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Kim, Kyumin,Jeon, Kwang-Won,Moon, Ki Woong,Kang, Min Kyu,Kim, Jongryoul IEEE 2016 IEEE transactions on magnetics Vol.52 No.7
<P>The coercivity and the remanence of sintered M-type ferrites are highly dependent on the microstructure of the ferrite particles, particularly the size, morphology, and crystal orientation of the particles. To control the microstructures of ferrite particles, it is strongly recommended to control the nucleation and grain growth of them. In this paper, molten NaCl was used to control the crystal orientation and shape of Sr ferrite (SrFe12O19) particles. By changing the calcination conditions, Sr ferrite particles were obtained which had a hexagonal plate shape, and whose c-axis was aligned to the normal direction of the plate. Without any sophisticated magnetic alignment, Sr ferrite particles calcined at 1050 degrees C showed a saturation magnetization of 73.5 emu/g and a coercivity of 3267 G. This method was shown to be effective for developing high-performance hard ferrites.</P>
Kim, Minyeol,Lee, Kwiyoung,Choi, Moosung,Kim, Jongryoul IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>The magnetic properties of ferrite powders are known to be strongly dependent on their morphologies, such as size and shape. Thus, it is critical to synthesize homogeneous single-crystalline ferrite powders in order to improve the magnetic properties of composite magnetic sheets containing ferrite powders. In this experiment, strontium ferrite powders were synthesized using the molten salt method to control the microstructures and morphologies of the powders. As a result, single-crystalline hexagonal plate-shaped strontium ferrite powders with an average size of 2–3 <TEX>$\mu \text{m}$</TEX> were successfully obtained by the sequential calcination process at 850 °C for 1 h and then at 1050 °C for 1 h. These synthesized ferrite powders measured a magnetic saturation of 72.9 emu/g and a coercivity of 3255 Oe.</P>
Effect of Titanium Addition on High Temperature Workability of High Manganese Austenitic Steel
KIM, Rosa,BAE, Cheoljun,HA, Yu-Mi,KIM, Jongryoul Iron and Steel Institute of Japan 2018 ISIJ international Vol.58 No.3
<P>In the present study, the high temperature workability of high manganese austenitic steel has been examined to prevent the grain boundary embrittlement cracking problems in the continuous casting process. As-cast Fe-22Mn-0.4C steel exhibited poor hot ductility behaviors at 900 degrees C tensile test. Phosphorus segregation and BN precipitation at grain boundaries were mainly responsible for this deterioration. In order to enhance the hot ductility, titanium was added to this steel, and high temperature workability was compared in view of reduction of area in tensile test at 900 degrees C. BN precipitation at grain boundaries was effectively suppressed by the formation of interior Ti(C,N) precipitates. Furthermore, phosphorus atoms, a grain boundary embrittlement element, were observed to segregate at Ti(C,N) interfaces in Auger electron spectroscopy and atom probe tomography. These results show that titanium addition in Fe-22Mn-0.4C steel can effectively improve the high temperature workability by decreasing the segregation of phosphorus at grain boundary.</P>
JinBae Kim,Sang-Geun Cho,Namseok Kang,Kwangyeol Choi,Jongryoul Kim IEEE 2012 IEEE transactions on magnetics Vol.48 No.11
<P>We present the results of the magnetic domain structures of BaAl<SUB>2</SUB>Fe<SUB>10</SUB>O<SUB>19</SUB> nanopowders prepared by a self-propagating combustion process. Amorphous precursors were calcined at 850 °C for 2 h with NaCl (Sample I) and without NaCl (Sample II). The transmission electron microscope and atomic force microscopy images evidently suggested that there was a topological difference between Sample I (plate- and rod-shaped nanopowders) and Sample II (rod-shaped nanoparticles). We observed a considerably enhanced coercivity in Sample II, compared to Sample I. This result can be understood by the change in the magnetic domain width due to the shape effect of the nanopowders, which was investigated by measuring the field-controlled magnetic force microscopy.</P>
나노 연/경자성 분말 재료를 이용한 Exchange-coupling 자석의 제조 기술
김종렬(Jongryoul Kim),조상근(Sang-Geun Cho),전광원(Kwang-Won Jeon) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.6
Magnetic materials has been applied to various fields due to their energy convertible properties between electrical and mechanical energy. Particularly, permanent magnets have been currently attracted much attention because they produce external magnetic field without any electrical current. For high efficiency, a demand for permanent magnets containing rare earth elements has been continuously increased, which abruptly raises the price and causes the supply difficulty of rare earth materials. Therefore, the development of permanent magnets with less or without rare earth elements become a urgent issue. In this report, the current trend and major issues on high efficiency permanent magnets, particularly exchange-coupling magnets, are discussed.