• 한국입자에어로졸학회지
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• 제19권2호
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• pp.31-42
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• 2023

The charge and magnetic characteristics of LM (Low-metallic) and NAO (Non-asbestos-organic) brake wear particles were analyzed. The ratio of charged particles from total particles is about 86% of the LM pad and about 92% of the NAO pad. Number of charge per particle from the NAO pad is also higher than that of the LM pad. The ratio of magnetic particles from total particles increases with the particle size. The ratio of magnetic particles from the LM pad is about 15% for the particles with the size of 1 ㎛, and about 74% for ones with 5 ㎛. The ratio from the NAO pad is about 5% for the particles with the size from 0.5 ㎛ to 2 ㎛, and about 80% for the particles with 5 ㎛. Through the analysis of the components of the two pads with SEM-EDS (Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy), it was found that the LM pad was occupied with more iron fraction than the NAO pad and that PM_2.5-10 was occupied with more iron fraction than PM_2.5. The particles smaller than 10 ㎛ (i.e. PM₁₀) from the LM pad contained about 83% of charged particles, about 43% of magnetic particles, and about 93% of charged or magnetic particles. PM₁₀ from the NAO pad contained about 88% of charged particles, about 15% of magnetic particles, and about 89% of charged or magnetic particles.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.19-23
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• 2022

We have been developing a magnetic separation device that can be used in low magnetic fields for paramagnetic materials. Magnetic separation of paramagnetic particles with a small particle size is desired for volume reduction of contaminated soil in Fukushima or separation of iron scale from water supply system in power plants. However, the implementation of the system has been difficult due to the needed magnetic fields is high for paramagnetic materials. This is because there was a problem in installing such a magnet in the site. Therefore, we have developed a magnetic separation system that combines a selection tube and magnetic separation that can separate small sized paramagnetic particles in a low magnetic field. The selection tube is a technique for classifying the suspended particles by utilizing the phenomenon that the suspended particles come to rest when the gravity acting on the particles and the drag force are balanced when the suspension is flowed upward. In the balanced condition, they can be captured with even small magnetic forces. In this study, we calculated the particle size of paramagnetic particles trapped in a selection tube in a high gradient magnetic field. As a result, the combination of the selection tube and HGMS (High Gradient Magnetic Separation-system) can separate small sized paramagnetic particles under low magnetic field with high efficiency, and this paper shows its potential application.

• 자원리싸이클링
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• 제6권1호
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• pp.17-22
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• 1997

미립의 자성/비자성 입자의 혼합분체로부터 자성 입자만을 연속적으로 분리할 수 있는 전자석 유동층이 제안되었고 본 선별기에 의해 분리된 입자분중 자성 분율에 대한 공탑 가스유속, 혼합분체내 자성 입자의 분율(=100-비자성 입자의 분율) 및 전자석으로 공급되는 전류 세기와 같은 조업변수의 영향이 규명되었다. 전자석 유동층에 의한 자성 분리는 미립의 혼합분체내 자성입자에 작용하는 전자서의 자력이 분체를 유동화시키는 가스흐름으로 인한 유체력보다 클 때 가능함이 밝혀졌다.

• 한국초전도ㆍ저온공학회논문지
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• 제20권2호
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• pp.11-15
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• 2018

In this study, a cancer treatment by accumulating and aggregating ferromagnetic particles in newborn blood vessels was examined. It is necessary for this treatment to control dispersion-aggregation property of ferromagnetic particles. Ferromagnetic particles required in this method disperse at low magnetic field, aggregate at high magnetic field and maintain the aggregation even after removal of the magnetic field. In order to control the dispersion-aggregation property, the surface of magnetite particles was modified with higher fatty acids having different lengths. As a result, we succeeded to prepare propionic acid-modified magnetite particles that form irreversible aggregation by magnetic field. The model experiments simulating newborn blood vessels showed that these particles can block the flow by the magnetic field, and the blockage was maintained after removal of the magnetic field.

• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.13-17
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• 2023

Magnetic separation technology for small paramagnetic particles has been desired for the volume reduction of contaminated soil from the Fukushima nuclear power plant accident and for the separation of scale and crud from nuclear power plants. However, the magnetic separation for paramagnetic particles requires a superconducting high gradient magnetic separation system applied, hence expanding the bore diameter of the magnets is necessary for mass processing and the initial and running costs would be enormous. The use of high magnetic fields makes safe onsite operation difficult, and there is an industrial need to increase the magnetic separation efficiency for paramagnetic particles in as low a magnetic field as possible. Therefore, we have been developing a magnetic separation system combined with a selection tube, which can separate small paramagnetic particles in a low magnetic field. In the previous technique we developed, a certain range of particle size was classified, and the classified particles were captured by magnetic separation. In this new approach, the fluid control method has been improved in order to the selectively classify particles of various diameters by using a multi-stage selection tube. The soil classification using a multi-stage selection tube was studied by calculation and experiment, and good results were obtained. In this paper, we report the effectiveness of the multi-stage selection tube was examined.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1334-1339
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• 2018

Spherical nickel ferrite nanoparticles were synthesized using the thermal decomposition method and coated with cetyl trimethyl ammonium bromide (CTAB) after the synthesis. Transmission electron microscopy images showed that the average diameter of the particles was 9.40 nm. The status of the CTAB-coating on the surface of the particles was checked using Fourier-transform infrared spectroscopy. Their hysteresis curve showed that the particles exhibited a superparamagnetic behavior. The $T_1$ and the $T_2$ relaxations of the nuclear spins were observed in aqueous solutions of the particles with different particles concentrations by using a magnetic resonance imaging (MRI) scanner, which showed that the $T_1$ and the $T_2$ relaxivities of the particles in water were $0.57mM^{-1}{\cdot}s^{-1}$ and $10.42mM^{-1}{\cdot}s^{-1}$, respectively. In addition, using an induction heating system, we evaluated their potentials for magnetic hyperthermia applications. The aqueous solution of the particles with a moderate concentration (smaller than 6.5 mg/mL) showed a saturation temperature larger than the hyperthermia target temperature of $42^{\circ}C$. These findings show that the CTAB-coated nickel ferrite particles are suitable for applications as $T_2$ contrast agents in MRI and heat generators in magnetic hyperthermia.

• 대한기계학회논문집B
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• 제41권7호
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• pp.455-462
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• 2017

외부자기장에 의한 타원형 야누스 자성입자 사이의 자성 상호작용을 직접수치해석을 사용하여 분석하였다. 유한요소법에 기초한 가상영역법을 사용하여 입자계 유동해석을 수행하였고, 자기장 문제에서는 자성 포텐셜에 대한 지배방정식을 입자와 유체를 포함하는 전체영역에 대하여 풀어 자기장을 구하였다. 이 때 구해진 자기장으로부터 구한 맥스웰 응력을 사용하여 개별 입자에 작용하는 자기력이 계산된다. 입자의 운동과 최종적인 조립구조는 입자의 형상비, 개별 입자의 배향, 입자의 초기 분포에 크게 영향을 받는 것이 확인되었다. 또한 입자의 배향은 입자 주위의 유체 유동에도 영향을 주었다. 외부자기장에 의한 타원형 야누스 입자의 최종 조립구조는 앞서 언급한 인자들에 의해서 영향을 받은 것을 수치해석을 통해 확인할 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.88-92
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• 2009

When exposed to uniform magnetic fields externally applied, paramagnetic particles acquire dipole moments and the induced moments interacting with each other lead to the formation of chainlike structures or clusters of particles aligned with the field direction. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is applied to solve flows with magnetic chains in simple shear flow. We assumed that the particles constituting the chains are paramagnetic, and inertia of both flow and magnetic particles is negligible. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a fully coupled manner, enabling us to numerically visualize breakup and reformation of the chains by the combined effect of the external field and the shear flow. Simple shear flow with suspended magnetic chains is solved in a periodic domain for a given magnetic field. Dynamics of interacting magnetic chains is found to be significantly affected by a dimensionless parameter called the Mason number, the ratio of the viscous force to the magnetic force in the shear flow. The effect of particle area fraction on the chain dynamics is investigated as well.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.3979-3989
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• 2021

Several parametric effects on the magnetic collection have been evaluated considering dimension, strength of external magnetic field, injected velocity and particle concentration in the working fluid. Besides, accidental environments, expected in the containment of nuclear power plants, have also been addressed for the capture efficiency. The capture efficiency is especially enhanced with magnetic particle size and magnetic field strength through increased magnetic force; the non-magnetic coating thickness and fluid velocity hinder the magnetic collection. Based on the assessment, the magnetic withdrawal system can effectively capture magnetic particles even under accidental environments. Withdrawal of multifunctional magnetic particles or filtering of magnetic impurities can be effectively realized through the system.

• 한국정밀공학회지
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• 제30권12호
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• pp.1253-1258
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• 2013

Ceramic particles as polishing abrasives are often used in a magnetic abrasive polishing process because they have strong wear resistance. Non-ferromagnetic ceramic abrasives should be mixed with ferromagnetic iron particles for controlling the mixture within a magnetic brush during the polishing process. This study describes the application of the ceramic particles for the magnetic abrasive polishing. The distribution of the magnetic abrasives attached on a tool varies with magnetic flux density and tool rotational speed. From the correlation between abrasive adhesion ratio in the tool and surface roughness produced on a workpiece, practical polishing conditions can be determined. A step-over for polishing a large sized workpiece is able to be selected by a S curve, and an ultrasonic vibration assisted MAP produces a better surface roughness and increases a polishing efficiency.