The sintering behavior and dielectric characteristics of Pb(Li_1/4Fe_1/4W_1/2)O₃-added Pb(Mg_1/3Nb_2/3)O₃ ceramics were investigated. Mixing the two end-members for 4h only formed a mixture, however, 48h-mixing mechanochemically induced the reactants to form partial perovskite solid-solutions. In the mixture specimen, the melt of Pb(Li_1/4Fe_1/4W_1/2)O₃ acted as a reactive liquid phase to substantially enhance the densification of Pb(Mg_1/3Nb_2/3)O₃, and caused grains to grow greatly and resulted in nonuniform microstructure. Regardless of mixing conditions, pure perovskite solid-solutions were formulated at 1000°C when the content of Pb(Li_1/4Fe_1/4W_1/2)O₃ was less than 10 mass%, whereas, adding excess Pb(Li_1/4Fe_1/4W_1/2)O₃ unfavorably caused polyhedral pyrochlore phase to form in the matrix. The addition of Pb(Li_1/4Fe_1/4W_1/2)O₃ decreased the broad maximum of dielectric permittivity of sintered specimens; nevertheless, this addition markedly suppressed the temperature dependence of dielectric permittivity. The ceramics fabricated by the mixture of two end-members possessed a larger apparent diffusiveness of dielectric permittivity than those prepared from the partial solid-solution, implying that a wider compositional fluctuation likely occurred in the former specimen.

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SiC-TiC composites with different C/Ti ratio were hot-pressed at 2050°C for 1h under vacuum. The ratio of C/Ti was controlled by the addition of Ti or C. Density of the sintered bodies decreased with increasing C content. The SiC-TiC composite with a low C/Ti ratio, i.e., doped with 2 mass% Ti, could be densified up to 98% of the theoretical value. On the other hand, relative density of the specimens with higher C/Ti ratio reached only about 80%. Density of the monolithic SiC doped with 2 mass% Ti was measured to be 73%. The presence of free Si and Ti₃SiC₂ phases was confirmed by XRD for the composites with lower C/Ti ratio. Diffraction intensity of these peaks decreased with increasing C content, and finally disappeared. Plastic deformation of TiC and formation of Si and Ti₃SiC₂ phases are believed to be the main factors to control the sintering behavior of SiC-TiC composite containing C deficiency.

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Amorphous LiNbO₃ powder compacts derived from completely hydrolyzed metal alkoxides were characterized in terms of Li⁺ coordination and conductivity at temperatures below 200°C. Amorphous LiNbO₃ powders were prepared by the dehydration of lithium niobium hydroxide hydrate gel at 200°C (LiNbO_m/2(OH)_6-m⋅nH₂O) which was precipitated by the complete hydrolysis of lithium and niobium double alkoxide with water. The powders heated at 200°C of amorphous LiNbO₃ powders, which were X-ray amorphous, showed broad bands on Raman spectra indicating an intermediate stage with a tendency to crystallization. The state of Li in the amorphous LiNbO₃ powders was also characterized by ⁷Li MAS NMR, and compared with that in polycrystalline LiNbO₃. ⁷Li MAS NMR spectra of amorphous LiNbO₃ showed an extra small broad band downfield shifted by about 13ppm from the main band. This extra band is attributable to the different Li state in amorphous structure from that in the polycrystalline structure. This disordered state of Li ions should give rise to the mobile Li ions that might attribute partly to the conductivity.

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To estimate the strength of commercially produced porcelains, specimens must be cut from the commercial products. In this study, the effects of sample preparation processes, such as cutting or grinding, and measuring methods on the bending strength and its distribution were investigated for the specimens cut from commercial products, and compared with those of slip-cast specimens. The bending strength of specimens cut from traditional porcelains, which is smaller than 150MPa, agreed well with that of slip-cast specimens irrespective of sample preparation method. On the other hand, in the case of high-strength glazed porcelain products, which show values larger than 250MPa, the bending strength was estimated accurately by eliminating the chipping in glaze or cracks in the body by means of grinding away over 150μm on one side with a #400 diamond wheel, and agreed well with that of slip-cast specimens.

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Porous cast-iron bonded diamond grinding wheels were fabricated and tested. Diamond grains of #100/120 were used as abrasive grains. Atomized cast-iron of various grain-sizes and carbon contents was used as bonding material. The capsule-free hot isostatic press (HIP) method was employed to obtain high mechanical strength and high porosity. Grinding tests were conducted under constant pressure grinding (CPG) conditions to avoid influences of Young's modulus of different grinding wheels and stiffness of grinding machines. The grinding ratio, grinding force and specific grinding energy were evaluated for the new and other commercial grinding wheels. Alumina and silicon nitride were ground for the evaluation. Grinding wheels bonded by cast-iron of low carbon content, i.e., 3.11mass%, and finer grain size, i.e., less than 20μm, had higher grindability. Scanning electron microscopic observation showed evidence of reaction between the diamond grains and the cast-iron particles, i.e., and diffusion of carbon from the diamond grains to the cast-iron particles. The total volume of diffused carbon from diamond to cast-iron affected the grindability. The porous cast-iron bonded grinding wheels showed an extremely higher grinding ratio and lower specific grinding energy than commercial resinoid wheels, vitrified wheels, and non-porous cast-iron bonded wheels.

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The synthesis and sintering behavior of AlON from a mixture of Al₂O₃-AlN by the reactive plasma treatment were investigated. AlN, Al₂O₃, Y₂O₃ and CeO₂ powders were used as starting materials. These powders were mixed and formed into a pellet. The pellet was sintered in the reactive Ar-N₂ plasma generated inductively in a quartz tube by using an r.f. generator (4MHz, 5kW or 10kW) and a work coil. High AlON content sample was obtained by 30min sintering of mixture with a composition which corresponds to the AlON single phase region, in the sintered body near the r.f. coil for a short time duration (5min). When a large amount of Al₂O₃ was added into the starting powder, a dense sample was obtained. At a low plate output (5.5kW), the density decreased with increase in distance between the sample and the lower end of the work coil. At a high plate output (7.7kW) of the r.f. generator, the density of the sintered sample near the coil decreased, because the plasma power was too high to sinter the sample without causing decomposition. At a higher plate output (10.0kW), similar tendency was observed in the sintered sample near the coil as to various sintering durations. At a low position which was far from the coil, the density reached a maximum value in 3min (10.0cm) and 20min (13.5cm) sintering. Therefore it seemed that the optimum sample position was existed. The linear shrinkage also increased to a maximum value at this position. From the SEM observation, the grain growth was observed after 30min sintering, but the grain size was several micrometer smaller than that by the usual sintering method. The density of the sintered sample using Y₂O₃ was higher than that using CeO₂ or without any additives. Nitrogen or hydrogen addition to Ar plasma was effective to promote sintering, because the enthalpy of plasma and heat transfer from plasma to the sample were remarkably increased.

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The friction and wear properties of oil-retaining porous silicon carbide and dense silicon carbide in air were studied by using a pin-on-disk friction machine. The tribological properties and morphologies of the worn surfaces of these ceramics were greatly changed depending on the test conditions such as loads applied and the combinations of materials (pin/disk). Dense SiC pin showed a lower and more stable friction coefficient and less wear than those of self-mated dense SiC, when it was slid against the oil-retaining porous SiC disk. The friction and wear mechanisms of these ceramics were discussed from the tribological properties obtained and the morphologies of the worn surfaces by SEM and three-dimensional surface roughness observation.

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A new hybridized process for preparing optical fibers has been developed. The process consists of overcladding a VAD-derived core rod with commercial silica powder by extrusion shaping technique. The single-mode optical fiber was fabricated by the process which used a core rod having a ratio of core/cladding diameter of 1/3.15 and silica powder of average particle diameter of 10μm. The transmission losses were 0.40dB/km at 1.3μm and 0.26dB/km at 1.55μm. In this study, we also clarified as follows: (1) The lamination which occurs at extrusion can disappear by using an extension cylinder with bolts. (2) Bubbles in the optical fiber preform do not occur by using plastic material in which surface active agent is added in the mixture consisting of silica powder, water and methyl-cellulose. (3) The soot preform which consists of a core rod and a porous body around it can be extruded by using an extruder which is reconstructed a commercially available one for hybridized extrusion.

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It is known that 4CaO⋅Al₂O₃⋅Fe₂O₃ (C₄AF) mineral gives high sulfate resistance to the cement hardening body in the portland cement. Crystalline C₄AF was synthesized at 1300°C from the mixture of CaCO₃, Al₂O₃ and Fe₂O₃ with a molar ratio of 4:1:1. Glassy C₄AF was prepared by quenching the melt with water from 1450°C. Glassy C₄AF becomes vitrified by the addition of 7 mass% of SiO₂. Mössbauer spectrum showed that the iron in glassy C₄AF was distorted. The fraction of the glass in C₄AF increase with decreasing hydration speed. Because, C₄AF glass formed strongly three-dimensional structure.

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Problems in the chevron notch method for fracture toughness and work-of-fracture measurement were pointed out. The authors proposed three independent conditions to achieve stable fracture in the chevron notch method. It was possible to realize the stable fracture when a JIS-type bending beam with a narrow chevron notch (0.2mm) at the center was fractured in three-point bending (span=30mm) with a rigid testing machine (>2×10^-7m/N) at a crosshead transfer speed of 0.005mm/min. The fracture toughness and the work-of-fracture of float glass, polycrystalline Al₂O₃ and SiC-whisker/Al₂O₃ composite were evaluated by three-point bending test with five kinds of chevron notched beam. The fracture toughness obtained by the chevron notch method almost agreed with that estimated by SEPB and IF methods according to JIS R 1607 in the case of the glass and the Al₂O₃ in which R-curve behavior did not affect the measured fracture toughness appreciably. On the contrary, in the case of the composite, the former fracture toughness was larger than the latter one and varied depending on the chevron geometry, which was caused by the R-curve behavior of the crack in the composite. Fracture toughness derived from work-of-fracture with the Irwin similarity relationship corresponded to the measured fracture toughness in the glass and the Al₂O₃, but was larger than the evaluated fracture toughness in the composite. That was also explained by the R-curve behavior. Therefore, the effect of the R-curve on fracture resistance was recognized by comparing the fracture toughness and the work-of-fracture using the Irwin similarity relationship.

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Porous ceramic materials are widely used as heat insulators, filters, and spacers. However, the shape, diameter and distribution of pores in these materials are not controlled precisely. Porous ceramic materials are used not only as structural materials but also as functional materials. In this study, porous BaTiO₃ ceramics were synthesized. A porous structure was obtained by sintering of spheres. The spheres were obtained using emulsification techniques. Ba-Ti mixed alkoxide was used as BaTiO₃ precursor. The alkoxide was dissolved in toluene-IPA (2-PrOH). PVB was then dissolved in this solution to aid the formation of spheres and to control the rate of hydrolysis. Water was dispersed in this solution to obtain a W/O emulsion. This W/O emulsion was redispersed in water to obtain a [(W/O)/W] emulsion. The [(W/O)/W] emulsion-derived spheres were dried and sintered. The sintered bodies consisted of spheres which were linked together, and open pores which were due to voids between packed spheres.

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A simulation program of temperature analysis was constructed for laser treatments of ceramics. It is based on axially symmetric, transient heat conduction equations governing laser heating process and takes the temperature-dependent material properties and moving heat source into consideration. The non-linear fundamental equation was transformed into finite difference equation to carry out the numerical computations. This simulation program was applied to the surface modification of alumina-sprayed coatings. The width and depth of the melted zone of the coatings were calculated for various parameters of laser treatments, the results of which were compared with the previous experimental ones. Both results were approximately in good agreements. The phase change region of the alumina coatings obtained experimentally was confirmed by this simulation technique. It is concluded that this simulation technique is useful to the surface modification process of ceramics.

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Fired bodies were prepared from the clay mineral (kaolin and pyrophyllite) and Y₂O₃-stabilized zirconia powders. The bulk density (ρ) dependence of the bending strength (σ) and Vickers hardness (H_V) were studied. The relation, σ∝H_V^n/m was obtained from the power law of σ∝ρⁿ and H_V∝ρ^m. Also, the relation, K_Ic∝σ^t, was proved. The fracture toughness (K_Ic) can be estimated easily from the measurement of σ. Moreover, an empirical equation χ=χ₀exp(-ñP) was derived theoretically using the power law, where χ is a physical quantity related to the mechanical properties and P is the porosity.

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The friction and wear properties of self-mated zirconia (ZrO₂) in unlubricated sliding contact were investigated by using a pin/disk friction machine. From the obtatined results and the morphologies of frictional surfaces observed by SEM and particle size distribution of wear particles, the friction and wear mechanism of ZrO₂ pin slide against ZrO₂ disk was discussed. In this system, the average friction coefficient was almost independent of the load applied, but the wear amount increased with an increase of the load. The wear particle sizes became larger with increasing sliding time and load applied. It is found that the friction and wear mechanism of ZrO₂ is dominated with the formation, delamination and fracture of surface film transferred on frictional surfaces by friction and adhesion, and that they are influenced by friction heat and the load applied.

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Single crystal Si was nitrided in a fluidized-bed reactor. The volume fraction of the α/β phases and the nitridation process were studied by X-ray diffraction and electron microscopy. No difference in the α/β ratio and the nitridation rate were found between pure Si single crystal and commercial Si powder including impurities. This indicates that the α/β ratio is not affected by the impurity content. Microstructural observation revealed the internal fracture of Si to several-micron pieces and the formation of Si₃N₄ needles in the early stage of nitridation. Pores were also observed in the fractured Si pieces and the size increased with the progress of nitridation. Aggregation of Si₃N₄ in a band shape and a group of dislocations, forming small angle boundaries, were also observed in the Si piece. The fracture of the Si single crystal appears to be caused by segregation of nitrogen along dislocations, introduced during fluidization, and subsequent formation of Si₃N₄.

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Abrasion test of high and low purity alumina balls is conducted in different types of mills under wet condition. The abrasion powder produced by abrasion of high purity alumina balls gave extremely large value of specific surface area over 30m²/g. The powder includes α-Al(OH)₃ of gibbsite type, while α-Al(OH)₃ is not included in an abrasion powder worn from the low purity alumina one. A considerable amount of amorphous aluminum hydroxide is contained in both abrasion powders. The amount of aluminum hydroxide in the powder increased as the milling becomes moderate and as the balls' size is small. The aluminum hydroxide in the abrasion powder is transformed into a single phase of α-alumina without forming κ- and θ-alumina phases at a relatively low temperature of about 900°C. This is completely different from the phase transformation of an ordinary powder of α-Al(OH)₃. The formation of α-alumina from abrasion powder at such low temperature is attributed to a seed-effect of fine α-alumina powder mixed uniformly in the abrasion powder. An abrasion powder worn in alcohol also enables us to sinter at comparatively low temperature.

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Crack configurations beneath Vickers indentations in 3mol% Y₂O₃-containing tetragonal zirconia polycrystals (Y-TZP) with grain sizes of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) were measured using a stepwise polishing technique. The crack configuration beneath the Vickers indentation in Y-TZP was Palmquist type. The depth of the crack beneath the Vickers indentation in Z3Y-II was smaller than that of the crack in Z3Y-I. Upheaval was observed around Vickers and Knoop indentations, and on both sides of induced cracks. The height of the upheaval was about 2μm around the corner and the edge of the Vickers indentation. However, the height of the upheaval around the induced crack decreased progressively away from the indentation. The upheaval had a maximum value of about 2μm at the end of the minor axis in the Knoop indentation. However, the upheaval at the edge decreased linearly away from the minor axis and was zero at the end of the apse axis. No crack was induced beneath the Knoop indentation even if Y-TZP was indented using a load of 490N.

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The sinterability, electric conductivity, expansion coefficient and chemical stability were examined for the perovskite-type oxides which are expressed as (La_1-XA_X)_1-ZMO_3-δ (A=Sr, Ca, M=Mn, Co, Cr). The sinterability depended on the A site composition X and the deficiency Z. The electric conductivity and the thermal expansion coefficient also depended strongly on the composition of the oxides. The electric conductivity was sensitive to the amount of Sr-substitution and the Co to Mn ratio and high conductivity could be attained without accompanying thermal expansion coefficient mismatch with YSZ. The chemical reaction between the perovskite-type oxides and YSZ resulted in the formation of La₂Zr₂O₇ and SrZrO₃ depending on the composition.

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The thermal decomposition process of the branched-type polyfluoroalkylsilane on silica-gels has been investigated based on TG-DTA/MS measurements. In air the decomposition occurred in hydrocarbon moiety of the fluorosilane. In argon trifluoromethyl group remains stable up to 700°C. In any cases the production of HF and F₂ was not detected at all.

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The alumina gels which form α-Al₂O₃ at heat treatment temperature as low as -500°C were prepared from aluminum-sec-butoxide by the sol-gel method under the ambient condition. Preparation of transparent alumina sol by hydrolysis of the alkoxide at a low temperature such as 0°C and aging the sol at a moderately low temperature, typically 8°C for a relatively long time up to 30 days were found to be important for obtaining such alumina gels.

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(1) D. C. conductivity of Mg(PO₃)₂ glasses at room temperature was drastically enhanced from -10¹⁵S·cm^-1 to -5×10^-4S·cm^-1 and the activation energy of the conduction was greatly reduced from 1.1eV to 0.18eV upon implantation of 120keV H⁺ to a fluence of 1×10¹⁸cm^-2. Almost the same changes in conductivities and the activation energy were obtained for the glasses implanted with 100keV D⁺ (the calculated depth, -1μm, corresponds to that of 120keV H⁺) to the same fluence. No high proton conduction (>10^-8S·cm^-1 at room temperature) was observed for SiO₂ glasses implanted with 120keV H⁺ to a fluence of 1×10¹⁸cm^-2.
(2) The observed conductivity in the H⁺ (1×10¹⁸cm^-2)-implanted Mg(PO₃)₂ glasses was higher by 8 orders of magnitude than the conductivity calculated using an empirical relation which was obtained for various oxides glasses containing residual X-OH groups (H₂O-free). The activation energy (-0.2eV) of the conduction was close to that in fast proton conducting crystals of hydrated heteropolyacids containing POH and H₂O such as H₃Mo₁₂PO₄⋅29H₂O. These results indicate that coexistence of acidic X-OH such as P-OH and molecular water is a structural requirement for the emergence of fast proton conduction in oxide glasses.

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The effect of A site substitution of Pb(Fe_1/2Nb_1/2)O₃ (PFN) and Pb(Sc_1/2Ta_1/2)O₃ (PST) with Na or La on the order-disorder transition and dielectric characteristics was examined. It was clarified that the degree of ordering at the B site did not change by the substitution though it has been reported that in case of Pb(Mg_1/3Nb_2/3)O₃ (PMN), the degree of ordering can be controlled by the A site substitution. The reason may be due to the difference in cation size ratio of B site, that is, Mg:Nb=1:2 for PMN and Fe:Nb and Sc:Ta=1:1 for PFN and PST. By partial substitution of A site by La or Na, the dielectric characteristics of PFN and PST drastically changed from normal ferroelectric to “relaxor ferroelectric”. This indicates that “relaxor ferroelectrics” can not be necessarily derived from the order-disorder state at the B site sublattice as understood so far. The “relaxor ferroelectric” property of Na or La doped PST and PFN would be classified into the same group of (Pb, La) (Zr, Ti)O₃ (PLZT) and La doped (Sr, Ba)Nb₂O₆ (SBN).

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