Carbothermal reduction behavior of a saponite/acriflavine complex in various atmospheres was examined and characterized by comparing with that of a saponite/carbon black mixture and raw saponite. There was no substantial difference in the reduction behavior between the complex and mixture when compared at the equal carbon contents (3.4 and 10.4%). It is because of the analogous crystalline state form in both samples before the carbothermal reduction occurs at 1673K. The reduction of carbon-containing samples, regardless of the complex and the mixture, was inhibited under CO atmosphere, and fine oxide spheres were obtained at 1873K.

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A new compound WAlB has been prepared using α-WB single crystals as a starting material and Al metal as a flux in argon atmosphere, and the optimum conditions for obtaining the compound in a pure phase were examined. A pure WAlB phase was obtained by heating a mixture of α-WB (0.66wt%) and Al at 1500°C for 10h. The crystal is orthorhombic with a space group either Cmcm, C2cm or Cmc2₁, and grows along ‹001› directions. It has lattice constants, a=3.205 (1), b=13.947 (1), c=3.108 (1)Å and a density, D_obs=10.61±0.04g/cm³. The oxidation of the compound in air proceeded above 440°C, and produced WO₃, Al₂(WO₄)₃ and Al₁₈B₄O₃.

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A new diffusion-couple method was developed to determine the solubility of MgO in Al₂O₃. The solubility was determined by electron probe microanalysis. The solubilities determined in air using a diffusion-couple of a single crystal and a large grain-sized polycrystal are approximately 55 and 95 wt ppm at 1973 and 2073K, respectively, much smaller than those previously determined by Roy and Coble. The cause of the large difference is attributed to the difference in the physical states of the samples. While single crystals and large grain-sized polycrystals were used in this work, powder was used in the previous work. When 400wt ppm MgO-doped polycrystalline Al₂O₃ was annealed in air for 2.5d at 2073K, second phase particles of spinel precipitated at grain boundaries, especially at triple grain boundaries.

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The fatigue behavior of 2 and 4mol% Y₂O₃-containing tetragonal zirconia polycrystals (Y-TZP) was studied by measuring their fracture strength σ_f as a function of stressing rate σ (dynamic fatigue technique). The average grain size of 2mol% Y₂O₃-containing tetragonal zirconia polycrystals (Z2Y) was 1.0-1.5μm, while Z4Y was composed of 2.0-2.5μm grains in the most part and above 3μm grains in the other part. Stress-deflection relationship of Z2Y at 20°C and Z4Y at 20° and 250°C showed elastic behavior prior to failure. Stress-deflection relationship of Z2Y at 250°C showed elastic behavior at the stressing rate over 3.02MPa/s, too. On the other hand, stress-deflection relationship of 0.301MPa/s (crosshead speed 0.005mm/min) showed inelastic behavior. The logσ_f-logσ relationships of Z2Y at 20° and 250°C were linear. Their crack growth parameter N's were 67.3 at 20° and 8.7 at 250°C. The logσ_f-logσ relationship of Z4Y at 20°C was linear, too. The N was 45.3. On the other hand, the fracture strength of Z4Y at 250°C increased below the stressing rate of 3.02MPa/s and kept a constant value over 3.02MPa/s, if stressing rate increased. The N value obtained from the linear relationship below 3.02MPa/s was 4.7. The fracture surface of Z2Y and Z4Y at 250°C tested at lower stressing rates showed fatigue fracture surface in the vicinity of the tensile surface side. The area of the fatigue fracture surface in Z2Y at stressing rate of 3.01MPa/s and in Z4Y at 0.302MPa/s occupied about one-fourth and one-half the fracture surface, respectively. Many cracks were observed on the tensile surface of Z2Y which showed inelastic behavior. The fracture surface of those specimens showed larger fatigue fracture surface than the specimens which showed the elastic behavior.

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An overcut fly-milling test with inclined workpiece was performed to accurately evaluate the cutting and wear characteristics of diamond and CBN grains, Namely, a quantitative evaluation of the chipping and tip wear of a single grain was made by tracing across the grooves with a stylus instrument. The milling experiment was carried out on a surface grinder, in dry, at cutting speeds 12.7 and 38.0m/s, and feeds 1.3 and 4.0m/min. The work materials used were hardened SUJ 2 steel, P 20 carbide, alumina, Si₃N₄, and silicon. The test grains were natural diamond, CBN, green SiC, and fused alumina, where grit size was #12 with an exception of CBN grain (#14-20). The CBN grain had the most high resistance to chipping and attritious wear for cutting SUJ 2 steel. However, the CBN grain as well as A and GC grains could not cut the other work materials due to grain fracture. The high chipping probability of the diamond grains was found on a Si₃N₄ ceramic. Also, the most fine chipping appeared on this work material. The attritious wear of the diamond grain was most remarkable on the P20 carbide.

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Void size dependency of the fracture strength of silicon nitride ceramics was studied to develop a failure model from a void. Fracture strength of silicon nitride ceramics including spherical voids generally decreased with increasing void size. A model of a spherical void with a circumferential crack was applied to estimate the crack extension. The length of the circumferential crack was calculated to be about 30μm, which corresponded to 10-15 times of the average grain diameter. Thus, it was assumed that the microcrack extension from a void occurred during loading before the maximum load was reached. Considering the transition of the fracture toughness from single-crystal to polycrystalline, it was concluded that the critical crach extension from the void was attributed to the dependence of the fracture toughness on crack size/grain size ratio.

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The influence of calcium ion on the initial alkali corrosion process of zirconia containing glass was investigated. Alkali-resistant glass fiber which contains about 15wt% zirconia was immersed in an alkali solution of pH 12.6 containing calcium ion ranging from 0 to 0.74mg/ml at 65°C. The amounts of Si dissolved, depth profiles of atomic ratios at near surface region by XPS analysis and morphology of glass surface by SEM varied with calcium ion concentration, immersion time and acid treatment. These changes showed that reaction process in the low calcium ion concentration region was different from that in the high concentration region. In the low concentration region, Si was dissolved and Zr-rich surface region was formed as in the case of NaOH immersion; however, surface reaction layer was formed by deposited Ca and decreased the reaction rate without showing any surface morphological change. In the high concentration region, calcium was deposited on surface despite little Zr-rich region formation. Thereafter the precipitates containing calcium began to encrust the surface reaction layer on the glass intermittently and this layer was corroded from the near site of these deposits. The concentration dividing these two regions was about 0.1mg/ml in case that surface area of the glass to soaking liquid volume ratio was about 5.75cm^-1. Reaction between zirconia containing glass and cement extract solution was considered to be determined by calcium ion concentration per unit glass surface area. The effect of other ion such as sodium or potassium was not observed under these experimental conditions.

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An aqueous solution of aluminum sulfate containing ultrafine ZrO₂ particles was dehydrated at 300°C to prepare the starting material of ZrO₂-Al₂O₃ composite. The effects of ZrO₂ additive on the decomposition of anhydrous sulfate into η-Al₂O₃, on the η→α phase transformation and on the sinterability of produced ZrO₂-Al₂O₃ composite powder were studied. The apparent crystallite size of the anhydrous sulfate decreased with increasing ZrO₂ content from 42nm (no additive) to 18nm (20vol% ZrO₂). The composite oxide powder, in which aggregated particle (50-100nm in diameter) of tetragonal ZrO₂ dispersed in the secondary grains of η-Al₂O₃, was obtained by decomposing the anhydrous sulfate. In the composite powder containing 20vol% ZrO₂, α-Al₂O₃ was found above 1100°C, while it formed above 1200°C for the single component Al₂O₃ powder. The grain growth of Al₂O₃ was prevented by ZrO₂ particles dispersed in the η-Al₂O₃ grains; that is, the primary particle size of Al₂O₃ decreased with increasing ZrO₂ content from 120nm (no additive) to 60nm (20vol% ZrO₂) after calcination at 1250°C for 1h. The composite powders had very low green densities and they were difficult to sinter. But ball-milling of the composite powders yielded high densities up to 94% for 10vol% ZrO₂ bodies fired at 1600°C for 1h in air. The ZrO₂ particles were located at the boundary of Al₂O₃, and the grain size of Al₂O₃ decreased from 3.0μm (no additive) to 1.2μm (10vol% ZrO₂) as the content of ZrO₂ increased.

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The Ge EXAFS (extended X-ray absorption fine structure) above its K absorption edge was measured for GeO₂-P₂O₅ glasses containing up to 49mol% PO_5/2 (here, chemical formula is defined as PO_5/2). The Ge-O distance was determined to be 1.72-1.76Å by the curve fitting method. It was shown that a part of Ge atoms changes their coordination number from 4 to 6 on introducing P₂O₅ into GeO₂ glass. The fraction of six-coordinated Ge atoms (N₆) was estimated from the Ge-O distances obtained by EXAFS analysis and the result agreed with the value of N₆ estimated from molar volume using partial molar volumes of V_p=24.20, V_Ge(4)=28.71 and V_Ge(6)=19.60cm³. N₆ approximately followed a formula N₆=x/2(1-x), where x is the molar fraction of PO_5/2.

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The monoclinic to tetragonal transformation in ZrO₂ at lower temperatures in ultrafine particles contacting with stabilizers was studied using several powders prepared by hydrolysis of ZrOCl₂ at 97°-200°C and preheat-treated before adding of stabilizers. ZrO₂ particles in the powders were aggregates less than 1000Å of primary particles of 30-50Å. The powders, dried under an IR lamp or preheat-treated at 150°-500°C, were mixed with oxides, nitrates or chlorides of Mg, Ca and Y, and heat treated at various temperatures. Identification and determination of monoclinic and tetragonal ZrO₂ were carried out by high temperature and room temperature XRD. Tetragonal ZrO₂ was detected even at 300°C for dried powders and its amount increased with increasing heat treatment temperatures. Preheat treatments without the stabilizers above 150°C resulted in the powders less active in the transformation. The preheat treatments at 150°-400°C decreased the water content and interplanar distance d₁₁₁ of monoclinic crystal, whereas they did not change specific surface area. Additives other than the stabilizers were not effective for the transformation. The transformation at low temperatures would be due to the large surface energy effect and free energy change by alloying with stabilizers. The surface energy effect is considered to stabilize the tetragonal form at low temperatures when it is alloyed with even a small amount of stabilizers. The alloying at such low temperatures as 300°C would be effected due to large surface area of the ZrO₂ powder, existence of H₂O and OH in the crystal and its lattice expansion.

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TTT diagram is necessary in glass forming systems to understand various phenomena such as phase separation and crystallization in supercooled liquid. A hot-thermocouple technique to establish the TTT diagram of glass forming systems has been proposed, which enables heating, temperature measurement, DTA and observation the state of the sample. Some TTT diagrams in the SrO-GeO₂ system have been determined by this method. In this system phase separation of nucleation-growth type was observed at high temperature in supercooled state. From the TTT diagram various cooling conditions can be determined for obtaining transparent glass and phase separated glasses of nucleation-growth, spinodal decomposition and crystallization types. It is concluded that the TTT diagram is important to develop “new glassy materials”.

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The purpose of this work is to study the effect of grain morphology in sintered Si₃N₄ on the leaching behavior under hydrothermal conditions. The pressureless-sintered Si₃N₄-Y₂O₃/Al₂O₃ specimens were produced using two kinds of commercial grade Si₃N₄ powders, i.e., prepared by the imide-decomposition method (specimen-A) and the silicon-nitridation method (specimen-B). Differences in microstructures were observed for sintered specimens from these Si₃N₄ starting powders, i.e., specimen-A resulted in a finer microstructure than specimen-B. Leaching test was carried out using an autoclave under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 days. The two specimens showed the similar trend of weight loss in leaching test, but larger weight loss was measured in specimen-B in the whole leaching time. A parabolic plot of weight loss suggested that the leaching mechanism consisted of two stages. SEM observation revealed that the both leached layers consisted of porous layer at the first stage and flakes on it at the second stage. The porous layer for specimen-A was finer than that for specimen-B and the traces of machining grooves was still visible on both porous layers. The results of this experiment showed that the leaching weight loss of sintered Si₃N₄ under hydrothermal conditions and the microstructures of the leached layer depended remarkably on the microstructural grain morphology of the sintered body generated by the starting powders and also on its mechanical history by grinding.

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The homogeneous precipitation method using urea was applied to the synthesis of fine particles of hydrated Al₂O₃ and Al₂O₃-coated Cr₂O₃ composite powders from aqueous solutions of Al₂(SO₄)₃ as well as Al(NO₃)₃. Hydrated Al₂O₃ particles from Al₂(SO₄)₃ solution were spherical having average particle size of 0.6-2.7μm for the initial Al³⁺ concentrations of 0.006-0.072M/l. Change of these products by heat-treatment was examined by powder X-ray diffraction measurement and DTA. It was found that those from the solutions with [Al³⁺]≤0.036M/l were the coprecipitate of amorphous hydrated Al₂O₃ and hydrated aluminum sulfate, and those from [Al³⁺]≥0.036M/l contained basic aluminum sulfate too. By heating at 1200°C for 1h, hydrated Al₂O₃ from Al₂(SO₄)₃ was transformed to α-Al₂O₃ without changing their original shape. Hydrated Al₂O₃ particles from Al(NO₃)₃ solution could be prepared by adding (NH₄)₂SO₄, and their average particle size decreased down to about 0.3μm. Hydrated Al₂O₃-coated Cr₂O₃ composite powders were prepared from both solutions of Al₂(SO₄)₃ and Al(NO₃)₃, and heat-treatment at 1200°C for 1h converted them to α-Al₂O₃-coated Cr₂O₃ composite powders.

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Bending strength, hardness, thermal expansion coefficient, fracture toughness and weight gain (1300°C, 100h in air) of the β-sialon and β-sialon-50wt% SiC composite hot pressed at 1850°C and annealed at 1900° and 2000°C were measured.
(1) The strength and hardness of β-sialon and β-sialon-50wt% SiC composite decrease with increase in annealing temperature.
(2) Fracture toughness of β-sialon and β-sialon-50wt% SiC composite is about 3.0MNm^-3/2 and 4.3MNm^-3/2 respectively. They are independent of annealing temperature.
(3) Thermal expansion coefficient of β-sialon as hot-pressed and annealed at 1900° and 2000°C is 2.4-2.5×10^-6°C^-1 That of β-sialon-50wt% SiC composite as hot-pressed and annealed at 1900°C is 3.0×10^-6°C^-1 and annealed at 2000°C is 3.5×10^-6°C^-1.
(4) Weight gain of both β-sialon and β-sialon-50wt% SiC oxidized at 1300°C for 100h is nearly zero.

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A high yield of aluminum alloys was difficult to achieve with a blast furnace, because both heating samples and reducing samples were done in the same chamber. In this report, we achieved a high yield of Al-Fe alloys, 70wt%, by carbothermic reduction of Al₂O₃-Fe₂O₃-C samples using a new indirect heating method. The method for preparing the sample to be reduced was based on the reduction mechanism of alumina. The sample was prepared by mixing graphite powders (0.3-0.5mm) coated with fine α-Fe₂O₃ powders (1μm) and α-Al₂O₃ powders (20-80μm) and subsequent compaction.

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Hydroxyapatite powders containing coprecipitated tricalcium phosphate in an arbitrary ratio could be synthesized by mixing solutions of calcium nitrate and diammonium hydrogen phosphate at a definite reaction temperature and aging temperature. Effect of tricalcium phosphate addition on the bending strength of sintered hydroxyapatite was investigated using the synthesized hydroxyapatite powder. The bending strength of the sintered hydroxyapatite containing 17mol% tricalcium phosphate was 1910kgf/cm², equivalent to the value of about 25% higher than that of the sintered bodies of pure hydroxyapatite. The crystal phase of the polycrystalline body consisted of hydroxyapatite and α-tricalcium phosphate.

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Hot-pressed silicon nitride test bars were oxidized in air flow at 1200°C for 480h. The observations by composition and topography image of SEM indicate that cristobalite crystals of 1-4μm are formed (appears as black spots) and cracks run in all directions all over the oxidized surface, and Y₂O₃⋅2SiO₂ crystals are clearly convex and the SEM image of cristobalites indicate that they are concave to the surface and this aspect is correspond to the COMPO image. The concentration of Al in the glass phase on the grain boundary is presumed to be high from the characteristic X-ray analysis. EDS analysis showed that a large amount of SiO₂ and a small amount of alkali were found in the cristobalite phase and a large amount of Fe₂O₃, CaO and K₂O are dissolved in the glass phase.

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Silicon nitride with a small quantity (0.1, 0.3 and 1wt%) of BeAl₂O₃ was sintered by HIP. Properties of sintered bodies were studied through measurement of bulk density, 4-point bending test and so forth. The bulk density of the sintered body containing 0.3wt% BeAl₂O₃ was almost theoretical when sintered above 1900°C at an applied pressure of 200MPa for 1.5h. Strength of Si₃N₄ containing 1wt% BeAl₂O₃ did not drop at all up to 1200°C. For less than 0.3wt% addition, a rise of strength was measured at high temperature (1200°C).

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