Controllability of operation of kilns and some characteristics of combustion gas produced by a natural gas fired-premixing burner were studied from various points of view with an experimental kiln. The radial and directory temperature distributions inside the kiln equipped with a premixing burner were more uniform than those with low-speed diffusion-type burners. Simultaneous control of the temperature and the firing atmospheres were achieved for a set period of time in which the temperature is varied at a constant rate. The equilibrium compositions of the gas flame calculated at different temperatures and air ratios were and compared with the measured compositions. The results calculated for CO₂, O₂, CO and H₂ agreed very well with the measured values, but the discrepancy was remarkable in NO owing to the low rate of NO formation. The average NO emission in the combustion gas was reduced by supplying substoichiometric quantities of primary air to the burner, while keeping the total air rate constant. The H₂/CO ratio in the reducing atmosphere was not constant, as has usually been assumed, but depend on the temperature and air ratio.

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Optical absorption spectra of Ni²⁺ ion (100-x) (PbO⋅GeO₂)⋅xRO⋅0.2wt% NiO glasses are measured, and the results are obtained as follows.
The value of 10Dq which represents the intensity of the ligand field shifts toward higher wave number with increasing alkaline earth metal content. The increasing intensity of the ligand field is considered to be the formation of GeO₆^8-, where the glass network was destroyed by alkaline earth metals. In this study, the ν₄ peak appears only at 20mol% BaO, which represents a Ni²⁺ ion with 4-coordination. In other systems the ν₄ peak does not appear clearly. It is considered that the Ni²⁺ ion does not become 4-coordination.
According to the measurements of infrared spectra, most of this system consists of Ge₆ groups, and the variation of coordination number of Ge with the alkaline earth metal contents hardly appear.

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The constitution of potassium borophosphate glasses of composition K₂O⋅2(1-x)B₂O₃⋅2xP₂O₅ has been discussed on the basis of the composition dependence of the molar volume and elastic constants. The fraction N₄ of the fourcoordinated boron atoms is derived as a function of x based on a few assumptions. Potassium oxide is distributed to B₂O₃ and P₂O₅ in proportion to their mixing ratio: (1-x) to B₂O₃ and x to P₂O₅. However, it is not possible at this stage to specify which mechanism represents the glass constitution, the formation of the KOBO_2/2 units or the coexistence of the B₃ and PO_2.5 units.

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TiO₂ deposition on alumina powders by the hydrolysis of titanium isopropoxide (TIP) was investigated as a model experiment of the uniform addition of a sintering aid. The rate of hydrolysis increased with increasing TIP/Al₂O₃ and H₂O/TIP molar ratios, and titania deposition occurred effectively at the H₂O/TIP ratio larger than 10. Examination of the coated powders by SEM, TEM, BET surface area measurement and electrophoresis showed that fine titania deposits adhered loosely to the alumina particles before calcination, but that after calcination at 500°C the deposits spread over the surface of the alumina particles, resulting in the tight coating. The hydrolysis reaction was accelerated by the addition of diethylamine (DEA); however the titania powders had a tendency to deposit separately from the alumina particles.

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The surface crystallization of glass with a composition MgO(16.7), Al₂O₃(22.3), SiO₂(61) (wt%) was investigated, using XRD, DTA and SEM. Aggregated particles of β-quartz precipitated from fire-polished surface of the glass. The aggregation of non-crystalline spherical particles of about 500-1000Å was observed in the region cotiguous to the surface layer containing β-quartz. However, the number of spherical particles decreased with depth from the crystallized surface by the logarithmic function, with substantially the same particle size regardless of the depth. The precipitation of β-quartz, petallite and α-cordierite was observed for the sample with mechanically polished surface. The surface crystallization in this case developed into the glass with the dendrite structure. In the glass having a fire-polished surface, the amounts of β-quartz and petallite passed through maxima during isothermal treatment at 950°C, whereas the amount of α-cordierite increased monotonously with time. This suggests that α-cordierite was formed not only by the direct precipitation from the glass, but also by the transformation of β-quartz and petallite.

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Local structures around Y³⁺ ions in stabilized tetragonal ZrO₂ with the chemical compositions of 94 ZrO₂⋅6YO_1.5 (Y6) and 86ZrO₂⋅4YO_1.5⋅10CeO₂ (Y4) were studied by Y K EXAFS (extended X-ray absorption fine structure) analysis. Using Y₂O₃ crystals (Y-O=2.28Å, six-fold coordination) as a reference sample, average Y-O distances for Y6 and Y4 samples were estimated to be 2.31 and 2.35Å by the curve-fitting method, respectively. Y atoms in the tetragonal zirconias seem to locate at seven-fold coordination sites, judging from the atomic distances. The average Y-cation distances for Y6 and Y4 samples were calculated to be 3.70 and 3.73Å, respectively. They are longer than the average cation-cation distances calculated from the lattice dimensions, but shorter than the average Y-Y distance of 3.77Å in the Y₂O₃ crystals. A Zr₂Y₂O₇ cluster was proposed as a model for local structures around Y³⁺ ions. The cluster consists of two ZrO₇ and two YO₇ polyhedra which share one oxygen vacancy. If one oxygen vacancy is introduced into the atomic arrangement of tetragonal ZrO₂, four equivalent cation sites change to two bigger and two smaller sites which are respectively positioned along the a axis. A pair of Y³⁺ ions probably occupies the bigger sites and as a result the c/a axial ratio decreases. Therefore this model is consistent with the fact that the c/a axial ratio decreases with an increase of Y₂O₃ concentration when Y³⁺ ions are added to tetragonal ZrO₂.

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Characterization of wear properties have been made with indentation fracture models. However, wear loss is not fully characterized, probably due to the following reasons. (1) This model was used without considering the limits of application. (2) The effect of roughness at the frictional surface on wear properties was not investigated. We attempted to estimate the wear properties quantitatively using an indentation fracture model. Pin-on-disk wear tests were carried out for some oxide ceramics. Oxides used were Al₂O₃, ZrO₂, TiO₂, MgSiO₃ and their composites. The relation between wear losses (V) and vertical load (P) was presented by V∝P^9/8 as inferred from this model, excepting for low vertical loads. Thus, this model was applicable to only the vertical load. The change in roughness at the frictional surface with wear has affected wear loss. By considering the change in conditions at the frictional surface, wear loss was characterized by the function of mechanical parameters (toughness, hardness, Youngs' modulus), which was derived from the indentation fracture model.

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The effects of high-temperature (200°-800°C)-and high-pressure (5 or 100MPa)-water on the low temperature degradation behavior of Y-TZP were investigated. Tetragonal (t) to monoclinic (m) transformation is markedly accelerated by the existence of water, under the hydrothermal condition at 200°-300°C, the surface of the specimen is spalled by the stress accompanied by the expansion of t→m transformation. The spalled layers and the surfaces of the unspalled bulk specimen consist of almost m-phase (≈90vol%). From SEM observation on these specimens, large cracks occurred from the corner of the specimen by the stress concentration, and then they propagated parallelly to the surface of the specimen and caused the spalling. An Arrhenius plot of the reaction rate estimated from the degraded thickness (spalled plus remained transformed thickness) gives the activation energy of about 16-17kcal/mol regardless the pressure or hydrothermal treatments. This value which seems to be the activation energy for the diffusion of OH^- in Y-TZP lattice, suggests that the degradation of Y-TZP under hydrothermal conditions seems to be controlled by the OH^- diffusion.

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Raman spectra of MO₂-PO_5/2 (M=Si, Ge) glasses were measured and their relative intensities were corrected. Two models were assumed for glass structure, In model 1, PO₃=O and MO₄ tetrahedra are randomly connected. In model 2, a part of M⁴⁺ changes its coordination number from 4 to 6 with coordination of two oxygen atoms of P=O bonds. In model 2, the intensity of P=O stretching vibration depends on the amount of 6-coordinated M⁴⁺. The composition dependence of intensities of P=O stretching vibration proposed the following change in the glass structure. In GeO₂-PO_5/2 glasses which have no P=O stretching vibration, 6-coordinated Ge⁴⁺ is formed in model 2 and its content increases with increasing PO_5/2 content. The structure of SiO₂-PO_5/2 glasses is described by model 1 and the coordination number of Si⁴⁺ is 4 up to 20mol% PO_5/2 content. In the composition range containing more than 20mol% PO_5/2, 6-coordinated Si⁴⁺ is formed in model 2. The observed difference between these two glass systems is interpreted as follows. Six coordinated Ge⁴⁺ can be formed if six tetrahedra connected to GeO₆ include at least two PO₄, whereas SiO₆ octahedron needs connection of PO₄ tetrahedra at many or all vertices.

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To understand the fatigue behavior of sintered silicon nitride ceramics under cyclic stresses, the tension-compression fatigue tests were carried out on rod specimens of button head type. Alternating loads reduced the fatigue strength as compared with pulsating loads. The failure diagram was constructed to show the effects of mean stress and stress amplitude on the fatigue strength. A design methodology proposed for the metal fatigue is applicable to the sintered Si₃N₄ examined in this study. Microstructural observations suggest that the progress of cyclic fatigue of the sintered Si₃N₄ is caused by the formation of microcracks at the grain boundaries.

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The effect of substitution of Si₃N₄ for SiO₂ on the physical properties of calcium silicate glasses such as the density, glass transition temperature, Young's modulus and thermal expansivity, were studied in order to study the behavior of nitrogen introduced into glass structure. Furthermore, the infrared and O1s and N1s XPS spectra of the glasses were studied.
(1) The density, glass transition temperature and Young's modulus increased with increasing the amount of N substituted for O, and the thermal expansivity decreased. However, the increase or decrease in these physical properties was not proportional to the amount of N introduced.
(2) The results of the infrared and O1s and N1s XPS spectra indicate that the bridging nitrogens bonded with two or three silicon ions are formed in the oxynitride glasses for the small amounts of nitrogen. However, when the amount of nitrogen becomes large, the non-bridging nitrogens start appear and rupture the glass network. The nonlinear dependence of physical properties on the amount of N substituted for O can be interpreted by this structural change.

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Alumina-iron composite ceramics were fabricated by hot-pressing from well mixed alumina and iron powders at 1550°C and 300kgf/cm² for 30min. Sintered bodies with nearly theoretical density were obtained for addition of less than 20wt% Fe, but the relative density decreased gradually with increasing Fe content more than that. The alumina-iron composites showed more extensive grain growth than pure alumina, and there were many open spaces around iron grains generated by the thermal expansion mismatch. The fracture toughness increased with increasing Fe content, reaching 4MN/m^3/2 at 50wt% Fe. The Vickers hardness, on the other hand, decreased rapidly around 10wt% Fe addition. The specific wear rate measured on a sintered alumina disk increased with increasing Fe content, but was lower than 10^-7mm²/kgf at 40wt% Fe, which is comparable to that of dense silicon nitride ceramics. The cutting resistance was reduced significantly by Fe addition. Especially, the tangential resistance of Al₂O₃-30wt% Fe composite was lower than that of pure alumina by the factor of 10. The iron which existed near the surface of composite was removed in the first few minutes when treated in boiling H₂SO₄, but no subsequent weight loss was observed. The fracture strength of the composite decreased gradually up to 600°C, and then rapidly at higher temperature.

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Densification of high-purity zinc sulfide was studied by the normal sintering at 800°-1200°C for 2h and hot-pressing at 700°-1100°C under the pressure of 10-40 MPa for 1 to 4h. Zinc sulfide densified slightly in normal sintering and marked grain growth accompanied by a slight increase in density was found above 1000°C. High density was achieved by the hot-pressing between 800° and 1000°C and under the pressure of 40MPa. The grain size was approximately 1μm, and no significant grain growth was observed below 900°C. Above 1000°C, the grain growth became increasingly significant with increasing temperature. At 1100°C, high density was not attained; phase transformation and abnormal grain growth were responsible.

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Single crystals of boron-containing apatite (BAP) were grown by standard flux growth technique with excess B₂O₃ as flux. A mixture with the composition 35CaO-5P₂O₅-60B₂O₃ (wt%) was heated at 1200°C for 10 hours and then cooled at a rate of 8.3°C/h. Hexagonal prismatic crystals (0.3mm×0.3mm×11mm) were obtained. The chemical composition of BAP's was expressed as a solid solution in the system Ca₁₀(PO₄)₅BO₄-Ca_9.5(PO₄)₆BO₂. BAP with the composition Ca_9.64(P_5.73B_0.27O₂₄) (BO₂)_0.73 is trigonal, space group P3 with a=9.456 (1), c=6.905 (1) Å and Z=1. The structure was refined to R=0.050 and R_w=0.044 for 1257 independent reflections. The structure is apatitic in character but the B atom at (00 1/2 forms a linear O-B-O group.

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In of ceramics like zirconia, in which nonlinear type fracture is brought about by stress induced transformation, the mechanical properties are affected by the process zone around the stress field in front of crack. Recently, some reports on this point studied by XRD analysis and Raman technique have been published. This paper discusses the relationships between some mechanical properties and fracture behavior in Y-TZP. Test specimens of Y-TZP were prepared by sintering powder produced by the solution technique, and their mechanical properties were measured, and stress induced transformation on the fracture surface was analysed by Raman spectrascopy. The monoclinic phase ratio on the fracture surface was correlated with bending strength but not with critical stress intensity factor. A distinct difference was observed in the morphology of fracture surface between specimens with strengths higher and lower than 80kg/mm².

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The main object of this study is to examine the sintering behavior of pure materials in low pressure plasmas. Here, Mo, Al₂O₃, and Si₃N₄ were chosen as examples of metallic, ionic, and covalent materials. The compacts were heated in a radio frequency inductively coupled plasma under low pressure, N₂, H₂, Ar, and H₂+Ar. The effects of the powder type and the plasma conditions were examined on the phase transition, the microstructural change, the loss of weight, and the shrinkage. The Mo powder compact can be sintered to 94.5%, and Al₂O₃ of 0.1μm powder can be sintered rapidly within 60s to 96% of the theoretical density. Si₃N₄ was found to be very difficult to sinter macroscopically and no appreciable shrinkage took place at this stage. These experimental results show that the plasma-compact interaction plays an important role in the specimen heating.

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An eutectic melt in the system (Bi₂O₃)_0.85(Nb₂O₅)_0.15-6Bi₂O₃⋅SiO₂(Ref. 1) was unidirectionally solidified in double crucibles, in which a pin hall was made at the center of the bottom of the upper one and a seed crystal was placed at the center of the bottom of the lower one (Fig. 1). A temperature gradient of 100°C/cm and a solidification rate of 0.5mm/h were maintained during the solidification in a temperature gradient furnace having SiC heating elements at the top and a water-cooled copper jacket at the bottom. The obtained ingot showed a uniform structure throughout the ingot, in which fibrous crystals of δ-(Bi₂O₃)_0.85(Nb₂O₅)_0.15 3.8μm in diameter were embedded in parallel in a matrix of γ-6 Bi₂O₃⋅SiO₂ single crystal (Figs. 2 and 3). This structure was in contrast to that obtained with a single crucible (Ref. 1), in which orientation of the fibrous crystals varied depending on the location (Fig. 2b). A transverse thin section of the ingot obtained with the double crucibles showed a high optical transmission like an optical fiber array (Fig. 5). Then, this may be useful for applications such as screen of a cathode ray tube of high resolution.

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Ten kinds of commercial ceramic tools were eroded by SiC and Al₂O₃ abrasives with an average diameter of 500μm at 250-300m/s. These ten kinds of commercial ceramic tools were classified into four groups from matrices (Al₂O₃ or Si₃N₄) and additives present. The hardness of ceramic tool consisting of Al₂O₃ as the matrix and TiC as the main additive is 20-22GPa (at a 20kg load), and the fracture toughness is 5.3-6.4MPa·m^1/2. The erosive wear resistance of this type of Al₂O₃/TiC composites was better than that of other three groups of ceramic tools, hot-pressed Si₃N₄, high purity Al₂O₃ and SiC whisker reinforced Al₂O₃, for both SiC and Al₂O₃ abrasives. The erosion rate of the ceramic tools was in the order of 10^-3cm³/cm³ for SiC abrasive and 10^-4cm³/cm³ for Al₂O₃ abrasive. The difference in erosion rate was caused by different erosion mechanisms depending on whether the Vickers hardness ratio of the ceramic tool to the abrasive is larger or smaller than unity.

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A new system has been designed for the direct introduction of gas from the diffusion-annealing furnace into a mass-spectrometer. A variable leak valve was used as an interface between the furnace and mass-spectrometer. Using this apparatus, a large number of data were obtained about 100 times as many as those from batch analysis. Some test data of powder materials are presented and compared with those of a sintered material.

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The thermoelectric power, S, of ternary rere-earth zinc silicides RZnSi was measured. The absolute values of S increased linearly with temperature, and the value of -dS/dT for RZnSi decreased with increasing atomic number of rere-earth atom, Z. These results and the speculation on the basis of a free electron model indicated that the change in S and dS/dT with increasing Z of RZnSi was caused by the change in the concentration of conduction electrons due to the lanthanoid contraction.

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This investigation was carried out to elucidate the influence of oxidizing atmosphere in the annealing process for making thermistor. Starting sample was prepared by mixing the nitrates of Mn, Co, Ni with molar ratio of 3.0:1.9:1.1. After fired at 1400°C, the sample was cooled to room temperature in the furnace. The oxide thus obtained was annealed in different atmospheres at 310° and 370°C. Electric conductivity change during the annealing process was followed for 15 days in the atmospheres of argon, air and oxygen. Electric conductivies changed depending on the type of atmospheres. In the oxidizing atmospheres, such as air or oxygen, electric conductivities decreased markedly with increasing annealing time at 370°C, whereas no detectable change was observed in the atmosphere of argon. No significant changes in the thermistor constants, however, were observed during the annealing process. X-ray diffraction study was made on the samples annealed in the atmospheres of argon and air. All the samples consisted of rock salt, cubic spinel and tetragonal spinel structures. A remarkable increase in axial ratio, c/a, in the tetragonal spinel structure was observed with increasing annealing time, particularly in the atmosphere of air at 370°C. The change in axial ratio, c/a, in the tetragonal spinel structure seems to be related to the electric conductivity change, because, when c/a exceeded 1.1, significant changes in the electric conductivities were observed. It can be assumed that changes of axial ratio in the tetragonal spinel structure were attributed to the Jahn-Teller distortion which was induced by the increase in Mn³⁺ concentration in the octahedral site with increasing annealing time.

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Thermal analysis of superconducting YBa₂Cu₃O_x ceramics was studied by TG-DTA between 25° and 900°C. The weight loss due to release of structural oxygen was 1.5%, 1.3% and 2.0% in air, oxygen and nitrogen, respectively. The YBa₂Cu₃O_x ceramics absorbed oxygen rapidly around 330°C. Change of oxygen content of this compound was reversible under the cycle of heat treatment in oxygen containing atmospheres. The phase transition from orthorhombic to tetragonal structure occurred at 570°C in nitrogen, 620°C in air and 680°C in oxygen atmospheres.

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