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RISS 인기검색어
- 검색키워드
- 저자 : Yun-Hwei Shen (검색결과 3 건)
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Effects of Additives of CaO and Rare-Earth Oxides on the Sintering Behavior of AlN Ceramics
Chih-Hung Chu,Yun-Hwei Shen,Chih-Peng Lin,Shaw-Bing Wen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
The effect of additives of CaO plus three different rare-earth oxides (Y, Sm and Gd, separately) on the sintering behavior of AlN ceramics has been evaluated at 1700℃ by using a MoSi2 heater and ambient atmosphere. The results of density measurements show that the atomic weight of the rare-earth element may substantially affect the apparent density of the sintered AlN specimen due to the kinetics of atomic diffusion during sintering. The optimum results of this study show that these additives are effective in obtaining an apparent density of 3.26 g/cm3 (approaching a 100 % theoretical density of AlN). The Vicker's hardness of the sintered AlN can reach a high value of 1310 kg/mm2 and an apparent density of 3.34 g/cm3. A longer soaking time of between 3 and 5 h is necessary to practically eliminate the minor oxide phases. The effect of additives of CaO plus three different rare-earth oxides (Y, Sm and Gd, separately) on the sintering behavior of AlN ceramics has been evaluated at 1700℃ by using a MoSi2 heater and ambient atmosphere. The results of density measurements show that the atomic weight of the rare-earth element may substantially affect the apparent density of the sintered AlN specimen due to the kinetics of atomic diffusion during sintering. The optimum results of this study show that these additives are effective in obtaining an apparent density of 3.26 g/cm3 (approaching a 100 % theoretical density of AlN). The Vicker's hardness of the sintered AlN can reach a high value of 1310 kg/mm2 and an apparent density of 3.34 g/cm3. A longer soaking time of between 3 and 5 h is necessary to practically eliminate the minor oxide phases.
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Chih-Peng Lin,Chih-Hung Chu,Shaw-Bing Wen,Yun-Hwei Shen 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.5
AlN samples doped with sub-micron Y2O3 and CaO powders as sintering additives obtained using the micro hot-pressed (MHPed) sintering method in a MoSi2 heating element furnace were investigated. The minor amounts of secondary phases were identified as Al5Y3O12, CaYAl3O7, and CaAl4O7, which are related to the low sintering temperature as well as the removal of oxygen-related defects in the system. Relative densities of over 96% of the theoretical value were obtained after sintering at 1600 oC for 8 h, indicating that an adequate amount of additives and the use of the micro hot-pressed (MHPed) sintering process help improve the densification and thermal conductivity of AlN ceramics. The high thermal conductivity of 130Wm−1K−1was attributed to the purification of the AlN lattice, the elimination of some secondary phases, and the grain boundary phase distribution.
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Fung Fuh Wong,Chun Min Lin,Kun-Lung Chen,Yun-Hwei Shen,Jiann-Jyh Huang 한국고분자학회 2010 Macromolecular Research Vol.18 No.4
Novel amphiphatic imidazole compounds were evaluated as thermal latent catalysts for the polymerization of diglycidyl ether of bisphenol A (DGEBA). Amphiphatic compounds 5-9, two commercially available catalysts 1 and 2, and compounds 3 and 4 were used to cure epoxy resin systems for an investigation of their thermal latency and storage stability. The results from the cure activation energy and viscosity-storage time of the catalysts, the order of thermally latent activity was 3-phenylpropanoic acid (4) > 2-amino-3-phenylpropinoic acid (5) > 2-amino-3-(imidazole-4-yl)-propionic acid (H-His-OH, 8) > N-tert-butoxycarbonyl-histidine (9) > imidazole-4-acrylic acid (6) >3-(imidazole-4-yl)propionic acid (7) > 1-cyanoethyl-2-ethyl-4-methyl-imidazole (2) > 2-ethyl-4-methylimidazole (1) > histamine (3). From the results, the amphiphatic imidazole catalysts 5-9 showed better thermal latency than commercialized catalysts 1 and 2, basic catalyst 3 and acidic catalyst 4. Concerning the glass transition temperature (Tg), the use of amphiphatic imidazole catalysts 5-9 provided complete or near complete curing systems at temperatures ranging from 152-163 oC, which were similar to two commercially available catalysts (151-152 oC, 1 and 2)and histamine (159 oC, 3). On the other hand, the Tg for compounds 4 and 5 could not be detected at 30-300 oC from the temperature scans because of their weak nucleophilicity and low cross-linking reactivity.
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