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김철만(C.M. Kim),백종현(J.H. Baek),김영표(Y.P. Kim),김우식(W.S. Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Natural gas pipelines are buried in 1.5m depth along the road. Because the rod are curved and the gab between top and bottom is very high in the majority of cases, bend pipes are used. They are classed as hot and cold bend pipe. In case of a very sharp curve road, the hot bend pipes are used such as crossing the river, the road and the railroad. Otherwise, the cold bend pipes are utilized. This research was designed to study the mechanical properties of cold bend pipes in the two types of bend pipes. The curved section(intrados, extrados, neutral) with bending deformation and original body pipe(tangent end) with non-deformation was studied. Cold bending procedure had little effect on thickness variation. The tensile strength and impact energy of the curved section and the tangent end showed somewhat similar results. In this respect of fracture mechanic through CTOD test, the cold bend pipe appeared that it had sufficient integrity.
Fe 이온이 단사결정 NiCr₂S₄에 미치는 자기적 성질에 관한 연구
김철성(C. S. Kim),고흥문(H. M. Ko),박재윤(J. Y. Park) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.3
Ni_xFe_(1-x)Cr₂S₄ has been studied by Mossbauer and X-ray technique and the crystal structure is found to be monoclinic in the composition range 0.9≤x≤1.0 Mossbauer spectra of Ni_xFe_(1-x)Cr₂S₄ have been taken at various temperatures ranging from 12 K to room temperature. The isomer shift indicates that the charge state of Fe ions is ferrous in character and temperature dependence of isomer shift is in good agreement with theoretical value. Magnetic ordering of antiferromagnetic nature exists below the Neel temperature, T_N=200 K and magnetic hyperfine and quadrupole interactions at 81 K have been studied, yielding the following results : Hhf=156 kOe, ΔE_Q= 2.15 ㎜/s, θ=59˚, Φ=90 0, and η=0.9 for Ni_(0.99)Fe_(0.01)Cr₂S₄. The Neel temperature T_N increases linearly, suggesting that the superexchange interaction for the Ni-S-Cr link is stronger than that for the Fe-S-Cr link.
Mossbauer Study of Co0.3Fe0.7Cr₂S₄
김철성(C. S. Kim),하민용(M. Y. Ha),이운화(W. H. Lee),윤성로(S. R. Yoon),서정철(J. C. Sur) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.3
Co_(0.3)Fe_(0.7)Cr₂S₄ has been studied by Mossbauer spectroscopy and X-ray diffraction, The crystal structure is found to be a cubic spinel with the lattice parameter α。=9.967 Å. Mossbauer spectra have been collected over the temperature range 12 K ~ 300 K. The absence of quadrupole splitting above the Neel temperature T_N indicates that iron ions occupy only the tetrahedral (A) sites, The isomer shift indicates that the charge state of a Fe ion is ferrous in character. It is notable that as the temperature decreases below T_N=184 K, both quadrupole splitting and asymmetrical line broadening appear and increase with decreasing temperature, suggesting the appearence of a dynamic Jahn-Teller distortion. The magnetic hyperfine field and quadrupole splitting at 12 K are found to be 193 kOe and 1.10 ㎜/s, respectively, Debye temperature is found to be 218 K.
산소 결핍에 따른 Fe가 도핑된 TiO<sub>2-δ</sub>의 상온 강자성 현상에 관한 연구
이희민,김철성,엄영랑,이창규,Lee, H.M.,Kim, C.S.,Uhm, Y.R.,Rhee, C.K. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.6
Effects of oxygen deficiency on the room temperature ferromagnetism in Fe-doped reduced $TiO_2$ have been investigated by comparing the air-annealed $Ti_{0.97}Fe_{0.03}O_2$ compound with secondly post-annealed one in vacuum ambience. The air-annealed sample showed a paramagnetic behavior at room temperature. However, when the sample was further annealed in vacuum, a strongly enhanced ferromagnetic behavior was observed at same temperature. $M{\"{o}}ssbauer$ spectra of air-annealed sample at 295K showed a single doublet of $Fe^{3+}$, suggesting that the Fe ions are paramagnetic. On the other hand, the absorption spectra after vacuum-annealing exhibited two doublets, in which one is the same component with air-annealed sample and the other is new doublet corresponding to $Fe^{2+}$ state. This result suggests that the occurrence of ferromagnetism in reduced sample may be interpreted as the contribution of unquenched orbital moment of $Fe^{2+}$ ions.