• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.414-417
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• 2014

LED scraps consisting of highly crystalline GaN and their leaching behavior are comprehensively investigated for hydro-metallurgical recovery of rare metals. Highly stable GaN renders the leaching of the LED scraps extremely difficult in ordinary acidic and basic media. More favorable state can be obtained by way of high temperature solid-gas reaction of GaN-$Na_2CO_3$ powder mixture, ball-milled thoroughly at room temperature and subsequently oxidized under ambient air environment at $1000-1200^{\circ}C$ in a horizontal tube furnace, where GaN was effectively oxidized into gallium oxides. Stoichiometry analysis reveals that GaN is completely transformed into gallium oxides with Ga contents of ~73 wt%. Accordingly, the oxidized powder can be suitably leached to ~96% efficiency in a boiling 4 M HCl solution, experimentally confirming the feasibility of Ga recycling system development.

• Journal of the Korean institute of surface engineering
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• v.44 no.5
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• pp.173-178
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• 2011

Separator of stack in polymer electrolyte membrane fuel cell (PEMFC) is high cost and heavy. If we make it low cost and lighter, it will have a great ripple. In this study, low carbon steel is used as base metal of separator because the cost of low carbon steel is very cheaper commercial metal material than stainless steels, which is widely used as separator. Low carbon steel has not a good corrosion resistance. In order to improve the corrosion resistance and electrolytic conductivity, low carbon steel needs to be surface treated. We made Chromium electroplated layer of $5{\mu}m$, $10{\mu}m$ thickness on the surface of low carbon steel and it was nitrided for 2 hours at $1000^{\circ}C$ in a furnace with 100 torr nitrogen gas pressure. Cross-sectional and surface microstructures of surface treated low carbon steel are investigated using SEM. And crystal structures are investigated by XRD. Interfacial contact resistance and corrosion tests were considered to simulate the internal operating conditions of PEMFC stack. The corrosion test was performed in 0.1 N $H_2SO_4$ + 2 ppm $F^-$ solution at $80^{\circ}C$. Throughout this research, we try to know that low carbon steel can be replaced stainless steel in separator of PEMFC.

• Journal of Korea Foundry Society
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• v.21 no.4
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• pp.253-259
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• 2001

There are many methods to produce metal foams, which can be classified into three groups according to the state of the starting metal i.e. liquid or powder or solid. Three types of defects such as cell closing, cell deformation or breakdown and cell misrun are thought to be occurred when we make the open cell aluminum foams by precision casting. Filling ability of the mold slurry between preform is related with cell closing, mold collapsibility is related with cell deformation or breakdown, mold temperature and pouring pressure are related with cell misrun. These factors can be evaluated by measuring slurry fluidity, burnout strength and permeability of the mold. Properties of the plaster mold were evaluated to find optimum mold conditions for high quality open cell aluminum foam in this study. Permeability was almost zero independent of burnout conditions, however, crack initiation was found on the surface of all specimens one or two minutes after taking out from the furnace. Crack has grown and disappeared with time. This crack may facilitate the mold filling when molten metal is poured, because of the improved mold permeability. It was considered that crack initiation and disappearance was closely related with temperature difference between the surface and inner part. Knocking-out the mold is a difficult problem due to the small cell size, because continuous mesh structure of the metal foam is not strong. It is not easy to remove molding material after pouring. We can expect that water quenching can facilitate the knocking-out the mold after solidification without damaging cell structures. Collapsed particles after water quenching became bigger with the increase in time.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.276-285
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• 2003

In the undercooled melt of $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy, the solidification behavior including nucleation and growth of crystals at the micrometer level has been observed in-situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy specimens were cooled from the liquid state to glass transition temperature. 575 K, at various cooling late under a helium gas flow. According to the cooling rate, the morphologies of the solidification front are changed among various types, irregular jog like front, columnar dendritic front, cellular grain, star like shape jog and fine grain, etc. The velocities of the solid-liquid interface are measured to be $10^{-5}{\sim}10^{-8}$ m/s which are at least two orders higher than the theoretical crystal growth rates. Combining the morphologies observed in terms of cooling rates and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy. The continuous cooling transformation (CCT) diagram was constructed from solidification onset time at various linear cooling conditions with different rate. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.5 K/s, which is in agreement with the previous calorimetric findings.

• Journal of Korea Foundry Society
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• v.29 no.5
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• pp.220-224
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• 2009

In order to investigate the microstructural morphology of the sulfide expected from the Fe-FeS phase diagram, a vacuum-sealed quartz tube where pure iron (99.9%) and sulfur (99.99%) powders were charged was heated upto $1000^{\circ}C$ in the electric resistance furnace, held for 96 hours and quenched in cold water and then, rod specimen was produced. Compositional difference of the sulfur between upper and lower parts of the rod was 7.5wt.% and segregation of the sulfur was gradually increased from the lower part to the upper one of the rod. The rod specimen was divided into three parts by the microstructural morphology of the sulfide. The upper part of the rod specimen revealed single phase FeS intermetallic. In the middle part of the specimen, hyper-eutectic microstructure where primary FeS was precipitated first and then, eutectic of $\alpha$-Fe and FeS was formed in the inter-dendritic region of the FeS. Especially, hypo-eutectic microstructure was appeared in the lower part of the specimen. After primary dendrite of $\alpha$-Fe solidified, FeS dendrite which included small amount of $\alpha$-Fe and FeS eutectic in the inter-dendritic region was formed.

• Journal of Hydrogen and New Energy
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• v.13 no.2
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• pp.151-158
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• 2002

The hydorgen storage alloys were produced by melting in arc melting furnace and then solution heat treated at $1,100^{\circ}C$ followed by pulverization. The chemical analysis on the samples showed that the major elements of misch metal(Mm) were La, Ce, Pr and Nd with impurity less than 1wt.%. X-ray diffraction indicated that the structure for these samples were a single phase of hexagonal with $CaCu_5$ type. Compared to the initial particle size $100{\sim}110{\mu}m$, the many fine cracks were found and particle size decreased to $14{\mu}m$ for $MmNi_{4.5}Mn_{0.5}$ after hydriding/dehydring test run. To activate the sample the vessel filled with hydrogen storage alloys was first evacuated for for at $70^{\circ}C$ and then treated for 10.5hr under hydrogen pressure of 20atm for $MmNi_{4.5}Mn_{0.5}$ alloy. The experimental data showed that the hydrogen storage alloy of $MmNi_{4.5}Mn_{0.5}$ had superior adsorption and description properties within a temperature rang of $40^{\circ}C{\sim}80^{\circ}C$ and also they had a good P-C-T curve.

• Journal of Hydrogen and New Energy
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• v.18 no.1
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• pp.46-51
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• 2007

LSM powder material for an oxygen-electrode(anode) of High Temperature Steam Electrolysis (RISE) was synthesized by a Modified-Glycine nitrate process(GNP). Amount of nitric acid and its concentration was varied to find out an appropriate composition for the oxygen-electrode(anode). In order to optimize the amount of Glycine used as an oxidant of self-combustion process, the ratio of Glycine to Anion was varied. $La_{0.8}Sr_{0.2}MnO_3$, $La_{0.5}Sr_{0.5}MnO_3$, and $La_{0.2}Sr_{0.8}MnO_3$ were synthesized in this study. Those LSM were dried for overnight to remove moisture from the material at $110^{\circ}C$ and were calcined 2 hours at $650^{\circ}C$ and were sintered in a furnace for 5 hours at $1400^{\circ}C$. Their structures, surface morphologies, surface areas, and weight changes were investigated with XRD, SEM, BET, and TG/DTA. The best perovskite phase for the oxygen-electrode of HTSE was obtained with $La_{0.8}Sr_{0.2}MnO_3$ formula in which 100 ml of 3M nitric acid was used in the preparation of its formula. The optimized ratio of Glycine to Anion was 2.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.63-66
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• 2007

This study investigates the fire resistance properties of high strength concrete, around 60MPa class, designed with various admixture types and fiber content. Test showed that the increase of fiber content decreased the fluidity and slightly inclined the air content of fresh concrete. However, the fiber content in concrete did not affect the compressive strength. For the addition of admixture, specimens adding the shrinkage-reducing-agent (SR) indicated the strength value at 70MPa, which is followed by incorporating silica fume (SF) at 66MPa, the combination of expansive admixture (EA) and SR at 63MPa, only EA at 59MPa, blast furnace slag (BS) at 58MPa and fly ash (FA) at 50MPa in an order. After completing the fire test, all specimens adding 0.05vol.% of polypropylene fiber exhibited protection of spatting, except for the specimens incorporating loft of SF and incorporating 20% of SF with only SR and the combination of EP and SRA, respectively. Therefore the most effective result of this study was shown in the specimens incorporating love of FA and 30% of BS and incorporating 20% of SF with 5 % of EA. It is expected that this test results will be crucial references in near future to develope the spatting resistance method of high strength concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.25-28
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• 2007

In this study we measured the changes according to time respectively on the basis of 0, 30, 60 and 90 minutes, taking into consideration the decline in fluidity of concrete according to elapsed time to analyze manufacturing capability of batcher plant according to elapsed time of ready-mixed concrete manufactured in batcher plant, and offer basic data for mixture design of ultra-high strength concrete. The proportion of water-binder was 23.55, water content was 160kg/m3, proportion of replacement of crushed sand was 0, 20 and 40% at 3 level, and we applied to the same condition of triaxial component using blast furnace slag powder and silica fume as admixture. And to meet the demand of certain fluidity, we measured respectively on property before and after hardening of ultra-high strength concrete using superplasticizer. As a result of experiment, before hardening of ultra-high strength concrete showed the best fluidity in conditions of crushed sand replacement rates of 20% and superplasticizer composition of 1.95%, but it appeared that fluidity drops as time goes by in the same composition condition. And it appeared that when it comes to hardened, the changes of compression strength according to elapsed time by crushed sand replacement rates were within 1MPa. Therefore, it turned out that the difference of strength according to elapsed time was low and compression strength of 280dys in composition mentioned above appeared highly as 88MPa.

• Journal of the Korea Institute of Building Construction
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• v.20 no.4
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• pp.305-311
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• 2020

Polymer modified cement mortar (PCM) can improve the performance of adhesion strength, flexural strength, chemical resistance, etc., compared with cement mortar, and is widely used when repairing RC structures. However, PCM causes a burst in an environment with high temperature and fire rate, which causes problems in the stability of the structure. In this study, for the purpose of developing explosive reduction PCM, the polymer mixing ratio is 2%, 4%, 6%, the fiber length is 6mm, 12mm, 6+12mm, and the PP fiber mixing rate is 0.05 Vol% and 0.1 Vol%. Furnace heating experiment (600℃, 800℃) was carried out. As a result of comparative analysis of the explosive properties, it was confirmed that the explosive reduction effect due to the fiber incorporation was insufficient when the polymer mixing amount was 6% or more.