Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this...Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.展开更多
Because Silicon carbide (SiC) ceramics have various excellent properties, the demand for larger and complicated shapes has been increasing. This paper introduces an innovative method that would not require a large fur...Because Silicon carbide (SiC) ceramics have various excellent properties, the demand for larger and complicated shapes has been increasing. This paper introduces an innovative method that would not require a large furnace, and further, would minimize the production cost and the thermal history, namely the “flash-bonding” technique. The borosilicate glass with low thermal expansion coefficient, Pyrex glass, was selected as the brazing material. In this work, as-is or surface-oxidized SiC plates were joined using Pyrex glass as brazing material, and the reaction and wetting of Pyrex glass on as-is or surface-oxidized SiC plate were investigated. It was found that the protective film of the surface-oxidized SiC lowered the oxygen partial pressure, and hence, generated many pores in the interface.展开更多
Due to its electron configuration (Xe) 4 f14 6 s2, Ytterbium (Yb) could form divalent oxide, YbO. In this study, the solid-state synthesis of metastable YbO was investigated by the oxidation of Yb metal at normal pres...Due to its electron configuration (Xe) 4 f14 6 s2, Ytterbium (Yb) could form divalent oxide, YbO. In this study, the solid-state synthesis of metastable YbO was investigated by the oxidation of Yb metal at normal pressure using two experimental conditions: 1) heat treatment of Yb metal under Ar gas atmosphere with metal carbonate as an oxygen source;and 2) heat treatment of Yb metal under the continuous gas flow condition using various gas atmospheres. Products were identified using the powder X-ray diffraction and scanning electron microscope. It was found that almost single phase YbO was obtained in the experimental condition 1) using the molar ratio of Ca-CO3/Yb = 0.4. Thermodynamic calculations suggested that the YbO formation be controlled not by thermodynamics but by kinetics, and further that the evaporation of Yb metal in the BN crucible played a key role for the formation of the meta-stable YbO.展开更多
Y-Si compounds with the composition of Y:Si = 1:2 were fabricated using Yttrium and Silicon raw powders with low and high purity in various atmospheres and temperatures. Although the latest Y-Si phase diagram shows th...Y-Si compounds with the composition of Y:Si = 1:2 were fabricated using Yttrium and Silicon raw powders with low and high purity in various atmospheres and temperatures. Although the latest Y-Si phase diagram shows that the α- and β-YSi<sub>2</sub> phases are the stable phases for the stoichiometric composition of Y:Si = 1:2, the current experimental results suggest that the high temperature phase with the hexagonal structure, β-Y<sub>3</sub>Si<sub>5</sub>, would be the stable phase for this composition, and that the high temperature phase with the orthorhombic structure, β-YSi<sub>2</sub>, would be the meta-stable phase with high oxygen impurity content. It was demonstrated that YSi<sub>2</sub> powders possess much superior chemical stability than Yttrium metal. It was found that the best dispersing solvent was 2-propanol for YSi<sub>2</sub> powder.展开更多
To fabricate polydopamine-sensitized solar cells with improved solar power conversion efficiency, the effects of pH, buffer, adsorption time and electrode potential for the electrochemical oxidation and polymerization...To fabricate polydopamine-sensitized solar cells with improved solar power conversion efficiency, the effects of pH, buffer, adsorption time and electrode potential for the electrochemical oxidation and polymerization of dopamine on TiO<sub>2</sub> film were investigated. The optimum pH was around 7. It was found that the use of a buffer, especially 2-(N-morpholino)ethanesulfonic acid, significantly deteriorated the electrochemical adsorption of polydopamine, and the highest solar power conversion efficiency was obtained without buffer. With increasing adsorption time, the amount of adsorbed polydopamine increased but the solar power conversion efficiency decreased, suggesting the increased resistivity of polydopamine with a larger degree of polymerization. It was suggested that the reversal of electrode potential from positive to negative would be essential for the electrochemical adsorption of polydopamine.展开更多
文摘Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.
文摘Because Silicon carbide (SiC) ceramics have various excellent properties, the demand for larger and complicated shapes has been increasing. This paper introduces an innovative method that would not require a large furnace, and further, would minimize the production cost and the thermal history, namely the “flash-bonding” technique. The borosilicate glass with low thermal expansion coefficient, Pyrex glass, was selected as the brazing material. In this work, as-is or surface-oxidized SiC plates were joined using Pyrex glass as brazing material, and the reaction and wetting of Pyrex glass on as-is or surface-oxidized SiC plate were investigated. It was found that the protective film of the surface-oxidized SiC lowered the oxygen partial pressure, and hence, generated many pores in the interface.
文摘Due to its electron configuration (Xe) 4 f14 6 s2, Ytterbium (Yb) could form divalent oxide, YbO. In this study, the solid-state synthesis of metastable YbO was investigated by the oxidation of Yb metal at normal pressure using two experimental conditions: 1) heat treatment of Yb metal under Ar gas atmosphere with metal carbonate as an oxygen source;and 2) heat treatment of Yb metal under the continuous gas flow condition using various gas atmospheres. Products were identified using the powder X-ray diffraction and scanning electron microscope. It was found that almost single phase YbO was obtained in the experimental condition 1) using the molar ratio of Ca-CO3/Yb = 0.4. Thermodynamic calculations suggested that the YbO formation be controlled not by thermodynamics but by kinetics, and further that the evaporation of Yb metal in the BN crucible played a key role for the formation of the meta-stable YbO.
文摘Y-Si compounds with the composition of Y:Si = 1:2 were fabricated using Yttrium and Silicon raw powders with low and high purity in various atmospheres and temperatures. Although the latest Y-Si phase diagram shows that the α- and β-YSi<sub>2</sub> phases are the stable phases for the stoichiometric composition of Y:Si = 1:2, the current experimental results suggest that the high temperature phase with the hexagonal structure, β-Y<sub>3</sub>Si<sub>5</sub>, would be the stable phase for this composition, and that the high temperature phase with the orthorhombic structure, β-YSi<sub>2</sub>, would be the meta-stable phase with high oxygen impurity content. It was demonstrated that YSi<sub>2</sub> powders possess much superior chemical stability than Yttrium metal. It was found that the best dispersing solvent was 2-propanol for YSi<sub>2</sub> powder.
文摘To fabricate polydopamine-sensitized solar cells with improved solar power conversion efficiency, the effects of pH, buffer, adsorption time and electrode potential for the electrochemical oxidation and polymerization of dopamine on TiO<sub>2</sub> film were investigated. The optimum pH was around 7. It was found that the use of a buffer, especially 2-(N-morpholino)ethanesulfonic acid, significantly deteriorated the electrochemical adsorption of polydopamine, and the highest solar power conversion efficiency was obtained without buffer. With increasing adsorption time, the amount of adsorbed polydopamine increased but the solar power conversion efficiency decreased, suggesting the increased resistivity of polydopamine with a larger degree of polymerization. It was suggested that the reversal of electrode potential from positive to negative would be essential for the electrochemical adsorption of polydopamine.
