Proof test is useful for rejecting ceramics of undesirable short life time. But the crack in the proof test survivors propagates in the unloading period of the proof stress. So the shortest life time of the survivors may be shorter than the needed life time. In this paper, the influence of unloading time on the shortening of the life time of the proof test survivors was studied on the basis of fracture mechanics of ceramics. Some formulae are derived for expressing the shortened life time of the survivor during unloading, the ratio of the shortened life time to the needed one, and the longest unloading time allowable to make the shortest life time of the survivors longer than the needed one. According to these formulae, the unloading time gives substantial influence on the life time of the survivors from the point of view of the shortening effect for the life time. The formulae expressing the ratio of shortened life time to the needed one tells that the unloading time must be of the order of 10μs to make the shortest life time negligibly small compared with the needed one, when the proof stress is selected so as to be the value which corresponds to the needed life time. In an actual application of proof test to ceramics, some safety factor is multiplied to the proof stress, so the safety factor is studied in correlation with the unloading time. According to the study, the unloading time can be increased in proportion to Δp/(1+Δp)², where (1+Δp) is the safety factor. Then, the unloading time reaches the maximum at the value of 2, in an approximation. But even when 2 is selected as the safety factor, the unloading time must be of the order of 5-10μs to make the shortest life time of the survivors equal to or longer than the needed value. Such a short unloading time seems to be inapplicable to the test. Therefore, it can be concluded that the complete elimination of the ceramics having undesirable short life time needs another complementary method such as AE monitoring for proof test.

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The preparation of a gel-like silica glass from silicic acid was investigated. This method requires the processes: (1) Extraction of silicic acid with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid, followed by concentration of an extracted solution to give “concentrated silicic acid”, (2) Preparation of silicic acid solutions with various concentrations and solvents to allow a moderate condensation, and (3) Formation of a gel plate by condensation polymerization of silicic acid with evaporation of solvent. Since gels are formed by the condensation which is highly dependent on the evaporation of solvent. Alcohols, acetone, methyl ethyl ketone, THF, formamide, dimethyl formamide, acetonitrile and water were used as solvent. Pieces of silica gels were obtained easily, but plate was not obtainable unless condensation was controlled. Gel plates without cracks were obtained when the solutions with the molar ratio (solvent/SiO₂) of 1-5 were aged.

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A glaze composition with the Segel formula of 0.30(K, Na)₂O⋅0.70BaO⋅0.45Al₂O₃⋅4.00SiO₂ containing 1.0wt% Fe₂O₃ was treated in a reducing atmosphere (N₂+10% CO) from 600° to 1200°C for various times, and fired at 1250°C in N₂. The effect of reducing atmosphere on the coloration of the iron glaze was studied by chemical analysis, color analyzer and ESR. Results are summarized as follows; (1) When the glaze was reduced below 1000°C, the reduction proceeded before the melting of the glaze. The reduction ratio in the glaze (Fe²⁺/(Fe²⁺+Fe³⁺)) increased with increasing temperature. As the reduction ratio increased, the color changed from light green tinged with yellowish brown to light blue, dark green tinged with yellowish brown and black at 100% reduction. The black color was assumed to arise from colloids of both iron metal and iron oxide compounds like hercynite dispersed in the glaze. (2) When the glaze was reduced at 1100°C, reduction and melting proceeded simultaneously, and the color changed into light blue or blue even above 90% reduction. (3) When the glaze was reduced at 1200°C, the reduction proceeded very slowly because of decreased surface area with melting of the glaze. Thus, the color turned light green tinged with yellowish brown.

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Spherical fine particles of SiO₂ were prepared from a partially hydrolyzed tetra-ethyl-ortho-silicate (TEOS) solution by an ultrasonic spray pyrolysis method at 400°-700°C. The starting solution was hydrolyzed with NH₄OH catalyst at 55°C in N₂ atmosphere. Its viscosity was measured by an Ostwald-type viscometer in order to calculate the intrinsic viscosity [η]. The powders prepared from solutions with [η] less than 0.009dl/g were the mixture of spherical and unspherical particles. While in the case of [η] larger than 0.009dl/g, the particles were spherical and their diameter was 0.36-0.56μm. In the case of the solutions of [η] larger than 0.015dl/g, it was observed by TEM that very fine particles (diameter: -0.03μm) precipitated from the solution during the refluxing. The particle from above solution is the aggregate of the primary particles which have similar size to the particles present in above solution. The effects of pre-hydrolysis of starting solutions on the shape and microstructure of paricles were discussed.

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Thermoluminescence (TL) glow curves and emission spectra were measured for crystallized glasses Li₂B₄O₇ doped with 0.03wt% CuCl₂, AgCl, MnCl₂ and TbCl₃. Two different samples were made: one was a plate of 1mm in thickness and the other was a thin film of 0.1mm bonded to a platinum plate. Both were annealed at three different temperatures, 620°, 820° and 910°C. TL-glow characters of the samples sticked to platinum plate revealed themselves very sensitive to the annealing temperature. The CuCl₂-doped sample annealed at 820°C on platinum plate showed the most intense TL peak at about 160°C, which can be practically used for dosimetry. The X-ray pattern analysis indicates some differences in distribution of microcrystal orientations corresponding to the two different samples. Possible mechanisms for the TL emission were discussed.

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Ultrafine powders of β-SiC containing 35wt% free Si produced by the gas evaporation method were sintered under the atmosphere of Ar at 1atm. When 5wt% amorphous B was added as a sintering aid, remarkable grain growth occurred. Thin wide plates larger than 500μm and round-shape polyhedra grew heterogeneously on the surface of sintered bodies at temperature higher than 2000°C within the closed graphite crucible. Clearcut growth steps were observed in the SEM images on the surfaces of both thin plates and round-shape polyhedra. The densification of sintered bodies was prohibited remarkably by the grain growth of such large crystals.

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The controlled hydrolysis of metal-alkoxides yielded an amorphous precursor powder with the composition of 3Al₂O₃⋅2SiO ₂. The SiO₂/Al₂O₃ ratio of the resultant fine powder determined by X-ray fluorescence analysis was 3:2 and mullite was identified above 1200°C. However, the traces of SiO₂ and α-Al₂O₃ were detected above 1400°C, probably due to the preferential hydrolysis of Al(OPrⁱ)₃. A sintered body with a relative density of about 95% was obtained by firing at 1600°C for 2h. The Vickers hardness, Young's modulus and stress intensity factor of the sintered body was about 11GPa, 230GPa and 3MPa·m^1/2, respectively.

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Influence of powder characteristics such as specific surface area, agglomerate size and shape, on their microstructures and mechanical properties of green and sintered bodies was studied for seven kinds of calcium hydroxyapatites. A heat treatment above 1300°C gave tricalciumphosphate (TCP) for all powders. Before the formation of TCP, decarbonation took place in carbonate-containing powders above 800°C, while carbonate-free powders were stable up to 1200°C. Powders with high specific surface areas (SSA), especially larger than 40m²/g, had good sinterabilities, and gave dense bodies about 99% relative density after a heat treatment at 1200°C. On the contrary, powders with lower SSA, about 10m²/g, had poor sinterabilities and gave porous bodies. Poor sinterability was mainly ascribed to the stability and needle like shape of the crystallites. Furthermore, presence of large voids among the agglomerates prevented densification of the compacts at the late stage of sintering. The high density Ca-HAP ceramics prepared in this report have mechanical properties comparable with those reported in the literatures.

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Physical factors correlating with the Curie-Weiss temperatures of displacive-type f erroelectrics and antif erroelectrics were surveyed. For oxide compounds with perovskite and tungsten-bronze structures, the covalent bond energy between an A-site ion and an oxygen ion was found to show a high correlation with their Curie-Weiss temperatures, Effective charges of the ions in these compounds, which were estimated by an extended Sanderson's theory, supported highly covalent nature of their chemical bonding. Relation between Curie-Weiss temperatures and ion radii were also examined.

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This study is concerned with the formation, structure and color development of the potassium-priderite type solid solutions in the system K_x(Ti, M)₈O₁₆ (M=Mg, Al, Sc, Cr, Mn, Fe, Co, Ni, Cu and Zn). The results are summarized as follows;
(1) Priderite-type solid solutions with the composition of K_2xM_xTi_8-xO₁₆ (M=Mg, Co, Ni, Cu and Zn) are formed in the following ranges: 0.75≤x≤0.9 in Mg-system, 0.85≤x≤1.0 in Co-system, 0.8≤x≤1.0 in Ni-system, x=1 in Cu-system and 0.75≤x≤0.9 in Zn-system.
(2) Priderite-type solid solutions with the composition of K_2xM_2xTi_8-2xO₁₆(M=Al, Cr, Mn and Fe) are formed at x=1 except for Mn-system.
(3) The unit cell volume of each solid sulution increases depending on the ionic radius of the octahedral site cation. In each system, the lattice parameter c expands by the replacement with larger divalent cations for the titanium sites. The lattice parameter a shrinks by the tunnel cavity contraction by the increasing amount of potassium ion.
(4) The reflectance spectra show typical six coordinated states of Co²⁺ and Ni²⁺ in the priderite-type solid solutions. The color of the priderite-type solid solutions is light yellowish brown in Co-system and changes from bright greenish yellow to strong greenish yellow in Ni-system.
(5) According to the results of the structure refinement by the pattern fitting method of X-ray powder diffraction patterns, the special position, 2 (a), is not occupied by K⁺-ions, but a half of the more stable site, 4 (e), is occupied by K⁺-ions in K₂CoTi₇O₁₆, K₂NiTi₇O₁₆, K₂Al₂Ti₆O₁₆ and K₂Sc₂Ti₆O₁₆(C. S.: tetragonal, S. G.: I4/m, Z=1).

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A New actuator device is proposed using semiconductive ferroelectric ceramics. This device is a single-plate actuator capable of bending equivalently to a bimorph. A significant difference is simple structure named as a “monomorph” as compared with a multi-stacked type in the bimorph. The bend in the monomorph device is realized by non-uniform electric field distribution in the piezoelectric ceramics, through the semiconductor-metal contact effect (Schottky barrier). The monomorph has been demonstrated in the solid solutions PbZrO₃-(K_1/2Bi_1/2)ZrO₃ and BaTiO₃-Dy₂O₃. Both systems reveal the tip deflectionof several hundred micrometers in a 0.5mm thick plate.

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The sodium borate glass system containing La₂O₃ and TiO₂ shows a marked trend toward microphase separation after heat treatment, resulting in water-soluble sodium borate and water-insoluble La₂O₃-TiO₂ ceramic phases. Then La₂O₃-TiO₂-rich skeletons can be obtained by leaching out the sodium borate phase. The application of thus obtained porous glass-ceramics with interconnected pores to a humidity sensor is of interest. Microstructure, such as surface area and pore size distribution, of the La₂O₃-TiO₂ glass-ceramic system is sensitive to the heat treatment and the subsequent leaching conditions, so that the humidity sensitivity of the element can be controlled favorably by the phase separation. The element, heat-treated at 600°C for 12h followed by leaching at 85°C for 34h, exhibits the most excellent humidity sensitive characteristics. The humidity sensitive characteristics of this element is superior to that of the element with the same composition of the leached La₂O₃-TiO₂ glass-ceramic prepared by solid phase reaction.

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Leaching behavior of pressureless-sintered Si₃N₄ containing MgO was studied under hydrothermal conditions using an autoclave. Si₃N₄ specimens were prepared from two kinds of commercial grade Si₃N₄ powders, by the imide-decomposition (specimen M-1) and silicon-nitridation methods (specimen M-2). They were doped with 10wt% MgO. No differences in microstructure were observed in the sintered specimens from these starting powders. Leaching test was carried out under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 d. Specific weight loss (mg/cm²) in leaching test for these specimens was more than that for the Si₃N₄-Y₂O₃/Al₂O₃ specimens in the previous work. The weight loss increased linearly with time with the same steep slope for both M-1 and M-2 in the early stage (up to 3 d) and leveled off in the later stage (4-10d); M-1 showed a larger saturated weight loss than M-2. The result in the early stage indicates that the leaching behavior depends on the grain morphology of sintered body as found in the Si₃N₄-Y₂O₃/Al₂O₃. Chemical analysis of a leaching solution showed that Si was the main leached element and Mg was leached little. EPMA and SEM observations revealed that the leached layer was composed of thin hydrated silica and magnesium silicate hydrate layers. Based on the experimental results, it is suggested that the leaching behavior of pressureless-sintered Si₃N₄ under hydrothermal conditions depends on the leaching characteristics of constituting ions in MgO and Y₂O₃-Al₂O₃ doped as sintering aid.

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Crystalline powder of Pb(Zr_0.52Ti_0.48)O₃ (PZT) was synthesized from Pb(NO₃)₂, ZrOCl₂ and TiCl₄ in KOH solution below 200°C. The PZT formation was strongly affected by the concentration of KOH and temperature. The reaction was accelerated by KOH, and PZT was not obtained in the absence of KOH. At the initial stage of PZT forming reaction, PbTiO₃ and PbZrO₃ were produced at low KOH concentration, and PbO-TiO₂ solid solution was produced at high KOH concentration. PZT formation was very fast in 10M KOH solution, and PZT was the only phase detected by X-ray diffraction within 30min at 200°C, 1h at 150°C, 5h at 100°C or 4d at 70°C. Each PZT particle had a euhedral shape, and was consisted of several crystals. The sizes of crystal and grain changed mainly with reaction temperature.

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Sintering characteristics of β-tricalcium phosphate (β-TCP) powders synthesized by three methods were studied. Dence β-TCP ceramics were obtained by the sintering of mechanochemicaly synthesized β-TCP powder at 1050°C, 50°-100°C lower than the firing temperature of β-TCP powders obtained by wet and dry process'es. Bending strength of the sintered body was 1340kgf/cm². Formation of α-TCP in the β-TCP ceramics decreased the bending strength and also the chemical durability.

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The deterioration of concrete containing dolomite and marine sand was studied mainly by SEM and EPMA. The SEM observation revealed that minute cracks were present in and around the coarse grain of dolomite in concrete. The EPMA line analysis showed that the Cl^- ion was combined with Mg-containing minerals such as dolomite. It was assumed that partially chlorinated dolomite was expansive and thus responsible for the deterioration of the concrete.

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Monticellite (CaMgSiO₄) and akermanite (Ca₂MgSi₂O₇) crystals were grown in molten alkali chlorides. Natural dolomite, silicagel and α-quartz were used as the starting materials, NaCl for monticellite and NaCl-CaCl₂ for åkermanite being the most suitable flux. Monticellite and åkermanite were synthesized under various experimental conditions of the following parameters, R₁ (silicagel or α-quartz/dolomite, molar ratio), R₂ (starting material/flux, weight ratio), R₃ (CaCl₂/NaCl, molar ratio), soaking temperature and soaking period. The results were as follows;
(1) Monticellite crystals had a maximum size of 32×41×95μm (euhedral prismatic, colorless) when soaked at 1150°C for 18h with R₁=0.5 and R₂=0.014.
(2) Åkermanite crystals had a maximum size of 6.0×6.0×0.5mm (plate, colorless) when soaked at 1100°C for 12h with R₁=2.0, R₂=0.02 and R₃=0.025.

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Hydroxyapatite powders prepared by wet method from Ca(OH)₂ and H₃PO₄ and calcined at 800°C were sintered in air at a temperature from 1100° to 1400°C for 2h. The obtained ceramics with relative densities of 73±2% (1100°C) -89±2% (1400°C) were HIP'ed under 100 or 500MPa of Ar at 900° or 1100°C for 2h without any capsules. The post-sintering at 1100°C under 500MPa brought about densification up to 97% for the samples more than 90% dense having closed pores, but it barely increased the density of samples with lower densities. Transparent apatite ceramics were obtained by HIP'ing.

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Mixture of BaCO₃, CuO and yttria-concentrate was heat-treated at 900°C in an open electric furnace, and a single phase material in the system Ln-Ba-Cu-O (Ln=rare earth elements, Y, Ce, La, Eu, Gd, Dy, Er, Ho, Yb, Sm, Nd and Pr) was prepared. X-ray diffraction study revealed that the structure of the material is similar to that of the perovskite-like phase as reported by Izumi et al. The superconducting state of this material was observed at liquid nitrogen temperature, 77K. Further heat-treatment at 900°C in oxygen gas (0.6l/min) increased the critical current density at 77K by 3 times.

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