Recently, SiC and Si₃N₄ whiskers have been synthesized using natural sources. However the yield is usually low. In the present study, having an eye to the fact that cryolite was often used to advance the purity of silica, in order to estimate an available possibility to natural sources, the mixture powder of silica and cryolite were used as a starting material and the effect of cryolite on the growth of SiC whiskers was investigated. As a result, SiC whiskers and Na₂Si₂O₅ were generated through the reaction of silica and cryolite under the existence of graphite in the stream of CH₄ mixture gas. Thus, the available possibility was suggested since SiC formed as a whisker through the reaction.

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We have investigated the photostriction response in the PLZT ceramics doped with various amounts of Ta and subsequently heat-treated in nitrogen. Both photovoltaic and piezoelectric properties were improved by doping with Ta. On the other hand, nitrogen-treatment heightened the photovoltaic response, but scarcely affected the piezoelectric parameters. By the combined effect of doping with Ta and nitrogenmtreatment, the photostriction response was confirmed to be markedly enhanced.

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PbX₂-PbO-SiO₂ (X=Cl, Br and I) glasses were prepared and their electrical properties were investigated. The sole carrier for these glasses is the X^- ion, which was estimated from the EMF (electromotive force) of the X₂ gas concentration cell and the electrical properties. The ionic conductivity was enhanced with a decrease in ionic radius and increase in content of the X^- ion in the glasses. The conductivities for the glass plates are about one order of magnitude higher than those for the pellets prepared from glass powder. For the X=I system, a maximum conductivity of 4.5×10^-7S⋅cm^-1 at 373K was obtained for the composition 0.59PbI₂⋅0.31PbO⋅0.10SiO₂. The glass formation region was determined for the PbI₂-PbO-SiO₂ system.

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Factors affecting the formation rate of zirconium nitride by the carbothermal nitridation method were studied. Use of finer particle-sized zirconia powder showed the higher formation rate of zirconium nitride. A single-phase of zirconium nitride with cubic symmetry was obtained by firing graphite and zirconia (0.35μm) mixed compact with a molar ratio C/ZrO₂=4 at 1400°C for 12h in flowing nitrogen gas. The formation process of zirconium nitride was in competition with partial nitridation of zirconia, occurring in the non-transformable tetragonal zirconia phase. It was not possible to obtain stoichiometric and pure ZrN by carbothermal nitridation method. The presence of ZrN seed crystals restrained the formation of zirconium nitride.

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Amorphous-type cordierite (2MgO⋅2Al₂O₃⋅5SiO₂) and hexacelsian (BaO⋅Al₂O₃⋅2SiO₂) precursor powders were prepared by a solution-polymerization route employing a Pechini resin or a PVA solution as a polymeric carrier. After calcination at 800°C for 1h under atmospheric conditions, the bulky precursors changed into very soft and porous powders. In case of the cordierite precursor prepared using PVA solution, the densification proceeded at lower temperature than in the case of the Pechini resin process. The densification was inhibited by the crystallization of amorphous silica in both cases and it was the reason for the coarse microstructure of the sintered cordierite. Sintered cordierite was closer to pure cordierite with low amount of amorphous-type cordierite phases as was observed in the case of the solution-polymerization route employing PVA solution. Hexacelsian precursor powder, which was prepared by the PVA solution process, was faster crystallized to hexacelsian and showed more sluggish reconstructive transformation behavior than the powder derived from the Pechini resin process.

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Double-oxide compounds of Ni(II)O, Al(III)₂O₃, Si(IV)O₂, Nb(V)₂O₅, and W(VI)O₃ with Li₂O were synthesized, and the vaporization rates of Li₂O from round pellet specimens were measured in air flow at constant temperatures. The log of the vaporization rates at an onset of the vaporization at 900°C were plotted against the values of the Z/r×EN product for M and M/Li, and a linear relation was obtained. The log of the vaporization rate decreases with higher covalency of M and M/Li ratios. The slopes in the primary stage on the log-log diagram for vaporization loss vs time increase with temperature and increasing Li₂O content.

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A phenomenon that crack was formed in the manufacturing process of Al₂O₃ products was analyzed with a simulation model developed in previous papers. The position of stress concentration by finite element analysis was compared with the cracked position to examine the model for its validity. Analytical results for tensile stress concentration and deformation agreed well with the actual phenomenon. Furthermore, the value of maximum principal stress analytically decreased with increasing thickness of the part at which the crack generated, and this also agreed with the actual phenomenon. A new developed FEM model for simulating the sintering process of ceramics was considered to be effective in predicting crack generation in products and in taking steps to prevent cracking.

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A-site cation substitution with Ba²⁺ or Ca²⁺ ions was made for the complex perovskite Sr(Ga_0.5Ta_0.5)O₃ phase to modify its dielectric properties. The largely sized Ba²⁺ ions could be incorporated in the A-site sublattice up to 55mol% without cation ordering. On the contrary, the A-site Sr²⁺ ions were completely replaced by the Ca²⁺ ions. The crystal symmetry of the (Sr, Ca)(Ga_0.5Ta_0.5)O₃ perovskites correspondingly changed from cubic to orthorhombic with increasing Ca content. Partial B-site cation ordering occurred when 10-50mol% Ca²⁺ ions were incorpolated in the A-site Sr²⁺ ions. The A-site cation substitution caused a very slight change in dielectric constant (ε_r) at microwave frequencies, suggesting a little effect of the substitution on the ionic polarization of the perovskite structure. A substantial lowering in microwave Q-value observed for the solid solutions containing 10-20mol% Ba²⁺ or Ca²⁺ ions might be related to the lack of long-range structure ordering. Temperature coefficient of ε_r at 1MHz changed from positive high values of the Ca²⁺-containing perovskites to nearly zero for compounds with 20-40mol% Ba²⁺ ions. This change was discussed in relation to the structual strain of (Ga, Ta)O₆ octahedra in the compounds.

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Fabrication of dense Ti-Al-C system composites by hot-shock consolidation was attempted. Ti (mean particle size: 45μm), Al (17μm) and graphite (1-2μm) raw powders were mixed by various molar ratios, and the mixtures tapped into a powder charging container, followed by the self-propagating high temperature synthesis (SHS) reaction. Immediately after, the obtained porous products were densified by underwater-shock consolidation using the detonation of explosive charge. This process was completed in about 20s. The specimens were characterized by XRD experiments, density measurements, micro Vickers hardness tests, microstructural observations and oxidation resistance tests. As a result, three kinds of intermetallic compounds (TiAl, Ti₂Al and Ti₃Al), and two kinds of ceramics (TiC and Ti₄Al₂C₂) were detected, mainly by the XRD experiments. The main phase detected for the compositions TiC-40mol% TiAl and TiC-60mol% TiAl was the Ti₄Al₂C₂ phase. It is considered that this phase was produced at the high temperature generated by the SHS reaction. Results of its density measurements and micro Vickers hardness tests indicated almost the same tendency as those of the Ti-Al system intermetallic compound. In addition, the microstructural observations revealed that the composites with compositions between TiC-40mol% TiAl and TiC-60mol% TiAl had a needle-like microstructure. The TiC-40mol% TiAl composite showed the highest oxidation resistance among the present specimens. The Ti-Al-C system composites are expected to be novel materials with light weight and excellent heat resistance.

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Thermal expansion coefficient and residual stress were measured in Ni/ZrO₂-8mol% Y₂O₃ (YSZ) cermet. The microstructure of the cermet was also examined. The average thermal expansion coefficient at 298 to 1273K became larger as the Ni concentration increased. The coefficient versus composition displayed an “S-shaped” curve, and it conformed to the calculated values from Turner's formula at above 44vol% Ni. Less than 32vol% Ni, however, the experimental values were smaller than the calculated ones. The reason was thought to be that most of the Ni particles were isolated and voids existed between the isolated Ni particles and YSZ phase as a consequence of releasing the expansion mismatch between Ni and YSZ. X-ray stress analysis confirmed that a tensile stress of 3 to 34MPa was generated in the Ni phase, and a compressive stress of 55 to 170MPa, in the YSZ phase. The direction of the redidual stresses agreed with that of prediction calculated by Kingery's equation. The experimental values, however, were smaller than the predictions. The reason for these discrepancy may be that the measurement positions were not in the bulk of the samples but on the sample surface region where exist smaller constraints.

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To improve the oxidation resistance of carbon, B(OH)₃ and Si(OC₂H₅)₄ were dispersed in phenolic resin, and then carbonized at 1300°C, 1600°C and 1900°C. The oxidation resistance was investigated by TG-DTA. The results showed that the carbon/ceramic composites with 9mass% of SiO₂:B(OH)₃=0:1 had optimum oxidation resistance when heated at 1600°C. On the other hand, the sample with SiO₂:B(OH)₃=2:1 had optimum oxidation resistance when heated at 1900°C. Samples containing B(OH)₃ were also heated to 1900°C and graphitic carbon was obtained.

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Thermal reactions and sintering characteristics were investigated to obtain dense cordierite ceramics using kaolin minerals (Al₂O₃⋅2SiO₂⋅nH₂O), such as kaolinite or halloysite, and chemically synthesized magnesium hydroxide in the form of ultrafine hexagonal tabular particles. Mixtures of magnesium hydroxide and submicron tabular-kaolinite particles in composition of MgO⋅Al₂O₃⋅2SiO₂ resulted in the formation of amorphous state at about 800-900°C after a reaction of thermal decomposition. The amorphous materials abruptly shrank at about 900°C up to a relative density of about 90%, above which crystallization of a μ-cordierite phase restrained further densification. Firing the mixtures to about 1300-1350°C yielded dense α-cordierite ceramics with a relative density higher than 95% and a negligible apparent porosity and showing a linear thermal expansion coefficient of 2.2×10^-6/K. On the other hand, mixtures of magnesium hydroxide and submicron needlelike-halloysite particles resulted in insufficient thermal reaction at about 800-900°C because of the less contact area of mixed particles which, affecting sintering and crystallization characteristics, produced several percents of apparent porosity by firing at 1350°C for 1h.

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The Griffith energy criterion for brittle fracture is extended to mode II fracture by postulating that crack extension occurs when the maximum energy release rate in non-coplanar crack extension is equal to the fracture energy rate required for mode II crack extension. This fracture energy rate is considered to be proportional to the critical magnitude of the area of the frontal process zone at the crack tip of inorganic materials, where the critical magnitude is the value at crack propagation. The frontal process zone area is simply assessed here from the area enclosed in the iso-stress contours of both the maximum principal stress and the maximum shear stress in the vicinity of the crack tip. The estimated K_IIC/K_IC ratio is 1.21 which is very close to experimental results previously presented.

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Crystallization of barium titanate (BaTiO₃) during heat treatment from partially crystallized BaTiO₃ xerogels has been investigated. The xerogels were derived from hydrolysis of concentrated Ba-, Ti-alkoxides precursor solution (0.4 or 0.8×10³mol⋅m^-3). Different pathways to crystallization for BaTiO₃ from amorphous Ba-Ti-O remained in the xerogels were confirmed depending on the aging time before heat treatment. Amorphous Ba-Ti-O included in the xerogels with a short aging time crystallized in the range 570-700°C by intermediary formation of an oxycarbonate phase, Ba₂Ti₂O₅CO₃CO₂. On the other hand, amorphous Ba-Ti-O remained after a long aging time crystallized into BaTiO₃ directly up to 600°C. Kinetics of BaTiO₃ formation during heat treatment and relations between thermal behavior and local structure of the gels in this sol-gel system are examined.

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The surface of β-tricalcium phosphate ceramics (β-TCP) was modified by exposing ceramic disks to a silane coupling agent for different periods of time, The number of organic groups introduced was determined as a function of exposure time. These results suggest that zeta potential, cell adhesion and growth, and adsorbed protein concentration can carefully be controlled by silane treatment.

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Five kinds of alkali-metal aluminosilicate ceramics, MAlSi₂O₆(M=Li, Na, K, Rb or Cs), were prepared by sintering a mixture of M₂CO₃, Al₂O₃ and SiO₂, and their properties as a solid electrolyte were investigated by designing a series of solid electrochemical cells such as (-)CO₂, O₂, Pt|MAlSi₂O₆|Au, M₂CO₃, CO₂, O₂(+), for the CO₂ gas sensor, where MAlSi₂O₆ functions as an alkali-metal ionic conductor. Electromotive force, EMF, increased linearly with an increase in the logarithmic value of carbon dioxide partial pressure, in accordance with the Nernst's law and the slope of the Nernst's equation suggests two electron reaction of carbon dioxide molecule at the detection electrode around 400°C. At this temperature, the 90% response times were about 1min for all of the sensors. The sensor prepared KAlSi₂O₆ as the solid electrolyte was found to work at the lowest temperature and over the widest temperature range.

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Waste concrete powders were reacted with CO₂ gas in water for the purpose of recovering calcium and the fixation of CO₂ gas in the form of CaCO₃. The 30-h bubbling of CO₂ gas at the flow rate of 5ml⋅min^-1 led to about 40% recovery of calcium, but the recovery or fixation rate of CO₂ gas was only less than 1%. The fourtime repeating of the 4-h bubbling of CO₂ gas nearly doubled both the recovery of calcium and CO₂ gas. Furthermore, the CO₂ recovery rate of 15% was achieved, if the calcium recovery was somewhat reduced. Runs carried out under such various conditions indicated the applicability of the carbonation reaction of waste concrete both to the recovery of calcium and fixation of CO₂ gas.

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The Sn⁴⁺-Sn²⁺ equilibrium in binary sodium borate melts was studied by means of differential pulse voltammetry. The half-wave potentials in the reduction of Sn⁴⁺ to Sn²⁺ shift to the negative with an increase in Na₂O content and a decrease in temperature. These results indicate that the population of Sn⁴⁺ increases with an increase in basicity. A linear relation between logr(r=[Sn²⁺]/[Sn⁴⁺]) and optical basicities was observed. Logr was also found to depend linearly on thermodynamic basicity, such as -loga(Na₂O) where a(Na₂O) denotes the activity of Na₂O in melts.

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Tri- and dibutylstannylated silica gels were prepared from water glass and tri- and dibutyltinoxide, respectively. Organofunctionalized silica gels were readily formed via reaction between the tri- and dibutylstannylated silica gels and acetoxyethyldimethylchlorosilane or acetoxyethylmethyl-dichlorosilane with the elimination of organotin groups. It was demonstrated that the organic groups were more effectively introduced in the stannylated silica gels than in non-stannylated silica gels.

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Amount of lead release from glaze, changes of the lead concentration distribution and structure in the surface layer of the glaze during firing in a water-vapor atmosphere were investigated. Lead ions in the surface layer of the glaze were released by surface exchange reaction of proton or hydronium ions in water vapor and lead ions at the surface of the glaze during firing in a water vapor atmosphere. Then the proton or hydronium ions which were introduced by the surface exchange reaction were released as water vapor by dehydration reaction, and the silica-rich layer was formed at the surface. This silica-rich layer comes to a protection layer and which makes waterproof of porcelain tableware.

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In order to obtain SiC whisker dispersed Si₃N₄, the reaction mechanism and the condition of SiC whiskerizing through the reaction between Si₃N₄+C was studied thermodynamically. In this work, Si₃N₄+C mixture was heat treated in 0.1MPa of Ar at temperatures from 1350 to 1750°C. SiC whiskers were obtained in the powder mixture heated above 1600°C. By using the Si₃N₄ powder heat treated at 1100°C for 24h in air, however, no SiC whiskers were obtained in the carbon mixed powder, indicating that the surface oxide of Si₃N₄ powder does not take part in the SiC whisker formation reaction. The experimentally measured nitrogen partial pressure during SiC whiskerizing was in good agreement with the equilibrium nitrogen partial pressure between Si and Si₃N₄, and it suggests that Si vapour is in equilibrium with Si₃N₄. Supersaturation for the carbothermal reduction of Si₃N₄ was calculated as a function of temperature. Supersaturation took value 10 to 20 during SiC whiskerizing.

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