• Resources Recycling
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• v.10 no.5
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• pp.29-35
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• 2001

This study was carried out to recover gold, silver and valuable metals from the printed circuit boards (PCBs) of waste computers. PCBs samples were crushed under 1 mm by a shredder and separated into 30% conducting and loft nonconducting materials by an electrostatic separator. The conducting materials contained valuable metals which were then used as feed materials for magnetic separation. 42% of magnetic materials from the conducting materials was removed by magnetic separation as nonvaluable materials and the others, 58% of non magnetic materials, was used as leaching samples containing 0.227 mg/g Au and 0.697 mg/g Ag. Using the materials of leaching from magnetic separation, more than 95% of copper, iron, zinc, nickel and aluminium was dissolved in 2.0M sulfuric acid solution, added with 0.2M hydrogen peroxide at $85^{\circ}C$. Au and Ag were not extracted in this solution. On the other hand, more than 95% of gold and 100% of silver were leached by the selective leaching with a mixed solvent (0.2M($NH_4$)$_2$$S_2$$O_3$,0.02M $CuSO_4$,0.4M $NH_4$OH). Finally, the residues were reacted with a NaCl solution to leach Pb whereas sulfuric acid was used to leach Sn. Recoveries reached 95% and 98% in solution, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.634-643
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• 2020

In this study, the rheological and tribological properties of urea grease were studied according to the type and amount of polytetrafluoroethylene (PTFE) powders added to the urea grease, which is the most widely used among solid lubricants, to develop an optimal lubrication system. Urea grease was synthesized using 4,4'-methylenebis(phenyl isocyanate)(MDI), oleylamine, and cyclohexylamine, and PTFE powders prepared by dispersion or suspension polymerization process were then added. The basic rheological and tribological properties of the prepared greases were compared. The worked penetration numbers of urea grease decreased with increasing amount of PTFE powders, but both PTFE powders caused no significant changes in heat resistance and copper corrosion resistance. The shear viscosity increased with increasing PTFE powder content, and the dispersion-type PTFE powder was more effective in increasing the viscosity. In the value of the loss coefficient = 1, the shear stress was higher for the grease containing PTFE powders than the non-PTFE added grease, and the dispersion-type PTFE-added grease showed higher viscosity than the suspension-type PTFE-added grease. Finally, urea grease was found to have a low-performance improvement in terms of wear reduction effects by adding PTFE powders, but the load-bearing performance was up to 2.5 times higher for the dispersion-type PTFE and five times higher for the suspension-type PTFE.

• Journal of Conservation Science
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• v.30 no.4
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• pp.345-351
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• 2014

Chemical and Pb isotope analysis were performed in order to determine the origin of bronze artefacts excavated from the Inyongsaji site in South Korea. The result of ICP-MS shows that they are tin bronzes in which lead was not intentionally added during production. Pb isotope data analyzed by TIMS are plotted in the southern region of Korea and China of the distribution map drawn by Mabuchi(1985). On the other hand, the identical isotope data are plotted in the Taebaek basin and the Olcheon metamorphic belt correspondent to zone2 and zone3 respectively. It is believed that the isotope data on the tin bronzes which have very low lead content can be used to trace the origin of copper ore rather than those of either lead or tin ore. Pb istope analysis allows diverse interpretation as it can be applied to any object containing trace amounts of lead. In addition, accumulation of isotope data as well as further studies will improve reliability of the provenance studies.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.624-633
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• 2002

In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, MmN $i_{4.5}$M $n_{0.5}$Z $r_{x}$(x=0, 0.025, 0.05, 0.1), are prepared by adding excess Zr in MmN $i_{4.5}$M $n_{0.5}$ alloy. The various parts in hydrogen storage vessel consisted of copper pipes reached the setting temperature within 4~5 minutes after heat addition, which indicated that storage vessel had a good heat conductivity required in application. The performance test on storage vessel filled with rare-earth metal alloys of 1000 gr was also conducted after hydrogen charging for 10 min at $18^{\circ}C$ under 10 atm. It showed that the average capacity of discharged hydrogen volume was found to be for $MmNi_{4.5}$ $Mn_{0.5}$ and $MmNi_{4.5}$ $Mn_{x}$ 0.5/$Zr_{samples}$ indicated that the released amount of hydrogen for this $AB_{5}$ type alloys was more than 92 % of theoretic value, and also it was found that the optimum discharging temperature for obtaining an appropriate pressure of 3 atm was determined to be $V^{\circ}C$ for $MmNi_{4.5}$ $Mn_{0.5}$$Zr_{x}$(x=0, 0.025, 0.05, 0.1) hydrogen storage alloys. The released amount of these hydrogen storage samples was 125 $\ell$ , 122.4 $\ell$ and 108.15 $\ell$/kg for $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{0.025}$ $MmNi_{4.5}$M $n_{0.5}$Z $r_{0.05}$, and MmN $i_{4.5}$ Mn_0.5$Zr_{0}$, at $70^{\circ}C$ respectively. Amount of the 2nd phases increase with increase on Zr contents in $MmNi_{4.5}$$Mn_{0.5}$ $Zr_{ 0.1}$/ alloy. This phenomenon indicates that$ ZrNi_3$ in $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{x}$ / phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage. As the Zr contents increase, the activation time and the plateau pressure decreases and sloping of the plateau pressure increases.creases.eases.s.

• Korean Journal of Ichthyology
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• v.23 no.1
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• pp.10-20
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• 2011

Genetic determinant for metallothionein (MT), a cysteine-rich protein playing essential roles in metal detoxification and homeostasis, was characterized in the Korean bitterling (Acheilognathus signifer, Cyprinidae), an endemic fish species. The full-length A. signifer MT (AsMT) cDNA (551 bp) is composed of a single open-reading frame (ORF) to encode a polypeptide of 60 amino acids containing 20 cysteine residues whose positions are conserved in most cypriniform MTs. At the genomic level, the AsMT (2,593 bp spanning the 5'-flanking region to the 3'-untranslated region) represented a conserved tripartite (three exons interrupted by two introns) structure with AT-rich introns. The upstream regulatory region (-1,914 bp from the ATG initiation codon) of AsMT displayed various sites and motifs for transcription factors involved in the metal-mediated regulation and stress/immune responses. The AsMT transcript was ubiquitously detected in various organs with variable expression levels, where the ovary and intestine showed the highest expression, while the heart and skeletal muscle represented the lowest level. During an exposure to copper (immersion in $0.5\;{\mu}M$ Cu for 48 h), the levels of AsMT transcripts were significantly elevated in the liver (more than 3.5-fold), moderately in the gill, kidney, and spleen (ranging from 1.5- to 2.5-fold), and barely in the brain and intestine. Results of this study could form a useful basis to explore the metal-related stress physiology of this endangered fish species.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.513-517
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• 2013

We investigated the properties of impregnated activated carbons, a commercial adsorbent for the individual protection equipment, and examined CO adsorption and oxidation to $CO_2$. The surface area, pore volume and pore size were measured for four commercial samples using Brunauer-Emmett-Teller/Barrett-Joyner-Halenda (BET/BJH), and atomic compositions of the sample surface were analyzed based on SEM/EDS and XPS. Impregnated activated carbons containing Mn and Cu for fire showed the catalytic CO oxidation to $CO_2$ with a high catalytic activity (up to 99% $CO_2$ yield), followed by the CO adsorption at an initial reaction time. On the other hand, C: for chemical biologial and radiological (CBR) samples, not including Mn, showed a lower CO conversion to $CO_2$ (up to 60% yield) compared to that of fire samples. It was also found that a heat-treated activated carbon has a higher removal capacity both for CO and $CO_2$ at room temperature than that of untreated carbon, which was probably due to the impurity removal in pores resulted in a detection-delay about 30 min.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.79-84
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• 2014

To investigate the plating properties of a diethylene glycol-based Ag immersion plating solution containing citric acid, silver immersion plating was performed in a range from room temperature to $50^{\circ}C$ using sputtered Cu specimens. The used Cu specimens possessed surface structure with large numbers of pinholes which were created with over-acid etching. The Ag immersion plating performed at $40^{\circ}C$ exhibited that the pinholes and copper surface were completely filled with Ag just after 5 min mainly due to galvanic displacement reaction, indicating the best plating properties. Subsequently, the surface morphology of Ag-coated Cu became rougher as the plating time increased to 30 min because of the deposition of silver nanoparticles created by chemical reduction in the solution. The specimen that its overall surface was covered with silver indicated the start of oxidation at temperature higher than around $50^{\circ}C$ in air as compared with pure Cu, indicating enhanced anti-oxidation properties.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.06a
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• pp.135-153
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• 1998

Nanofiltration (NF) is a recently introduced term in membrane separation. In 1988, Eriksson was one of the first authors using the word 'nanofiltration' explicitly. Some years before, FilmTech started to use this term for their NF50 membrane which was supposed to be a very loose reverse osmosis membrane or a very tight ultrafiltration membrane. Since then, this term has been introduced to indicate a specific boundary of membrane technology in between ultrafiltration and reverse osmosis. The application fields of the NF membranes are very broad as follows: Demeneralizing water, Cleaning up contaminated groundwater, Ultrapure water production, Treatment of effleunts containing heavy metals, Offshore oil platforms, Yeast production, Pulp and paper mills, Textile production, Electroless copper plating, Cheese whey production, Cyclodextrin production, Lactose production. The earliest NF membrane was made by Cadotte et al, using piperazine and trimesoyl chloride as monomers for the formation of polyamide active layer of the composite type membrane. They coated very thin interfacially potymerized polyamide on the surface of the microporous polysulfone supports. The NF membrane exhibited low rejections for monovalent anions (chloride) and high rejections for bivalent anions (sulphate). This membrane was called NS300. Some of the earliest NF membranes, like the NF40 membrane of FilmTech, the NTR7250 of Nitto-Denko and the UTC20 and UTC60 of Toray, are formed by a comparable synthesis route as the NS300 membrane. Commercially available NF membranes nowadays are as follows: ASP35 (Advanced Membrane Technology), MPF21; MPF32 (Kiryat Weizmann), UTC20; UTC60; UTC70; UTC90 (Toray), CTA-LP; TFCS (Fluid Systems), NF45; NF70 (FilmTec), BQ01; MX07; HG01; HG19; SX01; SX10 (Osmonics), 8040-LSY-PVDI (Hydranautics), NF CA30; NF PES 10 (Hoechst), WFN0505 (Stork Friesland). The typical ones among the commercially available NF membranes are polyamide composite membrane consisting of interfacially polymerized polyamide active layer and microporous support. While showing high water fluxes and high rejections of multivalent ions and small organic molecules, these membranes have relatively low chemical stability. These membranes have low chlorine tolerance and are unstable in acid or base solution. This chemical instability is appearing to be a big obstacle for their applications. To improve the chemical stability, we have tried, in this study, to prepare chemically stable NF membranes from PVA. The ionomers and interfacially polymerized polyamide were used for the modification of'the PVA membranes. For the detail study of the active layer, homogeneous NF membranes made only from active layer materials were prepared and for the high performance, composite type NF membranes were prepared by coating the active layer materials on microporous polysulfone supports.

• Journal of the Korean Society of Clothing and Textiles
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• v.17 no.3
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• pp.491-505
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• 1993

The influences of protease on the removal of various protein soils from cotton fabrics were studied. The human epidermal stratum corneum, hemoglobin and casein were used as protein soils. The soiled fabrics were denatured by steaming for 30 min. before washing and laundered using Terg-O-Tometer under washing conditions. The removal efficiency was evaluated by analysis of protein on the fabrics before and after washing by means of copper-Folin method. The relations between the removal and the characteristics of protease were discussed. Also the degradation of protein were examined by microscopy. The seperation of human epidermal stratum corneum after hydrolysis was examined by SDS-PAGE. The results obtained were as follow : 1. The protein from the soiled cotton fabric was removed effectively by adding protease. The removal of protein was increased in proportion to increasing of the enzyme concentration up to a certain point, but it began to decrease above the point. The removal effect was high in the order of casein>human epidermal stratum corneum>hemoglobin. Especially the protein was more effectively removed in ADS solution(pH 9.5) containing enzyme. 2. When protease was used with ADS. the removal of protein was efficiently showed in relatively short time(5~15min.) compared to using ADS only. It is due to the properties of this enzyme that reacts with very short time. 3. Even at low temperature the removal efficiency of enzyme was relatively higher compared with the activity of enzyme. The removal of protein soil was increased up to a maximum near $50^{\circ}C$, and then decreased. 4. The removal of protein by protease was improved with the increase of alkalinity in the pH range from 9.5 to 11.0 but it began to decrease above pH 11.0. 5. According to the increase of mechanical agitation, the removal effect was increased. But the removal efficiency of protease was more effective compared with the agitation in detergency. 6. According to the SDS-PAGE separation and micrograph it was confirmed that the human epidermal corneum was effectively hydrolysed by the enzyme added. So the fragments of protein were removed more efficiently by means of the interfacial reaction of AOS.

• Journal of Conservation Science
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• v.36 no.5
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• pp.405-420
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• 2020

A convergence research was conducted on glass beads excavated at the ruins of Hapgang-ri, Sejong, using the archeology and conservation approach. The period of appearance of Jugu Towangmyo in the ruins of Hapgang-ri can be estimated to begin in the late 2^nd century; for Jugu Towangmyo No. 15, the period spans from the late 2^nd to early 3^rd century. Form, color, and manufacturing techniques of complete glass beads were examined, and the cross-sections and chemical composition of 16 samples were observed. Based on these analyses, the glass beads were divided into blue, purple, and red colors. The blue-colored beads could be further sub-divided based on their gloss and brightness; in contrast, the red-colored beads were highly uniform with regard to these parameters. Based on the stripe and bubble arrangement on the surface of the glass beads, their drawing technique was identified. Traces of heat treatment or polishing were observed at the ends of the beads. According to their chemical composition, the 16 samples were classified into 3 potash glass and 13 soda glass groups; in the latter, the properties of the stabilizers were divided according to the blue and red bead colors. The stabilizers of the red beads are unique in that they allow the distinction among beads excavated in other areas in South Korea owing to their compositional differences. Colorants in blue- and red-colored beads are cobalt (containing MnO), and copper and iron, respectively.