The ²⁹Si and ³¹P nuclear magnetic resonance (NMR) chemical shifts and the Q_n distribution in ternary sodium phosphosilicate glasses were examined. In the NaPO₃-SiO₂ glasses, only the Si(Q₄) unit from SiO₂ and the P(Q₂) unit from NaPO₃ are observed. When the P₂O₅ content increases at fixed mole fractions of SiO₂ equal to 0.1 and 0.05, the 6-coordinated silicon atoms appear. The presence of 6-coordinated silicon atoms is expected in glasses where the [P₂O₅]/[Na₂O] composition ratio is greater than unity. Their appearances can be understood in terms of the relative acidic strength of SiO₂ and P₂O₅. The profile of Raman spectra changes appreciably due to the formation of 6-coordinated silicon atoms.

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Using mixed powder compacts, the products and mechanism of the reaction between Si₃N₄ and 18%Cr-8%Ni austenitic stainless steel (SUS304L) have been investigated under a nitrogen or an argon atmosphere at temperatures from 873 to 1573K.
Under a nitrogen atmosphere, the reaction of chromium in SUS304L with nitrogen gas yielded Cr₂N and CrN. During a long time heating, silicon was dissolved in SUS304L as a solid solution by the solid-state reaction between Si₃N₄ and SUS304L. The occurrence of such products resulted in the austenite-ferrite transformation of SUS304L. Above 1373K, iron silicide, Fe₃Si, also was produced.
Under an argon atmosphere, Cr₂N was produced and silicon was dissolved in SUS304L at lower temperatures. At higher temperatures and on prolonged heating, iron silicides were produced in the following order: Fe₃Si, Fe₅Si₃ and FeSi. Both chromium and nickel as the constituents of SUS304L are considered to form the solid solution with iron silicides.
Initial rate was described by a linear rate law, and the activation energy was 199kJ/mol below 1373K and 97kJ/mol above 1423K. The rate is considered to be controlled by a gas-phase diffusion or/and an interfacial reaction. The rate at the late stage of reaction obeyed a parabolic rate law. The activation energies were 521kJ/mol in the Fe₃Si region and 494kJ/mol in the Fe₅Si₃ region. The reaction rate is considered to be determined by the solid-state diffusion through the reaction layer formed around the particles of SUS304L.

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In many ceramics, stress corrosion cracking precedes fast fracture in an activated environment, and leads to degradation in strength during water quenching. The strength degradation during water-quench thermal shock testing, therefore, may be caused by both stress corrosion cracking and thermal shock cracking. In this study, the degree of strength degradation by water quenching is determined experimentally using alumina material, and the reduction behavior in strength is analyzed statistically and distinguished as stress corrosion cracking or thermal shock cracking. A new definition of the critical temperature difference in water-quench thermal shock testing is also proposed based on this statistical approach.

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Generation of higher harmonic voltages in piezoelectric ceramics driven at high-power resonance frequency levels was investigated. Rectangular bar samples with a high mechanical quality factor were prepared for this study. The samples were driven at a fundamental resonance frequency of the length extensional vibration mode by a constant current method, and their current, voltage and displacement were simultaneously measured. When the samples were driven at a constant current higher than the threshold level, distinct distortion in voltage waveform was observed while current waveform and displacement were exactly sinusoidal. By analyzing the distorted voltage waves with a spectrum analyzer, the distortion of the voltage wave was found to be due to the generation of higher harmonic voltages. The 2nd and 3rd harmonic voltages were measured as a function of current, and their magnitudes satisfied the power laws of square and cubic of the current, respectively. These experimental results can be explained by nonlinear piezoelectric equations derived from the ferroelectric theory.

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The effects of various sintering methods, such as pressureless-sintering, hot-pressing and spark-plasma-sintering, on the densification and mechanical properties of Si₃N₄/(0-30mass%) SiC composites were examined. Two sets of starting powders mixed with nitrates and oxides as sintering additives, respectively, were used. By pressureless-sintering, density of the Si₃N₄/SiC composites generally decreased with increase in SiC content, and the composites with nitrate additives were denser than those of oxide additives at the same amount of SiC. The Si₃N₄/SiC composites sintered by hot-pressing and spark-plasma-sintering were fully densified regardless of the type of sintering additives and amount of SiC. The mechanical properties strongly depended on the amount of SiC and sintering additives, i.e., on the sintered density and morphology of Si₃N₄ grains. The mechanical properties of the monolithic Si₃N₄ and the Si₃N₄/10mass% SiC composite fabricated by pressureless-sintering were nearly the same as those of hot-pressed specimens.

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A simulation model was developed to predict the shrinkage of ceramic compacts during sintering by finite element method. For different heating rates or compact sizes, the sintering shrinkage of compacts in the process of raising and holding temperature was calculated using the developed model and compared with the experimental data to examine the validity of the model. Results of simulation agreed well with the experimental phenomenon in which densification proceeds slowly for high rates of heating or large sizes of compacts. Thus, it became clear that the size change of a compact during sintering could be predicted for the unknown sintering conditions or compact size using this simulation model.

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The bubbles that generate during the enamel reaction were studied by TMA. The sample used in the study was a pellet of a mixture of Fe powder and frit powder. The expansion and the shrinkage of a pellet depended on the generation and the breakaway of the bubbles. The influence of cobalt and nickel on generation of the bubbles and its was examined experimentally. (1) The Co-porcelain enamel had a little quantity of bubbles, and the size was uniform. The Ni-porcelain enamel had a large quantity of bubbles, and the size was nonuniform. (2) The bubbles generation existed in the enamel calcination temperature range of 700-900°C. The bubbles of the Co-porcelain enamel were generated at about 740°C. The bubbles of the Ni-porcelain enamel were generated at about 740°C and about 870°C. (3) The generation cause of the bubbles was oxygen as a result of the reduction of superficially present iron oxide. When carbon was included in iron, the bubbles was generated as carbon dioxide, (4) The bubble quantity increased when carbon was included in iron. The Ni-porcelain enamel was more easily influenced by the carbon as compared with Co-porcelain enamel, and generated a large number of bubbles.

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For sillenite type crystals, 6Bi₂O₃⋅SiO₂, 6Bi₂O₃⋅GeO₂ and 6Bi₂O₃⋅TiO₂, T-T-T (Time-Temperature-Transformation) diagrams and C-C-T (Continuous-Cooling-Transformation) diagrams are presented based on Xray diffraction (XRD) analysis. These diagrams indicate growth parameters for obtaining γ-phase: melting temperature, holding time and cooling rate. The results are in good agreement with melting temperature, holding time and cooling rate in growth process of single-crystals reported elsewhere. In this paper, the authors will point out the needs and usefulness of T-T-T and C-C-T diagrams for growth of singlecrystals.

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Porous alumina precursors have been prepared from an aqueous solution of AlCl₃ by an addition of various n-alkylamines (C_nH_2n+1NH₂) at pH 6.2 and pH 9.6. Alkylamines with n≥6 produced the unknown phase, which showed a single X-ray reflection at 2θ=4-5°. The corresponding d values (1.99-2.42nm) depended on the carbon number of alkylamines. The XRD, FT-IR, and TG measurements suggested that the precipitate with the long periodicity is an intercalation composite between Al hydroxide, alkylamine, and water. The thermal decomposition of the precipitate obtained at pH 6.2 gave rise to the maximum BET surface area (374m²/g) at 500°C. The dependence of the surface area on the carbon number showed that the precipitate containing alkylamines of n≥6 is quite effective in producing porous alumina structure after calcination at 350-600°C. Gas evolution by the thermal decomposition of alkylamines incorporated into the structure of the precipitate appears to play a key role in the formation of the micropores.

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With artificially the pore size in porous, applications as soil filter and heat resistance materials can be taken into consideration. We tried to prepare porous bodies which were composed of β-eucryptite, by simultaneously inducing a foaming reaction between sodium hydroxide and aluminum powder, and a gelling and setting reaction between sodium silicate and sodium aluminate. Then, the dominant factors of the detained structures were investigated. Gelling/setting reactions and foam forming reactions were controlled lay varying the reaction temperature and the amount of aluminum powder, respectively. The factors of foam forming rates and shrinkage rates remarkably depended both on the reaction temperature and the weight rate of aluminate slurries to mixed slurries, respectively. Varying these factors, the pore size was found to be controllable in the range 70÷260μm.

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The effect of specimen size on the flexural strength of silicon carbide ceramics was studied using miniaturesize specimens. Fracture surface of these specimens was observed by SEM to determine the fracture origin. The strength of the miniature specimens increased with decreasing the specimen size, most of the fracture origins of the miniature specimens being located on the specimen tensile surface. The strength of a standard-size silicon carbide specimen could be estimated from the strength of the miniature specimens by invoking Weibull-size scaling with the effective surface area.

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This paper is concerned with the comparison of chemical reactivities of β-Ca₃(PO₄)₂(TCP) and α-TCP in solid-liquid reaction. A dilute aqueous solution comprising Ca(H₂PO₄)₂, Ba(H₂PO₄)₂ or NH₄H₂PO₄ was used as a liquid reactant. For comparison, Ba₃(PO₄)₂ was also used as a solid reactant. The solid-liquid reaction process to precipitate monohydrogen phosphate, CaHPO₄⋅2H₂O(DCPD) or BaHPO₄, was followed mainly by simultaneous measurement of heat flow and electric conductivity at 25°C. Variation of concentration for the filtrate was also measured by chemical analysis. The reaction process was discussed both in terms of dissolution-precipitation mechanism and charge leveling process between PO₄^3- and HPO₄^- anions, which is accompanied by an increase of electric conductivity. It was found that β-TCP does not appreciably react with Ca(H₂PO₄)₂(aq) or NH₄H₂PO₄(aq), whereas DCPD precipitates readily upon addition of α-TCP in the solution, accompanying heat evolution and decrease in electric conductivity. Minute quantities of BaHPO₄ derived from the mother liquid precipitate through the reaction between β-TCP and Ba(H₂PO₄)₂(aq), but three kinds of products, BaHPO₄, an unknown phase and DCPD, precipitate successively for α-TCP with the same solution. The charge balance process was confirmed by a slight increase in electric conductivity upon the addition of α-TCP in NH₄H₂PO₄ solution, which is followed by the precipitation of DCPD with heat evolution. The higher reactivity of the α-TCP is assumed to be related to a non-uniform electron distribution around PO₄^3- ions, which are much more subject to proton transfer from H₂PO₄^- ions to convert HPO₄^2- ions.

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The surface chemical binding states of NO-intercalated La_1.5Ba_0.5SrCu₂O_6-δ were investigated by X-ray photo-electron spectroscopy (XPS) analysis. The N1s XPS spectra suggested the occurrence of surface adsorption of NO₂^- and NO₃^- groups. The chemical shift of the Cu2p XPS peak indicated decreasing hole concentrations at the level of O2p with NO intercalation in contrast to the case of LaBaSrCu₂O_6-δ. In addition, the surface intercalation of NO-produced a chemical shift of the Ba3d and Sr3d XPS peaks. These results suggested that the Ba content affected the surface groups on the cuprates.

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The compositional homogeneity in the ceramic solid solutions is settled both by the process of the mixing of raw materials and by that of the diffusion during the firing. The mechanical mixing of raw materials is not effective against the homogenization below the grindable size. The homogenization process by the diffusion is not effective at large size. The gap where neither mechanical mixing nor diffusion is effective was considered to be the origin of the inhomogeneity in solid solutions. In order to verify this, a method to evaluate the region size of inhomogeneity was developed. Five areas having a certain size were randomly chosen on the EPMA image of a sample. Each area was divided into sixteen portions and the standard deviation of composition among these portions was estimated. This standard deviation can be considered as a degree of compositional inhomogeneity. The average standard deviation among the five areas was calculated. Such calculation was carried out for various sizes. The average standard deviations were plotted against the size. Plots for models, in which the distribution of the composition forms a check pattern, exhibited peaks. The position of the peaks corresponded to the size of the check patterns. This method was applied to PZT samples prepared by the solid state reaction. The plots revealed the presence of the gap where neither mechanical mixing nor diffusion is effective.

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Kutani ware is characterized by its overglaze decorating style using Japanese colors. In Kutani industry, it is empirically known that Japanese colors have the tendency of peeling off more often when the body is formed by pressure casting method. In this study, inhomogeneity of porcelain body is examined after measuring the body with applying a X-ray fluorescence analysis to detect the change of chemical composition in the layers from the surface to the center of the body. Converting the obtained values of chemical composition into mineral composition, it was found out that the body formed by pressure casting method becomes highly inhomogeneous; high amounts of clay minerals was observed at the surface and at 1040μm from the surface, a composition almost the same as the slip within a layer 300-960μm from the surface, and less clay minerals in the center layer. The result of this experiment also shows that it is possible to improve the homogeneity of the body by controlling the water content of the slip in order to achieve a less mobility of the clay particles.

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In order to design optimal particulate slurries to be applied in wet-shaping process, concentrated alumina slurries have been subjected to a centrifugal consolidation method, in which the mechanical properties of slurry are measured methodically by controlling the centrifugal effect. The slurry with high solid content is readily forced to form a particle network structure at the percolation threshold, the formation mechanism of which originates in a slight dehydration of slurry. The critical initial solid content for the network structure has been found to be as low as several vol%. It is demonstrated that it exists a relation between the centrifugal consolidation stress and the packing fraction, and that this relation can be interpreted to characterize the mechanical strength of the formed network structure, on which the solids content and the degree of flocculation exert a significant influence. Compared with the network structures formed from well-dispersed slurries, those from weakly-flocculated slurries have lower mechanical strength, accordingly leading to higher final equilibrium packing fraction of green bodies.

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Dipping a sintered Pd/SnO₂ sensor in a diethoxydimethylsilane sol solution, followed by calcination at 600°C, resulted in a considerable enhancement of gas sensitivity to H₂ but a marked decrease to CH₄ and C₃H₈. In good accordance with the variations in the gas-sensing properties, catalytic activity of the sensor material markedly decreased for CH₄ and C₃H₈ oxidation but increased for H₂ oxidation. TEM observation and EDX analysis revealed that the fine SnO₂ particles were coated with thin SiO₂ layers 2-3nm in thickness after dipping. Temperature programmed desorption chromatograms (TPD) of O₂ and H₂O were markedly influenced by the formation of thin SiO₂ layers; that is, the amount of active O^- or O^2- species on SnO₂ became considerably small, and the adsorbed species of H₂O changed from surface hydroxyl groups to molecular species hydrogen-bonded on the surface oxygen ions. The mechansim of the H₂ gas sensitivity enhancement was discussed from the viewpoint of the modifications in TPD characteristics.

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In this work, we studied the effect of various elements on the relative dielectric constant, ε_r, by adding 1-3mol% of an element to soda glass, 15Na₂O⋅15CaO⋅70SiO₂, the mother glass. The structure of the dielectric coating layer for the glass-lined discharge electrode was investigated in terms of the breakdown voltage and ε_r. It was found that most rare-earth elements (Pr, Lu, Eu, Gd, Sm) are more effective in increasing ε_r than other elements. From the viewpoint of the breakdown voltage of the glass-lined layer, it is desirable that a cover coating with a high ε_r is directly coated onto the base metal without using a ground coating with low ε_r, to obtain the optimum improvement effects. As the results of experiments, the 3CoO⋅3NiO⋅3MnO₂⋅3Pr₆O₁₁⋅30Bi₂O₃⋅20BaO⋅50B₂O₃ (mol%; CNMPBBB) glass was found to have a high ε_r of 16 and good adhesion with steel. CNMPBBB glass is highly promising for use in glass-lined discharge electrodes.

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The composites of alumina matrix and stainless steel rope were fabricated by hot pressing at 1573K. Most of the interfaces between alumina matrix and stainless rope were good contact, but a part of the interfaces had cracks probably because of thermal stress during cooling after the hot press treatment. The composites had about 400MPa in strength and owned a remarkable high fracture energy comparing with pure Al₂O₃ material. This composite also showed high thermal shock resistance (about 250MPa in strength after quenching from 400K) and excellent Charpy impact test performance (100 times over monolithic). Alumina based composite reinforced by stainless steel rope is expected to be applied to the high reliability in the mechanical properties.

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Amorphous gel powders were prepared by heating an ethylene glycol solution containing Fe(NO₃)₃⋅9H₂O and LiNO₃ (Li/Fe (in molar ratio)=0-0.31) at 353K under a N₂ flow. The powders without lithium crystallized to γ-Fe₂O₃ at 573K and to α-Fe₂O₃ above 773K. On annealing the powders of Li/Fe=0.18-0.31, a LiFe₅O₈-type phase appeared at 573K which coexisted with α-Fe₂O₃ at above 673K. The LiFe₅O₈-type phase without α-Fe₂O₃ could only be obtained on annealing the powder of Li/Fe=0.31 at 973K for 2h. The saturation magnetization of the powder was 0.29T (74% of LiFe₅O₈) and its coercive force was 10.5kA⋅m^-1, With increasing crystallite size of the LiFe₅O₈-type phase, the coercive force of the powder increased until equal to 13.2kA⋅m^-1 and then decreased. The estimated maximum single magnetic domain size was 40-50nm.

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