Rheological properties of electrostatically stabilized colloidal suspensions and properties of consolidated powder compacts (density and pore size distribution) were studied with an ultrafine amorphous SiO₂-Al₂O₃ powder of an average size of 80nm. Well-dispersed concentrated colloidal suspensions showing Newtonian flow were prepared with positively charged particles at pH 4.0. Green compacts with high densities and narrow pore size distributions were obtained by filtration of the Newtonian suspensions through a gypsum mold. The colloidal suspensions at pH 7.0 (isoelectric point) and pH 10.0 (negatively charged particles) showed Bingham flow and provided porous green compacts. The Bingham flow behavior was analyzed based on the Voight model representing a viscoelastic characteristic. Isostatic pressing of the porous green compacts increased the green densities and reduced the pore sizes.

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The mechanical behavior of smooth specimens is different from that of notched ones and is very important for practical use. From this point of view, cyclic fatigue behavior of smooth specimens of alumina ceramics was investigated. We carried out the cyclic fatigue test ranging from 10^-3Hz to 6×10²Hz. We used the resonance vibration method for high frequencies. We estimated the cyclic-dependent region and time-dependent region of fatigue life for alumina ceramics under the cyclic fatigue conditions. This estimation will be practically useful for predicting the fatigue life. The cyclic fatigue life is controlled by the cyclic-dependent mechanism for higher frequency region and by the time-dependent mechanism for lower frequency region. However, the transition area from time-dependent to cyclic-dependent mechanisms is revealed. This transition area is affected by applied gross stress level.

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Sliding wear properties of ceramics have been tested under various conditions, and many models have been proposed for the wear mechanism. However, systematic research on the relation between wear rate and wear mechanism has been insufficient in comparison with metal. In a previous study, we analyzed wear of ceramics by an indentation fracture model, and recognized the applicable limits of this model. In this study of SiC ceramics, the effect of material combination and sliding conditions such as vertical load and sliding speed on wear properties was studied with a pin-on-disk wear tester, Wear properties were classified to four kinds of mechanisms from observation of the frictional surface after sliding test using an SEM and optical microscope, and were rearranged systematically in a wear map, The extreme change of wear was observed at a vertical load or the sliding speed at which wear mechanism changes. In particular, when the data which were considered due to wear by indentation fracture were analyzed, the wear rate including SiC combinations with other ceramics could be assessed by this model, and the adequacy of this classification of wear mechanism was confirmed quantitatively.

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It has been observed that the resistivity of some single crystals and sinters of semiconducting BaTiO₃ decreases steeply just above the Curie point, contrary to well-known PTC-anomaly. All the stable NTC samples underwent forced orientation and reduction. Two types of surface donors on the tail-side surface of ferroelectric polarization and one type of surface acceptors on the head-side surface are assumed. For the crystal slab composed of a single domain, the resistivity across the opposed surface potential layers ρ_b was computed as a function of temperature. One of the experimental curves was simulated by adopting suitable values of the surface states. The anomalous NTC and the hysteresis characteristics are reasonably explained.

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The cation distribution in Co₂GeO₄-CoM₂O₄ and Co₂GeO₄-Co₂RO₄ systems (Co-I group), and in Ni₂GeO₄-NiM₂O₄ and Ni₂GeO₄-Ni₂RO₄ systems (Ni-I group), where M=Al or Cr, and R=Sn or Ti, has been studied by lattice constant variation, reflectance spectra and pattern fitting method of X-ray diffraction diagrams. The cation distribution in Co_1.2Zn_0.8GeO₄-Co_0.6Zn_0.4M₂O₄ and Co_1.2Zn_0.8GeO₄-Co_1.2Zn_0.8RO₄ (Co-II group), and in Ni_1.2Zn_0.8GeO₄-Ni_0.6Zn_0.4M₂O₄, Ni_0.8Zn_1.2GeO₄-Ni_0.8Zn_1.2RO₄ (Ni-II group), where M=Al or Cr, and R=Sn or Ti, has also been studied.
These results are summarized as follows.
(1) Spinel type solid solutions with the 6-coordinated sites occupied by Ge⁴⁺ ions are formed over the entire ranges of Co-II and Ni-II groups.
(2) In the Cr-, Al- and Sn-systems of Co-I and Ni-I groups, no spinel type solid solutions near Co₂GeO₄ and Ni₂GeO₄ compositions are observed. But in the Ti-system of Co-I and Ni-I groups, spinel type solid solutions in which Ti⁴⁺ ions are substituted for Ge⁴⁺ ions in the 4-coordinated sites are formed. In the composition range near the other end members of CoAl₂O₄, CoCr₂O₄, Co₂TiO₄ and Co₂SnO₄ (Co-I group), spinel type solid solutions in which Ge⁴⁺ occupy the 6-coordinated sites are formed over the wide range. In the composition range near the end members of NiCr₂O₄ or NiAl₂O₄ (Ni-I group), spinel type solid solution are formed over narrow range. The cation distiributions in the spinel type solid solutions were accounted for by the site preference of cations and Pauling's electrostatic valence rule. We proposed that this rule is one of the most important factors for determining the cation distribution in the spinel structure.

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Elastic modulus measurement of ceramics up to 1000°C was made practicable by improving the piezoelectric composite-bar method. The piezoelectric vibrators were made from an LiNbO₃ single crystal with the Curie temperature as high as 1210°C. The effective piezoelectric constants of the LiNbO₃ crystal were analyzed, and then the cutting direction which yields pure longitudinal vibration was determined. The present method was applied to measuring the Young's modulus E and the internal friction Q^-1 of 2Y-TZP with the dimension of 1×2×12mm, and anomalous behavior in E and Q^-1 was observed at ca. 300°C.

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Tin (II) oxide was prepared by homogeneous precipitation method at various concentrations of tin (II) sulfate and (NN₂)₂CO/SnSO₄ or various (CH₂)₆N₄/SnSO₄ molar ratios and for different heating times. The precipitation of tin (II) oxide depends on the concentration of urea or hexamethylenetetramine and heating time. Tin (II) oxide was produced with the high concentrations of the precipitant and for a long heating time. The chemical species had an effect on the formation process of tin (II) oxide.

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Relationship between sintering conditions and micro-hardness on fracture toughness were examined for fully densified silicon nitride ceramics, which were capsule-HIP sintered at temperatures between 1823 and 2023K under 60MPa for 1hour, Y₂O₃ and Al₂O₃ (in 6mol% in total) were used as additives. The micro hardness and the fracture toughness of the sintered Si₃N₄ were sensitively affected by elastic deformation (E. D.), the additive mole fraction and sintering temperatures as the following:
(1) The fracture toughness was improved with increasing β phase fraction. This behavior is explained by the tangling of β phase grains.
(2) The fracture toughness became also higher with rising E. D.. This relationship is opposite to what is expected by the theory of mechanical behavior. The E. D. may be applicable for estimating the degree of β grains tangling.
(3) The sintering temperature was the most significant parameter to control the β phase fraction, and was 1.2 to 150 times more effective than other factors, according to a dimentionless analyses.
(4) The maximum micro hardness was obtained at 50% of the β phase fraction.

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Dissolution of MgNH₄PO₄⋅6H₂O (MAP) in an aqueous suspension containing H-R (a strongly acidic ion exchange resin) leads to the formation of intermediate products owing to the selectivity of cation exchange reaction. The process was studied by measuring the changes in pH and κ (specific conductivity), and the quantities of eluted ions such as Mg²⁺, NH₄⁺ and PO₄^3- These results have led to the assumption that the dissolution process consists of the following reactions;
1) Initial stage, the dissolution proceeds with 100% PO₄^3- and ca. 30% Mg²⁺ in fractional solubility up to 1.52-1.78 of reaction molar ratio, H-R/MAP. The fact which the pH of the solution was kept at 7.0 suggests the formation of equimolar compounds consist of HPO₄^2- and H₂PO₄^- as shown in Eq. (1),
3MgNH₄PO₄+5(H-R)→Mg(H₂PO₄)₂+(NH₄)₂HPO₄+2(Mg-R₂)+NH₄-R (1)
2) Soluble Mg(H₂PO₄)₂ reacts subsequently with H-R accompaning by the decrease in Mg²⁺ concentration and increase in the acidity, Mg(H₂PO₄)₂+2(H-R)→Mg-R₂+2H₃PO₄ (2)
3) The increase in acidity causes to convert of (NH₄)₂HPO₄ with releasing NH₃ to yield NH₄OH in water.
4) Neutralization brings about a depletion in concentration of both [H⁺] and [OH^-] having high equivalent conductivity, which results a decrease in k level.
5) The reaction (1) and (2) may be combind into the overall reaction (3), which, unlike the dissolution promoted by a mineral acid, is characterized by the intermediate steps, 2MgNH₄PO₄+6(H-R)→2(Mg-R₂)+2(NH₄-R)+3H₃PO₄ (3)

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Using the isothermal method, the densification process of the pottery body was investigated. Feldspathic vitrified body with 57-59% of glassy phase and mullite vitrified body with 20-26% of glassy phase were found to have the Arrhenius relation between the temperature and the time necessary for the densification before the vitrification point. In addition, by developing this relation, the degree of the vitrification of pottery body under the heating-cooling and isothermal conditions can be expressed by the following equation.
Under the isothermal condition:
V=exp{-(A/T+C)}⋅t
Under the heating-cooling condition:
V=A/αexp(-C)[exp(-x)/x2F(x)]x2x1
F(x)=1-2!/x+3!/x2-…
where V is the degree of vitrification, A and C are the constants for body, T is the absolute temperature (K), t is the soaking time (mm), α is the heating or cooling rate (deg/min) and x=A/T. In order to investigate the validity of this equation, an experiment was carried out using a 58m long roller hearth kiln. The results of the calculation and the experiment showed a good correspondence. It is thus believed that, evaluation of the influence of the heating and cooling rates as well as that of the temperature on the degree of vitrification, not extensively studied so far, has become possible.

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Highly transparent and conducting SnO₂⋅Sb₂O₅ films were prepared by a Dip-Coating method The preparative conditions and electrical properties of the thin films were examined. The thin film was formed on the quartz glass substrate by dipping into the corresponding solution and calcinating at 600°C in O₂ gas. The conductivities of thin films were measured as a function of doped Sb contents. As a result, the thin film has a conductivity of logσ=+3(S/cm) and a transmission of about 80% in a visible light region.

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Mechanical properties of ZrSiO₄ sintered bodies, fabricated from a synthesized high purity ZrSiO₄ powder, were studied at various Si/Zr atomic ratios of ZrSiO₄ by the observation of microstructures, The ZrSiO₄ powder was prepared by calcining a homogeneous mixture of ZrO₂ and SiO₂ sols containing ZrSiO₄ seed particles, When fired at 1600° to 1700°C, ZrSiO₄ sintered bodies had densities of more than 95% of the theoretical density and the grain size was about 2-4μm. The mechanical strength was 320MPa from room temperature to 1400°C. This mechanical property depended on the Si/Zr atomic ratio, and showed the best results at the equimolar composition, Sintered ZrSiO₄ bodies had a thermal shock resistance superior to those of mullite sintered bodies or alumina sintered bodies having high stabilities at high temperature.

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The influence of production conditions of β-spodumene powder and firing temperature on the sintering and microstructure of mullite-β-spodumene composites has been investigated The mullite-β-spodumene composites were prepared from a commercial mullite powder and the β-spodumene powder synthesized using the sol-gel process. The sintering of the composites proceeded at a relatively low temperature by liquid phase sintering and then the composites in a relative density more than 90% containing 20-90wt% of β-spodumene were prepared at 1400°C. The firing temperature and composition of composites were affected by the microstructure of composites. When liquid phase was too much during sintering, some large pores of 5-10μm were formed in the microstructure of composite, and this situation caused the relative density to lower. The thermal expansion and contraction curve of composites showed an approximately reversible behavior in the process of heating and cooling. The curve of thermal expansion coefficient was nearly linear for the change of β-spodumene composition, though this curve was influenced by a small amount of α-Al₂O₃ in the composites.

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A relatively large amount of Al₂O₃ and P₂O₅ containing sodium borosilicate glasses phase-separated into two phases, SiO₂-AlPO₄ rich and B₂O₃-Na₂O rich phases. Porous glass ceramics in the system SiO₂-AlPO₄ was found to be obtained by the leaching with hot H₂O and weak organic acids. About 40wt% of P₂O₅ was remained and AlPO₄ crystal precipitated in these porous glass ceramics. These porous glass ceramics had pore volumes from 0.3 to 0.4cc/g and surface areas from 50 to 150m²/g.

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The formation of a manganese-metallized layer on the surface of silicon-nitride ceramics by the vapor-diffusion method was studied. The metallization was carried out in vacuum from 1173 to 1273K f or up to 57.6ks. Pure manganese powder was used as a vapor source. The metallized layer was composed of three sub-layers: Mn₆Si and a manganese-silicon alloy at the surface layer, Mn₆Si and manganese-silicon alloy with a trace of additive oxide particles at the middle layer, and mostly MnSiN₂ at the bottom layer. The growth of the product layer obeyed the parabolic law with the following rate constants (K_p): 3.2×10^-14m²⋅s^-1 at 1173K, 3.0×10^-13m²⋅s^-1 at 1223K, and 8.4×10^-13m²⋅s^-1 at 1273K The activation energy for layer growth (Q) was about 414kJ⋅mol^-1.

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Bi-Pb-Sr-Ca-Cu-O thin films were prepared by the rf magnetron sputtering method using multi targets: Bi_0.5Pb_0.5O_x, CaCu_0.75O_x and SrCu_0.75O_x, The composition of the as-deposited film was (Bi+Pb):Sr:Ca:Cu=1.47:1.00:0.92:1.80. High T_c films (T_c≥100K) were synthesized by the 2-step annealing process; preannealing at 720°-820°C for short time (2h) and annealing at 850°C for 15h. The obtained films contained a small amount (≤50%) of the high T_c phase as determined by XRD, but showed a high T_c (≥100K). Long time preannealing increased the amount of the high T_c phase, but the temperature dependence of resistance showed the double step superconducting transition and no zero resistivity at temperature over 100K. The grain boundary insulator phase is probably responsibile for such behavior.

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A Slip mixture containing an oxide ceramic powder was coated on the copper electrodes as a dielectric layer for ozonizing discharge by a processing technique for vitreous enamel, and a prototype ozonizer was constructed with these electrodes. Pb (Zr_0.53Ti_0.47)O₃, BaZrO₃, PbTiO₃, and BaTiO₃, were examined as an oxide. It was found that both generated ozone gas concentration and ozonizing efficiency increased with increasing dielectric constant of dielectric layer. In particular, an ozonizer with a dielectric layer of 30wt% BaTiO₃ worked well, that is, ozone concentration in ozonized air was 170ppm and calculated ozonizing efficiency was 13gO₃/kWh under the conditions of driving voltage=5kV, A. C. frequency=5kHz, and air flow rate=501/min. As a result of continuous running test, the gas concentration of ozone generated was 160±10ppm and the temperature of electrodes was 42±5°C, and they remained stabaly for more than 2 weeks.

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Three solid solution phases in the SrO-CaO-CuO system, Sr_2-xCa_xCuO₃(0≤x≤2), Sr_1-xCa_xCuO₂(0≤x≤0.5) and Sr_3-xCa_xCu₅O_y(0≤x≤1.8), were prepared at 1273K under 0.1MPa of oxygen. These phases showed semiconducting behavior below 300K. The highest conductivity of 6.3×10³S⋅ m^-1 at 300K was measured for Sr_3-xCa_xCu₅O_y(x=1.8).

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A bioactive β-tricalcium phosphate (β-TCP) coating onto alumina ceramic was studied. It is shown that the β-TCP adhered to the surface of an alumina ceramic by the use of anorthite, which was formed by a thermal treatment of a mixture of β-TCP, alumina and silica, as an intermediate layer.

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Highly pure Si₃N₄ powder without additives, sealed with a glass capsule using pure hBN powder as an insulation to be isolated from it, was treated by HIP under the condition that can be sintered and densified up to theoretical value. After HIP treatment, an oxygen content distribution in the inner parts of the glass capsule was analyzed. Oxygen content in sintered Si₃N₄ was increased, on the other hand in hBN was decreased, as compared with their starting materials. Both the oxygen contents changed remarkably on a boundary between them. A sintered Si₃N₄ had the least oxygen content in the center. Oxygen content in hBN near Si₃N₄ was constant, and on the other place in hBN it was correlated by a distance from the surface of Si₃N₄. Therefore, it was concluded that the permeation of oxygen into Si₃N₄ from impurities in hBN was dominant, and that supply of oxygen from glass of the capsule was almost negligible.

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