• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.497-505
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• 2019

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

• Resources Recycling
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• v.23 no.6
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• pp.22-29
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• 2014

Recycling process of iron should be developed for efficient recovery of neodymium (Nd), rare metal, from acid-leaching solution of Nd magnet. In this study, $FeCl_3$ solution as iron source was used for preparation of iron nano particles with the condition of various factors, such as, reductant, and surfactant. $Na_4P_2O_7$ and Polyvinylpyrrolidone (PVP) as surfactants, $NaBH_4$ as reductant, and palladium chloride ($PdCl_2$) as a nucleation seed were used. Iron powder was analyzed by using XRD, SEM for measuring shape and size. Iron nano particles were prepared at the ratio of 1:5 (Fe (III) : $NaBH_4$). Size and shape of iron particles were round-form and 50 ~ 100 nm size. Zeta-potential of iron at the 100 mg/L of $Na_4P_2O_7$ was negative value, which was good for dispersion of metal particle. When $Na_4P_2O_7$ (100 mg/L), PVP($FeCl_3:PVP$ = 1 : 4, w/w) and Pd($FeCl_3:PdCl_2$ = 1 : 0.001, w/w) were used, iron nano particles which were round-shape, well-dispersed and near 100 nm-sized range. In this condition, $FeCl_3$ solution changed with spent Nd leachate solution, and then it is possible to be made round-formed iron nano particles at pH 9 and at the reaction bath over 20 L which is not include any surfactant.

• Economic and Environmental Geology
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• v.42 no.6
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• pp.549-559
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• 2009

The objectives of this study are to investigate the biomineralization of goethite and lepidocrocite formed on the twisted-stalk and the sheathed-filament structure that is suggest microbe origin, and heavy metal in the yellow Fe-hydroxide. On the ratio of Cl and the Cl/Br ratios that are a pollution and non-pollution of groundwaters, it is indicated that the groundwater in this areas were relatively contaminated by human activity. The composition of the yellow Fe-hydroxide consisted mainly of $Fe_2O_3$ and $SiO_2$. The content of $Fe_2O_3$ ranges from 58.57 wt.% to 75.7 3wt.%, and $SiO_2$ content ranges from 5.8 wt.% to 16.17 wt.%. Heavy metal elements such as Zn(max. 6,160 mg/kg), Pb(max. 377 mg/kg), U(max. 503 mg/kg), Cr(max. 203 mg/kg), Cu(max. 77 mg/kg), V(max. 162 mg/kg), Ni(max. 105 mg/kg) were observed to be rich in those yellow Fe-hydroxide. The lath and platy crystals and needle-shaped crystals were clearly observed on the twisted-stalks and sheathed-filaments structure. The goethite, gypsum, and lepidocrocite were identified in the yellow Fe-hydroxide by x-ray powder diffraction.

• Resources Recycling
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• v.2 no.2
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• pp.27-38
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• 1993

In this study, we investigated the grinding and sedimentation(elutriation) process of the dusts for the effective separation of high purity iron and iron oxides. For characterization of the dust, particle size distribution and chemical composition, were examined. The results obtained in this study may be summarized as follows : 1. The converter CF(clarifier) dust of the Pohang 1st, 2nd steel making factory and EC(Evaporation Cooler), EP(Eltrostatic precititator) dust of the Kwangyang 2nd steel making factory are composed $\alpha$-Fe(21~50%), FeO(wustite)$Fe_3$$O_4$(magnetite), $Fe_2$$O_3$, CaO, $Al_2$$O_3$, $SiO_2$, and etc. 2. Pure iron has ductile characteristic in nature, particle size of the pure iron increase by increasing the grinding time. On the other hand, it is conformed that bo고 particles of hematite and magnetite become less than 325 mesh after 10 minutes grinding. 3. By applying the elutriation technique for the EC dust of the Kwangyang 2nd steel making factory, the iron powder of high content more than 99.17% of pure Fe was recovered with 37.8% yield at grinding time for 40 minutes. 4. By applying the elutriation technique for the CF dust of the Pohang 2nd steel making factory, the iron powder of high content more than 98.38% of pure Fe was recovered with 44.42% yield at grinding time for 40 minutes. 5. When magnetic separation was performed using plastic bonding magnet of 70 gauss, more than 98% Fe grade of iron powder was recovered in the size range +65 -200 mesh but the recovery of it was low.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.89-89
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• 2013

Rare earth (RE) - transition metal based high energy density magnets are of immense significance in various engineering applications. $Nd_2Fe_{14}B$ magnets possess the highest energy product and are widely used in whole industries. Simultaneously, composite alloys that are cheap, cost effective and strong commercially available have drawn great attention, because rare-earth metals are costly, less abundant and strategic shortage. We designed rare-earth free alloys and fabrication process and developed novel route to prepare $Nd_2Fe_{14}B$ powders by wet process employing spray drying and reduction-diffusion (R-D) without the use of high purity metals as raw material. MnAl-base permanent magnetic powders are potentially important material for rare-earth free magnets. We have prepared the nano-sized MnAl powders by plasma arc discharge and micron-sized MnAl powders by gas atomization. They showed good magnetic property, compared with that from conventional processes. $Nd_2Fe_{14}B$ powders with high coercivity of more than 10 kOe were successfully synthesized by adjusting R-D step, followed by precise washing system. It is considered that this process can be applied for the recycling of RE-elements extracted from ewaste including motors.

• Resources Recycling
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• v.9 no.4
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• pp.16-27
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• 2000

In order to produce raw material powder of advanced magnetic material by spray roasting process, newly modified spray roasting system was developed in this work. In this spray roasting system, raw material solution was effectively atomized and sprayed into the reaction furnace. Also, uniform temperature distribution inside reaction furnace made thermal decomposition process fully completed, and produced powder was effectively collected in cyclone and bag filter. This system equipped with apparatus which can purify hazard produced gas. In this study complex acid solution was prepared by dissolution of mill scale and ferro-Mn into the acid solution, and the pH of this complex acid solution was controlled about to 4. It was conformed that mill scale and ferro-Mn containing a lot of impurities such as $SiO_2$, P and Al could be used as raw material by reducing the impurities content of complex acid solution below 20 ppm. Complex oxide powder of Fe-Mn system was produced by spraying purified complex acid solution into the spray roaster through nozzle, and the variations of produced powder characters were studied by changing he reaction conditions such as reaction temperature, the injection velocity of solution and air, nozzle tip size and concentration of solution. The morphology of produced powder had spherical shape under the most experimental conditions, and concentration of solution. The morphology of produced powder has spherical shape under the most experimental conditions, and the composition and the particle size distribution were almost uniform, which tells the excellence of this spray roasting system. The grain size of most produced powder was below 100 nm. From the above results, it will be possible to produce ultra fine oxide powder from the chloride of Fe, Mn, Ni, Cu and rare earth by using this spray roasting system, and also to produce ultra fine pure metal powder by changing reaction atmosphere.

• Journal of Powder Materials
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• v.15 no.2
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• pp.114-118
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• 2008

Functional nanomaterial is expected to have improved capacities on various fields. Especially, metal nanoparticles dispersed in polymer matrix and metal nanofiber, one of the functional nanomaterials, are able to achieve improvement of property in the electric and other related fields. In this study, the fabrication of metal (Ag) nanoparticle dispersed nanofibers were attempted. The Ag nanoparticle dispersed polymer nanofiber and Ag nanofiber were fabricated by electrospinning method using electric force. First, PVP/$AgNO_3$ nanofibers were synthesized by electrospinning in $18{\sim}22kV$ voltage with the starting materials (Ag-nitrate) added polymer (PVP; poly (vinylpyrrolidone)). Then Ag nanoparticle dispersed polymer nanofibers were fabricated to reduce hydrogen reduction at $150^{\circ}C$ for 3hr. And Ag nanofibers were synthesized by the decomposited of PVP at $300{\sim}500^{\circ}C$ for 3hr. The nanofibers were analyzed by XRD, TGA, FE-SEM and TEM. The experimental results showed that the Ag nanofibers could be applied in many fields as an advanced material.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.5
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• pp.429-436
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• 2012

Mg and Mg-based alloys are regarded as strong candidate hydrogen storage materials since their hydrogen capacity exceeds that of known metal hydrides. One of the approaches to improve kinetic is addition of metal oxide. In this paper, we tried to improve the hydrogenation properties of Mg-based hydrogen storage composites. The effect of transition metal oxides, such as $Nb_2O_5$ on the kinetics of the Magnesium hydrogen absorption kinetics was investigated. $MgH_x$-5wt.% $Nb_2O_5$ composites have been synthesized by hydrogen induced mechanical alloying. The powder fabricated was characterized by X-ray diffraction (XRD), Field Emission-Scanning Electron Microscopy (Fe-SEM), Energy Dispersive X-ray (EDX), BET and simultaneous Thermo Gravimetric Analysis / Differential Scanning Calorimetry (TG/DSC) analysis. The Absorption / desorption kinetics of $MgH_x$-5wt.% $Nb_2O_5$ (type I and II) are determined at 423, 473, 523, 573 and 623 K.

• Journal of the Korea Convergence Society
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• v.8 no.2
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• pp.157-162
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• 2017

Inorganic stiffening agents were prepared by mixing paper sludge incineration ash, blast furnace slag fine powder quicklime, anhydrous gypsum and fly ash. The main components of the solidifying agent developed for sludge treatment were SiO, $Al_2O_3$, $TiO_2$, $Fe_2O_3$, $Mn_2O_3$, CaO, MgO, $Na_2O$, $K_2O$, $P_2O$, and $SO_3$. Unlike cement, the developed solidifying agent did not contain $Cr^{6+}$, which is known as a carcinogen. Heavy metals and oil contaminated soil were mixed with solidifying agent and cured for 7 days and the heavy metal content was below the environmental standard. Sewage sludge cake, food waste and solidifying agent were mixed with each other, and after 7 days curing, soil component test showed that the heavy metal content was below the environmental standard. After mixing the sludge, solidifying agent and additive mixture into the beaker, the ammonia concentration was measured to be 0 after 3 days.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.310-315
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• 2009

Perovskite-type ceramic powder, $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$, have been synthesized successfully by the citrate method. As a result of TGA for precursor, metal-citrate complex in precursor was decomposed in the temperature range of $150{\sim}650^{\circ}C$. XRD analysis showed the single perovskite structure was observed over $1,000^{\circ}C$ without impurities. Typical dense membrane with 1.6 mm thickness has been prepared using as-prepared powder by pressing unilaterally and sintering at $1,300^{\circ}C$. The electrical conductivity of $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ membrane increased with increasing temperature at atmosphere of air and then decreased over $600^{\circ}C$ due to oxygen loss from the crystal lattice. The oxygen flux of $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ membrane in the range of 700 to $950^{\circ}C$ increased with the increasing temperature from 0.045 to $0.415ml/cm^2{\cdot}min$. The activation energy for oxygen permeation was calculated to be 89.17 kJ/mol.