The relative grinding energy (RGE) and mechanical properties of (Ni_0.8Mg_0.2)O ceramics were measured. The (Ni_0.8Mg_0.2)O ceramics have much larger RGE than other ceramics, such as α-Fe₂O₃ and ZnFe₂O₄ ceramics with mechanical strength, hardness and K_IC similar to those of (Ni_0.8Mg_0.2)O ceramics. Addition of a small amount of SiO₂ to (Ni_0.8Mg_0.2)O ceramics does not influence the mechanical properties appreciably but lowers the RGE to a great extent. These results were discussed on the basis of the modulus of rupture (MOR) of these ceramics under bending and compressive conditions.

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When glycols (except ethylenglycol) were added to an isopropanol solution of zirconium n-butoxide, the corresponding glycolates were formed by the alcohol exchange reaction, and the precipitation of oxide by hydrolysis was strongly suppressed. Diethylene glycol was most effective as the glycol additive for the precipitation retarder. At the glycol/alkoxide ratio of 2 in the presence of water (water/alkoxide ratio=0-5), a stable sol was obtained from which transparent zirconia sol-gel films can be obtained. The film thickness can be controlled by the alkoxide concentration, water/alkoxide ratio, and the pulling-up rate of the substrate plate. The maximum thickness of uniform transparent zirconia films obtained in one dipping-drying-heating cycle was about 1500Å. Much thicker films can be obtained by repeating the cycle. The crystal form of the zirconia films obtained at 600°-650°C on a glass substrate was tetragonal, and transformed into monoclinic above 800°C. The refractive indices and densities of the films obtained at 600°-650°C were 1.9-2.0 and 4.7-5.5, respectively. The density increased to 5.8-6.0g/cm³ by the heat treatment at 1000°C. In the present system, an aqueous solution of yttrium or calcium nitrate could be added so as to prepare tetragonal of cubic transparent films of doped zirconia, respectively. When silver nitrate solution was added, the tetragonal AgO-doped zirconia films were obtained. Furthermore, it was found that the addition of titanium and aluminium-magnesium alkoxides allowed to form mixed oxide films ZrTiO₄ and spinel-doped ZrO₂.

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The effect of Y₂O₃ content on the stress-induced transformation of ZrO₂ in sintered Al₂O₃-ZrO₂ (Y₂O₂: 0-3mol%) composites was studied by using laser Raman spectroscopy and X-ray diffraction method, and their mechanical properties, such as Young's modulus, bending strength, Vickers hardness and fracture toughness, were measured. The tetragonal phase of ZrO₂ was 54mol% in the Y₂O₃-free composite, and increased with increasing Y₂O₃ content. From SEM observation, the particle size of ZrO₂ in the composites was from 0.9 to 1.2μm. The Raman measurement of ZrO₂ phases on the fracture and tensile surfaces after bending test indicated that the stress-induced transformation proceeded more extensively in the composites with low Y₂O₃ contents and near the fracture surfaces. Consequently, fracture toughness increased with decreasing Y₂O₃ content, and this tendency was related to the stress-induced transformation and the presence of microcracking. On the other hand, bending strength, Vickers hardness and Young's modulus decreased with decreasing Y₂O₃ content due to microcracking in Al₂O₃-ZrO₂ composites. The results obtained lead to the conclusion that the stress-induced transformation behavior is explained by the constraint of ZrO₂ particles in the matrix of Al₂O₃, and is influenced by the stabilization of tetragonal ZrO₂ by Y₂O₃.

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Fine Si₃N₄ powders were synthesized by combustion of Si mixed with a proper amount of Si₃N₄ under high nitrogen pressure of 10MPa. The obtained Si₃N₄ powders consisted of 30wt% α- and 70wt% β-Si₃N₄ free from unreacted Si, and had a mean particle size of 1.8μm. Dense Si₃N₄ ceramics with the bending strength of 700MPa were obtained by both HIP sintering without additives and pressureless sintering with Al₂O₃-Y₂O₃ additives. A sintered body obtained by HIPing had a high Vickers microhardness of 15GPa and high bending strength of 500MPa at 1200°C.

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This paper presented an etching method, facture method and taper polishing method for observing ceramic surface cracks induced by the single-point diamonds. These methods were tested for the crack observation of HP-Al₂O₃, HP-Si₃N₄ and S-SiC which were scratched by 2 and 45μm R single-point diamonds in minute depth of cut. These methods were found to be useful in observing the surface as well as the subsurface cracks in 1μm dimension and the microcrack cluster directly.

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Monolithic dried silica gels were synthesized from tetramethoxysilane (TMOS) solutions using N, N-dimethylformamide (DMF) as a drying-control chemical additive. Solutions of the system TMOS-DMF-CH₃OH-H₂O-NH₄OH (or HNO₃) with varying amounts of catalyst, concentrations of DMF and [H₂O]/[TMOS] molar ratios were reacted to obtain dried gel monolith, in order to find an optimum composition. A crack-free cylindrical rod of 32mm in diameter and 120mm in length could be obtained from the solutions of the composition 1 TMOS⋅1 DMF⋅2 CH₃OH⋅10 H₂O⋅5×10^-4NH₄OH in mole and some other compositions. The pore size distribution varied with the kind and amount of catalyst, the concentration of DMF, and the [H₂O]/[TMOS] molar ratio. The beneficial role of DMF in producing crack-free dried gel monolith was attributed to the effect of keeping the average pore size of the gel large and of lowering the surface tension of liquid filling pores in the drying gel. When the composition of the starting solution was appropriate, the dried gel monolith could be converted into transparent silica glass without cracking and bloating by heating to 1050°C and holding there for more than two hours. The change of gel structure of the dried gel was investigated by infrared and Raman spectroscopy.

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The erosion tests were performed for nine kinds of ceramics such as SiC, Si₃N₄ and Al₂O₃ and window glass using SiC, Al₂O₃ and glass powders as abrasive at the impingement angle (θ) of 90-20 degrees. The erosive wear (V) for many target and abrasive particle pairs is almost proportional to the square of the impingement angle as proposed by Bitter. However, there were several pairs for which the exponent n in V∝(sinθ)ⁿ deviates greatly from two. The pair of Si₃N₄ (9S) target and Al₂O₃ abrasive has a small n, 0.8. The small n value is explained by the fact that the erosive wear by brittle erosion mechanism in the high impingement angle region is suppressed because of large toughness of the target and that the erosive wear by scratching in the low impingement angle region is significant. The n's large than two were observed in glass abrasives. This is caused by a large change of effective stress with changing the impingement angle, and the larger change in stress resulted from the slip of abrasive particle on the surface of target which is caused by the melting of glass by the rubbing heat at the instant of impingement. The melting phenomenon of particles and/or targets was observed also for Al₂O₃. The exponent n for SiC particles are always larger than that for Al₂O₃ particles for the same target. Changing the impingement angle in the erosion test is considered to be effective for finding some clue to understand the erosion mechanism and mechanical or chemical phenomena occurring at a minute area of impingement.

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The effect of metal chlorides added to ZrOCl₂ solutions on the crystallization of monoclinic ZrO₂ in high temperature hydrolysis was studied. It was found that an increase in the amount of chloride ions decreases the crystallinity and forming rate of ZrO₂ and increases the size of ZrO₂ aggregated particles. The ZrO₂ aggregated particles were grown to about 0.4μm by hydrolysis at 150°C in a solution containing 0.2mol/l of ZrOCl₂ and 2mol/l of AlCl₃. In the preparation of 3mol% Y₂O₃-TZP, compacts of ultrafine powder obtained by hydrolysis densified at lower temperatures, along with larger shrinkage due to lower compactability. On the other hand, aggregated particles of about 0.4μm were well isolated and did not form further strong aggregates each other at calcination up to 1000°C, and then resulted in higher green density. The compacts did not densify at lower temperatures but sintered to nearly theoretical density with about 0.4μm grains at 1400°C.

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Ternary composite of Ti(C, N), TiB₂ and MoSi₂ was studied in order to improve the oxidation resistance of Ti(C, N)-TiB₂ composites. The following conclusions were obtained:
(1) Fully densified and strong compacts were obtained for the compositions of Ti(C, N)-TiB₂-MoSi₂ with Ti(C, N) less than 80wt%, TiB₂ less than 80wt%, and MoSi₂ less than 60wt%, by sintering above 2023K for raw powders of about 1μm.
(2) With a small Ti(C, N) content for all Ti(C, N) grains to be surrounded by TiB₂ and MoSi₂ grains, and with MoSi₂ content more than 20wt%, good oxidation resistance was observed above 1273K because a compact surface film of rutile and silicate glass was formed by oxidation, which worked as an oxidation-resistant layer. This layer was porous in the initial stage, but became dense after a sufficient amount of silicate glass was produced. The silicate glass was found to have flowed from the inner reacting sublayers to the outer sublayers.
(3) TiB₂-20wt% MoSi₂ composite sintered at 2073K in vacuum, resistant against oxidation, was found to have the bending strength of 600MPa, the Vickers hardness of 2100, and the fracture toughness K_IC of 3.7MPa·m^1/2.

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Single phase BaTiO₃ and SrTiO₃ powders were prepared by hydrolysis of Ba-Ti mixed alkoxide solutions in benzene and/or alcohol. Hydrolysis of mixed alkoxides at room temperature yielded amorphous powders, which were transformed to crystalline BaTiO₃ and SrTiO₃ by calcination over 400°C. When the mixed alkoxides were hydrolyzed at refluxing temperature, crystalline BaTiO₃ and SrTiO₃ were obtained. The effect of alkoxy group on the hydrolysis of barium alkoxide was investigated. As a result the electron micrographs of synthesized powder particles indicate that the shape and size of the powders are hardly influenced by the types of alkoxy group of starting alkoxides. EDX analysis showed that the synthesized SrTiO₃ is chemically homogeneous up to 1000°C. By the similar method, Sr(Ti, Zr)O₃ powders were also synthesized and characterized.

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Surface properties of commercial autoclaved light weight concrete (ALC) having 1.1nm-tobermorite as a major constitutional mineral were investigated. The effective field strength of the ALC surface was determined as 6.6×10⁵e.s.u./cm² from the slope of linear relation between heat of immersion (hi (sl)) and dipole moment of immersing media. And the relation of (hi (sl)) for water with evacuation temperature of the ALC was quite close to that of α-quartz indicating the maximum of (hi (sl)) near 300°C. Effective methods of surface modification for water repellent were found by either autoclaving at 234°C under 3.0MPa or reflux-boiling at 75°C under 101kPa, using solution of 1-hexadecanol diluted with hexane in each method.

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Gallium garnet crystals containing rare earth elements were decomposed in a sealed teflon vessel either with sulfuric acid at 200°C for 16h or with hydrochloric acid at 140°C for 16h. Gallium was separated chromatographically by anion exchange resin from other elements in the sample solution, and determined by titration with EDTA. Gadolinium, scandium, yttrium, lanthanum and lutetium in the sample solution were determined by direct or back titration. with EDTA, and neodium and chromium by spectrophotometry. Analytical results of eight samples are presented.

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A desired amount of water was slowly added to an equimolar solution of Si(OC₂H₅)₄ and ZrOCl₂⋅8H₂O dissolved in hot ethanol under stirring. By means of the sol-gel method, ZrO₂-SiO₂ composite materials were obtained, and the effects of amount of added water on the preparation of gels in the ZrO₂-SiO₂ system were investigated. The structure of resultant dry gel was affected by the amount of added water, and appeared in the form of fiber-like, plate-like or lump-like. With an increase of water content, a longer gelling time was required, ZrSiO₄ did not crystallize in the gels even at 1500°C. It would be important for the synthesis of ZrSiO₄ to increase the interaction of Si-O bond with Zr⁴⁺.

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The stability of tetragonal ZrO₂ in ZTA-Cr₂O₃ sintered bodies fabricated by an impregnation method was investigated in NaF, KF, Na₂SiF₆ and K₂SiF₆ at 900° and 1000°C. ZTA-Cr₂O₃ having relative density above 99%, flexural strength of about 450MPa and hardness of about 1600kg/mm² at R. T. was used for the corrosion test. ZTA-Cr₂O₃ exhibited higher corrosion-resistance in carbonate and sulfate salts than in fluoride salts. The corrosion-resistance of ZTA-Cr₂O₃ in molten fluoride salts increased with an increase in the addition of ZrO₂ to Al₂O₃. ZTA-Cr₂O₃ formed a reaction layer (on the sintered body) in molten fluoride salts. The reaction layer formed in KF consisted of K₃AlF₆ and Al₂O₃-Cr₂O₃ solid solution, and protected the t-ZrO₂ phase beneath the reaction layer. The stability of t-ZrO₂ phase was dependent on the thickness of the reaction layer. Three mol% Y₂O₃-ZTA-Cr₂O₃ was superior to the other ZTA with respect to the corrosion-resistance in molten fluoride salts.

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The diffusion profiles of ¹⁸O in La_0.9Sr_0.1FeO₃ and La_0.9Sr_0.1CoO₃ were measured with a secondary ion mass spectrometer. The gas-solid oxygen isotopic exchange reaction was strongly limited by a surface reaction. The depth profile data were carefully treated and the tracer diffusion coefficient of oxide ions in the oxides was determined successfully.

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Fracture toughness of hot-pressed silicon nitride was measured using the three-point bending test of a SENB specimen with precrack developed from Vickers' indent. Indentation loads used were 10, 30 and 50kgf. The effect of indentation load on the evaluation of fracture toughness was investigated. Fracture toughness values were found to decrease with increasing indentation load. The heat treatment of specimens (at 1000°C for 1h at 10^-5Torr) after indentation reduced the dependence of the fracture toughness evaluation on indentation load. It was shown that fracture toughness values were influenced by residual stresses caused by Vickers indentation even after precrack was developed.

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The effects of MgO addition on thermal expansion coefficient and dielectric constant of mullite substrate were studied. Thermal expansion coefficient and dielectric constant decrease with increasing MgO content and exhibit a minimum value at 1wt% MgO. However, above 5wt% MgO content both values increase. Results of X-ray diffraction analysis show that mullite compositions which include more than 0.5wt% MgO form cordierite. Spinel is also formed as well as cordierite in the compositions containing more than 5wt% MgO. These results indicate that addition of MgO affects the thermal expansion coefficient and dielectric constant of mullite substrates because of the formation of new phases; cordierite and spinel. The thermal expansion coefficient and dielectric constant are affected mainly by cordierite and spinel in the regions containing less than and more than 5wt% MgO, respectively.

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Reaction between silicon carbide and yttria-stabilized zirconia (YSZ) powders, ZrO₂+3/2SiC=ZrC+3/2SiO(g)+1/2CO(g), was appreciable above 1400°C in argon atmospheres. The reaction was suppressed by adding an appropriate amount of carbon monoxide to the atmosphere. This finding was applied to the pressureless sintering of SiC whisker-YSZ composites. In CO (33%)-Ar atmosphere, 5vol% SiC whisker-YSZ composite densified to 97% theoretical density by pressureless sintering at 1550°C for 1h. At higher whisker contents, however, the sintered density of composite decreased with increasing whisker content in the same firing atmosphere, due to the formation of network structure by SiC whisker.

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In this paper, the high temperature superconducting properties and microstructures of Y-Ba-Cu-O system will be reported. The compounds YBa₂Cu₃O_7-δ and Y_0.4Ba_0.6Cu_3-x were prepared by firing at 950° or 1000°C for 5-12h in air or oxygen atmosphere. X-ray powder diffraction analysis revealed that the material obtained at 950°C was single phased orthorhombic with superconducting properties. The material showed zero resistivity at 90K. Dense materials for TEM observation, fired at 1000°C, were mixture of superconducting and non-superconducting phases. Layered grains of the superconducting phase about 1μm thick were observed. They were consisted of fine twin structure, and twinning planes were identified as (110) by the electron diffraction analysis pattern. Twinning planes were continuous at the grain boundaries of two superconducting grains.

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