In nitriding of aluminum powders, several methods have been suggested for preventing the aggregation of melted particles of aluminum. In this study, the surface of aluminum particles was covered with hydroxide layers. Using the aluminum powders containing more than 1wt% oxygen, the nitridation reaction was completed successfully at 900°C for 2h. However, the aluminum powders containing less than 1wt% oxygen did not react with nitrogen, because of aggregation of aluminum particles. When the oxygen content in aluminum powder was 1wt%, the highest conversion of 98.9% was obtained and the oxygen content in the product: AlN was 1.3wt%. Since the nitriding proceeded rapidly at 900°C, the products sintered strongly by the heat of reaction. In order to decrease the nitriding rate, the nitrogen gas was diluted with argon gas. The product obtained by using diluted nitrogen gas was very easy to grind. The preferable concentration of nitrogen was 90%, considering the conversion and the grindability.

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Present investigation was undertaken to get useful technological informations for the suitable designing of the semiconductive glass composite having desired electrical properties. The composite has a microstructure in which semiconductive SnO₂ fine particles are dispersed in a glass matrix. The effects of the interaction between the glass and Al₂O₃ substrate and the sinterability of the glass particles were revealed. When the magnitude of the interaction between the glass and Al₂O₃ substrate was relatively large, many microcracks occurred in the composite and the electrical conduction path was broken because of the tensile stress parallel to the Al₂O₃ substrate in the thick film samples. It was supposed that these cracks were generated by the difference of the shrinkage between the matrix glass and Al₂O₃ substrate. On the other hand, when the sinterability of the glass particles was relatively large, the influence of the Al₂O₃ substrate on the electrical conduction path was scarcely large because the homogeneous microstructure and good mutual connection were developed during firing. Therefore, it is feasible to produce the thick film resistor having well-controlled electrical properties by the suitable selecton of the glass composition and of the firing condition.

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In Part 1 of the present paper the internal friction of XNa₂O⋅(1-X)B₂O₃⋅2SiO₂ glasses was measured and the cause for the high-temperature peak was explained on the basis of the theory on the structure of alkali borosilicate glass proposed by Dell et al. In the present paper diffusion coefficients of oxygen in the glasses of the same composition system described above have been measured at temperatures below the glass transition points, and the mechanism for oxygen diffusion in this temperature region has been discussed by the citation of the data from literature on diffusion in glasses. The activation energies for oxygen diffusion are in good agreement with those for a mechanism for high-temperature peak observed on the internal friction curves. It is concluded that the results described above present the proof that the high-temperature peak is caused by the movement of non-bridging oxygen under stress, and that the diffusion of oxygen below the glass transition point occurs in the presence of lattice defects frozen-in at the glass transition point.

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Ferric oxide particles were coated with silica by hydrolysis of ethyl silicate. When ethyl silicate (TEOS) was hydrolyzed in an ammonia alkaline ethanol suspension of Fe₂O₃ under ultrasonic agitation, silica precipitated on the surface of ferric oxide particles. The obtained coated particles were in monodispersed state. The coating conditions were affected by the amount of dispersed ferric oxide, the concentrations of TEOS, NH₃ and H₂O. Especially, when TEOS concentration became too high, silica particles precipitated also in the dispersing media. And a linear relationship was found between the limit of concentration of TEOS (C_T) against silica precipitation and the concentration of dispersed ferric oxide (C_F). Therefore, in order to prevent the separation of silica particles, TEOS concentration must be kept lower than this limiting line. The specific surface area and intensity of XRD for ferric oxide were greatly decreased by silica coating. The electrophoretic mobility curve of the coated particles was in agreement with that of silica particles. From these results, it was estimated that the surface of coated particles was perfectly covered with silica.

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The effect of AlN powder properties on thermal conductivity was studied by evaluation of powder properties, analysis of sintering behavior and measurement of thermal conductivity. Six commercially available AlN powders were used in as-received form. The as-received powders were mainly evaluated for particle size distribution, SEM observation and chemical analysis. Degree of aggregation of the powders was characterized by comparison of aggregation from SEM micrographs and the change of particle size distribution by ultrasonication. Each powder was processed by adding 5wt% of Y₂O₃ as a sintering aid, then green bodies were formed by CIP after uniaxial press and sintered at 1900°C for 3h in 0.203MPa N₂ gas. The sintering behavior was studied at 1500°, 1700°, 1800° and 1900°C. It was found that the powders containing hard aggregates densified slowly and their sintered bodies had low thermal conductivity in spite of low oxygen content. The mechanism of slow densification and decrease of thermal conductivity is explained by a mechanistic model. This model includes aggregate structure, condition of liquid phase formation and oxygen trapping.

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The thermal decomposition of polyvinylbutyral (PVB) and polyvinylbutyral/PLZT, PMN dielectric powder composite was studied using pyrolysis gas chromatograph method. On thermal decomposition of only PVB, at 255°C n-butanal was begun to eliminate and then many gas products which were n-butanal, acetaldehyde, 2-butenal, dihydrofuran, benzene, and propane etc., were clearly begun to eliminate at about 400°C. In the PVB/PLZT, PMN dielectric powder composite, PVB thermal decomposition was clearly begun at lower temperature that was about 300°C than only PVB case. The gas products were same. The velocities of decomposition of PVB and the activation energy were tried to be calculate. The velocity of thermal decomposition of PVB was 0.01s^-1 at 386°C. In the PVB/PLZT and PVB/PMN dielectric powder composite, these of thermal decomposition of PVB were respectively 0.65 and 2s^-1 at 386°C. The activation energy of PVB thermal decomposition was 70kcal/mol and in the PVB/PLZT, PMN dielectric powder composite that was 21kcal/mol.

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Formation of thin film resistors employing thermal decomposition of metallo-organic compounds was studied. It was found that RuO₂-TiO₂ thin films showed good uniformity and thermal stability owing to the formation of solid solutions in this system. In these films, solid solutions with rutile structure were formed over the entire concentration range. When Ti concentration range was 0-50mol%, the crystallographic structure of films showed a single phase of the solid solution. The solid solution was proved to be a metastable phase. It was revealed that the phase separation was dependent on impurities, which diffused from the substrate. Phase separation was observed above 700°C, if constituents of the substrate did not diffuse. On the other hand, if constituents of the glass substrate diffused into the film, the phase separation did not occur and the solid solution was stable above 700°C. As a result, a thin film resistor of good thermal stability and uniformity was obtained when a film with Ti concentration of 0-50mol% was formed on a substrate and the constituents of which diffuse into it.

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The corrosion behavior of mullite ceramics prepared from various starting powders in water was studied by the autoclave method at 300°C and 8.6MPa for times up to 10 days. The degradation of bending strength due to corrosion was also examined for selected specimens. The aqueous corrosion proceeded according to the reaction 3Al₂O₃⋅2SiO₂+3H₂O→6AlOOH+2SiO₂ with weight loss by dissolution of SiO₂ and formation of boehmite (AlOOH) residue layer. The extent of corrosion resistance was significantly dependent on the powder preparation method and chemical composition. Seventy four wt% Al₂O₃-mullite prepared from an alkoxide-derived powder showed the highest corrosion resistance. On the other hand, 75wt% Al₂O₃-mullite prepared from a sol-gel powder showed the lowest corrosion resistance under the experimental conditions studied. Mullite ceramics with high-corrosion resistance was found to be attained by homogeneous mixing SiO₂ with Al₂O₃ in an alkoxide-derived or coprecipitation powder. The bending strength of the corroded specimens reduced to around 2/3 of the original values in the early stage of corrosion, and then remained almost constant up to 10 days. An understanding of this sort of corrosion behavior is important and useful for improvement of mullite ceramics.

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AlN polycrystalline wafers polished with an ultra-fine alumina abrasive on a tin-disk were observed with a transmission electron microscope. It has been reported in a previous paper by the present authors that the surface layer is heavily dislocated when wafers are wetpolished with Al₂O₃ and Cr₂O₃ abrasives. Such damage was reduced remarkably in the present samples. Some dislocations were, however, still found and exfoliation of grains often occurred. Crystallographical nature of dislocations was analyzed. The origin of dislocation production during polishing was discussed.

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Monodispersed spherical BaTiO₃ powders were prepared by hydrolysis of Ba/Ti bimetallic alkoxide, and the influences of water concentration, volume ratio of acetonitrile in the mixed solvent, aging time and hydrolysis temperature on the morphology of the BaTiO₃ powders were investigated. The hydrolysis rate of Ba/Ti bimetallic alkoxide, which was prepared by refluxing titanium iso-propoxide and barium in n-octanol at 150°C in N₂, was controlled in the mixed solvent of n-octanol and acetonitrile. The optimum conditions for preparing spherical BaTiO₃ particles were; Ba/Ti Bimetallic alkoxide concentration 0.03mol/l, water concentration 0.2mol/l, volume ratio of acetonitrile in the mixed solvent 30vol%, aging time 1h and hydrolysis temperature 30°C. The average particle size and geometrical standard deviation of obtained particles were 0.082μm and 1.24, respectively. The obtained particles were amorphous and hydrated, which crystallized on heating at 600°C, and necks developed between particles at 1000°C.

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In V₂O₅-P₂O₅ glass system containing a large amount of V₂O₅, addition of Sb₂O₃ was very effective to improve the water durability. To clarify this effect, the influence of Sb₂O₃ addition on the glass structure was studied. The added Sb₂O₃ acted particularly on V-ions in the glass, and caused the following redox reaction. 2V₂O₅+Sb₂O₃→4VO₂+Sb₂O₅ (2V⁵⁺+Sb³⁺→2V⁴⁺+Sb⁵⁺) Decrease in V⁵⁺ -ions forming a layered structure and increase in V⁴⁺ -ions not forming this structure were considered to transform the glass structure from layered to three-dimensional network, which prevented water molecules from penetration. Further, this structural transformation decreased the number of sites which were attacked easily by water molecules, i.e., quasi-double bonding oxygens and three-coordinate oxygens in V₂O₅, P-O-P bonds and non-bridging oxygens, and increased stable two-coordinate oxygens (bridging oxygens). Both of the structural transformation and the increase in bridging oxygens were considered to be effective to inhibit the erosion of V₂O₅-P₂O₅ glasses with Sb₂O₃ addition by water. Further, the addition of Sb₂O₃ did not increase the characteristic temperatures of glass remarkably, because packing density of oxygens remain unchanged by the addition.

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Ceramic TiB₂-19.0-19.5wt% (2mol% Y₂O₃-ZrO₂) composites with 2.5-5.0wt% SiC were fabricated by hot isostatic pressing (HIP) with and without a glass encapsulation. The effects of SiC addition on the mechanical properties and siterability of TiB₂-20wt% (2mol% Y₂O₃-ZrO₂) HIP'ed bodies were investigated. The addition of SiC improved the sinterability of TiB₂-20wt% (2mol% Y₂O₃-ZrO₂) appreciably. Composites of TiB₂-19.0-19.5wt% (2mol% Y₂O₃-ZrO₂) with 2.5-5.0wt% SiC densified up to 96.7% of their theoretical densities by vacuum sintering at 1700°C for 14.4ks. These sintered bodies almost fully densified by capsule-free-HIP. On the other hand, TiB₂-20wt% (2mol% Y₂O₃-ZrO₂) densified up to 63.7% by the same vacuum sintering. The addition of SiC was also effective in retarding the grain growth of TiB₂ and ZrO₂. The grain sizes of TiB₂ and ZrO₂ of TiB₂-19.0-19.5wt% (2mol% Y₂O₃-ZrO₂)-2.5-5.0wt% SiC HIP'ed bodies were about 1.5 and 1.2μm, respectively. They were about 2/3 of those of TiB₂-20wt% (2mol% Y₂O₃-ZrO₂) HIP'ed bodies. The three-point bending strengths of TiB₂-19.0-19.5wt% (2mol% Y₂O₃-ZrO₂)-2.5-5.0wt% SiC glass-encapsulated-HIP'ed bodies were 1240MPa, which is slightly higher than that of TiB₂-20wt% (2mol% Y₂O₃-ZrO₂) HIP'ed bodies. Vickers hardness and fracture toughness were not affected by the addition of 2.5-5.0wt% SiC. The mechaical properties of TiB₂-(2mol% Y₂O₃-ZrO₂) HIP'ed bodies were controlled by the monoclinic ZrO₂ ratio in ZrO₂ and monoclinic ZrO₂ content in HIP'ed bodies, as we have reported in the previous paper. The addition of SiC affected them only slightly, so that the mechanical properties were also little affected.

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Chemical reaction between SiC ceramics and Ni or Fe foil has been used for making grooves on the sliding face of SiC ceramics. To accomplish the grooving process, the grooved face of SiC ceramics should be crack free and smooth. The reaction product layer between SiC ceramics and Ni foil was composed of deposited graphite, δ-Ni₂Si and Ni₃Si₂. Generation of cracks in SiC ceramics was not dependent on the product species, but dependent on the size of deposited graphite. Larger graphite grains more deteriorated reaction layers, and generation of cracks in SiC ceramics was prevented. Reaction between SiC ceramics and Fe foil yielded graphite, Fe₅Si₃ and Fe₃Si. Extended reaction vanished Fe₃Si and generated no cracks in SiC ceramics. The thickness of SiC ceramics consumed was calculated from the thickness of Ni or Fe foil and the product species and was shown to coincide with the observed value.

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New machinable glass-ceramics containing fine calcium-mica were prepared by crystallizing glasses in the system Ca_xK(_1-2x)Mg₃(Si₃AlO₁₀)F₂. TEM observation suggested that the host glasses were separated into two fine phases, and the precipitating crystal size decreased with increasing the potassium content. The machinability were improved with increasing the calcium content. The mechanical strength and the machinability of the glass-ceramics depended on both the amount of calcium-mica precipitated and the crystal size. Because of its high bending strength (≈300MPa) and its hardness compatible with natural teeth, it has great potential for dental prostethic applications.

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The phase diagrams of Al_2-xY_xO₃-SiO₂-Si₃N₄ system (x=0.75 and 1.06) at 1500°C were studied. Oxynitride glasses were prepared by quenching a liquid phase at 1500°C. The maximum concentration of N atoms in the glasses prepared by this method was in the range of 4.6-4.9 at%. The glass transition temperature, the softening temperature and the crystallization temperature of Al-Y-Si-O-N oxynitride glasses were measured as a function of composition and found to increase with increase in N concentration. The Vickers hardness of the glasses increased with increase in N concentration. Stability and oxidation of oxynitride glass in air at temperatures from 950°C to 1100°C and the solubility of Si₃N₄ into glass were also studied and discussed.

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To develop a complicated shape forming method for the fabrication of Si₃N₄ engineering ceramic parts slip casting was studied. As the powder characteristics, the isoelectric points of α-Si₃N₄ (by direct nitridation, median particle size=1.56μm), α-Al₂O₃ and Y₂O₃ were determined from zeta-potential measurement to pH=4.9, 8.33 and 9.55, respectively. The preparation conditions of well-dispersed slurries were determined for the solid (92wt%α-Si₃N₄, 4wt%α-Al₂O₃, 4wt% Y₂O₃) by using an organic polymer deflocculant. High-density green body (density=1.95-2.18g/cm³) was prepared from the slurry (75-80wt%solid) by vacuum filtration with a porous resin mold. Fully densified specimens were obtained by gas pressure sintering (at 1770°C for 4h at a N₂ pressure of about 0.9MPa). The flexural strength and weibull modulus of the specimen decreased from 726 to 611MPa and from 14.8 to 6.5 with increasing amount of binder from 0 to 4wt%.

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The grain boundary phase in gas-pressure sintered silicon nitride containing 1mol% (SN1) and 10mol% (SN10) of equi-molar Y₂O₃-Nd₂O₃ was investigated using a transmission electron microscopy. In SN1, grain boundary phases were observed in two-grain boundaries and multi-grain boundaries. In SN10, pockets of an additive-rich glassy phase were observed beside two-grain boundaries and multi-grain boundaries, showing that too much additive caused glassy pockets. SN1 contained silica-rich phase in the multi-grain boundary, although SN10 contained additive-rich phase. Silica-rich phase with a lower melting temperature contributed to increased sinterability of SN1.

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The yield of mullite produced by firing a mixture of New Zealand kaolin and alumina (Al₂O₃/SiO₂=1.0 in molar ratio) increased rapidly above 1500°C as compared with that for kaolin alone. The mullite was recovered by treating the fired body with fluoric acid. The mullite particles obtained by firing the kaolin-alumina mixture at 1600°C for 10h were granular. However, the needle-like mullite particles were produced by firing kaolin and a kaolin-alumina mixture both containing float glass powder (10wt%) at 1400°C. Needle-like mullite particles obtained by firing kaolin, kaolin-alumina, kaolin-glass and kaolin-alumina-glass at 1600°C for 10h were 6, 3, 13.5 and 12.5μm long, respectively. The growth rate of needle-like mullite particles produced in the samples mixed with glass could be expressed as L³=1.85×10¹⁸ exp (-5.57×10⁵/RT)t, where L is the length of needle-like mullite particles (μm), R the gas constant (J/K⋅mol), T the absolute temperature (K) and t the time (h). However, this equation was not applicable when the yield of mullite was close to 100%. The Al₂O₃/SiO₂ molar ratios of needle-like mullites obtained by firing kaolin-glass and kaolin-alumina-glass mixtures at 1600°C for 10h were 1.59 and 1.62-1.64, respectively, larger than 1.50 for the theoretical mullite composition. Their lattice constants a₀ were 7.669Å and 7.667Å, respectively. These values were also longer than 7.5456Å of JCPDS 15-776. The longer a₀ values might have resulted from the alumina-rich composition of the needle-like mullite particles.

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The temperature measurement of Y₂O₃ doped AlN during plasma sintering was studied. The temperature of specimen, T_s was measured using a (W-5%Re)-(W-26%Re) thermocouple buried in the specimen. T_s below 1100°C could be measured directly in-situ using a low pass filter. T_s above 1100°C could not be measured due to interference of plasma noise. Hence, T_s was measured by extrapolation of a cooling curve after extinguishment of plasma. The extrapolation curve was determined by simulating the cooling curve. The thermal conductivity and emissivity of the specimen could be also estimated from simulation of the cooling curves. The measurement of T_s and simulation of the cooling curve showed that T_s was elevated from 1800° to 2200°C by the change of surface morphology after AlN evaporation, but emissivity was kept constant in spite of the change in morphology. It was found that rapid re-heating and re-densification after AlN evaporation occurred by the increase in heating from plasma, which was enhanced by Y₂O₃ powder deposited on the specimen surface.

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Dehydration and rehydration characteristics of synthetic magadiite and kenyaite were investigated in a temperature range from R. T. to 1000°C, and also under high vacuum at R. T. Magadiite and kenyaite lost interlayered water in the range of R. T.-600°C accompanying the decrease of basal spacing. At 80°C-100°C, the “intermediate” step of dehydration was observed for both compounds with the basal spacing of 14.1Å for magadiite and 18.8Å for kenyaite. Reversible rehydration took place completely after heating up to 250°C. The layered structures decomposed at 550°C for magadiite and at 600°C for kenyaite. Under high vacuum, interlayered water of both compounds was eliminated completely from the interlayer space at 10^-5 Torr for 24h at R. T. However, the reversible rehydration was observed, when the “collapsed” products were kept in atmospheric air for 24h.

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Whiteware bodies composed of 20-50% alumina, 20-50% kaolin and 10-40% feldspar were investigated to study the effects of compositions and firing temperature on the microstructure of fired samples. The vitrification temperature, at which apparent porosity turns to almost zero, lowered with feldspar content. A high relative density of 98% was obtained at 1150°C for the body containing 40% of feldspar. Furthermore, the temperature range at which a body shows high density was limited, because of the bloating at elevated temperature. Nevertheless, the bloating at elevated temperature was restrained by controlling the ratio of the feldspar and kaolin contents in the range of 1:1 to 1:1.5, independent of the alumina content. It was explained by the increase of viscosity of matrix-glass, due to the dissolution of free silica from kaolin to matrix-glass and due to the formation of interlocking felt-like mullite needles.

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Alumina suspensions for extrusion were prepared by adding metylcellulose and glycerol to a system of water, ammonium polyacrylic acid, and alumina powder. The effect of the additives on the rheology of mixtures was evaluated. The mixtures which could be formed into a sheet of less than 100μm in thickness showed Bingham flow characteristics. As the flow characteristics of the mixture, an empirical equation, P/k=A+B ln R, was obtained, where P is the extrusion pressure for forming alumina sheets, k is the apparent yield stress of the mixture, A and B are constants, and R is the extrusion ratio. The effect of methylcellulose and glycerol on the particle packing and the flexibility of alumina green sheets was discussed. A dense, translucent, alumina sheet of 80μm thick was obtained after firing at 1400°C for 4h.

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Phenolic resin-based carbon fibers were prepared in a stream of N₂ gas with and without reactive gases. With increasing flow rate of N₂ gas, yields of fibers increased. The fiber prepared in a stream of N₂ gas without reactive gases had the specific surface area of 2m²⋅g^-1, the tensile strength of 2000kg⋅cm^-2, and the yield of 55%. The X-ray diffraction showed the interlayer spacing, d₀₀₂, of 0.38nm and the crystallite size of 1.63nm in the “c” direction. The fiber prepared in a stream of N₂ gas with reactive gases showed the area of 15.5m²⋅g^-1, the strength of 180kg⋅cm^-2, and the yield of 43%. Pores and cavities were observed on the surface of the fibers prepared in a stream of N₂ gas with H₂O and O₂, respectively.

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Porous ceramics were produced by pressureless sintering green compacts composed of Si₃N₄ and TiN powders without additives in nitrogen gas atmosphere at 1700°C. The microstructure and electrical-properties of the Si₃N₄-TiN porous ceramics in a humid atmosphere were investigated. The following results were obtained: (1) The pore size distribution showed a sharp peak at 2000Å. (2) Rod-like shaped crystals of Si₃N₄ and equiaxed crystals of TiN distributed uniformly in the matrix. A large number of Si₃N₄ fibers of about 5μm were observed for 50wt% TiN. (3) The pore volume and specific surface area decreased proportionally with increasing amount of TiN. However, anomaly in the pore volume and specific surface area was observed at 50wt% TiN. (4) A sharp decrease in the impedance was observed in a dry atmosphere from 1×10⁷ to 1×10³Ω⋅cm for ceramics containing 40-60wt% TiN. (5) The impedance dependence of humidity was observed for ceramics in impedance higher than 10⁵Ω⋅cm (less than 40wt% TiN content). In a high humid atmosphere, the impedance decreased with increasing specific surface area.

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A method for preparing SiO₂ M_xO_y (M=Ti, Sb, V, Zr, Sn) thin films and monolithic gels was investigated. The reaction of silicic acid (SA) with metal chlorides or oxychlorides in organic solvents gave homogeneous solutions. Transparent gel films and gels were obtained by dip-coating of a glass substrate and aging of the solutions in a polyethylene beaker, respectively. Heat treatment of the gel films yielded oxide thin films with thickness from 0.1 to 0.4μm with a transmittance of above 90%.

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