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Effects of Ordering on the Magnetic Properties of Gas-Atomized Fe–Si–Cr Powders
Jang, Pyungwoo,Choi, Gwangbo,Bae, Chuljun IEEE 2017 IEEE transactions on magnetics Vol.53 No.4
<P>Fe-9% Si-2% Cr powder was gas-atomized and then annealed in order to investigate the effects of DO3 and B2 ordered phases on high-frequency permeability of the powder. The B2 phase is formed during the atomization process. The DO3 phase began to form at 450 degrees C and grew rapidly when annealed at higher temperature as confirmed by X-ray diffractometer, whereas the existence of the DO3 phase in the as-atomized powder could be confirmed by electron transmission microscope. With the increase in the temperature, the average lattice parameter and the coercivity decreased. There was an abrupt increment of the coercivity in the powder annealed at 450 degrees C. Highest permeability could be obtained in the powder annealed at a relative low temperature of 150 degrees C and then the permeability real decreased with the temperature. The behavior of the coercivity and the permeability with the temperature could be successfully explained by the formation of the DO3 ordered phase and the change of the electrical resistivity.</P>
Order-disorder transition and magnetic properties of Fe-6.5Si alloy powder cores
Jang, Pyungwoo,Lee, Bonghan,Choi, Gwangbo WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12
<P>Magnetic properties of Fe-6.5%Si powder compact cores were analyzed when cores were annealed at 400 – 800 °C for up to 960 min. Hysteresis losses were larger than eddy current lossed in all cores. With increasing annealing temperature core loss decreased while eddy current loss showed minimum when annealed at 500 °C. Variation of DC and AC magnetic properties with annealing temperature and time could be successfully explained by order-disorder transition, magnetostriction, resistivity, lubricant burn-off, and surface oxidation of particles. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Feasibility study of micro-undulator for T-ray sources by using FEM
Jang, Pyungwoo,Rhie, Keungwon,Lee, Byungcheol WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12
<P>Possibility of development of micro-undulator utilizing perpendicular magnetic recording was explored by 2-D FEM simulation. In the simulation FePt and CoCr layer were compared as an appropriate recording layer of the undulator. Also variation of maximum field and THD with aspect ratio and gap height were simulated so that they should be optimized in a given thickness of recording layer. From both the simulation results and Bitter patterns recorded on FePt/Fe micro-undulator, the possibility of development of micro-undulator by utilizing perpendicular recording technique could be confirmed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Properties of Fe-Al Cores Made From Fe-Al Powders Annealed in a Damp Hydrogen Atmosphere
Pyungwoo Jang,Seungchan Shin IEEE 2013 IEEE transactions on magnetics Vol.49 No.1
<P>Gas-atomized Fe-4, 6wt.%Al powders were annealed in a damp hydrogen atmosphere with a dew point of 0<SUP>°</SUP>C and -17<SUP>°</SUP>C in order to cover the powder surface with a high electrical resistivity layer of Al<SUB>2</SUB>O<SUB>3</SUB> and then compressed into cores. The powders should be oxidized at a temperature higher than 800 <SUP>°</SUP>C in order to oxidize the aluminum alone on the surface of powder, as confirmed by simulation using the STANJAN program. An Al-rich layer, i.e., an Al<SUB>2</SUB>O<SUB>3</SUB> layer, was formed on the surface of the Fe-Al powder, as confirmed by SEM. Loss of the cores made from the selectively oxidized powders was much lower than those of the cores with phosphate coats, so the selectively oxidized powder can be used to fabricate electrical actuators with high levels of performance.</P>
Properties of Iron Powder Compressed Cores with Magnetite Thin Film Insulator
Pyungwoo Jang(장평우) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.1
It is very important to isolate soft magnetic particles electrically in order to reduce an eddy current loss of compressed cores. In this study, iron powders were oxidized in a mixed gas of N<SUB>2+</SUB>H₂O at 600℃ in order to encapsulate the powders completely by iron oxide and compressed into cores. The oxide film was analyzed to be Fe₃O₄ by XRD as well as its color and grew linearly through oxidation. With increasing oxidation time, its permeability increased whereas the density decreased. The core, eddy current and hysteresis losses of the oxidized cores were much lower than those of the cores with insulating powders. It was confirmed that the Fe₃O₄ film formed in a damp atmosphere could encapsulate the iron particles completely and ensured lower eddy current loss.
Effects of Silicon Content on the Properties of Gas-Atomized Fe–Si–Cr Powders
Jang, Pyungwoo,Choi, Gwangbo IEEE 2017 IEEE transactions on magnetics Vol.53 No.11
<P>Fe-7%, 8%, 9%, and 11% Si-Cr powders were gas atomized and then annealed at 25 degrees C-750 degrees C to investigate the effects of Si content, DO3 phase, and B2 phase on the high-frequency permeability of the powders. The formation of the B2 phase could not be suppressed during the atomization process of all the powders. The evolution temperatures of the DO3 phase in the Fe-7%, 8%, and 9% Si-Cr powders as measured by X-ray diffractometer were 550 degrees C, 550 degrees C, and 450 degrees C, respectively. As the annealing temperature was increased, the DO3 phase grew rapidly, and the lattice parameters of the powders were decreased except for those of the Fe-11% Si-Cr powder. The coercivity of all powders decreased with increasing temperature; however, the coercivity of the Fe-8%, 9% Si-Cr powders increased sharply after annealing at 450 degrees C. Permeability decreased rapidly with increasing temperature except for the Fe-11% Si-Cr powder; thus, the highest real permeability was obtained for the as-atomized Fe-8% Si-Cr powder. The changes in the coercivity and permeability of the powders with annealing temperature could be attributed to the evolution of the DO3 phase, Si segregation, and changes in electrical resistivity.</P>
정현파 자속밀도 제어와 디지털 궤환을 이용한 AC 손실 측정방법
장평우(Pyungwoo Jang) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.1
New digital feedback algorithm was developed to measure iron loss of soft magnetic materials under a condition of sinusoidal flux waveform. V<SUB>in</SUB>(B) curve was used instead of H(B) curve to decide next input waveform in the feedback module so that adjusting phases of current waveform, flux waveform, and input waveform could be removed. The effectiveness of the developed algorithm was verified when iron loss of ferrite cores was measured under frequencies of 1 and 10 kHz.