The viscosities of the four series of mixed alkali glass melts such as 25(Na₂O+K₂O)⋅75SiO₂, 25(Na₂O+K₂O)⋅5Al₂O₃⋅70SiO₂, 25(Na₂O+K₂O)⋅7.5Al₂O₃⋅67.5SiO₂ and 25(Na₂O+K₂O)⋅10Al₂O₃⋅65SiO₂ as well as their T_g were measured to elucidate a relation between property behaviors and mixed alkali effect models. The base mixed alkali glass melts (25R₂O⋅75SiO₂) showed a mixed alkali effect, namely viscosity minima at the composition K₂O/R₂O≈0.25, which become weaker as temperature increases. The activation energy for the viscous flow of this base glass melts showed also a minimum at this composition. However, the mixed alkali effect disappeared, as SiO₂ is substituted by Al₂O₃. This implies that the nonlinearity disappears with decreasing nonbridging oxygen content. In the case of T_g no clear tendency with respect to the Al₂O₃ content was found.
By comparison of the present work with the earlier work of resistivity, two distinct differences between the mixed alkali effects in viscosity and electrical conductivity were found. From these results, it was concluded that the mechanism for the mixed alkali effect in both properties should be treated independently.

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Ferromagnetic glass-ceramics can be expected to be useful as thermoseeds for hyperthermia of cancer, especially cancer located at deep parts of body, since hysteresis loss heating locally occurs at the cancer when they are subjected to an alternating magnetic field. Glass-ceramics containing a large amount of α-Fe fine particles in a CaO-SiO₂-based glassy matrix were obtained by heat treatment of Fe₂O₃-CaO-SiO₂ glasses under H₂ atmosphere. The α-Fe precipitated above 700°C, and its crystallite size and fraction increased with increasing heat treatment temperature to reach 150nm and 17mol% at 1150°C, respectively. The saturation magnetization of the specimen increased from 9 to 57emu·g^-1 with increasing heat treatment temperature from 650 to 1150°C. The coercive force of the specimen increased from 50Oe at 650°C to 237Oe at 750°C, and then decreased with increasing heat treatment temperature. The specimen heat-treated at 700°C showed the maximum heat generation, 3W·g^-1, under 300Oe and 100kHz. Thus reratively low heat generation of α-Fe-containing glass-ceramics could increase significantly if a magnetic field as large as 10kOe would be available, due to their large saturation magnetization and/or coercive force.

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Effects of the amount of sintering additives and that of SiC as a second phase on the densification and mechanical properties of Si₃N₄ and Si₃N₄/10-30mass% SiC composites were examined. Yttrium and aluminum nitrates as sintering additives were added to raw mixtures as methanol solutions. Powder compacts were pressurelessly sintered at 1750°C for 2h in N₂ atmosphere. The bulk density of the monolithic Si₃N₄ with 4mass% sintering additives reached 99% T. D. Both of the Si₃N₄/30mass% SiC with 8mass% sintering additives and the Si₃N₄/20mass% SiC with 6mass% sintering additives were sintered to 94% T. D. Fracture toughness of the dense Si₃N₄/SiC composites decreased compared with that of the monolithic Si₃N₄, due to the inhibitation of β-Si₃N₄ grain growth caused by the addition of SiC. Subsequently, the bending strength of these composites decreased. Furthermore, hardness of these composites increased. On the other hand, in the case of large amount of SiC addition or small amount of sintering additives, composites were not densified sufficiently, and bending strength, fracture toughness and hardness of these composites degraded markedly as compared with these of the monolithic Si₃N₄.

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Knoop hardness in α-Si₃N₄ on the surfaces of (1100), (1120) and (0001) was investigated. Hardness values had isotropic character on all surfaces. Effective resolved shear stress (ERSS) was calculated assuming the slip systems of (0001) ‹1120›, {1100} ‹1120›, {1100} ‹0001›, {1101} ‹1120› and {2201} ‹1120› to be activated. The ERSS curve of the {1101} ‹1120› slip system explains Knoop hardness better than those of other slip systems. This fact supports {1101} ‹1120› to be the primary slip system in α-Si₃N₄ at room temperature.

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For improvement of the image quality of X-ray CT, X-ray detector requires more sensitive and low afterglow scintillator. In order to realize the requirements, Gd₂O₂S: Pr ceramics scintillator which has a light output of 1.8 times of CdWO₄ is now in practical use. Ce doped in the Gd₂O₂S: Pr ceramics scintillator is effective for reducing undesirable afterglow. The effect of Ce on the radiation damage was studied in this paper. The radiation damage decreased with increase in Ce content. It was considered that Ce reduced the color centers and traps.

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New materials for plasma facing component such as divertor and the first wall armors in thermonuclear fusion were studied. The materials were fabricated by hot-pressing aggregates of unidimensionally oriented carbon fibers (CF) impregnated with boron carbide (B₄C) powder. The relation between density, thermal properties and sintering temperature of B₄C simple materials, bonding state between B₄C and CF interface by sintering, and the effect of CF volume and sintering temperature on microstructure, thermal and mechanical properties of B₄C/CF composite ceramics, were investigated in this study. As a result; Sintered body with high density over 95 percent was obtained, when sintered at 2100°C regardless of the CF content. Sintered body with thermal conductivity more than 150W/m·K was obtained when the sintering temperature was 2100°C and it contained more than 65 percent CF, and bending strength of the sintered body was over 500MPa and 20 to 30MPa for directions perpendicular and parallel to CF, respectively.

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The structural defects of β-Si₃N₄ grains were investigated by transmission electron microscopy (TEM). TEM analysis suggested the existence of dislocation, and α-type structure in β-Si₃N₄ grains. In paticular, TEM analysis of Si₃N₄ seeds annealed at 2473K under 30MPa in N₂ indicated that the β-Si₃N₄ grains contain an α-Si₃N₄ structure.

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In order to study the reaction area of the cathode of solid oxide fuel cells, the changes in microstructure of the cathode with a current-flow treatment were investigated. Cathode samples (La_0.9Sr_0.1MnO₃+10mass% ZrO₂) with two different microstructures were prepared. Decrease of cathodic polarization by the current-flow treatment was observed. The observations of microstructure change of the cathode suggested that the movement of oxygen ion and vacancy took place at boundary between electrolyte and cathode. The reason of decrease of cathodic polarization by current-flow treatment was discussed.

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The effect of the anti-galling and wear resistance of super fine SiO₂ particles (7-40nm in mean diameter) were investigated by using a Falex (pin/vee block) friction testing machine, when they were added into lithium soap-lubricating grease as solid lubricants. The SiO₂-added greases showed higher seizure loads and less wear amounts as compared with no-added grease. Especially, the addition of the finest 7nm-SiO₂ particles with the oleophilic surface treatment showed the highest seizure load. The lubricating actions of these super fine SiO₂ particles are due to their existences at the friction interface which decrease the metallic contact between frictional surfaces, thus result in high seizure loads and antiwear properties.

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Xmol% CeO₂-ZrO₂ (x=14-34) pseudo-single crystals grown by floating zone method were uniaxially compressed in the range of 0 to 1400MPa at 700°C to examine the effect of axial ratio (c/a) on the critical stress of ferroelastic domain switching. The critical stress markedly increased with axial ratio. It could be understood, considering the Landau theory and the ferroelastic domain switching model based on the tetragonal to cubic second order ferroelastic transition, that the critical stress was proportional to the cube of (c/a-1).

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Neodymium compounds were prepared by mixing Nd(NO₃)₃ solution with hexamethylenetetramine (HMT), urea and NH₄OH. The precipitates were characterized by TG-DTA, X-ray powder diffraction, IR and SEM. The composition of precipitate formed by the HMT method was Nd(OH)₃ and that by the urea method was NdCO₃OH. The difference in chemical composition was due to the presence of CO₂ in the decomposition product of urea. The particle size of precipitate by the HMT method was uniform but smaller than that by the urea method. Consequently, the powder formed by HMT method was sintered to the highest density at 1300°C.

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Various Co²⁺-substituted tetrasilicic micas having high contents of Co²⁺, such as KCoMgLi(Si₄O₁₀)F₂, KCo₂Li(Si₄O₁₀)F₂ and KCo_2.5(Si₄O₁₀)F₂, were synthesized through solid-state reaction techniques at 1000, 800 and 800°C, respectively. Lattice constants a, b increased with increasing Co²⁺-substitutions, reflecting the increase in the ionic radius of Co²⁺ against Mg²⁺, while c decreased due to the flattening of octahedral sheets. Both the micas KCoMgLi(Si₄O₁₀)F₂ and KCo₂Li(Si₄O₁₀)F₂ exhibited pink color while the mica KCo_2.5(Si₄O₁₀)F₂ turned blue due to the trace amount of tetrahedral Co²⁺-substitution. Site preference of Co²⁺ ions depended on formation temperature and composition of micas. UV-visible spectra of Co²⁺-micas were similar to that of [Co(H₂O)₆]²⁺. This can be explained in terms of both the nephelauxetic and spectrochemical series of F^-<H₂O<O_a (apical oxygen). IR spectra showed that the tetrahedral distortion changes with increasing Co²⁺-substitutions, i.e., the interatomic distance of Si-O_a lengthens. The Co²⁺-mica KCoMgLi(Si₄O₁₀)F₂ showed paramagnetism while the larger Co²⁺-substituted mica KCo₂Li(Si₄O₁₀)F₂ showed antiferromagnetism. On the other hand, the mica KCo_2.5(Si₄O₁₀)F₂ having the highest Co²⁺-content exhibited only a weaker magnetic interaction between Co²⁺ ions, probably due to the local variations of octahedral vacancy and Co²⁺-occupancy into two octahedral sites M1, M2 and tetrahedral sites.

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The addition of straight chain polyamines such as triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and 1, 4-diaminobutane in the course of carbonation of basic calcium carbonate promoted the formation of disk-like vaterite of 1-1.5μm in diameter and 0.1-0.2μm in thickness. On the other hand, cyclic polyamines such as piperazine, 1-(2-aminoethyl) piperazine and 1, 4-diazabicyclo [2, 2, 2] octane, and branching polyamine such as 2, 2-dimethylpropylene, promoted the formation of spindle-like calcite. Only polyamine in which N-N distance is 0.3nm or its integral multiple, promoted formation of the disk-like calcium carbonate, Hexagonal of basic calcium carbonate once dissolved in aquarious media and the disk-like calcium carbonate formed.

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Slip casting behavior of a cylindrical body was analyzed by FEM (finite element method). Based on the assumption that the cake is uniform and incompressible, Laplace equation for liquid pressure can be derived. Cake growth per unit time was calculated by a sequential combination of the Laplace equation, Darcy's law and mass balances. The profile of solid front (the interface between cake and slurry) changed with time from a cylindrical curve to a parabolic one. This three dimensional profile can be attributed to the interaction of filtration to the bottom and side-wall directions in the cylindrical mold. In the early stage of slip casting, the results of numerical analysis were in reasonable coincidence with the profiles experimentally obtained. It was shown that FEM simulation is valuable for prediction of three-dimensional cake growth which can not be expressed by one-dimensional analytical approaches.

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A basic lead calcium carbonate-swelling mica complex (surite-like material, SLM), Pb_2.11Ca_0.83Na_0.12(CO₃)_2.08(OH)_1.11(Si_3.95Al_0.04)Mg_2.66O₁₀(F, OH)₂⋅0.06H₂O, was prepared by treating a swelling mica hydrothermally at 250°C with lead powder, dry ice and calcium nitrate solution. The product showed the morphology of thin hexagonal plates of 4μm in diameter that have no swelling characteristics. Its symmetry is monoclinic; a=0.5204(3)nm, b=0.9080(9)nm, c=1.6231(8)nm, β=90.20(10)°. The X-ray powder diffraction pattern is characterized by a basal reflection of 1.62nm and its subsequent integer reflections up to the 14th order. The chemical analysis and one dimensional Fourier synthesis results proved that SLM has an interlayer structure similar to that of natural surite, while the octahedral cation in the 2:1 layer consists of only Mg unlike the 2:1 layer of natural surite. The thermal behavior of SLM is similar to that of natural surite in the point that the hydroxyl in the interlayer dehydrates prior to the decomposition of the carbonate structure in the interlayer and also that the carbonate structure decomposes accompanying the collapse of the 2:1 layer structure.

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A Na-X type zeolite is one of the effective material to collect and/or decompose chrolofluorocarbons, CFCs. The CFC-11 molecular adsorption and/or decomposition behavior in a Na-X type zeolite framework under the condition of various number of containing molecules and of two kinds of different temperatures were calculated by a molecular dynamics (MD) simulation. As the results of calculation, the crystal structure of Na-X zeolite absorbing few CFC-11 molecules was stable at both 300 and 1000K. Putting more CFC-11 molecules into Na-X zeolite pores, water and CFC-11 molecules less stabilized at 300K and CFC-11 molecules decompose easily at 1000K. The framework of Na-X zeolite including 80 molecules of CFC-11 destructed instantly even at 300K. When 80 CFC-11 molecules were in Na-X zeolite unit cell, the framework was decomposed. From the experimental result at 673K, hydrochrolic and hydrofluoric acid produced by decomposition of CFC-11 have attacked and alumina bonds in Na-X zeolite framework and less stabilized. The MD simulation is consistent with these experimental results which we have reported previously.

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A commercial portland cement mixed with many functional additive powders was spheroidized by the mutual impaction of particles in a high speed pneumatic field. An improvement on the frost durability of non-asbestos fiber reinforced cement board (FRCB) was succeeded by reducing the water absorption of the FRCBs which were fabricated from such a spheroidized cement raw powder. It was found that the reduction of water absorption of the FRCBs depends on the forming method and the W/C ratio.

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Composite ceramics of alumina mixed with 20vol% titanium carbide whiskers were fabricated by spark plasma sintering (SPS) and hot-pressing at 1300 to 1650°C under 30MPa for 5min. The SPS brought about dense titanium carbide whisker/alumina composites at a sintering temperature of 1500°C, which was about 100°C lower than that in the hot-pressing process. The composites obtained by SPS had mechanical properties slightly higher than those obtained by hot-pressing. The alumina matrix grains in the composites prepared by SPS grew larger than those by hot-pressing. The cutting performance (wear resistance and fracture resistance) of dense sintered bodies fabricated by SPS resulted to be slightly improved over those by hot-pressing, due to their higher mechanical properties.

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Three types of Si₃N₄-based sintered ceramics were fractured in an ultra-high vacuum and the gases generated during the fracture were analyzed by quadrupole mass spectroscopy. Various gases such as H₂, CH₄, N₂, CO, Ar and CO₂ were detected after the fracture event in all the materials. The emission peak intensities of the gases and the total pressure changes in the chamber depended on the types of materials, but the gas compositions were similar to each other. These gases are thought to be released mainly from residual pores formed during sintering. Some of the gases may be produced at the moment of fracture. This method is expected to be applied to fundamental studies on the processing and fracture of advanced ceramics.

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ZrO₂ and Y₂O₃-doped ZrO₂ gel films were obtained by spin-coating of a sol from Zr-n-propoxide, n-propanol, acetylacetone, water, and nitric acid on a silica glass as a substrate. The dried-gel films crystallized to monoclinic, tetragonal, cubic and their mixed phases, depending on the firing temperature and Y₂O₃ content. The ZrO₂ films with highly preferential orientation were successfully obtained from a solution containing a large amount of n-propanol. The highly oriented ZrO₂ film was found to have high transparency compared with the non-oriented films.

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The oxidation of silicon boride (SiB₄) powder at high temperatures was investigated in order to determine the possibility of its high-temperature utility. SiB₄ powder with an average particle size of about 10μm was used in this experiment. The sample oxidized at 200 to 1100°C for 5min to 50h in air; the weight changes were measured to estimate the oxidation resistance. The oxidation of sample, at the short oxidation time of 5min, started at 500 to 600°C, and weight gain changes with increasing oxidation temperature. The sample at the oxidation time of 0.5 to 1h, exhibited weight gain change with increasing oxidation temperature, and then the oxidation saturated at 900°C. On the other hand, at the oxidation time of 10h, it had the maximum value of the weight gain at 600°C, after that the weight gain monotonically decreased with increasing oxidation temperature. SiB₄ is oxidized to vitreous SiO₂ and B₂O₃ at about 700°C. The B₂O₃ of oxidation product vaporized above at 900°C. The vitreous SiO₂ transformed into the cristobalite.

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