Showing papers in "Journal of the Ceramic Society of Japan in 1991"
TL;DR: In this paper, intergranular nanocomposites were found to have two to five times higher toughness and strength at room temperature than those of monolithic materials, and the hardness, toughness, strength and fracture resistance for creep and fatigue at high temperatures as well as the thermal shock fracture resistance were also strongly improved for these composites.
Abstract: Ceramic nanocomposites can be divided into three categories: intergranular nanocomposite, intergranular nanocomposite and nano/nano composite. The intra- and intergranular nanocomposites were found to show the two to five times higher toughness and strength at room temperature than those of monolithic materials. The hardness, toughness, strength and fracture resistance for creep and fatigue at high temperatures as well as the thermal shock fracture resistance were also strongly improved for these composites. On the other hand, the new function such as machinability and superplasticity was observed for the nano/nano composites. The fabrication processes of these nanocomposites by sintering methods, micro and nanostructure observations, improvements of mechanical properties were reviewed and the roles of the nano-size dispersoids were discussed. Finally the new approach on structural materials design will be given.
1,218 citations
TL;DR: In this paper, the authors review what is known about the structures and optical properties of point defects in silica glass and other amorphous forms of SiO2 using electron spin resonance (ESR) spectrometry.
Abstract: This paper reviews what is known about the structures and optical properties of point defects in silica glass and other amorphous forms of SiO2. The available structural information derives mainly from the results of electron spin resonance (ESR) spectrometry-a method which is directly applicable only to the subclass of defects which are paramagnetic. The intrinsic paramagnetic centers so far identified by ESR include E' centers (≡Si·), nonbridging-oxygen hole centers (≡Si-O·), peroxy radicals (≡Si-O-O·), and self-trapped holes. Examples of intrinsic diamagnetic defects believed to occur in silica in include neutral oxygen vacancies (≡Si-Si≡), two-coordinated silicone (O-Si-O-), and peroxy linkages (≡Si-O-O-Si≡). The most common extrinsic defects are associated with hydroxyl and chloride impurities. Radiolytically induced H0 and H2 play important roles in the post-irradiation growth and decay kinetics of defects in glasses containing_??_100ppm OH. A compendium of ESR/optical correlations taken from the literature points to the most likely origins of many defect-related optical absorption bands in the visible, ultraviolet and vacuumultraviolet spectral regions. Others of these bands have been ascribed to interstitial O2, O3 and Cl2 molecules on the basis of similarities of their spectral positions and widths to those of the corresponding species in the gas phase.
536 citations
TL;DR: In this paper, a review of self-setting calcium phosphate cements (CPC) is presented, focusing on the cement setting reactions, the products formed, the effects of the products on properties of the cement, and in vivo characteristics of CPC.
Abstract: This paper reviews recent studies on self-setting calcium phosphate cements (CPC). Discussions are focused on the cement setting reactions, the products formed, the effects of the products on properties of the cement, and in vivo characteristics of CPC. Although cementation can occur in systems based on several different mixtures, data in the literature at present indicate that mixtures of tetracalcium phosphate and dicalcium phosphate (or dicalcium phosphate dihydrate) may be most desirable because they produce cements that have greater strengths and contain nearly pure hydroxyapatite. The strengths of CPC are considerably lower than ceramic calcium phosphate biomaterial and are also lower than some of the dental cements. On the other hand, the combination of self-setting capability and high biocompatibility makes CPC a unique biomaterial. Near perfect adaptation of the cement to the tissue surfaces in a defect, and an optimum resorption rate followed by new bone formation are some of the distinctive advantages of CPC. In its present state CPC appears to be suitable for a number of applications. Much remains to be done to further improve its properties to meet the requirements for different applications.
280 citations
TL;DR: In this paper, the apatite formation on the surfaces of glasses in the system CaO-SiO2-P2O5 was examined in the simulated body fluid, and the results were interpreted in terms of ions dissolved from glasses.
Abstract: The essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body. The apatite layer can be reproduced on their surfaces even in an acellular simulated body fluid which has ion concentrations almost equal to those of the human blood plasma. In the present study, in order to investigate the compositional dependence of bioactivity of glasses fundamentally, the apatite formation on the surfaces of glasses in the system CaO-SiO2-P2O5 was examined in the simulated body fluid. Thin-film X-ray diffraction, Fourier transform infrared reflection spectroscopy and scanning electron microscopic observation were used for detecting the apatite formation. It was found that CaO-SiO2 glasses free form P2O5 as well as those containing small amounts of P2O5 form the apatite layer on their surfaces, whereas CaO-P2O5 glasses free from SiO2 as well as those containing SiO2 do not form it. This indicates that bioactive glasses and glass-ceramics are obtained in compositions based on CaO-SiO2 rather than CaO-P2O5, contrary to the general view. These results were interpreted in terms of ions dissolved from glasses.
187 citations
TL;DR: In this article, factors governing the bioactivity have been considerably revealed and new kinds of bioactive materials with other different functions such as high fracture toughness as well as low elastic modulus also might be developed from glasses in near future.
Abstract: Since discovery of Bioglass in 1971, various kinds of bioactive glasses and glass-ceramics with different functions such as high mechanical strength, high machinability, fast-setting ability and ferrimagnetism have been developed. Some of them are already clinically used as important bone-repairing implants and also have been proved to be useful even for cancer treatments. Factors governing the bioactivity have been considerably revealed. On the basis of these findings, new kinds of bioactive materials with other different functions such as high fracture toughness as well as low elastic modulus also might be developed from glasses in near future. Non-bioactive but inert glasses and glass-ceramics with various functions such as good workability, natural appearance and radioactivity also have been shown to be useful for biomedical applications such as dental crown and radioactive carrier for a cancer treatment. Glass-based materials will occupy more important positions in biomedical materials in the next decade.
146 citations
TL;DR: In this article, cyclic fatigue, and specifically fatigue-crack propagation in ceramics, is reviewed both for monolithic and composites systems, and implications are discussed in terms of the primary crack-tip shielding (toughening) mechanisms and potential mechanisms of cyclic crack advance.
Abstract: Cyclic fatigue, and specifically fatigue-crack propagation, in ceramic materials is reviewed both for monolithic and composites systems. In particular, stress/life (S/N) and crack-propagation data are presented for a range of ceramics, including zirconia, alumina, silicon nitride, SiC-whisker-reinforced alumina and a pyrolytic-carbon/graphite laminate. S/N data derived from unnotched specimens often indicate markedly lower lives under tension-compression compared to tension-tension loading; similar to metals, 108-cycle “fatigue limits” generally approach -50% of the tensile strength. Crack-growth results, based on studies on “long” (>3mm) cracks, show fatigue-crack propagation rates to be markedly power-law dependent on the applied stress-intensity range, ΔK, with a threshold, ΔKTH, of the order of -50% of Kc. Conversely, for “small” (<250μm) surface cracks, fatigue-crack growth is seen to occur at ΔK levels some 2 to 3 times smaller than ΔKTH, and to show a negative depen-dency on applied stress intensity. At ambient temperatures, lifetimes are shortened and crack-growth rates are significantly accelerated by cyclic, compared to quasi-static loading, although limited data suggest the reverse to be true at very high temperatures in the creep regime. Such results are discussed in terms of the primary crack-tip shielding (toughening) mechanisms and potential mechanisms of cyclic crack advance. Finally, implications are discussed of long and small crack cyclic fatigue data to life prediction and safetycritical design of ceramic components.
120 citations
TL;DR: In this paper, the fracture toughness increases up to 11.3MPa·m1/2 with the increase in the grain size, and a prominent crack bridging along the fracture surface behind the propagating crack tip is found to be the possible toughening mechanism.
Abstract: Improved KIC values of monolithic Si3N4 ceramics will be expected by growing-in a matrix of microcrystals of β-phase Si3N4-an appreciable amount of extensively large, rod-shape crystals of the same phase. It is anticipated that the large grains should play as crack impediments like whiskers mixed in composite ceramics. The test materials prepared by changing firing conditions had such well-grown crystals of different sizes, ranging from 2 to 10 microns in diameter. The fracture toughness (measured by the SEPB method) increases up to 11.3MPa·m1/2 with the increase in the grain size. Prominent crack bridging along the fracture surface behind the propagating crack tip is found to be the possible toughening mechanism.
119 citations
TL;DR: In this paper, the pore size, surface area, pore volume and refractive index of sol-gel dip-coating solgel films are controlled by several factors, such as size and opacity of fractal precursors.
Abstract: During sol-gel dip-coating, inorganic precursors are rapidly concentrated on the substrate surface by gravitational draining with concurrent evaporation and condensation reactions. We have presented examples of several factors that influence the structure of the deposited films: (1) size and opacity of fractal precursors; (2) relative rates of condensation and evaporation; (3) capillary pressure; (4) shear resulting from surface-tension-gradient-driven-flows; and (5) substrate withdrawal speed. By control of these factors it is possible to tailor the pore size, surface area, pore volume and refractive index of the deposited film for applications ranging from dense protective or passivation layers to films with precisely controlled pore sizes for sensor surfaces and separation membranes.
101 citations
TL;DR: In this paper, the authors proposed a method to obtain a superior thermal resistant composite material having excellent thermal barrier characteristics, thermal resistance and thermal stress relaxation, however, the recent trend in the development study is to consider FGM as a possible material superior in not only thermal characteristics but also in electrical, optical and chemical functions.
Abstract: Functionally Gradient Materials (FGMs) characterized by the material having continuously varying material property from one surface to the other, have been prepared using gas, liquid or solid as starting material via several methods such as CVD, PVD, ion plating, plasma spraying, sintering or self-propagating high temperature synthesis. The initial research in the development of the Functionally Gradient Materials was to obtain a superior thermal resistant composite material having excellent thermal barrier characteristics, thermal resistance and thermal stress relaxation, however, the recent trend in the development study is to consider FGM as a possible material superior in not only thermal characteristics but also in electrical, optical and chemical functions. In the application of Functionally Gradient Materials for the thermal barrier material the concentration of the dispersion phase is gradually varied in the material to obtain the required thermal stress relaxation.
73 citations
TL;DR: In this article, the authors investigated the crystallization process of an Fe2O3 40, CaO⋅SiO2 60wt% glass and revealed principles for obtaining ferrimgnetic and bioactive glass-ceramics useful as thermoseeds for hyperthermia of cancer.
Abstract: The crystallization process of an Fe2O3 40, CaO⋅SiO2 60wt% glass was investigated as well as magnetic properties of the crystallized products, in order to reveal principles for obtaining ferrimgnetic and bioactive glass-ceramics useful as thermoseeds for hyperthermia of cancer. When the glass was heat-treated up to temperatures 700° to 950°C, magnetite particles were homogeneously precipitated in a CaO⋅SiO2-based glassy and/or crystalline matrix. The diameter and content of the magnetite increased from 6 to 30nm and 10 to 36wt%, respectively, with increasing temperature of the heat treatment from 700° to 950°C. Above 1000°C, a part of the magnetite was converted into hematite (α-Fe2O3). The glass showed maxima in saturation magnetization and coercive force, 32emu/g and 500 Oe, respectively, when heat-treated up to 950°C. The variation of the magnetization with heat treatment temperature could be well quantitatively interpreted in terms of the content of the magnetite, whereas that of the coercive forces could be explained only qualitatively in terms of the particle size of the magnetite. The coercive forces of the magnetite-containing glass-ceramics were much higher than those of the magnetite powders of the corresponding particle sizes which were prepared from aqueous solutions.
60 citations
TL;DR: The sol-gel technique offers a low temperature method for synthesizing amorphous inorganic solids which contain trapped organic molecules with deliberately chosen optical properties as mentioned in this paper, such as luminescent or photochromic properties.
Abstract: The sol-gel technique offers a low temperature method for synthesizing amorphous inorganic solids which contain trapped organic molecules with deliberately chosen optical properties. The poor thermal stability of organic molecules has precluded their incorporation in traditional oxide host materials because of the elevated processing temperatures involved with these materials. Using the sol-gel approach, a wide variety of organic molecules have been incorporated in sol-gel matrices and demonstrated that they retain their specific optical properties in the sol-gel environment. Thus, it has been possible to use the sol-gel method to prepare photonic materials which are luminescent or photochromic, which possess nonlinear optical properties or which exhibit laser action. This paper reviews the two principal areas where sol-gel methods are used to produce organic-doped photonic materials. One area of activity involves the utilization of the organic dopants as luminescent probes of the sol-gel process. Examples of matrix rigidity and solvent chemistry changes are shown. The second area concerns the synthesis of new photonic materials whose optical properties are induced by the addition of specific dopants. Significant results involving tunable solid-state lasers, nonlinear optical properties and photochromic materials are presented.
TL;DR: In this paper, the electrophoretic deposition method was used to form an alumina layer with a thickness of about 1mm, which was then sintered at 1100°-1500°C in air.
Abstract: The electrophoretic deposition method was used to form an alumina layer with a thickness of about 1mm. Alpha alumina powders with average diameters of 0.2 and 0.6μm were dispersed in water at pH 2.5 to provide positive charge. Positively charged alumina particles in the aqueous suspension of 15vol% solid were deposited on a cylindrical carbon electrode by passing direct current of 5-200mA at 50-300V. The weight of the alumina layer was proportional to the deposition time and applied voltage. Electrolysis of the HCl solution occurred together with the electrophoretic deposition of alumina particles. The deposition efficiency calculated from the deposition rate of alumina particles was in the range of 0.13 to 0.15. The density and thickness of the formed alumina layer increased periodically with deposition time. The alumina layers with relative densities of 56-62%, formed from the 0.6μm-alumina powder, were sintered at 1100°-1500°C in air. The densification rate was reduced above 1400°C by large pores (200-500μm).
NGK1
TL;DR: Vue d'ensemble des mecanismes du frittage et des facteurs influant sur le frittages for des systemes a base de nitrures contenant des additifs solubles ou insolubles.
Abstract: Vue d'ensemble des mecanismes du frittage et des facteurs influant sur le frittage pour des systemes a base de nitrures contenant des additifs solubles ou insolubles. Discussion des relations microstructure-proprietes. Presentation de quelques applications (composants de moteurs, paliers et billes de roulement, outils de coupe).
TL;DR: In this paper, an orthorhombic phase was synthesized at pressures above 4GPa in the temperature range from 400° to 1000°C and at a pressure from 3 to 6GPa.
Abstract: Monoclinic hafnia (HfO2) powders were treated from 400° to 1100°C and at a pressure from 3 to 6GPa. The products were identified by powder XRD. The results indicated that an orthorhombic phase was synthesized at pressures above 4GPa in the temperature range from 400° to 1000°C. Although the monoclinic-orthorhombic transition pressure is almost the same as that of ZrO2, orthorhombic HfO2 is more stable at high temperatures than ZrO2. The Rietveld analysis showed that the orthorhombic HfO2 is isostructural with one of the two orthorhombic ZrO2 (ortho I).
TL;DR: In this paper, the authors investigated the changes in microstructure and the annihilation of stacking faults and found that stacking fault annihilation occurs parallel with grain growth which is controlled by surface diffusion and/or vapor tansport.
Abstract: Beta-SiC specimens possessing 13% stacking fault density were annealed at various temperatures for various time periods in an Ar or a N2 atmosphere, and the changes in microstructure and the annihilation of stacking faults were investigated. Stacking fault annihilation was found to occur parallel with the grain growth which is supposedly controlled by surface diffusion and/or vapor tansport. Lattice strain enhanced by the incorporation of nitrogen into the SiC lattice was considered to be the most important factor to suppress the mass transport rate.
TL;DR: In this paper, le potentiel d'amelioration de la resistance a la rupture des ceramiques par lincorporation de phases de zircone subissant une transformation martensitique induite par une contrainte mecanique, or par l incorporating de phases discontinues resistantes telles que des trichites.
Abstract: On considere le potentiel d'amelioration de la resistance a la rupture des ceramiques par l'incorporation de phases de zircone subissant une transformation martensitique induite par une contrainte mecanique, ou par l'incorporation de phases discontinues resistantes telles que des trichites. Dans le cas des ceramiques contenant de la zircone quadratique, on discute du renforcement en termes de caracteristiques de microstructure et de composition influant sur la transformation martensitique. Pour les composites renforces par des phases discontinues, on decrit les parametres contribuant a l'amelioratiuon de tenacite en termes de pontage des fissures par le renfort.
Journal Article•
TL;DR: In this paper, the formation d'apatite sur les surfaces des verres dans le systeme CaO-SiO 2 -P 2 O 5 din le liquide corporel simule, qui a des concentrations en ions egales a celles du plasma sanguin humain.
Abstract: On etudie la formation d'apatite sur les surfaces des verres dans le systeme CaO-SiO 2 -P 2 O 5 dans le liquide corporel simule, qui a des concentrations en ions egales a celles du plasma sanguin humain
Journal Article•
TL;DR: In this paper, a TTT diagram for the process of the thermal decomposition and the phase transformations of ammonium aluminum carbonate hydroxide (AACH) to α-alumina has been determined.
Abstract: The thermal decomposition and the phase transformations of ammonium aluminum carbonate hydroxide (AACH) to α-alumina have been studied. Amorphous-, γ- and θ-alumina were identified as intermediate products. A TTT diagram for the process of the thermal decomposition and the phase transformations was determined. Kinetic analysis of the θ- to α-aluminas transformation by the Avrami-Erofeev equation showed that the transformation occurred by the nucleation and growth mechanism. Results of transmission electron microscopy (TEM), however, suggested that the transformation occurred by the synchro-shear mechanism. The maximum particle size of θ-alumina and the minimum particle size of α-alumina were approximately 30 and 40nm, respectively. A model of the transformation was presented from the viewpoint of crystallography.
TL;DR: A major barrier for commercial production of powders by controlled hydrolysis of metal alkoxides is the fundamental requirement for dilute solutions, and thus low yield, to obtain monodisperse particles as discussed by the authors.
Abstract: Powders derived from metal alkoxides, irrespective of the specific process, have been demonstrated to possess most of the desirable characteristics for ceramic fabrication and sintering. Particularly impressive gains have been reported for silicates and in the expansion of the compositional range of alkoxide derived powders. While most research has focused on synthesis of simple metal oxide powders, advances in the chemistry of mixed metal alkoxides should pave the way for powder synthesis of more complex, multicomponent oxides.Besides the high chemical costs, a major deterrent for commercial production of powders by controlled hydrolysis of metal alkoxides is the fundamental requirement for dilute solutions, and thus low yield, to obtain monodisperse particles. Continuous processes such as aerosol reactions, spray pyrolysis, seeded growth and, potentially, emulsion processes, may overcome the barrier of low rate of production.A technical impediment for commercial use of alkoxide derived particles stems from their structurally porous character. Although the other physical characteristics allow for lower temperature densification, the large sintering shrinkage associated with porous particles is undesirable and poses a significant barrier to industrial application. As a reasonably mature field, future advances will require the modeling and detailed analysis of the above processes.
TL;DR: In this article, the phase separation and crystallization behavior of glass in Al2O3-Y2O-3-SiO2 system were studied by X-ray diffraction, differential thermal analysis, scanning electron microscopy and Xray microanalysis.
Abstract: Subsolidus phase equilibria in Al2O3-Y2O3-SiO2 system and the phase separation and crystallization behavior of glass in this system were studied by X-ray diffraction, differential thermal analysis, scanning electron microscopy and X-ray microanalysis. Phase relations, liquidus and solidus temperatures in this system were obtained. Phase equilibrium was not confirmed in a lower temperature than solidus temperature near 1340°C. The glass transition temperature (Tg) the starting temperature of crystallization (Tc), the 1st and 2nd peak temperatures of crystallization (To and To' respectively) were studied as a function of composition. The activation energy of crystallization ΔE was determined by analyzing the heating rate dependence of To and found to be in a range of 472-890kJ/mol, depending on the composition. ΔE had a tendency to increase with decrease in liquidus temperature, suggesting that the glass becomes stable in compositions with lower liquidus temperatures. During heat treatment of glass at 1300°C, the phase separation was found to occur as an early stage of crystallization.
TL;DR: Among numerous microfracture processes and mechanisms of fiber-reinforced composites with brittle matrix, it is emphasized that the first matrix cracking, fiber bridging, and the fiber pullout processes are by far the most important for toughening composite materials as mentioned in this paper.
Abstract: Among numerous microfracture processes and mechanisms of fiber-reinforced composites with brittle matrix, it is emphasized that the first matrix cracking, fiber bridging, and the fiber pullout processes are by far the most important for toughening composite materials. In the quantitative assessment of composite fractures, to characterize separately these fundamental micro-fracture processes and mechanisms is most essential. The individual processes and mechanisms are addressed and reviewed based on not only theoretical but also experimental aspects.
TL;DR: In this paper, the effects of Al2O3, ZrO2 and carbon coating to the surface of whiskers were studied for interfacial control, and the flexural strength and the fracture toughness of Si3N4 composite containing Al 2O3-coated whiskers by decomposition of aluminum stearate, were stronger (1107MPa) and larger (10.2MPa·m1/2) than those of the composite with noncoated worms.
Abstract: In order to strengthen and toughen Si3N4 ceramics by addition of SiC-whiskers, we tried the control of interfacial properties between whisker and matrix and of orientation of whiskers. For interfacial control, the effects of Al2O3, ZrO2 and carbon coating to the surface of whiskers were studied. The flexural strength and the fracture toughness of Si3N4 composite containing Al2O3-coated whiskers by decomposition of aluminum stearate, were stronger (1107MPa) and larger (10.2MPa·m1/2) than those of the composite with noncoated whiskers. TEM observation revealed that Al2O3-coated whiskers in the composite had smoother surface than non-coated whiskers and that a film-layer was formed at the interface between whisker and matrix. For orientation control, the flexural strength and the creep rupture resistance at 1250°C of Si3N4 composite, reinforced with uni-directionally oriented whiskers by the doctor-blade method, were much stronger (1180MPa) and much larger than those of monolithic Si3N4 ceramics. After creep testing, the new stacking fault and dislocation in the whiskers were observed by TEM. On the basis of these results, the mechanisms of toughening and high-temperature strengthening of SiC(w)/Si3N4 have been discussed.
TL;DR: Porous SiO2-ZrO2 glass was prepared from a sol con-taining polyethylene glycol (PEG) by the sol-gel method.
Abstract: Porous SiO2-ZrO2 glass was prepared from a sol con taining polyethylene glycol (PEG) by the sol-gel method. After air-drying at room temperature, the gel was baked at 600•Ž. The ZrO2 content in the porous glass was 30wt%. The median pore diameter of the porous glass was 2nm regardless of the molecular weight and amount of PEG added. The reproducibility of the pore size distribution was good, and the pore volume and surface area were linearly proportional to the amount of PEG added. Alkali resistance of the porous glass was much larger comparing to the porous SiO2 glass.
TL;DR: The results of the VAMAS international round robin test for evaluating fracture toughness of ceramics were reported in this paper, where the results showed that the toughness values evaluated by the SEPB method have relatively wide scatter among the participants, suggesting some difficulty with this technique; the IS method gave the smallest scatter and the IF method the largest scatter.
Abstract: This report describes the results of VAMAS international round robin test for evaluating fracture toughness of ceramics. Thirteen laboratories in Japan, France, Germany, UK, Canada, Belgium and CEC (JRC Petten) took part in the test. The values of fracture toughness obtained by the SEPB, the IF and the IS methods were compared with one another for gaspressure sintered silicon nitride (GPSSN) and zirconia-alumina composites (ZAC). Also examined were indentation load dependence of fracture toughness measured by the IF and the IS methods and loading rate dependence of fracture toughness by the SEPB method. The results showed that the toughness values evaluated by the SEPB method have relatively wide scatter among the participants, suggesting some difficulty with this technique; the IS method gave the smallest scatter and the IF method the largest scatter. Fracture toughness measured by the SEPB method was dependent on the loading rate, especially for ZAC. This may have been caused by stress corroson cracking. The values measured by the IF and IS methods depended apparently on the indentation load.