The results in the present study are summarized as follows;
(1) The carbonation reaction of synthetic 11Å tobermorite in aqueous solution occurs through two rate-determining steps, that is, the rate-determining step changes from the surface reaction to the internal diffusion process with the progress of carbonation. This phenomenon is considered to be due to the increase in the diffusion resistance with the formation of CaCO₃ in the reaction layer of tobermorite.
(2) The rate law for the surface reaction control process is expressed as -d[CaO]/dt=k[CaO][CO₂]_aq, where k is 1.67M^-1min^-1 at 30°C and the activation energy for k is 35.3kJ/mol.
(3) The carbonation rate of synthetic 11Å tobermorite in the aqueous solution is relatively fast. Hence, it is expected that tobermorite is applicable as the material for fixation and solidification of ¹⁴CO₂ by finding the optimal conditions.

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Theoretical and experimental studies of thermal downshock testing of barium borosilicate glass (Corning Code 7059) substrate for liquid crystal display are presented. The transient thermal stress of a substrate under thermal downshock test is analyzed by both an approximate analytical solution and the finite element method. Strength and flaw severity at the edges of the substrate are evaluated in reference to the edge finishing and geometrical features of the substrate. It was found that the edge flaw severity is strongly affected by the grinding material and less so by the edge shape and the thickness of the substrate. The finite element analysis shows that fracture of the substrate normally occurs by the longitudinal mode, consistent with the experimental results.

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TiB₂-B₄C composites were fabricated by pressureless sintering at 1600°C using Ni and C as densification aids. X-ray diffraction revealed the presence of TiB₂, B₄C and NiB. Up to 20vol% B₄C additive content, dense composites with -94% of the theoretical density were obtained. The dispersion of B₄C particles inhibited the grain growth of TiB₂ and improved the fracture toughness and bending strength. The maximum fracture toughness and bending strength of the composites were 6.1MPa⋅m^1/2 and 530MPa, respectively, in contrast with 5.1MPa⋅m^1/2 and 380MPa for a sintered body without B₄C. The crack deflection by B₄C particles was considered to be the main toughening mechanism for this composite system. With increasing B₄C additive content, the thermal expansion coefficient of the composites decreased and the electrical resistivity increased. The relation between the resistivity and composition was discussed based on the effective medium theory.

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Two alumina cylinders of commercial purity, 10mm high and 10mm in diameter were bonded together using an aluminum film. In addition to the normal bonding process, bonding under alternating bonding pressure was performed, and the effect of the alternating applied stress on the bonding strength of the joint was investigated based upon the statistical analysis. A fairly good agreement is obtained between the calculated and the observed strength distributions of the joint. The present analysis has led to the conclusion that alternating stress imposed during the bonding process is effective to reduce the formation of macro bonding flaws, resulting in higher bonding strengths.

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Silicon-carbide ceramics were metallized with manganese by the vapor-diffusion method. Pure manganese powder as a vapor source was used to metallize SiC ceramics at 923K to 1223K for up to 90ks in a dynamic vacuum atmosphere. The structure and composition of the metallized layers were investigated by scanning electron microscopy, electron-probe microanalysis, and X-ray diffraction analysis. At the initial stage of the metallization, manganese vapor reacted preferentially with the carbon in the grain boundaries of SiC ceramics to form a manganese carbide, and then a metallized layer with four sub-layers was formed. The four-sublayers were composed of manganese carbide (Mn₂₃C₆) at the surface layer, a mixture of ternary compound (Mn₈Si₂C) and manganese carbide (Mn₂₃C₆) in the outer layer, manganese suicide (Mn₅Si₂) at the middle layer, and a mixture of ternary compound (Mn₈Si₂C) and SiC particles at the bottom layer. Growth of the metallized layer with the four-sublayer structure obeyed the parabolic law at the initial stage, and then slowed down due to the formation of the manganese carbide layer (Mn₂₃C₆) on the top surface. The parabolic rate constants (k_p) for the growth of metallized layers were 10^-16-10^-13m²⋅s^-1 at 1073-1223K. The activation energy for the growth of metallized layers (Q_kp) was 225kJ⋅mol^-1.

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The influence of grain size and secondary phase on the fracture toughness (K_IC) of sintered MgO bodies was investigated. Sintered MgO bodies doped with 1-10wt% Fe₂O₃ were made by hot-pressing. The grain size was changed by annealing. The fracture toughness (K_IC) was measured by a chevron-notched beam method. The fracture toughness of sintered MgO bodies doped with Fe₂O₃ was independent of the grain size. However, it increased with the increase of the amount of Fe₂O₃, and reached 2.5MPa√m at the sintered MgO body doped with 10wt% Fe₂O₃, which is 50% larger than that of pure MgO. The fractography revealed that the toughening of Fe₂O₃-doped MgO bodies corresponded to the increase in the fraction of stepwise transgranular fracture on the fracture surfaces. It was considered that the change in fracture mode resulted from residual thermal stresses generated around MgFe₂O₄ precipitates.

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Dielectric relaxation was observed in a porous glass (Corning 7930), and its characteristics were the same as those of oxide glass. When pores of the porous glass were removed by heat treatment at 1200°C, the dielectric relaxation disappeared. The porous glass was reduced to powder and a solid sample was made by heating the powder at 1400°C. Characteristics of the dielectric relaxation of the sample were different from those of oxide glass. These results suggest that the dielectric relaxation of oxide glass is ascribable to microscopic conducting path structure of the interconnected structure type.

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For quantitative analysis of surface segregation of PVA, a one-dimensional drying model for PVA-water-alumina was taken, and transfer of PVA in the drying process was mathematically simulated based on drying rate of slurry and diffusion coefficient of PVA. The results of simulation agreed well with the measured results. The surface segregation of PVA was found to result from the migration to the surface caused by a capillary force and the back-diffusion driven by the concentration gradient. In the simulation, forming of a gelated region of PVA was considered during the constant rate drying period at higher drying temperatures. The gelated region is the reason to reduce the drying period in this system. Adsorption of PVA on the particle surface appeared to affect the surface segregation of PVA in the cases of lower drying temperatures and lower concentrations of PVA.

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Phase transition and oxygen deficiency in electrochemically reduced Y-, Ca-PSZ crystals were investigated using XRD and thermogravimetric techniques. PSZ samples were reduced in air at 1650°C with d. c. current for 0 to 2h and were oxidized at 1650°C, or were quenched to room temperature keeping their reduction states. Reduced Y-, Ca-PSZ's were divided into two regions; severely reduced cathode and weakly reduced anode ones. A metastable tetragonal (t′) phase appeared in the cathode region of Y-PSZ samples reduced and oxidized or of those reduced and quenched. Reduced t′-phase had a small c/a ratio and its lattice volume was slightly contracted compared to the oxidized t′-phase. Phases of cathode region for Ca-PSZ samples reduced and oxidized or of those reduced and quenched were cubic (c). The lattice parameter of the reduced c-phase was slightly smaller than the oxidized c-phase. In thermogravimetric analyses in oxygen from room temperature to 1000°C for reduced Y-PSZ and Ca-PSZ, two steps of weight gain were observed. The first step seems to be due to oxidation in weakly reduced anode region and the second to that in severely reduced cathode region. The oxygen deficiency in weakly reduced regions was independent of the electrochemical reduction time.

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In the ZrO₂-Mg-CH₄ system, ZrC fine powders have been prepared by two different methods; (1) direct preparation from ZrO₂ and Mg in a CH₄ gas flow and (2) reduction of ZrO₂ with Mg in an Ar flow and subsequent carbonization of the reduced materials in a CH₄ flow. The formation process of the ZrC powders of single phase has also been studied. In the method (1), the appropriate synthesis conditions were Mg/ZrO₂ molar ratio≥4, heating temperature≥700°C and heating time=1h. In the method (2), on the other hand, the optimum conditions were as follows; Mg/ZrO₂ molar ratio=4, and reduction time=1h in an Ar flow and carbonization time=1h in a CH₄ flow at 800°C. The formation process of ZrC powders in the ZrO₂-Mg-CH₄ system was as follows: in the case of Mg/ZrO₂≥4 molar ratio, (1) 600°-; ZrO₂+2Mg→α-Zr+2MgO, (2) 650°-800°C; 3CH₄+2Mg→Mg₂C₃+6H₂, (3) 650°-750°C; α-Zr+H₂→δ-ZrH₂, (4) 700°C-; Mg₂C₃→2Mg+3C, (5) 750°C-; δ-ZrH₂→α-Zr+H₂ and (6) 700°C-; α-Zr+C→ZrC. Comparison of the two methods (1) and (2) indicated that the former was highly efficient because of an exothermic reaction by the thermite reaction.

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Cryptomelanes [K_x(Mn³⁺, Mn⁴⁺)₈O₁₆(1.1≤x≤2.0)] with different occupancies (55% to 100%) of K-ion in the one-dimensional tunnels were synthesized by solid state reaction. The critical formation temperatures of cryptomelanes with low occupancy are lower than those with high occupancy. Cryptomelanes with low occupancy change to those with high occupancy accompanied with bixbyite (Mn₂O₃) during the heating. The deformation temperature measured by DTA is a function of the K-ion occupancy. A certain amount of K-ions of cryptomelane is elutriated quickly from the tunnels by water. The K-ion occupancy can be determined from the functional relationship between the deformation temperature and the K-ion occupancy, based on the deformation temperature measured by DTA.

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Chemical reaction between SiC ceramics and Ni foil has been used for making grooves on the sliding face of SiC ceramics. The grooved face should be crack free, and then generation of cracks was already understood to be dependent on the size of deposited graphite in reaction product layer. To investigate the growth of graphite in detail, graphite remained after dissolving other reaction products with acid, and the mean diameter of the graphite particles was determined from SEM photos. The graphite particles grew as a function of cube root of time. When the mean graphite particle diameter was larger than about 3μm, cracks were not generated on the SiC face. The influence of sintered SiC structure on the reaction product layer was investigated. Reaction between Ni foil and low density SiC or SiC as with extraordinarily large grains yielded graphite, δ-Ni₂Si and Ni₃Si₂, as with normally sintered SiC. The size of graphite particles in reaction product layer of low density SiC was smaller than that of other sintered bodies, and craks were generated on the surface of low density SiC. In low density SiC, the smaller size of graphite particles was considered to promote crack formation, in addition to the low strength due to the low density.

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Using Tyranno fiber containing 13% O (T-2), suppression of pyrolysis with oxide film was investigated at temperatures from 1573 to 1773K. The gas stream was changed to Ar, immediately after an oxide film of a given thickness was formed on the fiber in O₂. At temperatures lower than 1723K, the pyrolysis was suppressed. The core fiber crystallized slightly, and the oxide film changed from amorphous silica into cristobalite. The tensile strength was 1.26 to 1.45GPa when treated at 1723K. At 1773K, the oxide film disappeared, and the core fiber decomposed completely to β-SiC. The resulting fiber was too weak to measure the strength. These results were compared with those obtained in Tyranno fiber containing 18% O (T-1) and Nicalon fiber (NL200).

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Polycrystalline Al-C-O-N films were prepared by microwave plasma chemical vapor deposition using an AlBr₃-H₂-N₂-N₂O-CH₄-Ar gas mixture on an Si (100) substrate. The composition, structure and crystallinity of films as a function of N₂O gas flow rate (0 to 10 sccm) and CH₄ gas flow rate (0 to 60 sccm) were examined at a total gas pressure of 0.4 Torr, and a substrate temperature of 530°C. The Al-C-O-N films contained 0 to 53mol% oxygen and 0 to 6mol% carbon. Crystallinity of the films as a function of N₂O and CH₄ gas flow rates were classified following three regions: (1) highly c-axis oriented AlN, (2) the lower oriented AlN, (3) amorphous. The unit cell volume of AlN films in (1) and (2) increases with increasing carbon concentration in the films. Results of XRD, TEM and IR indicate that carbon and oxygen atoms take the place of nitrogen in the AlN lattice. Vickers microhardness of the polycrystalline Al-C-O-N film containing 4.3mol% of carbon and 3mol% of oxygen was about 26GPa, and higher than that of AlN (14GPa).

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Electron-cyclotron-resonance (ECR) plasma etching was applied to gas pressure sintered Si₃N₄, β′-SiAlON and α′/β′ composite SiAlON. The etching was successfully performed within about 15min, and the shapes of Si₃N₄ and SiAlON grains were clearly observed. Also the grains of α′-SiAlON were distinguishable from β′-SiAlON grains and grain boundaries. The volume ratio of α′ phase to β′ phase obtained from the area of the etched surface was almost consistent with the value obtained from X-ray diffraction. However, the grain boundary area observed from the etched surface did not correspond to that obtained from back scattered electron image.

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Wear of six kinds of media balls during the ball milling of Si₃N₄ raw powder with additives was tested. The materials of the ball were α′/β′-SiAlON, β-Si₃N₄, high purity Al₂O₃, Al₂O₃ (HD-11), SiC and tetragonal ZrO₂. The material of the least wear was α′/β′-SiAlON. The Si₃N₄ powder milled with SiC ball resulted in the mixture of Si₃N₄ with 13vol% of SiC. The powder consolidated to almost full density by the conventional gas pressure sintering.

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The filament of MoSi₂ for light source was made by the powder extrusion method under the optimized shaping condition. A high temperature of 1600°C in air and high emissibility was obtained. Emitted light power of the new material at 1600°C was higher than that of the conventional light source at 1000°C. Applicability of MoSi₂ as a light source was confirmed by testing in the FT/IR system.

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The films have been prepared by the dip-coating technique using nickel nitrate hexahydrate, Ni(NO₃)₂⋅6H₂O, as starting material and ethylene glycol as solvent. In order to obtain uniform films the withdrawal speed should not exceed 12cm/min. The crystalline phase formed after firing at 500°C for 2h is nickel oxide, NiO, which belongs to the cubic system with lattice parameter a₀=4.1769Å. The conductivities of NiO films are on the order of 10^-6S⋅cm^-1 in our measurements.

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The relationship between the hydrolysis conditions of titanium tetraisopropoxide (TTIP) and the thermal transformation of the hydrolysis products was investigated as a part of study on the properties of TiO₂ formed by the hydrolysis of titanium alkoxide. The amorphous products formed under the HNO₃ and HCl acidic conditions transformed to anatase at about 200°C. This temperature was about 100°C higher than that of the amorphous products formed with neutral water, and was not correlated with the H₂O/TTIP molar ratio. On the other hand, the anatase-rutile transformation was significantly accelerated under the acidic condition. In particular, the single-phase rutile particles which were needle-shaped and about 0.1μm in length were formed at room temperature when the concentrations of acids were more than 6wt% for HNO₃ and more than 4wt% for HCl at the molar ratio of H₂O/TTIP=20. In the case of the hydrolysis product formed under H₂SO₄ acidic condition, on the contrary, the temperatures of the amorphous-anatase and anatase-rutile transformations were higher than those of hydrolysis products with neutral water, and its values were 300 and 700°C, respectively.

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The electromotive force (e. m. f.) of mullite ceramics with a density of 97.9% T. D. as a solid electrolyte for oxygen concentration cell was measured between 873 and 1573K in the oxygen pressure range of 1.0×10^3.5 to 1.0×10^-2Pa. The measured e. m. f. indicates that the ionic transport number (t_i) of oxygen is higher than 0.8 above 1273K at oxygen pressures above 1.0×10^2.5Pa. The t_i decreased with decreasing oxygen pressure and was not sensitive to oxygen pressure below 1073K. Above results were discussed in relation to the electronic conduction due to thermal decomposition of lattice oxygen of mullite in a reduced atmosphere.

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Zirconium oxide films were prepared at 600° to 1000°C by chemical vapor deposition using a β-diketone chelate of Zr as a source material and a mixture of H₂ and CO₂ as a oxidation gas. The deposition rate of the films increased from 4 to 10μm/h with increasing deposition temperature. The film obtained at 650°C was amorphous. The films deposited at 850° and 1000°C consisted of the tetragonal phase and the mixture of the tetragonal and monoclinic phases of ZrO₂, respectively. A fine-grain structure was observed for all the films prepared at 600° to 1000°C.

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The mixed-mode fracture toughness of a silicon nitride ceramic was studied to evaluate the parameter C in Shetty's empirical equation. The measurement was conducted at room temperature and 800°C by the four-point bending method using the controlled surface flaw technique. The obtained Shetty's parameter C was 1.58 at room temperature and 1.35 at 800°C. These values are in good agreement with those obtained by multiaxial strength tests.

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