The crack growth resistance (R-curve) behavior of non-phase-transforming polycrystalline ceramic materials is reviewed. Experimental and theoretical results are presented and discussed. Its importance to the microstructural design of polycrystalline ceramics is discussed and the potential application to structural design with ceramic materials is noted. The revelation that the increased toughening with increasing crack length is due to phenomena in the following wake region of an extending crack and not in the frontal process zone is emphasized.

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Effects of quenching and annealing on the crystal structure of single phase superconducting oxide ceramics, Y₁Ba₂Cu₃O_7-xF_y (y=0.4), were studied by X-ray powder diffraction analysis. X-ray analysis revealed that the orthorhombic phase of Y₁Ba₂Cu₃O_7-xF_y was formed by thermal quenching from 900°C to room temperature, in contrast to Y₁Ba₂Cu₃O_7-x in which the tetragonal phase was frozen by such quenching. The lattice-parameter ratio b/a (a<b) in the orthorhombic phase, which showed superconductivity at low temperature, increased on fluorine doping into Y₁Ba₂Cu₃O_7-x.

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The internal friction, dynamic modulus of elastically (G′), D. C. conductivity and dielectric properties in the glasses of 30 R₂O-xB₂O₃-(70-x)P₂O₅ (R=Li, Na, K: x=0-70mol%) system were measured. The temperature dependence of D. C. conductivity in 30 R₂O-xB₂O₃-(70-x)P₂O₅ system was described by the Rasch-Hinrichsen equation: σ=σ₀exp(-ΔH_dc/RT). The D. C. conductivity curve showed a maximum with a minimum activation energy at x=35mol% when the same alkali oxide is contained. The D. C. conductivity was largest for Li followed by Na and then by K for a mixed borate content. The activation energy was smallest for K followed by Na and Li. The frequency at which the peak of dielectric loss appeared was lowest and increased for Na and K in the order started. The activation energy of dielectric loss was nearly equal to that of the D. C. conductivity. One or two internal friction peaks were obserbed in the temperature range from -100° to 350°C at about 1Hz. The peak at lower temperature was due to the motion of alkali ions, because the activation and the peak temperature changed with x in a way similar to those in the D. C. conductivity and dielectric loss. On the other hand, the peak at higher temperature was due to migration of non-bridging oxygen. The dynamic modulus of elasticity (G′) on internal friction was calculated by considering the shape factor. G′s in glasses of 30 Na₂O-xB₂O₃-(70-x)P₂O₅ were 1.5 to 4.0GPa in the range x=0 to 70mol%. G′s showed a maximum at x=35mol%. It was considered that BPO₄ unit analogous to SiO₂ were produced in the glass network.

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Fatigue behavior of tetragonal zirconia polycrystals (TZP) containing 2mol% Y₂O₃ with an average grain size of 0.46μm was studied by measuring the failure time t_f as a function of applied stress σ from 525 to 710MPa at 250°C (static fatigue technique). A linear relationship was observed between log σ and log t_f for applied stress over 560MPa. The crack growth parameter N obtained from the slope was 10.8, smaller than the N value (21.9) from dynamic fatigue. However, the log σ and log t_f relationship under 560MPa deviated from the linear relationship and showed a tendency corresponding to fatigue limit. The monoclinic zirconia contents on the fracture surface increased with increasing holding time and reached the maximum value (72%) in 9 hours. The maximum value was kept up to 29 hours. However, if failure time was longer than 29 hours, the monoclinic zirconia content decreased with increasing failure time. Fatigue fracture surface increased with increasing failure time.

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Significant solubility of a sintered hydroxyapatite (HAp) tablet was observed by soaking in aqueous suspension with strongly acidic ion exchange resin, H-form (H-R), compared with the conventional chemolysis reagent for renal calculi. The pH value after soaking was nearly 2 for self-exhausted H₃PO₄ by the ion exchange reaction. The dissolution tendency of an HAp tablet depended on the pH value of H₃PO₄ solution used. From these facts, the dissolution mechanism of HAp in aqueous suspension with H-R was studied for various suspensions with 0-3.0g of H-R and 0-600mg of HAp powders. Analysis of Ca²⁺ and PO₄^3- by ion chromatography and measurements of pH and specific conductivity were performed for the filtrate, and Ca/PO₄ molar ratio values thus obtained were discussed from the view point of formation of soluble Ca(H₂PO₄)₂. Variations in these parameters can be expressed as contour maps on the plane of HAp (mg) and H-R (g) axes. In conclusion, the dissolution of HAp proceeds by the cation exchange reaction with H-R (Eq. 1) followed by the successive exchange reaction in the presence of sufficient of H-R (Eq. 2).
Ca₁₀(PO₄)₆(OH)₂+14(H-R)→3Ca(H₂PO₄)₂+7Ca-R₂+2H₂O (1) Ca(H₂PO₄)₂+2(H-R)→Ca-R₂+2H₃PO₄ (2)
Furthermore, H₃PO₄ formed by Eq. (2) contributes to successive dissolution of HAp to enhance the solubility.

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The purpose of the present investigation was to establish the production technique of porous compacts of ceramics containing fine pores. Alumina powders of various particle sizes blended with solvent were pressed under 300kg/cm² and then fired at 1000°-1375°C, and the characteristics of the obtained compacts were measured. Combination of ultrafine alumina having primary particle diameter of 20nm with liquid paraffin (viscosity at 40°C was 14 cSt, quantity was 3.5 times of the true volume of alumina) gave highly porous compacts containing fine pores. However the ultrafine alumina powder had to be pretreated by water to prevent cracking in firing. Porosity and specific surface area were 78% and 53m²/g, respectively, for the compact fired at 1000°C, and 66% and 6m²/g for that at 1350°C. Pore diameter in the compacts fired at 1000° and 1350°C were less than 12μm and distributed having peaks at 0.03 and 0.26μm, respectively.

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β-Tricalcium phosphate (β-TCP)-Al₂O₃-SiO₂ composite ceramics were investigated for developing high strength β-TCP ceramics as a bioceramic material. Bending strength of the sintered β-TCP admixed with 2wt% Al₂O₃ and 6wt% SiO₂ was 2760kgf/cm². Addition of either Al₂O₃ or SiO₃ was not effective for improving the strength. When both Al₂O₃ and SiO₂ were added to β-TCP in the process of firing, the following reactions proceeded; (1) formation of a liquid phase, (2) formation of AlPO₄ in the liquid phase, (3) formation of a solid solution of AlPO₄, and (4) inhibition of the phase transformation of β-TCP into α-TCP as a result of formation of the solid solution.

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Amorphous silicon nitride powder (particle size: 0.04μm) obtained by the vapor phase reaction of Si(CH₃)₄-NH₃ system was compacted into pellet and heat-treated in N₂ to investigate the crystallization behavior. The amorphous powder crystallized to 100% α-Si₃N₄ by the heat treatment for 1h at 1550°C. The equiaxed crystalline particles having the size of 1-2μm were obtained when powder was compacted, whereas acicular particles were produced when powder was not compacted. When Si₃N₄ powder was used as powder bed which covered pellet, the crystalline particles grew extensively and the crystallinity increased with a decrease in the packing fraction of particles in pellet. The heat-treated powder with a low crystallinity consisted of fine amorphous particles and coarse crystalline particles. The crystallization seemed to proceed by a vapor phase growth mechanism, in which SiO vapor takes part as silicon carrier between amorphous particles and crystalline ones. When BN powder was used as powder bed, the crystallization and grain growth were retarded, and the crystal phase contained a small amount of β-Si₃N₄. Crystallization inhibitor, e. g. boron oxide, may have penetrated into pellet from BN powder.

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Mechanical strengths of porous BaTiO₃ thick films were measured after dielectric breakdown, the bending stress was applied to the position where the electric field had been applied. Comparison of the Weibull plots of mechanical strength between electrically failed and unfailed (as-sintered) specimens has shown that no damage due to dielectric breakdown occurred and that the poling process naturally involved in the dielectric strength measurement increased the mechanical strength. Mechanical strength before dielectric breakdown was estimated by taking into account this strengthening effect which depended on the poling voltage, time and temperature. A clear correlation between mechanical and dielectric strengths was obtained with the correlation coefficient of 0.73.

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PbTiO₃ was deposited on a (110) sapphire substrate by chemical vapor deposition using PbO and titanium tetra-i-propoxide (Ti[OCH(CH₃)₂]₄: TTIP). PbO and TTIP vapors generated at 1100°-1270°C and 64°-174°C respectively were transported to a substrate with carrier gases of Ar (350ml/min) and O₂ (350ml/min). One-phase PbTiO₃ was obtained at substrate temperatures (T_s) from 600° to 1150°C. Morphology of PbTiO₃ formed on the substrate was fine particle (T_s=600°-800°C), large particle (800°-1100°C) and platelet (1100°-1150°C). Good adhesion was observed between the deposit and the substrate above T_s=800°C. The platelets had crystalline preferred orientation. The crystallographic plane parallel to substrate changed from (111) to (100) and (001) with increasing TTIP evaporation temperature.

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A process for reduction and simultaneous sintering in air was developed by a laser beam irradiation method, and VO₂ films were prepared from V₂O₅ printed on alumina substreates. Thick V₂O₅ films 40μm thick screen-printed on alumina substrates were irradiated by a ruby laser beam for 2ms in air at 350°C. The energy density of the beam was varied from 0 to 26J·cm^-2. X-ray analysis and measurement of the electrical resistance were carried out at various temperatures including the phase transformation temperature. The change of film thickness by the irradiation was measured also. Irradiation energy densities lower than 9J·cm^-2 caused only the sintering of V₂O₅ films. However, the reduction of V₂O₅ into lower oxides took place at the energy densities higher than 9J·cm^-2. By 9J·cm^-2 irradiation, a mixture of V₃O₇ and VO₂ was obtained. Between 10 and 26J·cm^-2, only VO₂ was obtained. In the latter case, concentration ratio of VO₂ to residual V₂O₅ in a specimen was estimated to be about 1:2. VO₂ crystals thus obtained had a tendency to orient with their [001]_r axes parallel to the substrate surface, where the suffix “r” indicates the axes for the rutile-type lattice. The logarithmic electrical resistance of specimens irradiated with 26J·cm^-2 beam decreased by a factor of 2.1 above the critical temperature. After 300 heat cycles between 40° and 100°C, the logarithmic resistance ratio decreased to 1.1. The lattice parameters and the unit volume were determined by X-ray analysis.

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A piezoelectric ceramic mechanical damper with a controllable damping factor has been developed. Mechanical vibration energy is transformed through the piezoelectric effect into electrical energy which is dissipated through an external resistance. A significant variation in damping factor is realized when the external resistance is changed.

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A test technique for loading the arbitrary stress and a method for strength evaluation were studied to develop a reliability testing method. (1) The test technique for loading arbitrary stress was developed by using thermal stress. (2) The thermal stress reached a maximum immediatly after cooling, and then decreased monotonically. (3) The maximum thermal stress increased with an increase of both temperature and thickness of specimen. (4) The strength of brittle materials was evaluated by using a relationship between temperature and the maximum stress.

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Several measurement techniques were investigated on the setting expansion of a phosphate-bonded investment for lost-wax casting. Measuring the vertical expansion of a cylindrical investment molded in a vessel which was internally lined with an appropriate buffer material, gave a high expansion value. The friction or restriction by the vessel wall accompanied by the progress of the expansion, influenced the expansion value. In the case of measuring the expansion with a differential transformer, an expansion suppressing effect was generated by the load from the sliding-tip of the differential transformer. However, the load was reduced by modification of the differential transformer, which has enabled us to obtain values nearly equal to those by a non-contact type LASER displacement measuring apparatus.

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A new combination of α-Ca₃(PO₄)₂(TCP) and CaHPO₄⋅2H₂O (DCPD), each of which alone had a low or no hydraulicity, was proposed and investigated on its hydraulic properties. This combination showed a high hydraulicity probably due to the complementarity that the hydrolysis of TCP to octacalcium phosphate (OCP) was accelerated by the coexistence of DCPD and vice versa. Setting times were 9-30 min and reaction products were OCP only in the range of 1.20 to 1.47 in the mixing molar ratio Ca/P. Hardened bodies soaked in 0.9% NaCl solution at 37°C for 1 day had a porosity of 49±3% and a wet compressive strength of 14-19MPa, in comparison with 52±4% and 6-11MPa for a Ca₄(PO₄)₂O-DCPD combination and 66±2% and ca. 2MPa for a DCPD-CaCO₃ combination.

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Cr-containing compounds with crystal structures similar to AACH (Ammonium Aluminum Carbonate Hydroxide) were synthesized. Synthesized compositions were Al/(Al+Cr) (atomic ratio)=1, 0.5 and 0. These compounds were examined by infrared spectroscopy and X-ray diffractometry. Infrared absorption bands in the lattice vibration region shifted to the lower wave number direction and X-ray diffraction peaks shifted to the lower angle direction with increasing Cr content. Al atoms in AACH were considered to be substituted by Cr atoms. The compound with the composition Al/(Al+Cr)=0.5 was considered to be a solid solution of Al and Cr compounds. The Formation process of α-(Al₂O₃-Cr₂O₃) solid solutions from Al/(Al+Cr)=0.5 compound was also investigated. The samples heat-treated below 500°C were considered to be γ-(Al₂O₃-Cr₂O₃) solid solutions. A part of chromia crystallized as α-Cr₂O₃ about at 600°C. The γ-(Al₂O₃-Cr₂O₃) solid solution remained up to 1100°C and transformed to α-(Al₂O₃-Cr₂O₃) solid solution containing about 60mol% Al₂O₃ above 1100°C. The final α-(Al₂O₃-Cr₂O₃) solid solution was formed below 1300°C.

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