Raman spectra have been measured for the potassium borophosphate glasses. The observed bands are assigned to six-membered borate rings, phosphate chain or network composed by O=PO_3/2 or KPO₃ units and six-membered borophosphate clusters incorporating [PO_4/2]⁺ or O=PO_3/2 units by taking the Raman bands characteristic of the borate and phosphate units in the literature as the reference. Crystalline BPO₄ type network is absent in the present glasses. The following four bands have been attributed to the borophosphate units; 1030cm^-1 to PO₂ with the P atom bonded to B, 720cm^-1 to the breathing vibration of six-membered B-O-P rings, 600 and 550cm^-1 to P-O-B bonds. The coexistence of the BO₃ and PO_2.5 have also been proposed.

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The effect of the measurement technique on the apparent fracture toughness, or K_IC value of a transparent polycrystalline MgAl₂O₄ spinel was investigated. Results from macronotched specimens are compared with those of microflaw techniques from room temperature to 1000°C. Contributions of the process zone wake in terms of grain bridging and interlocking frictional effects are qualitatively addressed and the effects of grain size are also discussed.

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To investigate the effect of grain size and temperature on the fracture energy (γ_eff) of polycrystalline alumina ceramics γ_eff of sintered pure alumina bodies having various grain sizes was measured by work of fracture test from room temberature to 1600°C. At room temperature, γ_eff of polycrystalline alumina increased and then decreased with increase in grain size of alumina, passing through a maximum at the grain size around 16μm. The values of γ_eff and its grain size dependence for polycrystalline alumina agreed well with the literature data obtained from work of fracture test. The grain size, which gives a maximum in the γ_eff values, shifted from 16 to 42μm at 1200°C. γ_eff of alumina bodies having grain size of 2μm showed no significant variations up to 1200°C, but increased extremely over 1400°C. γ_eff of alumina bodies having grain sizes of 16, 22 and 42μm passed through maxima at 1000° and 1200°C, and remarkable increases in γ_eff were observed at 1500° and 1600°C. On the other hand, γ_eff of an alumina body having grain size of 70μm was smaller than that of other bodies and decreased gradually up to 1500°C and increased at 1600°C.

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Combined tension/torsion and compression/torsion tests for sintered silicon nitride specimens were carried out at room temperature to investigate the fracture behavior of ceramics under multiaxial stress states. Tension, torsion and 4-point bending tests have been also carried out in order to estimate Weibull's two parameters for predicting the fracture stress under multiaxial loading. The maximum tensile principal stresses at fracture for combined tension/torsion and compression/torsion tests increased with increasing ratio τ(torsion)/σ(tension). The fracture stresses predicted from the data of uniaxial tests by Weibull statistical theory of uniaxial fracture and the statistical theory of multiaxial fracture for shear-insensitive cracks were in agreement with the experimental data. However, the fracture stresses predicted by the statistical theory of multiaxial fracture based on various fracture criteria for shear-sensitive cracks were lower than the experimental data. These results indicate that the actual flaws in the ceramic components are not shear-sensitive cracks. The statistical theory of multiaxial fracture which has a little contribution of shear stress to fracture can be used for designing components made of sintered silicon nitride.

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β-sialon, with z=0.5, was fabricated by hot-pressing of a spray dried mixture of α-Si₃N₄ powder and aluminumdydroxide aqueous solution prepared by hydrolysis and peptization of aluminum-iso-propoxide. Flexural strength, phase composition and microstructure of the sintered bodies have been investigated. Phases identzfied by XRD in the sintered body were β-sialon and O'Sialon. Hydrolization of Si₃N₄ during mixing with aluminumhydroxide solution gave an increaseing amount of O'sialon compared with a sample prepared without water i.e., aluminum-iso-propoxide dissolved in C₆H₁₄ solution. The microstructure study showed that β-sialon consisted of 0.5-2μm equiaxed grains and a small amount of 2-5μm plate-like grains which was assumed to be O'sialon. The room temperature flexural strength (3-point bending) was 119kg/mm². This value was slightly lower than that of β-sialon obtained/from aluminum-iso-propoxide solution. However it was remarkably higher than that of β-sialon obtained from Al₂O₃ powder mainly due to a finer and more homogeneous microstructure. The degradatiom of the strength as compared with β-sialon from aluminum-iso-propoxide solution has been explained by the existence of plate like grains which occurred due to a higher amount of oxgen from the hydrolysis of Si₃N₄.

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Effects of gas pressure on Ellingham diagrams are considered to evaluate the difference of sintering behavior of silicon nitride under normal, hot-press and encapsulated HIP sintering. Special attention was focussed on the stability of carbon impurities. The results are summarized as follows:
(1) Although exact internal pressures in capsules under HIP sintering are not possible to measure, the gas pressure is higher than hot-press sintering, if there are gas generation reactions. The minimum temperature of silicon carbide formation from carbon impurity in the HIP'ed silicon nitride increases with higher gas pressures. This can be explained by the free energy change of the reactions under high pressures, i.e. high pressure Ellingham diagrams proposed by the authors.
(2) The reaction, SiO₂+3C→SiC+2CO was observed in the normal sintered and hot-pressed silicon nitride. This reaction was limited in HIP sintering, because carbon becomes stable under high gas pressures.

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Pore radius and tortuosity of an alumina membrane were calculated from the flux through the membrane and liquid capillary rise rates of several solvents, and compared with the values obtained by convensional methods. Tortuosity value by this method agreed well with that obtained by the measurement of effective ionic conductivity of the alumina membrane. However, pore radius by this method was 1.17 times larger than that by the Hg intrusion method. This difference was explained by the pore geometry that is, pores in the alumina membrane are rectangle because the membrane was prepared by packing alunina particles. By the Hg intrusion method, measured pore radius corresponds to that of inscribed circles for rectangle alumina pores. On the other hand, measured value by the transport phenomena of liquids through membrane voids is equivalent to the radius of a circle of which area is comparable to the cross sectional area of a rectangle alumina pore. Therefore, geometrical coefficient which accounts for the discrepancy of pore shape from circle was derived by comparing the pore radius values by this method with those by Hg intrusion method.

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The nitridation of silicon powder with or without 5 volume percent iron oxides, Al₂O₃ and AlN, was studied by thermogravimetry under constant heating rate from room temperature to 1350°C. The activation energy of nitridation at the initial stage was estimated at 670kJ/mol by using Jander's diffusion model, and the initial nitridation layer of silicon particles was about 200Å thick. The starting temperature of nitridation dropped and the activation energy decreased by adding a small amount of iron oxides into silicon powder. Thus, iron oxides were effective as a catalyst. On the other hand, addition of aluminum compounds increased the activation energy. The activation energy is closely related to the crystal structure of the material to be nitrified. The material was entirely composed of α-Si₃N₄ single-phase when the activation energy was less than 460kJ/mol. Both α-and β-Si₃N₄ phase were observed when the activation energy was greater than this value.

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Composite porous glass membranes were prepared by formation of porous glass layer of about 100μm thick on base porous ceramics with pore diameter of about 1.5μm. The permeation rate of composite membrane obtained was about 14 times as large as the ordinary type of porous glass membrane and it was clear from the measurement of separation coefficient of hydrogen of hydrogen-nitrogen gas mixture that the membrane was defect-free. The conditions for obtaining defect-free membranes were as follows:
(1) The value of thermal expansion coefficient of mother glass baked on base ceramics was about 80-90% of that of base ceramics.
(2) The baking temperature was 780°-810°C.
(3) The composite membrane which was acid-treated was dried by the critical point drying method methanol.

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²⁹Si MAS NMR spectra were measured in SiO₂-PO_5/2 crystals and glasses. MAS NMR spectrum of SiP₂O₇ crystal indicated only one peak at about -215ppm, which was assigned to 6-coordinated Si⁴⁺. In the spectrum of Si₅O(PO₄)₆ crystal, two peaks were observed at about -215ppm and -120ppm. The latter was assigned to 4-coordinated Si⁴⁺. In 28mol% PO_5/2 72mol% SiO₂ glass, only the peak at about -120ppm was found and 4-coordinated Si⁴⁺ was present. The amount of 6-coordinated Si⁴⁺ was zero or very small. In 50mol% PO_5/2-50mol% SiO₂ glass, the MAS NMR spectrum indicated two peaks at about -120ppm and -215ppm. Both 4-coordinated and 6-coordinated Si⁴⁺ coexisted in this glass.

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Effects of hot isostatic pressing (HIP) conditions on the densification were studied for alumina powder compacts having various particle characteristics. HIP conditions examined are temperature, pressure and time. Powder characteristics were represented by particle size. The results were analyzed with the Ashby's model, and the mechanism of densification as well as the validity of the model was discussed. Alumina densified by the grain boundary diffusion mechanism in HIPing. The densification rate increased markedly with increasing temperature and pressure, and with decreasing particle size. The rates found were much lower than those predicted by the model for all conditions. The difference between the model and the experiment became increasingly significant with decreasing particle size of the powders and with increasing apparent density. The difference is approximately constant for each powder for the apparent density below 90%, but increased markedly with increasing apparent density over 90%. The disagreement between the model and the experiment was attributed to the uncertainty of grain boundary diffusion coefficients applied to the analysis, the agglomeration of powder particles and the grain growth occurring in the final stage of densification.

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Lead-based relaxor material, Pb(Zn, Nb, Fe, W)O₃ for multilayer ceramic capacitors was ground by ball-milling with partially stabilized zirconia balls of 1, 3 and 15mm in diameter in order to examine the effects of particle size on the sintering and dielectric properties. Particle size distribution, contamination from the balls and the residual strain of the powder were examined. The use of small zirconia balls in ball-milling was effective to grind the powder to submicronmeter. Average particle sizes of powders ball-milled for 128 hours using 1, 3, 15mmφ balls were 0.24, 0.35 and 0.68μm, respectively. The structural distortion of the ball-milled powders increased with decreasing particle size in contrast with little change in the lattice strain. The contamination from zirconia balls in ball-milling was examined with fluorescent X-ray analysis, and it was made clear that the ball-milled powders were free from the contamination. The average grain size of sintered ceramics from the fine powder with average particle size of 0.24μm was rather fine than that of sintered ceramics at the same temperature from 0.68μm powder. The densification of the fine powder was enhanced at lower firing temperature, and the dense dielectric ceramics were obtained at the firing temperature of 750°C which was lower by 100°C compared with the optimum firing temperature for the powders with average particle size of about 1μm. Relative permittivity of the fine grained sample fabricated from 0.24μm powder at 750°C was above 10⁴ at room temperature and less DC bias field and less temperature dependences compared to that of coarse grained sample fabricated from the usual powder.

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The packing fraction of ultrafine particles was estimated by computer simulation. In the simulation, it was assumed that particles, onec contacted with others on tentative places, keep the contact, and a function (Shake Off function) which selects either of expelling a particle from or fixing it to the tentative place was introduced. As a result of the simulation, the packing fractions by volume of cubic and spherical particles were 0.22-0.59 and 0.20-0.40, respectively. On the other hand, the observed values of the packing fraction of alumina particles in the fired compacts prepared by mixing alumina (mean value of diameters, 20nm) with a large quantity of forming agents and firing were in the range of the values obtained from the computer simulation.

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Investigation on amorphous ferrite in the system CaO-Bi₂O₃-Fe₂O₃ has been carried out. Large magnetization values were obtained near the compositions of the mixture of BiFeO₃ and CaFe₄O₇. Especially, an amorphous (CaO)₂₀(Bi₂O₃)₁₅(Fe₂O₃)₆₅ specimen has a magnetization value of about 17.8emu/g at 0K (10kOe) and Curie temperature of about 760K. ⁵⁷Fe Mössbauer absorption spectra indicate that this specimen is composed of two amorphous phases, antiferromagnetic phase and ferromagnetic phase. It seems that the data obtained in DTA and magnetic measurements are well explained by the simple ferrimagnetic-like magnetic structure model.

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Sinterability of non-stoichiometric calcium hydroxyapatite (Ca-HAP) prepared by the conventional solution reaction was studied, and microstructure and mechanical properties such as compressive strength, Vickers hardness, and fracture toughness of sintered bodies were examined. Sinterability and grain growth rate of Ca-HAP decreased with decreasing Ca/P ratio. Tricalcium phosphate (TCP) formed in the sintering gracess of the non-stoiohiometric Ca-HAP The amount and morphology of TCP were dependent on the Ca/P ratio. The non-stoichiometric Ca-HAP with Ca/P=1.655 heat-treated at 1100°C gave compressive strength and frapture toughness higher than those in literatures. The maximum compressive strength (mean value) and fracture toughness (mean value) were 10300kgf/cm² and 1.52MPa·m^1/2, respectively.

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Ten kinds of commercial ZrO₂ ceramics were eroded at 250-300m/s by SiC abrasive with an average diameter of 500μm. These ZrO₂ ceramics were classified into three groups; one is Y₂O₃-doped tetragonal ZrO₂ (TZP), another is the composite of Y₂O₃-doped tetragonal ZrO₂ and Al₂O₃, and the other is MgO-stabilized ZrO₂ including cubic ZrO₂ as the main crystal phase. Among these three groups, TZP showed the lowest erosion rate, 2.1-2.8×10^-3cm³/cm³, which is comparable to that of hot-pressed Si₃N₄. The excellent erosion resistance of TZP is explained by elevated fracture toughness due to the reorientation of tetragonal ZrO₂ domains by the impact stress of abrasive.

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Ultrafine SiC powders with average size of about 0.1μm were produced by arc discharge between silicon (positive) and carbon (negative) electrodes in about 50KPa argon containing 0.7KPa methane. The obtained powders were purified by removng silicon and carbon, and then compacted into cylinders 3mm in diameter and 3mm high. The cylinders were pressed at a pressure 6GPa at 1600°C for 10min. They sintered to almost full density with the grain size less than 1μm. Vickers hardness was 36.3GPa for one of the sintered samples and K_IC-value was 4.91MNm^-2/3, for other one.

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Fracture toughness (K_IC) of structural ceramics such as alumina, silicon nitride, silicon carbide was evaluated using a single edge precracked beam (SEPB) technique. An indentation crack or a sawed notch was introduced into the specimen as an origin for sharp precrack, followed by developing an atomically sharp pop-in crack from the crack or notch. The sharply precracked specimens were fractured by 3-point bending under a cross-head speed of 0.5mm/min at room temperature. The K_IC values obtained from each measurement showed a good repoducibility for alumina and silicon carbide. For silicon nitride, however, the values scattered a little, especially when a sharp pop-in crack was introduced from the indentation crack. The causes of the scattering were discussed on based the observation of inclined precrack front and deflected fracture surface.

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Mirror finishing of hot-pressed silicon nitride ceramics was studied by grinding using conventional abrasive wheels. In order to obtain mirror finished surface, it is necessary to grind at lower grinding pressure using a proper abrasive wheel of I-K grade. In this case, rubbing without cutting results in a large amount of residual stock and mirror finished supface free from thermal cracks. Then, in this method, the finishing surface of 0.04-0.02μm R_max was obtained for some kinds of fine ceramics.

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A dense composite of hydroxyapatite (HAp)-PSZ was obtained without decomposition of HAp to tri-calcium phosphate (TCP). The condition necessary for the sintering was a supply of water vapor stream to the atmosphere. It was also clarified that the solid-state reaction between HAp and ZrO₂ does not necessarily cause decomposition of the apatitic structure. Considering the thermal stability of partially dehydrated oxyhydroxyapatite, the effect of water vapor on the solid-state reaction between HAp and PSZ was discussed in relation to the decomposition of the apatitic structure in HAp-PSZ composites.

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The effect of substitution of Ge for Si in the system Na_1+3xZr₂(P_1-xSi_xO₄)₃ on the phase and electrical conductivity was investigated. The compositions x=0.17 and 1.0 gave rhombohedral structure below 1100°C, with the skifts of X-ray diffraction lines to lower diffraction angles as compared with NaZr₂P₃O₁₂ and Na₄Zr₂Si₃O₁₂, respectively. However, a difference in the diffraction patterns of Na₃Zr₂PGe₂O₁₂ and NASICON (Na₃Zr₂PSi₂O₁₂) was recognized. Arrhenius plots of σT for Na₃Zr₂PGe₂O₁₂ sintered at 1000°-1090°C broke in two straight lines indicating activation energies of 8.3-9.2 and 13.4-14.2koal/mol in high (500°-320°C) and low (320°-230°C) temperature regions respectively. The system Na_1+3xZr₂(P_1-xGe_xO₄)₃ showed lower electrical conductivity and higher activation energy than the system Na_1+3xZr₂(P_1-xSi_xO₄)₃.

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