Unidirectionally reinforced carbon fiber/carbon composite whose matrix was derived from thermoset... more Unidirectionally reinforced carbon fiber/carbon composite whose matrix was derived from thermosetting resin, was prepared.
Pressureless-sintered AlN and hot-pressed, pressureless-sintered and reaction-bonded SiC were neu... more Pressureless-sintered AlN and hot-pressed, pressureless-sintered and reaction-bonded SiC were neutron irradiated at temperatures between 100 and 785'C up to a fiuence of 5.2 x 10 24 njm 2 • The hardness was increased by up to 51;'~ in AIN and 84 y,~ in SiC. The hardness decreased after annealing at temperatures around the irradiation temperature. At the same temperatures. the macroscopic length, which was increased by irradiation. also began to decrease. The hardness and length were almost recovered after 1.200-1,400oC annealing. Thus, hardening in irradiated AIN and SiC is controlled by the number of point defects, or, more precisely, by the strain caused by small point defect clusters which pin down dislocation movement. Dislocation loops were still observed in some samples after 1,400oC annealing while the hardness was almost recovered to that in the unirradiated state. Thus, the existence of dislocation loops is not grounds for hardening in irradiated AlN and SiC.
Tyranno SA fibre was higher strength at high temperatures and higher thermal conductivity than th... more Tyranno SA fibre was higher strength at high temperatures and higher thermal conductivity than that of Hi-Nicalon fibre. Therefore, the aim of this study was to investigate the effect of reinforcements on the mechanical and thermal properties of SiC/SiC composites containing non-coated Tyranno SA short fibres. SiC/SiC composites containing 30 vol.% short fibres were fabricated by tape-casting and hot-pressing at 1650 o C-1750 o C under a pressure of 40 MPa using an Al 2 O 3 -Y 2 O 3 -CaO mixture as sintering additives independent of fibre type.
Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites have been... more Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites have been recognized as key materials for aerospace industries, high-temperature gas turbines and future nuclear and fusion applications because they show a pseudo-ductile fracture behavior and excellent fracture tolerance. Fiber/matrix interfaces act as an important role for toughening and strengthening SiC/SiC composites. Currently, carbon or hexagonalboron nitride has been formed on SiC fibers as the interphases, and these interphases have been generally formed by chemical vapor infiltration (CVI), chemical vapor deposition (CVD) or solution-coating/pyrolysis process. However, these processes generally require long manufactuiring time and complicated apparatuses, and they use toxic, flammable or combustible reactant gases, resulting in much higher production cost and an increase in environmental load. Present authors paid attention to EPD process to form interphases on SiC fibers in SiC/SiC co...
In this study, SiC/SiO2 core-shell nanowires (SiCNWs) were fabricated by thermal evaporation meth... more In this study, SiC/SiO2 core-shell nanowires (SiCNWs) were fabricated by thermal evaporation method without any catalyst, using pre-oxidized silicon powder and methane (CH4) gas as precursors. The reaction temperature was 1340°C in an inert atmosphere. The SiCNWs produced by this process had a single crystal β-SiC core ranging from 20 to 80 nm in diameter and low-crystalline SiO2 shell about 10-20 nm thick, and up to 1 mm long. The exhaust gas from the production system was analyzed by gas chromatography and the growth activity of SiCNWs was captured by digital camera during a soaking period. From the results, CO gas was detected only when SiCNWs were growing and was not found when methane gas was stopped. It was clarified that CO gas was produced as a by-product during the formation of SiCNWs. The formation mechanism of SiCNWs synthesized by thermal evaporation method was suggested to be oxide-assisted growth mechanism.
A simple thermal evaporation technique without catalysts from an exterior has been developed to s... more A simple thermal evaporation technique without catalysts from an exterior has been developed to synthesize SiC–SiO2 composite nanowires. Silicon powder of micrometer size or coarser silicon powder was heated in a horizontal tube furnace up to 1350°C under CH4 gas flow. Large quantity of as-grown wool-like products was obtained on the silicon powder oxidized at 800°C in air for 1h.
Green sheets of the composites using polycarbosilane (PCS)-infiltrated (coated) Tyranno SA short ... more Green sheets of the composites using polycarbosilane (PCS)-infiltrated (coated) Tyranno SA short fibers, submicron SiC powder and Al2O3–Y2O3–CaO mixtures as sintering additives were prepared by tape-casting. These green sheets were stacked and hot-pressed at 1750 °C. Most of all SiC short fibers were oriented along the tape casting direction. The bulk density of the composites was about 2.66 g/cm3. The bending
Mg-Al LDH intercalated PtCl4 2-anion (PtCl4-LDH) was synthesized by a reconstruction method using... more Mg-Al LDH intercalated PtCl4 2-anion (PtCl4-LDH) was synthesized by a reconstruction method using potassium tetrachloroplatinate and its thermal changes were investigated at various temperatures. The PtCl4-LDH included 17 mass% Pt was synthesized by a reconstruction method using K2PtCl4 solution of 10 mM to adjust the pH with NaOH to about 11. The obtained PtCl4-LDH shows high crystallinity and has low content of CO3 2-. The basal spacing of the obtained PtCl4-LDH was 0.83 nm expanding slightly from 0.78 nm of starting LDH. The XRD patterns of the obtained PtCl4-LDH showed that the second 00l diffraction line (006) became more accentuated than the first one (003) according to the intercalation of Pt components. Pt fine particles in the several nm were directly observed by TEM after firing at 500°C. However, the diffraction patterns of Pt or Pt components were not detected via XRD in the same sample. This is due to the coagulation of Pt components by the narrow basal spacing of the PtCl4-LDH.
MgO·3AlâOâ single crystals were irradiated with neutron fluences of 8.3 à 10²²n/m² at 100 c a... more MgO·3AlâOâ single crystals were irradiated with neutron fluences of 8.3 à 10²²n/m² at 100 c and 2.4 à 10²ⴠn/m² at 470 C (E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness
Neutron-irradiation-induced defects in 3C-SiC irradiated to 2.8-4.2 Â 10 26 n/m 2 at 480-735 °C w... more Neutron-irradiation-induced defects in 3C-SiC irradiated to 2.8-4.2 Â 10 26 n/m 2 at 480-735 °C were investigated by XRD measurement, isochronal annealing and DFT calculation. The XRD peak shift revealed different features between the specimens irradiated at 480 °C and higher temperature than 585 °C. The peak shifts were larger at the higher angle in the specimen irradiated at 480 °C, while the specimens irradiated at higher temperature than 585 °C, amounts of their peak shifts were not simply related to the diffraction angles. Crystal lattice of the specimen irradiated at 480 °C was considered to expand isotropically due to the irradiation. On the other hand, that of the specimens irradiated at higher temperature than 585 °C would expand anisotropically. Modification of XRD profile by the formation of various kinds of point defects and their clusters in 3C-SiC was simulated using Rietveld method based on the DFT calculation results. Formation of the C C100 dumbbell complex defect expressed well the XRD peak shifts of 3C-SiC irradiated above 585 °C.
Neutron irradiation effects on cation distribution in non-stoichiometric Mg-Al spinel were examin... more Neutron irradiation effects on cation distribution in non-stoichiometric Mg-Al spinel were examined by ALCHEMI (Atom Location by Channeling Enhanced Microanalysis) method. Parameter n, or non-stoichiometry of MgO AE nAl 2 O 3 of the specimens, were n = 1.00, 1.01, 1.10, 1.48. These specimens were neutron-irradiated up to a fluence of 2.3 • 10 24 n/m 2 (E > 0.1 MeV) at 500-530 °C in JMTR. Some specimens contracted by the irradiation and the arrangement of cations became more disorder. The other specimens showed very small swelling by the irradiation and the cation distribution became slightly ordered. The cation distribution of the contracted specimen returned stepwise to the pre-irradiated condition after the annealing at 700 °C. The cation distribution of the slightly swollen specimens did not change after the annealing up to 700 °C. Cation distribution in the T-site was more sensitively influenced by the irradiation.
Pyrochlore-type yttrium titanate (Y 2 Ti 2 O 7 ) nanoparticles were successfully synthesized by a... more Pyrochlore-type yttrium titanate (Y 2 Ti 2 O 7 ) nanoparticles were successfully synthesized by a simple soft-chemistry technique viz. citric acid sol-gel method (CAM). The preparation process was monitored by X-ray diffraction, thermogravimetric-differential thermal analysis and Fourier transform-infrared experiments and the microstructures and average size of as-prepared products were characterized by transmission electron microscopy and high resolution transmission electron microscopy images. It was found that compared with traditional solid state reaction (SSR), Y 2 Ti 2 O 7 nanopowders were synthesized at a relatively low temperature (750 • C) for shortened reaction time. Detailed analysis showed that the as-prepared Y 2 Ti 2 O 7 with good dispersibility and narrow size distribution were quasi-spherical; the average size was about 20-30 nm, also, the obtained products had higher BET surface area (50 m 2 /g). These properties are very helpful for a photocatalyst to achieve excellent activity and may result in better behaviour in hydrogen storage.
In order to examine the effects of sintering additives on microstructure and mechanical propertie... more In order to examine the effects of sintering additives on microstructure and mechanical properties of SiC shortfibre-reinforced SiC composites, a ZrO 2-Y 2 O 3-Al 2 O 3 additive system was applied in this study. The aim of this study was to investigate the influence of the sintering additives on the mechanical properties of SiC/SiC composites using Tyranno SA short fibres. A ZrO 2-Y 2 O 3-Al 2 O 3 mixture was chosen for fabrication of the shortfibre-reinforced SiC composites as sintering additives because of their relatively low densification temperature and non-reactivity with SiC. Compare with the previous results, the influence of sintering additives on the mechanical and thermal properties of the SiC/SiC composites was discussed.
The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabri... more The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabricating SiC fiberreinforced SiC-based matrix composites (SiC f /SiCs) for high-temperature structural applications. SiC f /SiCs were fabricated by the melt-infiltration method using a eutectic Si8.5 at%Hf alloy to evaluate their dry oxidation behavior at 8001200°C for times ranging from 10100 h. The oxidation behavior of monolithic HfSi 2 (Monolith) fabricated by spark plasma sintering was also evaluated in dry air. The oxidation behavior of the composite matrix and Monolith obeyed the parabolic law in dry conditions. The steps to form the oxidation layer were expected to produce HfO 2 and Si, followed by SiO 2 , and, finally, HfSiO 4. The oxidation rate of the matrix was similar to that of Monolith and 10 2 10 4 times larger than that of Si. The oxidation activation energy employed in oxidation of HfSi 2 was calculated as 258 kJ/mol in dry air.
Unidirectionally reinforced carbon fiber/carbon composite whose matrix was derived from thermoset... more Unidirectionally reinforced carbon fiber/carbon composite whose matrix was derived from thermosetting resin, was prepared.
Pressureless-sintered AlN and hot-pressed, pressureless-sintered and reaction-bonded SiC were neu... more Pressureless-sintered AlN and hot-pressed, pressureless-sintered and reaction-bonded SiC were neutron irradiated at temperatures between 100 and 785'C up to a fiuence of 5.2 x 10 24 njm 2 • The hardness was increased by up to 51;'~ in AIN and 84 y,~ in SiC. The hardness decreased after annealing at temperatures around the irradiation temperature. At the same temperatures. the macroscopic length, which was increased by irradiation. also began to decrease. The hardness and length were almost recovered after 1.200-1,400oC annealing. Thus, hardening in irradiated AIN and SiC is controlled by the number of point defects, or, more precisely, by the strain caused by small point defect clusters which pin down dislocation movement. Dislocation loops were still observed in some samples after 1,400oC annealing while the hardness was almost recovered to that in the unirradiated state. Thus, the existence of dislocation loops is not grounds for hardening in irradiated AlN and SiC.
Tyranno SA fibre was higher strength at high temperatures and higher thermal conductivity than th... more Tyranno SA fibre was higher strength at high temperatures and higher thermal conductivity than that of Hi-Nicalon fibre. Therefore, the aim of this study was to investigate the effect of reinforcements on the mechanical and thermal properties of SiC/SiC composites containing non-coated Tyranno SA short fibres. SiC/SiC composites containing 30 vol.% short fibres were fabricated by tape-casting and hot-pressing at 1650 o C-1750 o C under a pressure of 40 MPa using an Al 2 O 3 -Y 2 O 3 -CaO mixture as sintering additives independent of fibre type.
Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites have been... more Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites have been recognized as key materials for aerospace industries, high-temperature gas turbines and future nuclear and fusion applications because they show a pseudo-ductile fracture behavior and excellent fracture tolerance. Fiber/matrix interfaces act as an important role for toughening and strengthening SiC/SiC composites. Currently, carbon or hexagonalboron nitride has been formed on SiC fibers as the interphases, and these interphases have been generally formed by chemical vapor infiltration (CVI), chemical vapor deposition (CVD) or solution-coating/pyrolysis process. However, these processes generally require long manufactuiring time and complicated apparatuses, and they use toxic, flammable or combustible reactant gases, resulting in much higher production cost and an increase in environmental load. Present authors paid attention to EPD process to form interphases on SiC fibers in SiC/SiC co...
In this study, SiC/SiO2 core-shell nanowires (SiCNWs) were fabricated by thermal evaporation meth... more In this study, SiC/SiO2 core-shell nanowires (SiCNWs) were fabricated by thermal evaporation method without any catalyst, using pre-oxidized silicon powder and methane (CH4) gas as precursors. The reaction temperature was 1340°C in an inert atmosphere. The SiCNWs produced by this process had a single crystal β-SiC core ranging from 20 to 80 nm in diameter and low-crystalline SiO2 shell about 10-20 nm thick, and up to 1 mm long. The exhaust gas from the production system was analyzed by gas chromatography and the growth activity of SiCNWs was captured by digital camera during a soaking period. From the results, CO gas was detected only when SiCNWs were growing and was not found when methane gas was stopped. It was clarified that CO gas was produced as a by-product during the formation of SiCNWs. The formation mechanism of SiCNWs synthesized by thermal evaporation method was suggested to be oxide-assisted growth mechanism.
A simple thermal evaporation technique without catalysts from an exterior has been developed to s... more A simple thermal evaporation technique without catalysts from an exterior has been developed to synthesize SiC–SiO2 composite nanowires. Silicon powder of micrometer size or coarser silicon powder was heated in a horizontal tube furnace up to 1350°C under CH4 gas flow. Large quantity of as-grown wool-like products was obtained on the silicon powder oxidized at 800°C in air for 1h.
Green sheets of the composites using polycarbosilane (PCS)-infiltrated (coated) Tyranno SA short ... more Green sheets of the composites using polycarbosilane (PCS)-infiltrated (coated) Tyranno SA short fibers, submicron SiC powder and Al2O3–Y2O3–CaO mixtures as sintering additives were prepared by tape-casting. These green sheets were stacked and hot-pressed at 1750 °C. Most of all SiC short fibers were oriented along the tape casting direction. The bulk density of the composites was about 2.66 g/cm3. The bending
Mg-Al LDH intercalated PtCl4 2-anion (PtCl4-LDH) was synthesized by a reconstruction method using... more Mg-Al LDH intercalated PtCl4 2-anion (PtCl4-LDH) was synthesized by a reconstruction method using potassium tetrachloroplatinate and its thermal changes were investigated at various temperatures. The PtCl4-LDH included 17 mass% Pt was synthesized by a reconstruction method using K2PtCl4 solution of 10 mM to adjust the pH with NaOH to about 11. The obtained PtCl4-LDH shows high crystallinity and has low content of CO3 2-. The basal spacing of the obtained PtCl4-LDH was 0.83 nm expanding slightly from 0.78 nm of starting LDH. The XRD patterns of the obtained PtCl4-LDH showed that the second 00l diffraction line (006) became more accentuated than the first one (003) according to the intercalation of Pt components. Pt fine particles in the several nm were directly observed by TEM after firing at 500°C. However, the diffraction patterns of Pt or Pt components were not detected via XRD in the same sample. This is due to the coagulation of Pt components by the narrow basal spacing of the PtCl4-LDH.
MgO·3AlâOâ single crystals were irradiated with neutron fluences of 8.3 à 10²²n/m² at 100 c a... more MgO·3AlâOâ single crystals were irradiated with neutron fluences of 8.3 à 10²²n/m² at 100 c and 2.4 à 10²ⴠn/m² at 470 C (E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness
Neutron-irradiation-induced defects in 3C-SiC irradiated to 2.8-4.2 Â 10 26 n/m 2 at 480-735 °C w... more Neutron-irradiation-induced defects in 3C-SiC irradiated to 2.8-4.2 Â 10 26 n/m 2 at 480-735 °C were investigated by XRD measurement, isochronal annealing and DFT calculation. The XRD peak shift revealed different features between the specimens irradiated at 480 °C and higher temperature than 585 °C. The peak shifts were larger at the higher angle in the specimen irradiated at 480 °C, while the specimens irradiated at higher temperature than 585 °C, amounts of their peak shifts were not simply related to the diffraction angles. Crystal lattice of the specimen irradiated at 480 °C was considered to expand isotropically due to the irradiation. On the other hand, that of the specimens irradiated at higher temperature than 585 °C would expand anisotropically. Modification of XRD profile by the formation of various kinds of point defects and their clusters in 3C-SiC was simulated using Rietveld method based on the DFT calculation results. Formation of the C C100 dumbbell complex defect expressed well the XRD peak shifts of 3C-SiC irradiated above 585 °C.
Neutron irradiation effects on cation distribution in non-stoichiometric Mg-Al spinel were examin... more Neutron irradiation effects on cation distribution in non-stoichiometric Mg-Al spinel were examined by ALCHEMI (Atom Location by Channeling Enhanced Microanalysis) method. Parameter n, or non-stoichiometry of MgO AE nAl 2 O 3 of the specimens, were n = 1.00, 1.01, 1.10, 1.48. These specimens were neutron-irradiated up to a fluence of 2.3 • 10 24 n/m 2 (E > 0.1 MeV) at 500-530 °C in JMTR. Some specimens contracted by the irradiation and the arrangement of cations became more disorder. The other specimens showed very small swelling by the irradiation and the cation distribution became slightly ordered. The cation distribution of the contracted specimen returned stepwise to the pre-irradiated condition after the annealing at 700 °C. The cation distribution of the slightly swollen specimens did not change after the annealing up to 700 °C. Cation distribution in the T-site was more sensitively influenced by the irradiation.
Pyrochlore-type yttrium titanate (Y 2 Ti 2 O 7 ) nanoparticles were successfully synthesized by a... more Pyrochlore-type yttrium titanate (Y 2 Ti 2 O 7 ) nanoparticles were successfully synthesized by a simple soft-chemistry technique viz. citric acid sol-gel method (CAM). The preparation process was monitored by X-ray diffraction, thermogravimetric-differential thermal analysis and Fourier transform-infrared experiments and the microstructures and average size of as-prepared products were characterized by transmission electron microscopy and high resolution transmission electron microscopy images. It was found that compared with traditional solid state reaction (SSR), Y 2 Ti 2 O 7 nanopowders were synthesized at a relatively low temperature (750 • C) for shortened reaction time. Detailed analysis showed that the as-prepared Y 2 Ti 2 O 7 with good dispersibility and narrow size distribution were quasi-spherical; the average size was about 20-30 nm, also, the obtained products had higher BET surface area (50 m 2 /g). These properties are very helpful for a photocatalyst to achieve excellent activity and may result in better behaviour in hydrogen storage.
In order to examine the effects of sintering additives on microstructure and mechanical propertie... more In order to examine the effects of sintering additives on microstructure and mechanical properties of SiC shortfibre-reinforced SiC composites, a ZrO 2-Y 2 O 3-Al 2 O 3 additive system was applied in this study. The aim of this study was to investigate the influence of the sintering additives on the mechanical properties of SiC/SiC composites using Tyranno SA short fibres. A ZrO 2-Y 2 O 3-Al 2 O 3 mixture was chosen for fabrication of the shortfibre-reinforced SiC composites as sintering additives because of their relatively low densification temperature and non-reactivity with SiC. Compare with the previous results, the influence of sintering additives on the mechanical and thermal properties of the SiC/SiC composites was discussed.
The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabri... more The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabricating SiC fiberreinforced SiC-based matrix composites (SiC f /SiCs) for high-temperature structural applications. SiC f /SiCs were fabricated by the melt-infiltration method using a eutectic Si8.5 at%Hf alloy to evaluate their dry oxidation behavior at 8001200°C for times ranging from 10100 h. The oxidation behavior of monolithic HfSi 2 (Monolith) fabricated by spark plasma sintering was also evaluated in dry air. The oxidation behavior of the composite matrix and Monolith obeyed the parabolic law in dry conditions. The steps to form the oxidation layer were expected to produce HfO 2 and Si, followed by SiO 2 , and, finally, HfSiO 4. The oxidation rate of the matrix was similar to that of Monolith and 10 2 10 4 times larger than that of Si. The oxidation activation energy employed in oxidation of HfSi 2 was calculated as 258 kJ/mol in dry air.
Uploads
Papers by Toyohiko Yano