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Fabrication of Alumina Free-standing Objects by Electrophoretic Deposition
Uchikoshi Tetsuo,Furumi Seiichi,Suzuki Tohru S.,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.
Aqueous Processing of Textured Silicon Nitride Ceramics by Slip Casting in a Strong Magnetic Field
Zhu Xinwen,Uchikoshi Tetsuo,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
This work will report a highly textured β-Si3N4 ceramic by aqueous slip casting in a magnetic field and subsequent pressureless sintering, Effects of the sintering aids, polymer dispersant, pH and stirring time on the stability of the Si3N4 slurries were studied. The textured β-Si3N4 with 97 % relative density could be obtained by slip casting in a magnetic field of 12 T and subsequent sintering at 1800 oC for 1 h. The textured microstructure is featured by the alignment of c-axis of β-Si3N4 crystals perpendicular to the magnetic field, and the Lotgering orientation factor, f, is determined to be 0.8.
Bending Strength of Textured Alumina Prepared by Slip Casting in a Strong Magnetic Field
Suzuki Tohru S.,Uchikoshi Tetsuo,Morita Koji,Hirage Keijiro,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The mechanical properties of ceramics materials can be tailored by designing their microstructures. We have reported that development of texture can be controlled by slip casting in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina. A strong magnetic field of 12T was applied to the suspension indcuding alumina powder to rotate each particle during slip casting. The sintering was conducted at the desired temperature in air without a magnetic field. C-axis of alumina was parallel to the magnetic field. Bending strength of textured alumina depended on the direction of oriented microstructure.
홍상휘,문지훈,Kouji Mimura,Makoto Mikami,Masahito Uchikoshi,Minoru Isshiki 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2
We have investigated the effect of annealing in an O2 atmosphere on the electrical properties of high-quality ZnO single crystals grown by seeded chemical vapor transport (SCVT). A temperature dependent Hall-effect technique indicates that the dominant donor in as-grown ZnO crystals has an ED of 42.8 meV and ND value of 2.8 × 1017 cm−3. After heat treatment in the O2 atmosphere at 1000 oC for 5 h, the color of the crystal changed from an orange color to transparent, and the ND value decreased to 4.3 × 1016 cm−3, while the ED value did not change. It can be deduced that the dominant donor in as-grown ZnO single crystals is a donor type native defect, which has a donor binding energy of about 42.8 meV.
Characterization of Microstructure and Mechanical Properties of High-Purity Iron Added with Copper
( O Taguchi ),( Su Yeon Lee ),( M Uchikoshi ),( M Isshiki ),( Chan Gyu Lee ),( S Suzuki ),( Vladimir S Gornakov ) 한국열처리공학회 2012 熱處理工學會誌 Vol.25 No.1
An influence of the addition of copper (0.5, 1.0 and 1.5 mass% Cu) on the microstructure and mechanical properties of high purity iron (99.998 mass%) was characterized. The microstructure and microhardness of high-purity iron based samples, which were rolled at room temperature and subsequently annealed, were investigated in this work. The microstructure of the samples has been observed by electron back scattering diffraction (EBSD) and the mechanical properties have been studied by using micro-Vickers hardness test. The results of microstructural observation showed that deformation band was formed in high purity iron by rolling at room temperature, and it was recovered by annealing up to about 900 K. The microhardness results showed that the softening of high-purity iron occurred by annealing up to about 900 K, while the hardness of iron added with about 0.5-1.5 mass% copper was kept over 100 Hv and at the early time of annealing reached a maximum. The hardness of iron added with a small amount of copper may be attributed to precipitation hardening as well as solution hardening. The orientation of crystal in recrystallized grain was almost same as that of deformed grain. (Received November 21, 2011; Revised December 28, 2011; Accepted January 19, 2012)
Impurity Behavior in Cu Refined by Ar Plasma-Arc Zone Melting
G. M. Lalev,임재원,N. R. Munirathnam,G.-S. Choi,M. Uchikoshi,K. Mimura,M. Isshiki 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.5
Purification of a 4N grade Cu rod by argon plasma-arc zone melting (APZM) was carried out. Detailed impurity analysis of the Cu rod was performed using glow discharge mass spectrometry (GDMS). Three impurity behavior groups based on segregation and evaporation during APZM were discussed using the GDMS analysis. Although the impurities with segregation coefficient ko < 1 were theoretically expected to be segregated towards the end of the Cu rod, it was found that the segregation effect by APZM can occur when the equilibrium distribution coefficient (ko) is less than 0.4 due to the strong affinity of Cu for some metallic and non-metallic impurities. On the other hand, the impurities for which ko > 1 had no significant reduction in their impurity concentrations. Some impurities, like Mg, S, Cd and Zn, were reduced much faster than the others in Cu. This was ascribed to the removal by zone refining coupled with the evaporation of impurities for Pimp/PCu > 102. Purification of a 4N grade Cu rod by argon plasma-arc zone melting (APZM) was carried out. Detailed impurity analysis of the Cu rod was performed using glow discharge mass spectrometry (GDMS). Three impurity behavior groups based on segregation and evaporation during APZM were discussed using the GDMS analysis. Although the impurities with segregation coefficient ko < 1 were theoretically expected to be segregated towards the end of the Cu rod, it was found that the segregation effect by APZM can occur when the equilibrium distribution coefficient (ko) is less than 0.4 due to the strong affinity of Cu for some metallic and non-metallic impurities. On the other hand, the impurities for which ko > 1 had no significant reduction in their impurity concentrations. Some impurities, like Mg, S, Cd and Zn, were reduced much faster than the others in Cu. This was ascribed to the removal by zone refining coupled with the evaporation of impurities for Pimp/PCu > 102.