The effect of additives on carbothermal reduction-nitridation was investigated for the preparation of AlN powders from the Al₂O₃-C-N₂ system. According to the role of additives in nitridation, they were divided into three categories: “promote”, “have no effect” and “disturb”. In particular, CaF₂ was an excellent nitridation promoter providing spherical AlN particles. The apparent activation energy of nitridation for CaF₂ addition was 190kJ/mol, while those for Y₂O₃, Yb₂O₃ and without additive were around 250kJ/mol. CaF₂, Y₂O₃, Yb₂O₃ and transition metal compounds strongly affected AlN grain morphologies, supplying spherical and rod-like shapes of AlN. It was estimated that the reduction-nitridation proceeds through the formation of intermediates like CaF₂⋅5Al₂O₃ and Y-aluminates.

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The complex impedance of pitch-based carbon fibers was investigated under different relative humidities at 25°C in the frequency range of 5Hz to 13MHz. The resistance of pitch-based carbon fibers was humidity sensitive and the sensitivity decreased with increasing temperature of carbonization, which was consistent with the results of resistance measurement by D. C. two-probe method. The characterization of the carbon fibers by WARD and FT-IR, showed that the pitch-based carbon fibers had a randomly oriented layer structure and that oxygen-containing functional groups were formed on surface. It was suggested that the humidity sensitive properties of pitch-based carbon fibers be related to exposed active carbon atoms at the edge sites of the graphite-like basal plane and oxygen-containing functional groups on the surface of carbon fibers.

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As a material for a heat insulation engine, the development of ceramics with high strength, low thermal conductivity and low thermal expansion coefficient has been required. And composite of reaction bonded ceramics was thought to be promising candidate. The influence of composition and oxidation temperature on the thermal conductivity of porous Si-Ti-O-N ceramics, reaction-sintered using Si and Ti as starting powders, were studied, and the following results were obtained. (1) The thermal conductivity of an as-nitrided specimen decreased with the amount of Ti in raw material. (2) Simple calculation showed that the thermal conductivity of the solid part in porous ceramics also decreased with increasing Ti amount. (3) The thermal conductivity was minimum when oxidized at 700°C. Above 700°C, it increased with increasing temperature. This behavior was explained by the phase change of TiN to TiO₂ with lower thermal conductivity and by the decrease in porosity caused by the oxidation reaction. (4) The weight gain in oxidation showed increased linearly with increasing amount of Ti, suggesting that the oxidation of TiN_0.9 occurred more preferentially than Si₃N₄.

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Dielectric properties of (Ba, Sr)TiO₃ ceramics doped with up to 2.0at% nickel were measured at frequencies from 10^-3 to 10Hz. The results indicate that the ceramics have extremely high dielectric constants as large as 10000. The relaxation time obtained from the dielectric loss maximum varied by the Arrhenius law with an activation energy of 1.2eV. The TSC (Thermally Stimulated Current) study strongly suggests that the dielectric relaxation phenomena are mainly due to dielectric rotation of impurity-vacancy dipoles at gain surfaces.

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Localized corrosion and water adsorption have been studied for soda-lime-silicate glass films and silica glass films prepared by sputtering using an atomic force microscope (AFM). The in-situ AFM observation was carried out for the thin films exposed to a humidity-controlled environment. Water adsorption was distinguished from localized corrosion, based on the reversibility to humidity change, thus opening the possibility of nano-scale localized corrosion identification. Surface roughness on soda-lime-silicate glass films was increased with increasing relative humidity. On the other hand, surface roughness on silica glass films was decreased with increasing relative humidity. The localized corrosion developed in regions with extensive water adsorption for soda-lime-silicate glass films.

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A YSZ/NiO-YSZ two-layer ceramic for a tubular SOFC was fabricated by the MSC (Multilayer Slurry Casting) process. Carbon powder was added to NiO-YSZ slurries to prevent the fracture of the two-layer ceramic during co-sintering. The shrinkage and porosity of NiO-YSZ layers were affected by the carbon content in the slurry. The optimum two-layer ceramic was obtained with the addition of 12wt% carbon powder. Fracture of the two-layer ceramic was observed during co-sintering in case of a lower carbon content than this, while the addition of excess carbon powder caused cracking in the two-layer ceramic green body during drying in an ambient atmosphere.

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Harmonics current measurements were conducted on YSZ/M(Pt, Au), O₂ electrochemical reaction and the results were compared with ac impedance data. It was found that the processes which are not distinguishable from each other by AC impedance measurement alone because of their almost identical time constant can well be discriminated by the harmonics current analysis. Platinum and gold electrodes showed very dissimilar harmonics current spectrum and it was concluded that the major difference in electrode behavior between gold and platinum comes from the difference in the surface diffusivity of adsorbed oxygen atoms.

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Slip casting of silicon nitride powder produced by imide decomposition (median particle size=0.55μm in diameter) was studied to fabricate Si₃N₄ engineering ceramic parts with a complicated shape. The zeta potential of α-Si₃N₄ showing the isoelectric point of pH=7.0 was +32mV at pH=2 and -47mV at pH=11. Preparation conditions of well-dispersed slurries were investigated for the mixed powders of 92wt% α-Si₃N₄, 4wt% α-Al₂O₃, and 4wt% Y₂O₃, using an organic polymer deflocculant (polyacrylic ammonium). High-density green bodies (density=1.76-1.82g/cm³) were prepared from the slurries containing solids of 67 to 70wt% by vacuum-filtration with a porous polymer resin mold. High-density Si₃N₄ ceramics were obtained by gas pressure sintering at 1775°C for 4h at about 0.9MPa of N₂ pressure. The samples showed an average flexural strength of 814MPa and a Weibull modulus of 10.4 at room temperature.

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Joining of silicon nitride as well as silicon carbide to itself was studied by the microwave heating method. The joining was carried out easily in a short time by covering the joining part with a mullite insulating fire brick during application of microwave. There was a peak in the bending strength-heating time curve. The maximum value increased and the time, at which the maximum value was reached, decreased with increasing joining temperature. The hardness of the joined region was higher than that of the matrix. The maximum bending strength of the joint of silicon nitride ceramics was 87% of the matrix strength when joined at 1750°C and 5MPa for 10min. On the other hand the maximum bending strength of silicon carbide ceramics was 71% of the matrix strength when joined at 2050°C and 8MPa for 5min.

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Deposits in the system of TiO₂-SnO₂ were prepared at 625°C on fused-quartz or NaCl substrates by CVD using TiCl₄, SnCl₄ and H₂O as sources. The deposits obtained at Sn/(Sn+Ti) of 0-30at% in the sources, were single phases of TiO₂-SnO₂ solid solutions. Two-phase mixtures of anatase-type and rutile-type phases, were prepared at Sn/(Sn+Ti) of 40-70at% in the sources. Rutile-type single phases deposited at 80-100at% in the sources. Dendritic structure was observed for the deposits of the anatase-type single phases. The deposits of the two phases of anatase-type and rutile-type structures, were dense films. Faceted columnar textures were observed for the deposits of the rutile-type single phase. The transmission electron microscope observation of a two-phase mixture showed that the grains of the rutile-type structure, about 500nm in size, were contained in the matrix of an anatase-type solid solution. Lattice parameters of the anatase-type solid solutions increased linearly with increasing SnO₂ in the solid solutions. The maximum Sn/(Sn+Ti) found in the anatase-type solid solutions was 41at%. In the rutile-type phases, Sn/(Sn+Ti) was over 96at%.

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Electrical properties of a Vycor-type borosilicate glass were changed by heat treatment at 650°C. The following conclusions were obtained. (1) The observed dielectric relaxation is caused by a conducting path structure. (2) Electrical characteristic of Na₂O⋅B₂O₃ phase in the borosilicate glass are different from those of Na₂O⋅B₂O₃ glass with the same composition. (3) The inherent dielectric relaxation does not occur in both Na₂O⋅B₂O₃ and SiO₂ phases. These results suggest that the dielectric relaxation of oxide glass is ascribable to the conducting path structure.

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Influence of water addition and catalysts such as HCl and NH₄OH on the gel region and the gelation behavior of alkoxide solutions was examined in the B₂O₃-Na₂O system. The resuls are as follows: (1) With the water addition r=0-1, where r=water added/water necessary for complete hydrolysis, gel region was found in the range of B₂O₃=60-90mol%. With water addition of r>1 gel region was reduced. Crystals precipitated with the addition of HCl. The gel region with NH₄OH addition was the same as that observed with water addition. (2) Gelation time was reduced by water addition. No effect on gelation time was found by NH₄OH addition. (3) From the measurements of pH and temperature rise in the B(OBu)₃-NaOCH₃ mixtures, it was inferred that sodium-borate precursors (complex) such as B(OBu)₃(ONa) and B(OBu)_3-n(ONa)_n formed in the B(OBu)₃-NaOCH₃ mixtures. With water addition, the formation of hydroxide complex such as B(OH)₃ONa and B(OH)_3-n(ONa)_n was also inferred.

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SiC whisker-reinforced Si₃N₄-based composites without additives were compacted by underwater-shock wave. The composites contained 10, 20 and 30vol% SiC whisker as reinforcements. There were no macrocracks in all shock compacted composites. The as-compacted and specimens sintered at various temperatures for 5h were characterized by the measurements of relative density, micro Vickers hardness and fracture toughness. The relative density of a sintered Si₃N₄-10vol% SiC whisker composite was higher than that of sintered Si₃N₄-20 and 30vol% SiC whisker composites, and reached the theoretical density by sintering at 1973K. Hardness of each composite increased up to 1823K in proportion to sintering temperature, and then saturated above 1823K. The hardness and fracture toughness of the Si₃N₄-30vol% SiC whisker composite sintered at 1973K were about 29GPa and 5.0MPa√m, respectively. The fracture toughness was 25% higher than those of monolithic Si₃N₄ and other obtained composites sintered at the same temperature. SEM observation showed that whisker bridging and deflection were observed in sintered composites and that the matrix of the Si₃N₄-30vol% SiC whisker composite consisted of plate-like and submicron order fine needle-like β-Si₃N₄ grains.

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Tin Oxide thin films were prepared by sol-gel method using colloidal particles derived from an inorganic salt. The thickness (t) of SnO₂ films and the pulling rates (v) of substrates from dipping solutions were correlated with an expression of t∝v^0.53. The formation process of SnO₂ thin films was studied. Well-crystallized SnO₂ thin films were obtained above 550°C after successive dehydration of OH groups. SnO₂ thin films prepared at 550°C were composed of very fine particles with 10-20nm in diameter. Firing at higher temperatures caused the grain growth without substantial densification of the films, leading to coarse microstructure.

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Preparation conditions and formation process of HfB₂ fine powders from HfO₂, amorphous B and Mg under an argon flow were examined. Fine powders of single phase HfB₂ were prepared by heating powder mixtures of HfB₂: amorphous B: and Mg in molar ratios of 1:2:7-10 at 800°C for 1h. The HfB₂ powders had particle sizes of 0.03-0.3μm. The formation process of HfB₂ was composed of the following reactions: (1) 650°C-: HfO₂+2Mg→α-Hf+2MgO, (2) 550-750°C: Mg+2B→MgB₂, (3) 750°C-: MgB₂→Mg+2B, (4) 800°C-: α-Hf+2B→HfB₂ and (5) 850°C-: 2MgB₂→MgB₄+Mg. MgB₂ did not interfere the formation of HfB₂ because it decomposed above 750°C, whereas MgB₄ interfered the boridation of α-Hf above 850°C because it is thermally stable. For the preparation of single phase HfB₂ powders, it is most important to suppress the formation of MgB₄ by controlling the reaction temperature below 850°C.

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Sliding friction and wear tests of sintered titanium boride were conducted in air from room temperature to 1000°C. At room temperature, the coefficient of friction was about 0.8 independent of both the applied load and the sliding speed. It increased at intermediate temperatures around 400°C, particularly at lower applied loads. The wear loss decreased with increasing temperature up to 600°C. The coefficient of friction abruptly decreased at 600°C and exhibited a minimum value of about 0.3 at 800°C. A weight gain was observed after the tests at 800°C and above. X-ray diffraction analysis of the wear surfaces revealed that titanium boride oxidizes even at lower temperatures. Since the oxidation yields B₂O₃ of low melting point, it would exist as a liquid at the friction interfaces and therefore should have a critical effect on the friction and wear characteristics. High viscosity of liquidized oxides increased the coefficient of friction but decreased the wear loss at intermediate temperatures. The dependence of friction coefficient on both the applied load and the sliding speed suggests that the sliding is in a hydrodynamic lubrication regime because of the presence of a substantial amount of melted oxides at 800°C and above, resulting in a low coefficient of friction.

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Using the isothermal method, the influence of type and particle size of feldspar, a flux component, on the densification process was investigated in the feldsparquartz-kaolinite system which was a representative ceramic composition for building construction. Type of feldspar greatly influenced the vitrification temperature. Sodium feldspar vitrified 40°C lower than potassium feldspar. This is attributed to the different viscosities of the liquid of feldspar. The particle size of feldspar also greatly influenced vitrification; the coarser the particle size, the higher the vitrification temperature was. In addition, it was clarified that the bulk density of the body at the vitrification point decreased as the particle size of feldspar became coarser. These results indicate that the dispersion state of feldspar changes due to its particle size in the body and the coarser the particle, it requires a higher temperature because liquid phase should widely disperse to fill the body and as the increase of temperature, gas pressure of the closed pores increases lowering the density of the body.

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To investigate the solute and solvent interaction in the formation of monodispersed Al₂O₃ particles by hydrolysis of aluminum sec-butoxide (ABu^s) in a mixed solvent of n-octanol and acetonitrile, acetonitrile and water were added separately into an n-octanol-ABu^s solution. At first, acetonitrile was added into n-octanol-ABu^s solution, and then water dissolved in solvents such as ethanol, n-octanol and acetonitrile was added. In the first step, solubility of the solution was decreased rapidly by the addition of acetonitrile and consequently a part of the dissolved alkoxide was precipitated as droplets. This emulsion was stabilized with an emulsifier, hydroxy propyl cellulose. In the next step, hydrolysis of alkoxide droplets resulted in hydroxide particles of about 200nm and at the same time, oligomers were derived from the dissolved alkoxide. Subsequently, the oligomers diffused onto the surface of particles and played an important role in the particle growth. When ethanol was used as the solvent for dissolving water, the resultant particles had an average particle size of 0.5μm and a geometrical standard deviation of 1.10.

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Al metal powder added to MgO-C refractories plays important roles in suppression of carbon-oxidation. Size of Al grain causes difference in the behavior of Al, namely, in microstructure and properties of the refractories. Al reacts with carbon to give Al₄C₃(s) which forms a surface layer about 20μm thick. Thus, Al grains smaller than 40μm change to Al₄C₃(s) almost completely during early stages of heating, and then an aggregate of Al₄C₃(s) crystals gradually reacts with CO(g) to form C(s) and Al₂C₃(s) from it's surface. On the other hand, for Al grains larger than 40μm, an Al₄C₃(s) surface layer is formed and Al(l) left inside vaporizes by crashing through the layer of Al₄C₃(s). As a result, pores are formed, resulting in strengths lower than that for Al grains smaller than 40μm.

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Intergranular glassy phase of sintered Si₃N₄ was quantitatively evaluated by three methods. Four specimens with 6 to 15wt% additives were sintered for evaluation. The amounts of glassy phase in these specimens were evaluated by the three methods and compared with the mechanical properties. The following results were obtained.
(1) The XRD analysis was thought to be most reliable for the quantification of glassy phase in sintered Si₃N₄, considering the objectivity of the method. Highly pure and homogeneous β-Si₃N₄ was required as the standard material for increasing the accuracy.
(2) The results of image analysis agreed with those of XRD analysis in this study. However, the results were remarkably influenced by the definition of threshold intensity of back-scattered electron image. This method was found to have experimental difficulties to apply for fine-grained Si₃N₄ ceramics.
(3) The calculation method was found to overestimate the glassy phase content when a large amount of additives was contained. The reason was thought to be caused by the inadequete estimation of glass composition.
(4) The differences between the glassy phase contents evaluated by experimental methods and the amounts of additives were 1 to 3.6wt%. It was considered that the differences depended on the impurity oxygen in the Si₃N₄ powder.
(5) The high temperature strength of sintered Si₃N₄ decreased dependng on the glassy phase content.

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The effect of Na₂O, K₂O, Li₂O, ZnO, Al₂O₃ and F contents in frit on the glass transition temperature T_g, water-durability and coloring of red enamel containing CdS-CdSe pigment was investigated by means of DTA-TG, chemical analysis, spectral reflectance and a Hunter color difference. Increase in Na₂O, K₂O and Li₂O contents in frit darkened the color of the red enamel, while increase in F, ZnO and Al₂O₃ contents brightened the color of the red-enamel. ZnO was favorable for coloring of the enamel, lowering of T_g, and water-durability of the frit in boiling water. The firing temperature of the porcelain enamel frit developed was 690°C, 120°C lower than that of the commercial one.

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The powder mixtures of tholeiite-type basalt containing 5, 10 and 20wt% of simulated high-level nuclear wastes were sintered at 1000, 1050, and 1100°C for 5, 10, 30, 50 and 100h. Compressive strength, thermal expansion coefficient, chemical durability, apparent density, porosity, leaching test into alkali and acid solution were examined. The maximum compressive strength of the sample sintered at 1100°C for 100h was slightly greater than that of commercial quartz glass-rod. Judging from the results of various tests, the optimum condition of sintering for a good waste disposal material is as follows: amount of simulated waste; 10wt%, firing temperature; 1100°C, sintering duration; 100h.

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A polycrystalline silicon carbide ceramic was treated with 5% fluorine in He at 250-600°C for 30min, and the surface change was studied by FT-IR, ESCA, XRD and SEM techniques. The contact angle of dropping distilled water increased from 74° to 115° by the treatment at 400°C due to the formation of C-F bond on the SiC surface. The contact angle decreased, however, by the treatment above 400°C because the surface became rough due to severe corrosion by fluorine.

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The effects of diols on specific surface area and pore size distribution of alkoxy-derived silica gels were investigated. The specific surface area of dried gels decreased and the fractional pore volume of large pores increased with an increase of chain length of diols used in starting solutions. These results were explained in terms of inhibition of coalescence among primary particles caused by the formation of chemical bonds between silicon or oxygen atoms on the surface of primary particles and hydroxy groups of diols.

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A new simplified method of the synthesis for Bi-Pb-Sr-Ca-Cu-O superconductor was found through a convensional solid-state reaction. Samples have been prepared by mixing powders of Bi₂O₃, PbO, SrCO₃, CaCO₃ and CuO and short-term ((5+5)h) sintering at 1133K. The samples have 91% high T_c 2223 phase in volume fraction and exhibit the zero resistance temperature of 105K in the superconducting transition. It is stressed that our synthesis method offers high quality sample in high speed with great advantage on low cost.

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Crack propagation and secondary crack generation in tempered soda-lime-silica glass were studied by high-speed photography. About 70% of the total secondary cracks observed developed within 1ms after the initiation of main cracks.

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