The electrical conductivity of β-alumina ceramics prepared from the metal alkoxides was measured in the temperature range of 85° to 700°C in dried N₂ atmosphere by an A. C. impedance method between 120Hz and 1 MHz. The specific resistivities of β-aluminas with densities of 2.95 to 3.14g/cm³ were 21 to 27Ω⋅cm at 700°C. The activation energies of Na ion migration through bulk (grain interior) and across grain boundary were 10.6 and 45.0kJ/mol, respectively. The Arrhenius plots of σT exhibited two bends, and were divided into three temperature regions. This result was discussed by assuming a parallel circuit of migration resistance (R) of Na ions; R_g (through bulk) +R_gb (across grain boundary) and R′_gb (along grain boundary). In this model, the conductivities of low, intermediate, and high temperature regions were dominated by R_gb, R_g and R′_gb, respectively.

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A F-doped Bi (Pb)-Sr-Ca-Cu-O superconductor shows a higher T_c value than that without F doping in AC susceptibility measurement. Specimens were sintered in two stages. The doping of CaF₂ in starting powders caused a considerable amount of Ca₂PbO₄ as an intermediate phase on the first sintering, which eventually resulted in the formation of Pb-enriched Ca₂CuO₃ and then the enhancement of the 2223 phase during the second sintering. The EPMA results revealed that Pb is mostly trapped in Ca₂PbO₄ after the first sintering and incorporated in the grains of the 2223 phase after the second sintering. F exists in finely distributed SrF₂ among the grains. It is made clear according to DTA that the temperature range for socalled partial melting is lowered and widened, i.e. the optimum synthesizing temperature for the 2223 phase is lower than 840°C.

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An easy, convenient and widespread applicable detection of chemical species in a liquid was realized by using a contact of p- and n-type semiconducting ceramics (it was called p-n hetero-contact). This p-n hetero-contact was constructed by mechanically pressing together the polished surfaces of p-type CuO and n-ZnO sintered pellets. When this system was put into an alcohol and a. c. bias was applied across its interface, a characteristic current-voltage (I-V) relation with hysteresis and rectifying nature was observed, depending both on the kind and the concentration of the alcohol. It was possible to discriminate the chemical species and to estimate the alcohol concentration in alcoholwater solutions by estimating three parameters reflecting the magnitude of hysteresis, current flow and rectifying nature, respectively, calculated from the observed I-V curve. That is, the former two parameters decreased and the latter one increased, when the number of carbon atoms in an alcohol molecule increased, or when the water content in an alcohol solution decreased. It was recognized that the observed I-V relation is generated not only from the physical properties of the liquid, such as electrical conductivity and dielectric constant, but also from the interface states formed by the chemical interaction between alcohol molecules and semiconductor surfaces.

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The hydration characteristics of cement in hardened cement paste, mortar and concrete were investigated and discussed from the stand points of hydration degree, pore structure, composition and structure of hydrates. In hardened cement pastes, area proportion of a darkest part in the back scattered electron image of its polished surface closely correlated with the volume of pores more than 50nm in diameter. In the cases of hardened mortar and concrete, however, the abovementioned correlation was not so good, since they had additional porous structures called a transitional zone, which was composed of Ca(OH)₂ precipitated around aggregate grains. Dense C-S-H layer in hardened mortar and concrete formed around unhydrated alite was thicker and its average Ca/Si molar ratio was by 0.2 lower than that of hardened cement paste. This phenomenon is considered to be caused by the low Ca ion concentration in a liquid phase due to the presence of an aggregate, by the high degree of hydration of cement and by local precipitation of Ca(OH)₂ around an aggregate in hardened mortar and concrete.

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The properties of acoustic emission (AE) signal from glass and new ceramics on machining with a surface grinder were studied. First, both the amplitude and level of power spectrum decreased due to the propagation of AE wave passing through the medium. Next, in dry grinding of glass, the levels of power spectrum are greater than those under wet condition over the frequency range studied. Furthermore, it is noteworthy that the AE signal at the low frequency band is associated with the destructive chipping. In SiAlON, the power of high frequency was higher than that of plain carbon steel S45C. The levels of power spectrum increased with increasing depth of cut in the special band.

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Gel formation and drying characteristics in the system aNa₂O-bZrO₂-(100-a-b) SiO₂ (a=0, 7, 13, 18, b=3, 6, 10mol%) were investigated. Gelling time decreased with increasing Na₂O content, perhaps due to the catalytic reaction of NaOH released from NaOC₂H₅. The release of NaOH was confirmed from pH measurements of sol mixtures with or without water. The weight loss-time curve indicated that the falling rate period decreased with increasing Na₂O content, which corresponds to a gel structure with large pore size at high Na₂O cocentrations. This was confirmed by measurement of pore size distribution on dried gels. The linear shrinkage of Na₂O-containing gels was smaller than that of Na₂O free compositions. The tendency of crack formation in gels increased with increasing Na₂O content, but decreased with increasing ZrO₂ content. It was inferred that this was due to an easy deformable gel structure made up of linear molecules in Na₂O-free gels, or to a rigid gel structure made up of particle molecules in Na₂O-containing gels.

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The sliding wear properties of mullite and mullite/ZrO₂ composite ceramics have been investigated with a pin-on-disk wear tester using Al₂O₃, Si₃N₄ or SiC as the disk material. There was no remarkable difference in the specific wear rate and coefficient of friction of two mullite ceramics. These sliding wear properties were independent of the particle size and its distribution of mullite. On the other hand, the specific wear rate decreased in the case of mullite/ZrO₂ composite as the pin and Al₂O₃ as the disk material. These results suggested that dropped-out ZrO₂ particles might lubricate at the interface, when the hardness of the pin was similar to that of the disk material. Wear mechanism was roughly classified to three patterns from the observation of frictional surface, which mainly depended on the sliding velocity. For pattern I, the surfaces of pin and disk were smooth and the wear rate of pin depended only on the load. For pattern II, the adhesion and spark caused by the heat of friction were observed. For pattern III, microfracture due to lateral crack was mainly observed, therefore the wear mechanism was explained by the indentation fracture model. The wear rate of mullite ceramics could be estimated only with their mechanical properties under the same sliding condition.

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In a permeable MgO ceramic containing TiO₂ and Al₂O₃ as matrix MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solutions were detected and no Al₂O₃⋅TiO₂ was observed. Therefore, the solid state reaction among MgO, TiO₂ and Al₂O₃ with excess MgO was studied at various firing temperatures. The formation mechanism of MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solutions was studied from the results of interface reactions between MgO-TiO₂ and MgO-Al₂O₃. MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solutions were detected at 1573-1673K and increased with the firing temperature. 2MgO⋅TiO₂ was formed in the system MgO-TiO₂, but was not produced in the system MgO-TiO₂-Al₂O₃, because the amount of Mg diffusion at the interface of aggregate and matrix additives was not enough due to the large aggregate size of MgO. MgO⋅Al₂O₃ and 2MgO⋅TiO₂ formed at the interface between MgO-TiO₂ and MgO-Al₂O₃ decreased with the firing time at 1873K. On the other hand, MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solutions increased. Mg was recognized in the matrix without addition of MgO as a matrix. Al diffused in the layer of MgO-TiO₂, in opposition Ti diffused in the layer of MgO-Al₂O₃ by EPMA analysis. From the above results, the formation mechanism of a MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solution was proposed; (1) Mg diffusion at the interface of MgO aggregate and matrix additives, (2) formation of MgO⋅TiO₂ and MgO⋅Al₂O₃, (3) formation of 2MgO⋅TiO₂ due to the reaction with MgO⋅TiO₂ and MgO, (4) reaction of the solid solution with MgO⋅Al₂O₃ and 2MgO⋅TiO₂. In the reactions between MgO-TiO₂ and MgO-Al₂O₃ the product layer of MgO⋅Al₂O₃-2MgO⋅TiO₂ solid solution increased as the firing time increased. The diffusion coefficient of Mg was about 4.8×10^-7(cm²/s), in a good agreement with that of Mg which was reported.

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Silicon nitride ceramics was joined to a stainless steel using a Ni-Cr-P amorphous solder (MBF65) and two MBF 65 solders with Cr or Mn thin films vapor-deposited. Bonding layers were composed of a chromic silicate layer close to the ceramics surface and a duplex phases of a chromic nitride and a nickel solid solution containing small amounts of chromium and silicon. Growth of the bonding layer was parabolic at the initial stage and then slowed with decreasing in chromium contents in the solder. A parabolic rate constant of the joints with the MBF65 and MBF65-Mn solders was 1.0×10^-15m²⋅^-1 at a temperature of 1333K. Fracture strengthen increased with decreasing in thickness of the bonding layer, that is, they were 50 to 140MPa for the joint with a MBF65 solder, 120 to 170MPa for the joint with a MBF65-Cr solder, and 130 to 200MPa for the joint with a MBF65-Mn solder.

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The mechanism of oxidation of Si-C-O fibers has been investigated. The oxidation rates of two different types of Nicalon fibers (NL400 and NL200) were measured with a thermo-balance in O₂ gas stream at temperatures from 873K to 1773K. The reaction products were examined by SEM observation and X-ray diffraction. The results were compared with those of Tyranno fiber. The oxide film was amorphous silica at the beginning of oxidation and at low temperatures, and tended to crystallize on prolonged heating and at high temperatures. The formation of cristobalite increased the oxidation rate. The oxide film suppressed the pyrolysis of the amorphous core of Nicalon. The oxidation rate was analyzed by the parabolic rate law. The temperature dependence of the rate constant k was complicated, because there was a wide variation in the morphology of the oxide film. It is considered that the oxidation of Nicalon was controlled by the diffusion of gas through pores in the oxide film. The oxidation of Tyranno was slower than that of Nicalon at high temperatures, because of the dense SiO₂-TiO₂ film of Tyranno.

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In order to find the sintering aids for obtaining SiC whisker (SiC (w))/Si₃N₄ composite ceramics with high fracture toughness, the effect of nine rare earth oxides on the β-Si₃N₄ acicular grain size in the monolith was investigated in the first step. In the second step, the fracture toughness of SiC(w)/Si₃N₄ composite ceramics with addition of main four rare earth oxides was investigated in relation to the Si₃N₄ grain size. It was found that the Si₃N₄ grain size in the monolith was largely affected by the chemical species of rare earth oxides and that the order of the grain size was expressed as follows; Y₂O₃>Er₂O₃≅Dy₂O₃>Pr₂O₃>Sm₂O₃≅Gd₂O₃>Tb₄O₇>Nd₂O₃>MgO>Eu₂O₃. The Si₃N₄ grain size in SiC(w)/Si₃N₄ composites was nearly equal to that in the corresponding monolith with the same sintering aid, and the values of K_IC of the composites were higher for larger β-Si₃N₄ grains than for the smaller β-Si₃N₄ grains, in the same manner as the monolith.

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Fe-Si-O thin films were prepared by Ionized Cluster Beam method, and the effect of oxygen content and heat treatment on their thermoelectric properties and microstructure were examined. As-deposited films were in amorphous state and they showed semiconducting properties with low Seebeck coefficients depending on the amount of oxygen in the temperature range from R. T. to 400°C. Above 450°C, migration of atoms, change of chemical bonds, and growth of microcrystals proceeded remarkably. As a result, the conductivity of the samples with a small amount of oxygen showed some enhancement and that of the samples with a large amount of oxygen showed a remarkable decrease. It is elucidated that the changes of conductivity is dependent on the amount of Si-O amorphous insulator; whether or not the conduction paths between Fe-Si microcrystals were separated by Si-O amorphous insulator caused the different conduction mechanism.

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By centrifugal casting, an alumina powder was formed to a green body with high densities. This study showed the effect of particle size distribution on the uniformity of the calcined body. Alumina particles with a narrow particle distribution were dispersed more uniformly in the calcined body than those with a wide distribution. The bending strength of the resultant body increased with increasing centrifugal force for casting. It was also found that the centrifugal casting method was applied to the body not only of cylindrical form but also of complicated form.

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Preparation of hydroxyapatite (Hap) was investigated by a homogeneous precipitation technique. The precipitates were obtained by mixing solutions of Ca (NO₃)₂, (NH₄)₂HPO₄, EDTA-Na and H₂O₂ at 90°C. The products were identified as carbonate-containing hydroxyapatite by the X-ray diffraction and IR spectrometry. When pH value of the reacting solution was higher than 10, Ca/P molar ratio of the precipitate was 1.67. Synthesized Hap powders by this method had specific surface area of 5-35m²/g, and the Hap particles showed clear hexagonal pyramidal ideomorphic shapes.

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In order to evaluate the feasibility of applying ceramics (AlN, SIALON, Si₃N₄) to casting equipment for copper-based alloys, the reactivity of copper oxides with nitride ceramics and their oxide additives (Al₂O₃, Y₂O₃, SiO₂, MgO) was examined. Ten weight percent Cu, Cu₂O and CuO were mixed with powders of nitrides and oxides, and kept at temperature between 700° and 1300°C in air and at 1200°C in a nitrogen atmosphere having oxygen partial pressure (P_o2) of-3×10^-1 and -3×10^-3 Pa for one hour. In air, CuO accelerated the oxidation of the nitride ceramics, and the three kinds of nitride samples oxidized above 1200°C. Silicon nitride ceramics did not oxidize below 1000°C, and may be used to brass casting. Al₂O₃ and Y₂O₃ reacted with the copper oxides. SiO₂ did not react, but melted above 1050°C. MgO seemed to form a solid solution with CuO. On the other hand, CuO in the mixture was reduced to Cu, and all the seven kinds of ceramics were stable above 1200°C under nitrogen atmosphere with P_o2 below 1Pa. Therefore, the seven kinds of ceramics may be used for casting of copper-based alloys at P_o2 below 1Pa.

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By measuring ion conductivity of the specimens using the complex impedance method at 400°-900°C in the air, a study has been made with the sintered bodies, which were prepared from (YO_1.5)_1-x(NbO_2.5)_x (x=0.05-0.35) powders obtained by the solid phase reaction. In case of x=0.15 composition samples, the total and grain boundary conductivity reached the highest values. On the other hand, the grain conductivity was nearly constant at x=0.15-0.35 composition samples. From the relationship between the crystal phase and the conductivity of the above stated composition samples, it is suggested that the high conductivity of the x=0.15 composition samples is very susceptible to the precipitation of Y₂O₃ whose conductivity is lower than that of Y₃NbO₇. Thus, the conductivity of Y₃NbO₇-Y₃Al₅O₁₂ and Y₃NbO₇-MgO sintered bodies, which were prepared by the addition of Al₂O₃ and MgO, lower conductivity materials, to Y₃NbO₇, was measured. Their grain boundary conductivities took a figure up one place in the maximum. It was proved that the grain boundary conductivity enhances by the addition of lower conductors to the basic materials.

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Corrosion behavior of gas pressure sintered silicon nitride ceramics was investigated in sulfuric acid solution with respect to the effect of solution temperature and to the microstructure of corroded layer. Weight loss of samples after corrosion test was severe in boiling solution as compared with in 90°C solution. Nevertheless strength degradation occurred similarly in each solution. The gradual growth of corrosion is considered to be controlled by the dissolution reaction of grain boundary phase of silicon nitride ceramics in sulfuric acid solution. The drastic strength degradation at initial stage is considered to be ascribed to the relaxation of the residual compressive stress during corrosion which was introduced on surfaces of specimens by machining.

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Humidity sensor elements using xLi₂O⋅Al₂O₃⋅2SiO₂ porous ceramics were produced and the effect of sintering temperatures and Li₂O(x) contents on the humidity sensitivity, the response time, and the long-term stability was investigated. Eucryptite (Li₂O⋅Al₂O₃⋅2SiO₂) sintered at 1100°C was desirable for a humidity sensor with respect to sensitivity, linearlity, hysteresis, and long-term stability. The impedance changed from 10⁷ to 10⁴Ω⋅cm, linearly in the humidity range of 20-90% RH. The response time was about 3min with a quick change of relative humidity from 90 to 60% RH. Detected relative humidity by using Li₂O⋅Al₂O₃⋅2SiO₂ was accurate within ±2% RH even after 300 days storage in a laboratory air.

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The authors have succeeded to prepare dense sintered bodies of perovskite LaNiO₃, which shows a metallic conduction, by HIPping without flux such as Na₂CO₃. The stoichiometric mixture of La₂O₃ and NiO was precalcined in air at 900°C for 5h. The ground sample was then sintered at 1100° or 1300°C in air for 20h. The sintered bodies were composed of La₂NiO₄ and NiO, and had the densities of up to 95%. The single phase perovskite LaNiO₃ of 95% density was obtained from its presintered body by HIPping under 101MPa (in Ar gas containing 20% oxygen) and 1400°C for 2h. A very low resistivity of 2.2×10_-6Ω⋅m was measured for this HIP_ped body of LaNiO₃. The stability region for the perovskite compound LaNiO₃ in P-T diagram was discussed.

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A new process of preparing ceramics fibers by use of sodium alginate has been studied. In this paper, titanium oxide fibers synthesized by heat-treating in air and under reduced pressure at various temperatures using titanium alginate as a starting material is reported. Thermal decomposition of titanium alginate was investigated by differential thermal analysis and thermogravimetry. Titanium oxide fibers were investigated by powder X-ray diffraction technique and scanning electron microscope. Heat-treatment in air collapsed titanium oxide fibers easily. The fibers were dense when heat-treating under reduced pressure.

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