectively. The films were amorphous up to 300 or 500°C and highly transparent from 500 to 2000nm. The χ⁽³⁾ values obtained were mostly in the order of 10^-12 esu although the films had high porosity, and the values of 10^-11 esu were expected for fully dense amorphous films.

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Alumina-zirconia composite powder were prepared from aluminium iso-propoxide, zirconium n-butoxide and various organic ligands which were 1, 2-ethanediol, 1, 2-propanediol and 1, 3-propanediol. The effect of organic ligands on properties of the alumina-zirconia composite powder was investigated. It was suggested that the amount of organic compounds in the dry gels and the homogeneity of the alumina-zirconia composite powder changed with the species of organic ligand. The specific surface area, the pore volume and the pore size distribution of the alumina-zirconia composite powder depended on the organic ligand, and the pore size of the alumina-zirconia composite powder is distributed from 1 to 4nm in radius. The control of pore size distribution by varying the kind of organic ligands was suggested.

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Oxidation behavior of titanium boride (TiB₂) powder was investigated by thermal analyses (DTA and TG) and X-ray diffraction. From the DTA and TG analyses, a broad exothermic peak with a continuous weight gain was observed between 450 and 750°C. The exothermic peak was bimodal with a minimum around 550°C. High-temperature X-ray diffraction spectra taken around this temperature were featureless. These observations suggest that a high viscosity liquid-phase of B₂O₃ forms as a thick surface coating which then prevents further oxidation of the underlying material. The X-ray diffraction analyses revealed that the reaction products were TiO₂ (anatase) at lower temperatures and TiO₂ (rutile) at higher temperatures. TiBO₃ was also identified in the material after heating to 1000°C.

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Whisker formation on alumina particles was attempted through growth of a number of fine mullite whiskers by the thermal decomposition of clay for porcelain at 1400 to 1600°C. After firing, the excess silica phase was hydrothermally dissolved in 2N NaOH solution at 180°C. The effect of firing temperature, and compositions of alumina and clay on the formation of mullite whiskers on alumina particles was investigated. In case of 18.8mass% alumina and 81.2mass% calcined clay, the growth of whiskers enhanced by the decomposition of clay was promoted, and alumina particles were coated with a number of mullite whiskers 50 to 200μm in length and 1 to 3μm in diameter just like sea urchin. Furthermore, alumina particles reacted with the excess amorphous silica in the fired clay to form small pillarlike mullite crystals in an alumina particle. But growth of whiskers was inhibited with increasing amount of alumina.

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