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고에너지볼밀을 이용한 PVA 고분자가 표면 코팅된 B<sub>4</sub>C 나노복합재 제조
엄영랑,김재우,정진우,이창규,Uhm, Young-Rang,Kim, Jae-Woo,Jung, Jin-Woo,Rhee, Chang-Kyu 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.2
Mechanical coating process was applied to form 89 %-hydrolyzed poly vinyl alcohol (PVA) onto boron carbide ($B_4C$) nanopowder using one step high energy ball mill method. The polymer layer coated on the surface of B4C was changed to glass-like phase. The average particle size of core/shell structured $B_4C$/PVA was about 50 nm. The core/shell structured $B_4C$/PVA was formed by dry milling. However, the hydrolyzed PVA of $98{\sim}99%$ with high glass transition temperature ($T_g$) was rarely coated on the powder. The $T_g$ of polymer materials was one of keys for guest polymer coating on to the host powder by solvent free milling.
뫼스바우어선원 적용을 위한 <sup>58</sup>Ni 표적체 및 Co가 확산된 Rh복합재 제조
엄영랑,최상무,김종범,손광재,Uhm, Young Rang,Choi, Sang Mu,Kim, Jong-bum,Son, Kwang Jae 한국분말야금학회 2015 한국분말재료학회지 (KPMI) Vol.22 No.6
The en-riched $^{58}Ni$ powders are dissolved in acid solution and coated on a Cu target for proton irradiation at cyclotron to produce $^{57}Co$ radioisotope. The condition of the plating bath and the coating process are determined using the en-riched powders. To establish the coating conditions for $^{57}Co$, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a rhodium plate. The thermal diffusion of electroplated Co into a rhodium matrix was studied to apply a $^{57}Co$ Mssbauer source. The diffusion depth from surface to matrix of Co is depended on the annealing temperature and time. The deposited Co atoms diffuse completely into a rhodium (Rh) matrix without substantial loss at an annealing temperature of 1200 for 4 hours.
엄영랑,이창규,김철성,Uhm Young-Rang,Rhee Chang-Kyu,Kim Chul-Sung 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.2
[ $R_{1/3}Sr_{2/3}FeO_{3}$ ](R=Pr, Nd, and Sm) was synthesized and their magnetic properties and charge ordering(CO) transition related with lattice dynamics and oxygen vacancy were systematically investigated. The charge disproportion ation(CD) in $R_{1/3}Sr_{2/3}FeO_{3}$(R=Pr,Nd) was in which two kins of iron with valence state $Fe^{3+}$ and $Fe^{5+}$ were found with ratio of 2:1. In this charge ordering state a sequence of $Fe^{3+}Fe^{3+}Fe^{5+}Fe^{3+}Fe^{3+}Fe^{5+}$ exists aligned along the [111] direction of the pseudocubic perovskite structure. The charge ordering exist in distorted structure involving $t_{pd}$ hybridization. The disordering phases coexist in distorted structure as temprature in creases that is controlled amount of oxygen vacancy. The magnetic hyperfine fields indicate charge tranfering temperature as it dissapeared drastically.
엄영랑(Young Rang Uhm),이창규(Chang Kyu Rhee),김철성(Chul Sung Kim) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.2
The Ag nanoparticles attached La<sub>0.7</sub>Sr<sub>0.3</sub>Co<sub>0.3</sub>Fe<sub>0.7</sub>O<sub>3?δ</sub> (LSCF) perovskites were prepared by plasma method. The Ag nanoparticles with size of several nanometers deposited from the Ag target were coated on the surface of LSCF powders with size range from 0.2 to 3 μm. The agglomeration of Ag particles annealed at 800℃ under inert gas of Ar were rarely observed. The inter-diffusion between surface Ag and core LSCF is effectively strong to prevent aggregation of Ag nanoparticles. The wave number of FT-IR spectra for LSCF were largely shifted as the concentration of Ag on LSCF up to 2.11 wt.%. The ionic states of irons in LSCF were measured by Mossbauer spectroscopy. The small amount of Fe<sup>4+</sup> ions are converted to Fe<sup>3+</sup> ions after Ag nanopartcles were coated on LSCF.
Sol - gel 합성에 의한 자성 garnet Y₃-xBixFe5O₁₂의 결정학적 및 Mossbauer 분광학 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim),이재광(Jae-Gwang Lee) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.4
Crystallographic and magnetic properties of single phase garnet Y_(3-x)Bi_xFe_5O₁₂(x=0.0, 0.25, 0.5, 0.75, 1.0) were studied by using x-ray diffraction, Mossbauer spectroscopy and vibrating sample magnetometer (VSM). Ultra-fine polycrystalline cubic samples have been prepared by sol-gel method. The lattice constant increase linearly with increasing an amount of Bi. Annealing temperature was larger than 800 ℃ for the growth of a single-phase garnet powder. The second phase of garnet, BiFeO₃ was at 1000 ℃ for x=0.75, and 950 ℃ for x=1.00. From Mossbauer spectroscopy and VSM measurements, the magnetization and the coercivity were decreased and the Curie temperature Y_(3-x)Bi_xFe_5O₁₂(x=0.0, 0.25, 0.5, 0.75, 1.0) was slightly increased as increasing the Bi content.
Sol - Gel 법에 의한 Y₃-xLaxFe5O₁₂(0.0≤X≤1.0) 분말과 박막의 합성 및 자기적 특성에 관한 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim),임연수(Yun Soo Lim),이재광(Jae-Gwang Lee) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.6
Y_(3-x)La_xFe_5O₁₂ (x=0.0, 0.25, 0.5, 0.75, 1.0) powders and thin films were fabricated by a sol-gel method and their magnetic properties and crystal structures were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. XRD and Mossbauer spectroscopy measurements show that garnet powders annealed at 900 ℃ for 8 hours were single-phased and that thin films fired at 800 ℃ for 2 hours were crystallized without any preferred direction. X-ray diffraction patterns of Y_(3-x)La_xFe_5O₁₂ powders annealed at 1000 ℃ had only peaks of the garnet structure in case of x≤0.75 but those of Y₂LaFe_5O₁₂ powders consisted of peaks from garnets and LaFeO₃. Mossbauer sepectra of garnet powders grown by the sol-gel method had a similar shape of those of powders grown by a conventional ceramic method. Grain sizes of garnet powders were 200~300 ㎚ and the averaged surface roughness was 3.17 ㎚. Results of VSM measurements show that powders and thin films had soft magnetic properties and that the garnet powders had the largest saturation magnetization, 30 emu/g, and the lowest coercivity, 52 Oe.
엄영랑(Young Rang Uhm) 한국자기학회 2014 韓國磁氣學會誌 Vol.24 No.5
Iron-oxide nanopowders were synthesized by a pulsed wire evaporation (PWE) in various ambient gas conditions. SEM measurement indicates that the spherical iron nanoparticles are about 50 nm in diameter. The phase analysis for the produced ironoxide powders was systematically investigated by using Mossbauer spectra and the results show that classified phases of Fe₂O₃ and Fe₃O₄ can be controlled by regulating the oxygen concentration in the mixed gas during the PWE process. A quadrupole line on the center of Mossbauer spectrum represents the superparamagnetic phase of 12 % from γ-Fe₂O₃ phase.
Perovskite Gd₁-xSrxFeO₃-y(x = 0.0, 0.5)의 Mossbauer 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim),서정철(Jung Chul Sur),오영제(Young-Jei Oh) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.2
Crystallographic and magnetic properties of perovskite Gd_(1-x)Sr_xFeO_(3-y) (x = 0.0, 0.5) substituted Sr²+ having larger ionic radius than Gd³+ at GdFeO₃ have been studied by x-ray diffraction, Mossbauer spectroscopy, and VSM. The crystal structures are found to be orthorhombic with the lattice parameters : a_0 = 5.53 Å, b_0=5.608 Å, c_0=7.724 Å for Gd_(0.5)Sr_(0.5)FeO_(3-y), Gd_(1-x)Sr_xFeO_(3-y) (x=0.0, 0.5) have been investigated over temperature range from 4.2 to 690 K using the Mossbauer technique. The Neel temperature of Gd_(1-x)Sr_xFeO_(3-y) system is 690 K with x value of 0.0 and 515 K with x value of 0.5. Analysis of Mossbauer spectra and Mohr's salt analysis for Gd_(1-x)Sr_xFeO_(3-y) demonstrated the existence of the mixed valence states of iron and the coordination state of Fe³+ and Fe⁴+ ions. The Corresponding hyperfine parameters for GdFeO₃ are compatible with S = 5/2 Fe³+ in octahedral coordination.
부양증발응축법으로 제조된 Ni과 Ni@C의 자성특성 및 Biginelli 합성 촉매 적용연구
엄영랑(Young Rang Uhm) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.3
Carbon-encapsulated Ni and metal Ni nanoparticles were synthesized by levitational gas condensation (LGC). Methane (CH₄) gas was used to coat the surface of the Ni nanoparticles. The Ni particles had a core diameter of 10 ㎚, and were covered by 2~3 ㎚ thin carbon layers with multi-shells structure.The low magnetization comparing with the Ni nanoparticles without carbon-shell results in the coexistence of nonmagnetic carbon and a large surface spin percentage with disordered magnetization orientation for the nanoparticles. Biginelli reactions in the presence of L-proline and Ni and carbon encapsulated Ni nanoparticles were carried out to change the ratio between stereoisomers. The obtained S-enantiomers for 3,4-dihydropyrimidine (DHPM) using catalysts of Ni, and Ni@C was an excess of about Δ~7.4% and Δ~19.6 %, respectively. The nanopowders were fully recovered using magnet to reuse as a catalyst. The Ni@C was shown at same yield to formation of 3,4-DHPM, though it was recycled for catalyst in the reaction.
Garnet Y2.5La0.5Fe5O₁₂의 Mossbauer분광학 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.1
Y_(2.5)La_(0.5)Fe_5O₁₂ is fabricated by a sol-gel method and the magnetic properties of single phase garnet are investigated by using X-ray diffraction, vibrating sample magnetometer, scanning electron microscopy and Mossbauer spectroscopy. The single phase powders garnet was fired at 1000 ℃ for 8 hours. The crystal structures of samples are cubic garnet. Mossbauer spectroscopy were measured from 13 K to 750 K. Mossbauer spectra show that the iron exist ferric trivalence in sample. The spin wave constants were determined B_(3/2)=0.32±0.05, C_(5/2)=0.18±0.05 and Debye temperature were determined 382 K at 24(d) site and 246 K at 16(a)-site. The saturation magnetization (Ms) of powder is 25 emu/g.