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Li₂O·Al₂O₃·4SiO₂ 결정화 유리 및 전이금속 산화물의 원적외선 방사 특성
허남정,양중식 慶熙大學校 材料科學技術硏究所 1991 材料科學技術硏究論集 Vol.4 No.-
The far infrared radiation characteristic for Li₂O·Al₂O₃·4SiO₂ (LAS) glass, the LAS glass-ceramic and sintered transition metal oxides such as CuO, Fe₂O₃ and Co₃O₄, were investigated. LAS glass and LAS glass-ceramic has radiation characteristics of far infrared radient. Infrared emissivity of the LAS glass-ceramic was higher than that of the LAS glass. Heat-treated CuO and Co₃O₄ had radiation characteristic of high efficiency infrared radiant, and heat-treated Fe₂O₃ had radiation characteristic that infraerd emissivity decreased in higher wave length above 15μm.
Frequency-Dependent Dielectric Anomalies in Magnetic Oxides
허남정,박영안,송기명 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6
In the last few years, there have been many studies on the dielectric properties of magnetic oxides, mostly in the aspect of the coupling between ferroelectricity and magnetism. These studies have been focused on dielectric anomalies at the magnetic transition temperature, the magnetodielectric effect, the magnetic relaxor ferroelectricity, materials with high dielectric constants, etc. However, it appears that some of these studies were based on an erroneous interpretation of the dielectric functions measured by using LCR meters. Here, we report rare examples of two-step dielectric anomalies in TbMnO3 and Bi2Fe4O9 that show peculiar frequency dependences. We point out that the thermally-activated charge carriers in isolated impurities are the most probable origin of the dielectric anomalies with the typical relaxor-like frequency dependence.
비수계 분산중합에 의해 제조된 PMMA Seed-core 입자의 Surface Morphology
許南禎,李基昌 慶尙大學校生産技術硏究所 1995 生産技術硏究所論文集 Vol.11 No.-
Various types of non-aqueous acrylic dispersion particle were prepared by 2 stage dispersion polymerization in aliphatic hydrocarbon media. The surface morphology and the degree of wrinkles of the resulting PMMA seed-core particles were found to be greatly influenced by polymerization parameters, such as polymerization process, initial amount of AIBN. EGDMA concentration, feeding time of monomer mixture and polymerization temperature at the second-stage polymerization. The reaction conditions for formation of the "raisin-like" particles were found to be semi-continuous process in the presence of 0.29g EGDMA cross-linker and 0~0.0llg AIBN as a initial catalyst in second-stage polymerization using butyl-rubber stabilized PMMA seed latex. The surface morphology of the PMMA seed-core particles, prepared using butyl rubber stabilized PMMA seed panicles, was found to be greatly influenced on the initial amount of AIBN, mode of polymerization process, amount of cross-linker, feeding time of monomer mixture, and polymerization temperature. In semi-continuos process, when the initial amount of AIBN used in second-stage was in range of 0 ~ 0.011g. the resulting PMMA seed-core particles showed deeply wrinkly, raisin-like appearance. On the other hand, when the initial amount of AIBN was 0.11g, degree of wrinklesof the PMMA seed-core particles was significantly decreased. The degree of wrinkles on the particle surface of the PMMA seed-core particles, ingeneral, showed a tendency of decrease with increasing AIBN concentration as a initial catalyst in second-stage polymerization. The degree of wrinkles on the panicle surface of the PMMA seed-core particles as EGDMA concentration was decreased with going away from 0.29g EGDMA cross-linker concentration. The degree of wrinkles of the resulting PMMA seed-core particles was found to be increased with increasing the feeding time of the monomer mixture. The PMMA seed-core particles prepared at 105℃, were found to be well separated-stable latexes independent of presence or absence of EGDMA. On the other hand, the latexes prepared at reaction temperatures lower than 105℃ and only in the absence of EGDMA cross-linker were found to be all stable. In cases of the preparations with EGDMA, gelation of the PMMA seed-core particles was occurred with formation of lots of secondary nucleated small particles. In batch process, the initial amount of AIBN was little effect on the exterior morphology of PMMA seed-core particles. At 0.29g EGDMAcross-linker, all coagulated latexes with the occurrence of secondary nucleated small particles were formed. Although numerous ?? as to the detailed mechanism of particle nucleation and growth in dispersion polymerization havebeen proposed, no generalized conclusions have been drawn. It is ?? that the butyl rubber-stabilized PMMA seed particles, prepared in this study, have an interpenetrating network(IPN) structure, with the butyl rubber component of the PMMA-butyl rubber graft copolymer forming aninterconnecting network throughout the interior of the PMMA seed particles. This IPN structure in the PMMA seed particles could be important factor in controling the surface morphology of the PMMA seed-core particles prepared under various reaction conditions described above. We do not have the detailed mechanistic solutions to the experimental results obtained in this study at the moment. More work should be done on this subject.
허남정(Namjung Hur) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.3
Principles in the synthesis of small-sized high-quality crystals for the experimental condensed matter physics will be discussed in this paper. Synthesis process and cautions will be introduced especially for the synthesis methods which can be easily accessible to researchers. Starting from the solid state reaction which is the most common synthesis method, I will explain the quartz tube sealing that is crucial for making polycrystalline materials as well as single crystals in various conditions. Finally, basics of single crystal growth and various techniques will be introduced on the whole for the researchers who are not familiar with the material synthesis.
Synthesis and Charaterization of bile acid conjugated Low Molecular weight Water-soluble Chitosan
허선행 ( Sun Heang Heo ),반성진 ( Seong Jin Ban ),임수일 ( Su Il Lim ),강민종 ( Min Jeong Kang ),장진선 ( Jin Sun Jang ),남정표 ( Joung Pyo Nam ),김동곤 ( Dong Gon Kim ),정창남 ( Chang Nam Jeong ),장미경 ( Mi Kyeong Jang ),나제운 한국공업화학회 2008 응용화학 Vol.12 No.2