The chemical states of iron in fired red clay containing iron in high concentration and the phase transformation occurring during firing in various atmospheres were studied by X-ray diffraction, ESR and ESCA. It was pointed out that the reduction of Feions to metallic iron and the formation of hercynite (FeAl₂O₄) took place competitively during the firing of the clay at 1000°-1200°C under reducing conditions. The color of the clay fired below 1250°C in a reducing atmosphere was dependent only on the firing temperature, but not on the atmosphere.

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A ferroelectric powder consisting of perovskite type single phase (100%-perovskite powder) could be prepared by firing a batch mixture containing an excess amount of MgO and/or ZnO in the series Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃. As for the excess amount, the following conditions were needed: x+y≥1.4 and x≥1.0 when the composition of a batch was represented in the chemical formula Pb{(Mg, Zn)_1/3Nb_2/3}O₃. In order to prepare a mono-sheet capacitor from ferroelectric powders, addition of a small quantity of glass is necessary as a bonding agent. The perovskite type niobate in this series, however, is apt to be decomposed to a pyrochlore type compound and the ferroelectricity is lost in the presence of glass during firing. Accordingly, inert glasses for the perovskite type niobate have been requested. In this report the effects of oxides on the decomposition were investigated by adding 10% various oxides to the 100%-perovskite niobate powder one after another, firing at 850°C for half an hour and determining the perovskite fraction. It was shown that the oxides of multi-valent metal or “acidic oxides” accelerated the decomposition of the perovskite phase and that the oxides of divalent metals were inert. Probable reasons of these phenomena were discussed on the basis of the crystal structure and the single bond strength of the oxides. On the basis of the experimental results, inert glasses were searched. Several glasses in the system PbO-Bi₂O₃-SiO₂ were found to be promising for practical use. A glass composition, 35PbO⋅60Bi₂O₃⋅5SiO₂ (in mol%) has been recommended.

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The non-isothermal crystallization kinetics in ZrF₄-BaF₂ and ZrF₄-BaF₂-NaF-AlF₃ glasses were analyzed based on the method for determining the activation energy for crystal growth from DSC curves obtained at various heating rate. In binary system ZrF₄-BaF₂, most stable glasses were formed around the composition of 2 ZrF₄⋅BaF₂ (molar ratio) and the glass transition and crystallization temperatures increased as the glass composition approached to ZrF₄⋅BaF₂. It was found that the crystal particles grow two-dimensionally in thin film glass specimens. The activation energies for crystal growth were determined to be about 170 and 130kcal/mol in the composition range in which β-BaZrF₆ and β-BaZr₂F₁₀ crystals precipitated respectively. In ZrF₄-BaF₂-NaF-AlF₃ system, it was found that the crystal particles formed in the bulk specimens grow three-dimensionally and that the surface crystallization is predominant in powder specimens. The activation energies for crystal growth were below 120kcal/mol, much less than that for viscous flow. The crystallization mechanisms were discussed in detail.

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The electrical conductivity of glasses in the system 2 R′₂O⋅RO⋅7SiO₂(R′: Li, Na, K, Cs; R: Be, Mg, Co, Sr, Ba, Zn, Pb) has been measured in the temperature range 350°-1200°C. Different effects of divalent cations on the electrical conductivity in a series of glasses containing a given alkali were observed in molten state (>T_g) and in solid state (<T_g). The electrical conductivity in molten state decreased with increasing difference in ionic radii between alkali and divalent cation, while the conductivity in solid state decreased monotonously with increasing ionic radius of the divalent cations. When a divalent cation is introduced into an alkali silicate glass, an alkali ion probably forms a pair with a divalent cation such as R′⁺…O…R²⁺ bond, giving weaker Coulombic repulsive force for the next nearest neighbor cations than in the R′⁺…O…R′⁺ bond and decreasing of the electrical conductivity. This effect appears only in molten state. However, in solid state, the mobility of alkali ions is considerably affected by frozen network structure depending on the transition temperature of these glasses, that is, the geometical factor for alkali migration and the electrical conductivity is reaponsible for the different from molten state. The explanation described above can be applied to the mixed alkali effects in glass also.

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The silicic glass stones, assumed as a remnant of silicic minerals in molten glasses, were picked out from the significant numbers of glass stones collectd from bottle glasses. They are always larger than the maximum size of quartz sand which is used as a raw material. This fact indicates that the main origin of silicic glass stones is the large grains of silicic minerals present in cullet or calcareous raw materials. A rectangular bar of quartz crystal prepared by grinding was used as the coarse grains of silicic minerals. The high temperature reaction between quartz crystals and cullets of bottle glasses was studied. The structures and minerals produced by the thermal reaction were studied by optical microscopy, EPMA and X-ray diffraction method. The cristobalite crystals grow on the surface of quartz crystals in the reaction at a low temperature (1300°C). The aggregation of wedge-like crystals of tridymite is produced by the reaction at moderate temperature (1350-1400°C) and the size of crystals is affected by the heating conditions of quartz crystals. In the reaction at high temperature (1400°-1450°C), the quartz crystals change to aggregated graunlar or dendritic crystals of cristobalite. These structures were also found in the silicic glass stones. The behavior of silicic grains in molten glasses is discussed from the correlation of both structures. Most grains seem to have passed through the high temperature zone and minor part of them passed through the surface zone in which temperature is the highest in molten glasses.

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The phase stability of tetragonal zirconia specimens in various molten salts was studied by a corrosion test. The corrosion test was examined using 3 mol% Y₂O₃-partially stabilized ZrO₂(3 Y-PSZ) with high thermal phase stability. XRD results indicated that the phase transformation of 3 Y-PSZ from tetragonal (t) to monoclinic (m) phase (t→m transformation) was observed only in molten fluoride salts. when 3 Y-PSZ was dipped into molten Na₂SiF₆ salt, more than 90% tetragonal phase on the surface of 3 Y-PSZ transformed into monoclinic one in 5 min-dipping. The corrosion depth accompanied by the t→y m transformation reached 300μm for 200 min-dipping. From the results of corrosion tests with alkaline metal fluorides, the rate of t→m transformation on the surface of a sintered body and the rate of depth increase from surface to inside depended on the ionic radius of univalent rations. In the same test with PbF₂, the sintered body was heavily attacked, but no remarkable t→m transformation was observed on the surface of the sintered body. Raman spectra for the surface of test samples gave dispersed bands characteristic of the tetragonal phase. The result indicated that Pb restrains tetragonal particles. The corrosion depth for 3 Y-PSZ-Al₂O₃ was the same as that for 3 Y-PSZ. EPMA results indicated that the region enriched with Si or Na was equivalent to the t→m transformation range over 90% by XRD analysis. Remarkable t→m transformation is considered to be influenced by these Cations. The activation energy was measured to estimate the t→m transformation rates The activation energies of 3 Y-PSZ, 3 Y-PSZ-Al₂O₃ and 3 Y-PSZ-Cr₂O₃ were 12, 44 and 154kJ/mol, respectively. The t→m transformation depth of 3 Y-PSZ-Cr₂O₃ was the smallest among the three 3 Y-PSZ complexes. 3 Y-PSZ-Cr₂O₃ had high phase stability in molten fluoride salts.

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The thermal expansion, thermal stability and bending strength of aluminumtitanate (AT)-mullite composites prepared from synthesized AT, Newzealand kaolin and aluminum hydroxide were investigated. The results obtained are summarized as follows; (1) The average linear thermal expansion coefficient from 100° to 1100°C increased slightly with increasing amount of AT up to 50wt%, and decreased with further increase in the amount of AT, approaching to be value of fired AT. The average linear thermal expansion coefficients from 1100° to 1400°C in heating and from 1400°C to the turning point in the cooling stage increased monotonously with increasing AT content. (2) The degree of thermal expansion hysteresis decreased with decreasing amount of AT. (3) The bending strength of the composites containing 10-30wt% AT was the highest, and decreased with further increase in the amount of AT. (4) The decomposition of AT in the composites was restrained almost completely.

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A method was developed to determine fluctuations of x and y independently in Pb{(Zr_xTi_1-x)_1-y(Mg_1/3Nb_2/3)_y}O₃ solid solution. This solid solution has tetragonal symmetry in the compositional range investigated (0.1≤x≤0.4, 0≤y≤0.4). The lattice constant a did not vary with the value of y but with the value of x. On the other hand, the lattice constant c did not vary with x but y. Using these relations, the fluctuation of composition, x, was estimated from the value of Δa/a, and the fluctuation of y, from the value of Δc/c. Δa/a and Δc/c were determined from the slope of the relation between β cosθ and sinθ, where β is the net broadening of an X-ray diffraction peak. The results showed that the solid solution prepared by the ordinary solid state reaction had large compositional fluctuations. The decrease in the compositional fluctuation by firing was small. An altenative repetition of firing and grinding was effective to reduce the fluctuations. However, the compositional fluctuations could not be eliminated completely even by repeated firing.

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Fracture toughness for Si₃N₄ composite containing 0-30wt% SiC whisker was measured by Indentation Microfracture (IM) and Chevron Notch (CN) methods. The results obtained by IM method showed that K_IC, calculated on the basis of Palmqvist-type crack, varied from 6.3MN/m^-3/2 for the matrix Si₃N₄ to 7.2MN/m^-3/2 for the composite containing 15wt% whisker, on the other hand, K_IC obtained from CN method varied from 5.1MN/m^-3/2 for the Si₃N₄ to 6.3MN/m^-3/2 for the composite having 30wt% whisker. These results indicate that fiber reinforcement with whisker is an effective way to toughen Si₃N₄ ceramics. Microscopic observations of the cracks induced by indentation showed that the crack propagation is often prohibited by the whisker, and that the crack is deflected to the interface between the whisker and the matrix. This crack deflection may be attributed to the stress fields set up at the interface, due to thermal expansion difference between the whisker and matrix. Considering such crack-whisker interaction, it is suggested that the dispersion of the whisker having larger diameter is effective in toughening Si₃N₄ ceramics.

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Phase relations in the pseudo-binary system MnO₂-BaMnO₃ have been examined by means of solid state reaction. We obtained two binary compounds, hollandite (Ba_xMn₈O₁₆, 1.23<x<1.36) and a unknown phase X (Ba_xMn₈O₁₆, x≅2), both giving X-ray diffraction patterns similar to that of natural hollandite. They occurred stably up to 880°C and between 860° and 1050°C, respectively, Between 880° and 985°C hollandite of low occupancy is gradually converted to one of higher occupancy with concomitant precipitation of bixbyite (Mn₂O₃), in accordance with a constant rate of weight loss in TG and a consecutive endothermic peak in DTA in this temperature region. Bixbyite thus formed changes to hausmannite (Mn₃O₄) prior to the decompositon of hollandite into hausmannite and the phase X, giving a shoulder on the deep endothermic peak (1015°C) due to the latter change. By contrast, hollandite of high occupancy gives no such thermal changes until it is decomposed directly, without producing bixbyite, into hausmannite and the phase X at 990°C. The phase X is subsequently decomposed to 2-layer BaMnO₃ and hausmannite at 1120°C.

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The plasma sprayed CeO₂-ZrO₂-Y₂O₃ thermal barrier coating was developed, and thermal conductivity, thermal expansion, bending strength and hot corrosion resistance were evaluated. The results indicated that CeO₂-ZrO₂-Y₂O₃ compositions are useful for the plasma sprayed thermal barrier coatings. The thermal conductivity of the sprayed CeO₂-ZrO₂-Y₂O₃ coating was 1-2W/m·K, lower than that of sintered materials of the same composition and one of the lowest thermal conductivities of ceramics. Thus, the CeO₂-ZrO₂-Y₂O₃ coating is useful for the thermal barrier, since the sprayed layer is expected to insulate heat flow well. The thermal expansion coefficient of the sprayed CeO₂-ZrO₂-Y₂O₃ coating was 12×10^-6/K, comparable to that of the metal substrate 16×10^-6/K. The bending strength was 2-3kgf/mm², favorable for the excellent thermal fatigue property. The hot corrosion resistance was almost the same as that of Y₂O₃-stabilized ZrO₂ thermal barrier coatings in a low vanadium environment.

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Calcination tests of a pellet made of coal ash were performed in order to obtain the data for design and operation of a moving bed shaft kiln. Factors controlling calcination process in a fixed bed are found to be gas flow rate, G_g, oxygen concentration of gas, y_o20, as well as carbon content of the pellet, x_c. From the theoretical consideration on calcination in the fixed bed, the fixed bed behavior can be characterized by the rate, v, of travel of the position where a bed has a maximum temperature, T. The v can be expressed as a function of G_g, y_o20, and x_c. Using velocity, v, and temperature, T, properties of the calcined product are represented in the v-T plane as the isolines of the product properties. It is shown that isolines determine the desirable operational condition.

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This study was conducted to obtain a fine powder of β-tricalcium phosphate as a startinig material of high strength calcium phosphate ceramics. Calcium-deficient hydroxyapatite was synthesized by the trituration and reaction of a slurry, a mixture of calcium hydrogenphosphate dihydrate and calcium carbonate at the molar ratio 2:1 prepared in a pot mill. for 24h. Calcium-deficient hydroxyapatite was converted to β-tricalcium phosphate by the calcination at 750°C for 1h. The average particle diameter and specific surface area of the synthesized β-tricalcium phosphate were 0.44μm and 27.4m²/g, respectively. The present method was superior to the previous dry process: 1) no requirement of adjustments of pH value and reaction temperature, 2) lower calcination temperature, and 3) easy preparation of a fine powder of β-tricalcium phosphate.

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A computer program was written using a conventional microcomputer to analyze the back-reflection Laue photographs of any crystal system and in any orientation. This program draws a calculated Laue pattern of a given orientation from the lattice constants, and defines the orientation of the crystal referring to the incident X-ray beam from the suitable indices of three diffraction spots and their distances from the center of the photograph. An experimental Laue photograph can be interpreted using this program by the following steps: (i) Draw calculated Laue patterns in various orientations, (ii) Index the diffraction spots by visual comparison of the experimental photograph with the calculated Laue patterns, (iii) Define the orientation of the crystal, (iv) Verify the coincidence between the photograph and the calculated pattern in the defined orientation. This program provides easy and quick interpretation of Laue photographs of crystals with lower symmetries.

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The volume of gases released from two grades of nuclear graphites, SM 1-24 and 7477 PT, was measured by gas mass-spectrometric method for estimating the open porosity of these materials. Metallic dummy specimens with the same dimensions as those of the graphite specimens were used to compensate the gap volume between specimen tube and specimen itself. The results indicated that the composition of gas released from these graphites was similar to that of air, and that the open porosity ranged from about 40 to 60% of their total porosity which was calculated from the true and bulk densities.

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Silicon nitride with a small amount of additive BeAl₂O₄ was sintered by HIP treatment in glass capsules. The sintered body of Si₃N₄ was for the most part β phase. BeAl₂O₄ dissolved into β-Si₃N₄ completely. The effect of isostatic pressure was significant in HIP sintering. For example, the bulk density of sintered body containing 3wt% BeAl₂O₄ was almost theoretical, and its microstructure was homogenous when sintered above 1700°C and at an applied pressure 200MPa.

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Compressive deformation of 80wt% ZrO₂ (3mol% Y₂O₃)/20wt% Al₂O₃ composite was studied in air at temperatures from 1400° to 1550°C Extraordinary large deformation (up to -1.8) was observed at strain rates from 10^-3 to 10^-4s^-1. The stress exponent was from 1.2 to 2 and activation energy was 620±40kJ/mol. It was observed that the Al₂O₃ aggregate evolved during the deformation. This phenomenon was explained by the grain rearrangement model as a consequence of grain switching doring the superplastic flow.

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Single crystals of a new compound K_x[Ga₈Ga_8+xTi_16-xO₅₆] was synthesized by the flux method. The best crystal was obtained by slow-cooling after keeping at 1300°C for 10h using a mixture of 20mol% crystal composition of (K₂O)₁(TiO₂)₁(Ga₂O₃)₁ and 80mol% flux composition of (K₂O)₁(MoO₃)_1.5. The crystal structure consists of a framework of new type with a tunnel structure. The ac ionic conductivity for K ion was 5.0(S·cm^-1) at 254K and 32.5GHz. The thermal conductivity of a sintered material was 0.022 and 0.024(W·cm^-1·K^-1) at room temperature and 948K, respectively.

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