• 한국산학기술학회논문지
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• 제18권4호
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• pp.438-445
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• 2017

탄자니아에는 풍부한 구리 매장량이 있으나, 적절한 구리 회수 공정의 결핍과 광산 기술 개발을 위한 자금 부족으로 구리 금속의 추출량은 여전히 낮은 상태이다. 이에 따라 소규모 구리 채굴을 위한 간단한 처리공정 개발에 중점을 두어 구리광석에서 구리를 추출하기 위한 침출법과 용매 추출법을 연구하였다. 사용된 구리광석은 규공작석이었으며, 침출 시약으로 황산을 사용하였다. 침출 공정에서 시료의 입경이 $53{\mu}m$보다 작고, 98%(w/w) 황산 농도가 5.0 g/L, 교반 속도가 60에서 80 rpm일 때 최대 구리 회수율이 95.1% 이었다. 용매 추출에서 구리 2가 양이온의 최고의 선택 비율은 등유에 녹인 15 % LIX-70을 이용하여 얻어졌다. pH가 0.5에서 3.0까지, 구리 2가 양이온 추출 효율은 pH가 증가함에 따라 증가했다. 그러나 3.0이상의 pH에서는 다른 금속 이온이 구리 2가 양이온보다 유기물층으로 더 많이 추출되었다. 최고의 용매 추출율은 15% LIX-70를 사용하여 각각 pH 2.0 및 3.0에서 96.5% 이었다.

• 한국재료학회지
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• 제29권4호
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• pp.205-210
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• 2019

$Pb(Zr,Ti)O_3$ (PZT) is used for the various piezoelectric devices owing to its high piezoelectric properties. However, lead (Pb), which is contained in PZT, causes various environment contaminations. $(K,Na)NbO_3$ (NKN) is the most well-known candidate for a lead-free composition to replace PZT. A single crystal has excellent piezoelectric-properties and its properties can be changed by changing the orientation direction. It is hard to fabricate a NKN single crystal due to the sodium and potassium. Thus, $(Na,K)NbO_3-Ba(Cu,Nb)O_3$ (NKN-BCuN) is chosen to fabricate the single crystal with relative ease. NKN-BCuN pellets consist of two parts, yellow single crystals and gray poly-crystals that contain copper. The area that has a large amount of copper particles may melt at low temperature but not the other areas. The liquid phase may be responsible for the abnormal grain growth in NKN-BCuN ceramics. The dielectric constant and tan ${\delta}$ are measured to be 684 and 0.036 at 1 kHz in NKN-BCuN, respectively. The coercive field and remnant polarization are 14 kV/cm and $20{\mu}C/cm^2$.

• 한국재료학회지
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• 제14권3호
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• pp.181-185
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• 2004

The mechanical properties of a bulk amorphous alloy ($Zr_{41.2}$ $Ti_{13.8}$ /$Cu_{10}$ $Ni_{10}$ $Be_{22.5}$ /at.%) before and after an annealing treatment were investigated. For the bulk amorphous alloy, the compressive strength was about 2.0 GPa, irrespective of the strain rates in the range of $10^{-4}$ to $10^3$$ sec^{-1}$ . Fine-sized nanocrystalline particles (10～100 nm) were precipitated homogeneously in the bulk amorphous matrix after the annealing treatments. Compared to the bulk amorphous materials, these composite materials, composed of the nanocrystalline phases and a bulk amorphous matrix had much different mechanical properties. The strength and strain of coposite materials measured by a compressive test showed a peak-maximum values at 7 vol.% of the nanocrystalline phases. The values in higher volume fraction of the crystalline phases in the amorphous matrix were decreased, as measured by both quasi-static and high strain rate. The decrease in fracture strength is due to presence of the dispersed large-crystalline phases in the amorphous matrix.

• 전기학회논문지
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• 제61권2호
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• pp.339-341
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• 2012

The high Tc superconductor of YBCO system with the nominal composition of precursor was prepared from mixed powders of $Y_2O_3$, $BaCO_3$, CuO and $TiO_2$ by the thermal pyrolysis method. The effect of $TiO_2$ doping to Y based ceramics superconductors fabricated by the thermal pyrolysis reaction, to investigate the effect of the dopant on the superconductivity. The voltage appearing across the field-cooled HTS sample increased with external magnetic field. The improvement of critical current property as well as the mechanical property is important for the application. The improvement of the critical current can be achieved by forming the nano size defect working as a flux pining center inside the superconductor. We simply added $TiO_2$ to starting materials to dope $TiO_2$ and observed an increase in the trapped field and the critical current density up to at least 5 wt % $TiO_2$. The $TiO_2$ was converted to fine $BaTiO_3$ particles which were trapped in YBCO matrix during the sintering process. We observed a peak effect of Jc that can be attributed to $TiO_2$ doping and results suggest that introducing a proper amount of pinning centers can significantly enhance current density.

• 한국산업융합학회 논문집
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• 제21권1호
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• pp.29-36
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• 2018

Low pressure casting process for unidirectional carbon fiber reinforced aluminum (UD-CF/Al) composites which is an infiltration route of molten Al into porous UD-CF preform has been a cost-effective way to obtain metal matrix composites (MMCs) but, easy to cause non-uniform fiber distribution as CF clustering. Such clustered CFs have been a problem to decrease the density and thermal conductivity (TC) of composites, due to the existence of pores in the clustered area. To obtain high thermal performance composites for heat-sink application, the relationship between fiber distribution and porosity has to be clearly investigated. In this study, the CF distribution was evaluated with quantification approach by using two-dimensional spatial distribution method as local number 2-dimension (LN2D) analysis. Note that the CFs distribution in composites sensitively changed by sizes of Cu bridging particles between the CFs added in the UD-CF preform fabrication stage, and influenced on only $LN2D_{var}$ values.

• 한국환경과학회지
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• 제24권2호
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• pp.245-251
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• 2015

The main objective of this study is to recovery valuable metals with metal particle size distributions in waste cell phone PCBs(Printed Circuit Boards) by means of pulverization and nitric acid process. The particle size classifier also was evaluated by specific metal contents. The PCBs were pulverized by a fine pulverizer. The particle sizes were classified by 5 different sizes which were PcS1(0.2 mm below), PcS2(0.20~0.51 mm), PcS3(0.51~1.09 mm), PcS4(1.09~2.00 mm) and PcS5(2.00 mm above). Non-magnetic metals in the grinding particles were separated by a hand magnetic. And then, Cu, Co and Ni were separated by 3M nitric acid. Particle diameter of PCBs were 0.388~0.402 mm after the fine pulverizer. The sorting coefficient were 0.403~0.481. The highest metal content in PcS1. And the bigger particle diameter, the lower the valuable metals exist. The recovery rate of the valuable metals increases in smaller particle diameter with same leaching conditions. For further work, it could improve to recovery of the valuable metals effectively by means of individual treatment, multistage leaching and different leaching solvents.

• 한국환경농학회지
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• 제15권4호
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• pp.494-500
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• 1996

To investigate the relationship between the atmospheric pollution level and the pollution level of soil adjacent to the roadside in Suwon suspended particles and soil samples were collected in August to October 1993, and analyzed by AAS and ICP. The Ca, K, Mg concentration in atmosphere were observed as high level and assumed that it was effected by the acid-rain originated from the erosion of concreate vicinity to the roadside, and the Pb, Zn concentration were higher at outer area than that of central area. Hazardous heavy metal (Cu, Pb, Zn) concentrations in soil were observed as high level at all sampling sites. The relationship between the heavy metal concentrations in the atmosphere and those in the soil were analyzed, by using the correlation coefficient value(r) and the result was appeared similarly. And this study indicated that the atmospheric pollution affect the level of the soil pollution adjacent to the road side.

• Transactions on Electrical and Electronic Materials
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• 제15권4호
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• pp.189-192
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• 2014

Yttria-stablized zirconia (YSZ) is the most commonly used electrolyte material, but the reduction in working temperature leads to insufficient ionic conductivity. Ceria based electrolytes (GDC) are more attractive in terms of conductivity at low temperature, but these materials are well known to be reducible at very low oxygen partial pressure. The reduction of electrolyte resistivity is necessary to overcome cell performance losses. So, thin YSZ/GDC bilayer technology seems suitable for decreasing the electrolyte resistance at lower operating temperatures. Bilayer electrolytes composed of a galdolinium-doped $CeO_2$ ($Ce_{0.9}Gd_{0.1}O_{1.95}$, GDC) layer and yttria-stabilized $ZrO_2$ (YSZ) layer with various thicknesses were deposited by RF sputtering and E-beam evaporation. The bilayer electrolytes were deposited between porous Ni-GDC anode and LSM cathode for anode-supported single cells. Thin film structure and surface morphology were investigated by X-ray diffraction (XRD), using $CuK{\alpha}$-radiation in the range of 2ce morphol$^{\circ}C$. The XRD patterns exhibit a well-formed cubic fluorite structure, and sharp lines of XRD peaks can be observed, which indicate a single solid solution. The morphology and size of the prepared particles were investigated by field-emission scanning electron microscopy (FE-SEM). The performance of the cells was evaluated over $500{\sim}800^{\circ}C$, using humidified hydrogen as fuel, and air as oxidant.

• Tribology and Lubricants
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• 제25권6호
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• pp.404-408
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• 2009

본 연구에서는 마이크로/나노입자를 이용한 연마가공 공정에서의 입자-표면간 접촉상황에서 접촉계면의 기계적 성질과 재료제거율간의 관계를 실험적으로 고찰하였다. 연마가공 공정에서의 입자-평면간 접촉을 모사하기 위하여 팁 대신 실리카 입자를 부착한 콜로이드 프로브를 이용한 원자현미경 실험을 통하여 마찰력과 강성을 실험적으로 측정하였다. 실험결과와 이론적 접촉해석으로부터, 마찰계수는 횡방향 접촉강성에 따라 대체적으로 증가하고 재료제거율은 실리카 입자와 Cu, PolySi, Ni과 같은 다양한 재료표면간 접촉에서의 마찰계수들과 지수함수적인 비례관계를 가지고 있음을 규명하였다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2001년도 총회 및 춘계학술발표회
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• pp.222-225
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• 2001

In urban environments, the surface land impermeability fundamentally related to urban growth emphasizes the environmental problems such as the storm water peak flow (so-called the urban flooding) and the pollution. The conventional urban drainage system provides a number of temporary reservoirs intercepting and retaining surface-derived pollutants following their introduction to and deposition upon the impermeable surface. Gully-pots are common features in urban drainage systems in Korea, which were installed for draining rainwater to prevent regurgitation in rainy season and retaining larger particles, hence minimizing pipe blockage problems. When the road runoff conveying sediment enters a gully-pot, the sediment mixes with the gully liquor causing direct pollution of receiving waters. The characteristics of local sediment contamination are usually related to the types of land use activities that take place or have taken place within the area., This study was undertaken to evaluate the spatial and temporal variations of the contamination of gully-pot sediments in Seoul with respect to heavy metals such as As, Cd, Co, Cr, Ni, Pb, Cu and Zn. The heavy metal data were examined according to the land use type. In this paper, sampling sites in Seoul were divided into six groups (commercial area, industrial area, residental area, motor way, rural area, and local pollution).