• 자원리싸이클링
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• 제3권1호
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• pp.38-43
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• 1994

국내의 반도체 회사에서 발생한 IC칩 스크랩의 기계적인 전처리를 통하여 귀금속 및 유가금속을 분리하는 연구를 행하였다. IC칩 스크랩을 절단, 분쇄한 뒤 분쇄된 스크랩의 입자크기에 따른 금속의 분포도를 조사하였으며 함유되어 있는 금속편을 자력선별에 의하여 분리하였다. 일련의 분쇄공정을 통하여 얻어 진 IC칩 스크랩 분쇄물의 입도분포는 +3 mm가 7.5%, 3~1 mm가 17.0%, -1 mm가 75.5%야였다. 분쇄물을 $700^{\circ}C$에서 배소하였을 때 중량감소율은 약 18%이였으며 입도분포에 따른 금속의 함량은 十3mm에서 97%, 1~3mm에서 96%, 1~0.595 mm에서 13% 및 0.595~0.5mm에서 3.7%이었다. Au는 99%가 -lmm의 분쇄물에 존재하였다. 자력선별기를 사용하여 700 및 1,500 Gauss로 Ni, Fe, Cu, Sn, Pb를 분리 회수할 수 있었다.

• 자원리싸이클링
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• 제7권4호
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• pp.43-49
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• 1998

다양한 hard ferrite용 국산 산화철(${\alpha}Fe_2O_3$)의 분체특성이 Sr-ferrite의 자기특성에 미치는 영향을 조사하였다. 산화철의 평균입도와 입도분호는 철강 냉연공장의 염산폐액 정제방법에 따라 서로 구분되었으며, Sr-ferrite의 자기특성과 미세조직에 큰 영향을 주었다. Ruthner 산화철의 응집현상은 Sr-ferrite의 포화자화를 감소시켰으며, Chemirite(CY) 산화철의 $0.80{\mu}\textrm{m}$이상의 조대한 입자는 Sr-ferrite의 고유보자력을 감소시켰다. 평균입도가 $0.14\mu\textrm{m}$로 가장 작은 Chemirite 포항2냉연(EP) 산화철을 사용하여, 5.8mol, $1150^{\circ}C$/1시간의 하소조건에서 제조된 Sr-ferrite는 포화자화가 68.2emu/g, 고유보자력이 4300Oe인 최적의 자기특성을 나타내었다.

• 한국자기학회지
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• 제5권5호
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• pp.366-371
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• 1995

High performance magnetic materials are characterized by the combination of outstanding magnetic properties and optimized microstructures, e.g., nanocrystalline composites of multilayers and small particle systems. The characteristic parameters of the hysteresis loops of these materials vary over more than a factor of $10^{6}$ with optimum values for the coercive field of several Tesla and permeabilities of $10^{6}$. Within the framework of the computational micromagnetism (nanomagnetism) using the finite element method the upper and lower bounds of the coercive field of different types of grain ensembles and multilayers have been determined. For the case of nanocrystalline composites the role of grain size, exchange and dipolar coupling between grains and the degree of grain alignment will be discusses in detail. It is shown that the largest coercivities are obtained for exchange decoupled grains, whereas remanence enhancing requires exchange coupled grains below 20 nm. For composite permanent magnets based on $Nd_{2}Fe_{14}B$ with an amount of ~ 50% soft $\alpha$-Fe-phase coercivities of ${\mu}_{0}H_{c}=0.75\;T$, a remanence of 1.5 T and an energy product of $400\;kJ/m^{3}$ is expected. In nanocrystalline systems the temperature dependence of the coercivity is well described by the relation ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}{\mu}_{0}M_{s}$, where the microstructural parameters $\alpha$ and $N_{eff}$ take care of the short-range perturbations of the anisotropy and $N_{eff}$ is related to the long-range dipolar interactions. $N_{eff}$ is found to follow a logarithmic grain size size dependence ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}(\beta1nD){\mu}_{0}M_{s}$. Several trends how to achieve the ideal situation $\alpha$->1 and $N_{eff}$->1->0 will be discussed.

• Journal of Magnetics
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• 제20권1호
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• pp.26-30
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• 2015

The crystallographic and magnetic properties of gallium-substituted cobalt ferrite ($CoGa_xFe_{2-x}O_4$) were investigated. The new material was synthesized using conventional ceramic methods, with gallium substituted for ferrite in the range of x = 0.0 to 1.0, in steps of 0.2. X-ray diffraction and M$\ddot{o}$ssbauer spectroscopy were used to confirm the presence of crystallized particles in the $CoGa_xFe_{2-x}O_4$ ferrite powders. All of the samples exhibited a single phase with a spinel structure, and the lattice parameters decreased as the gallium content increased. The particle size of the samples also decreased as gallium increased. For $x{\leq}0.4$, the M$\ddot{o}$ssbauer spectra of $CoGa_xFe_{2-x}O_4$ could be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of $Fe^{3+}$ with A- and B-sites. However, for $x{\geq}0.6$, the M$\ddot{o}$ssbauer spectra could be fitted with two Zeeman sextets and one doublet. The variation in the M$\ddot{o}$ssbauer parameters and the absorption area ratio indicated a cation distribution of $(Co_{0.2-0.2x}Ga_xFe_{0.8-0.6x})[Co_{0.8+0.2x}Fe_{1.2-0.4x}]O_4$, and the magnetic behavior of the samples suggested that the increase in gallium content led to a decrease in the saturation magnetization and in the coercivity.

• 한국지형학회지
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• 제17권3호
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• pp.31-47
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• 2010

구룡천 하류의 안골유역에 있어서 최종빙기 이후 유역을 구성하고 있는 구릉사면에서 기원한 사면물질이동의 이력을 구명하였다. 이를 위하여 층상해석·층서해석, 탄소연대측정, 입도분석, 대자율분석 및 안골유역의 지형분석을 실시하였다. 약 40,480~9,850yrBP에 걸쳐서 안골유역의 구릉사면에서 유역의 곡저로 이동·퇴적된 사면기원 무기물층의 사면물질이동은 최소 5회가 존재했으며, 약 9,850yrBP~현재까지 조사유역에서 발생한 사면물질이동은 적어도 4회가 있었다. 퇴적상 연구결과는 대자율 분석과 입도분석의 결과와도 조화롭게 나타나고 있다. 본 연구의 결과는 향후 천안 일대 소유역에 있어서 구릉사면의 삭박과정 및 최종빙기 이후 기후변화 복원에 유용한 자료가 될 것이며 나아가 우리나라 다른 지역연구를 위한 유용한 사례연구가 될 것이다.

• 천문학회보
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• 제46권1호
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• pp.52.1-52.1
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• 2021

We present the results of multi-epoch, multi-frequency monitoring of a blazar 4C +29.45, which was regularly monitored as part of the Interferometric Monitoring of GAmma-ray Bright AGNs program - a key science program of the Korean Very long baseline interferometry Network (KVN). Observations were conducted simultaneously at 22, 43, 86 and 129 GHz during the 4 years from December 2012 to December 2016. We also used additional data from the 15 GHz Owens Valley Radio Observatory (OVRO) monitoring program. From the 15 GHz light curve, we estimated the variability time scales of the source during several radio flux enhancements. We found that the source experiencesd 6 radio flux enhancements with variability time scales of 9-187 days during the observing period, yielding corresponding variability Doppler factors of 9-27. From the multi-frequency simultaneous KVN observations, we were able to obtain accurate radio spectra of the source and hence to more precisely measure the turnover frequencies 𝜈_r of synchrotron self-absorbed (SSA) emission with a mean value of ${\bar{\nu}_r}=28.9GHz$. Using jet geometry assumptions, we estimated the size of the emitting region at the turnover frequency. Taking into account these results, we found that the equipartition magnetic field strength is up to two orders of magnitudes higher than the SSA magnetic field strength (0.6-99 mG). This is consistent with the source being particle dominated.

• 열처리공학회지
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• 제36권1호
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• pp.22-32
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• 2023

In general, when scrap is dissolved in an electric arc furnace, the amount of electric furnace steel dust (EAFD) generated is about 1.5% of the scrap charge amount, and the electric furnace steel dust collected by the bag filter is charged into the Rotary Kiln or Rotary Hearth Furnace (RHF), and the zinc component is recovered as crude zinc oxide, at which time a clinker of Fe-Base is generated. In this research, first, for the efficient resource conversion of electric furnace steel dust, a reduction and roasting experiment was conducted and the reaction kinetics was examined. As a result of the experiment, it was observed that the reduction and roasting reaction was actively conducted in the range of 1100~1150℃, and melting occurred in the range of 1250℃. In the past, this clinker was widely used as a roadbed material for road construction and an Fe-Source for cement production, but in recent years, it has been mainly reclaimed due to strengthening environmental standards. However, landfill treatment is by no means a desirable treatment method due to environmental pollution caused by leachate, expensive landfill costs, and waste of Fe resources. Therefore, in order to more actively recycle the Fe component in the clinker, first of all the clinker was pulverized into an optimal particle size, and anthracite and binder (starch) were added to the magnetic material obtained by specific gravity and magnetic separation for briquet. As a experimental results, it was possible to efficiently separate clinker as Fe component and other slag component by specific gravity and magnetic force. As a results of loading and dissolving the manufactured briquet clinker in an electric arc furnace, it was observed that the unit of power and production yield were clearly improved and the carbon addition effect in molten metal was also somewhat.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1388-1398
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• 2011

Air pollution in subway tunnel is primarily caused from the wear of metallic materials. As undesirable substance, PM(Particulate Matter) can especially harm the health of passengers and workers as well as clog the main parts of rolling stock such as inverters. To improve the air quality in subway tunnel, SMRT(Seoul Metropolitan Rapid Transit Corporation) has developed anti-pollution devices such as Magnetic Dust Collector, Vacuum Cleaner For Rail Road and Particulate Removing Sprinkler Vehicle. Introducing these mechanical devices, this paper is mainly devoted to explaining the characteristics of collected dust according to the result of particle-size analysis and componential analysis.

• 천문학논총
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• 제15권spc2호
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• pp.53-56
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• 2000

We investigate the critical issue on how the BBF (bursty bulk flow) is related to the substorm current wedge formation. Observationally, after analysing data sets from Geotail spacecraft at near tail and many ground magnetic observatories for 9 months period of 1996, we find three BBF events that clearly occurred at the center of the wedge with region I type FAC (field-aligned current), and two other BBF events that were seen outside the wedge sector. Theoretically, we suggest that the substorm current wedge generation by BBF is most likely when the h' VB contribution is dominant in the well-known MHD $J_{II}$ expression (Vasyliunaus, 1984) or when the divergence of the cross-tail current carried by the particle's gradient/curvature drift is predominantly sufficient at the moment of the BBF arrival at near tail.

• 한국세라믹학회지
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• 제27권1호
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• pp.13-22
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• 1990

The magnetite ferrofluids of which solvents are water or kerosene have been prepared by making surfactant absorbed on the surface of the magnetite which have been synthesized by air oxidation of Fe(OH)2 at pH 11 and 75$^{\circ}C$, and their basic properties have been measured by XRD, SEM, DTA, TG, viscometer, magnetometer and B-H tracer. The results are as follows ; 1) The shape of magnetite prepared by air oxidation is found to be sphere-like shape and its particle size is smaller than 200A. 2) The maximum amount of sodium oleate adsorbed on the surface of magnetite is about 20% in the weight of the magnetite including the adsorbed sodium oleate. And when magnetite is well dispersed into solvent, R(the weight ratio of the added sodium oleate to Fe3O4) is 0.40-0.48. 3) The dispersion ratio, the viscosity and the magnetization of magnetite ferrofluid are constant regardless of the added amount of sodium oleate above R=0.40-0.48. 4) The magnetic hysteresis curves of magnetite ferrofluid show superparamagnetism-like behavior.