• 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 Ceramic Society
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• v.41 no.7
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• pp.508-512
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• 2004

For abutment of dental implants, (Y, Nb)-TZP/Alumina composites were prepared by addition of 10-90 vol% alumina at an interval of 10 vol％ into tetragonal zirconia solid solution which consists of 90.24 mol% Zr $O_2$, 5.31 mol% Y$_2$ $O_3$, and 4.45 mol% Nb$_2$O$\_$5/. Biaxial flexure strength and fracture toughness of composite were optimized by adding 10 vol% alumina, which resulted in 900 MPa and 8.9 MPam$\^$1/2/, respectively. The composite did not undergo low temperature degradation even after autoclave treatment at 200$^{\circ}C$ for 10 h. 65 of (Y, Nb)-TZP/Alumina composite abutments were employed into 40 patients and any adverse reaction, screw loosing, or fracture of abutments was not observed for the span of 2 years, indicating that the ceramic abutments can be safely used for restorations.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.48-53
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• 1995

The structure, magnetic properties and magnetoresistance phenorrena of Ag-Co nano-granular alloy films prepared by a thermal co-evaporation were studied. Supersaturated fee Ag-Co solid solution and fee Co clusters coexisted in the as-deposited state. As Co content increases from 20 to 55 at.% Co, the grain size of the Ag matrix decreases from 147 to $67{\AA}$, and the Co solubility in the Ag matrix increases from 2.5 to 6.7%. Ag-Co alloy films having composition below 25 at.% Co showed mainly superparamagnetic behavior and above that composition, they showed both paramagnetic and ferromagnetic l::ehavior in the as-deposited state. The maximum magnetoresistance of 19% at R. T. and 10 kOe was obtained in the as-deposited 30 at.% Co alloy film. Heat treatment did not improve the MR ratio tecause most of the Co was already precipitated in the as-deposited state.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.72-77
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• 2010

Glass-ceramics were fabricated by heat-treatment of glass obtained by melting a coal bottom ash with $Li_2O$ addition. The main crystal grown in the glass-ceramics, containing 10 wt% $Li_2O$, was $\beta$-spodumene solid solution, while in $Li_2O$ 20 wt% specimen was mullite, identified using XRD. The activation energy and Avrami constant for crystallization were calculated and showed that bulk crystallization behavior will be predominant, and this expectation agreed with the microstructural observations. The crystal phase grown in $Li_2O$ 10 wt% glass-ceramics had a dendrite-like shaped whereas the shape was flake-like in the 20 wt% case. The thermal expansion coefficient of the $Li_2O$ 10 wt% glass-ceramics was lower than that of the glass having the same composition, owing to the formation of a $\beta$-spodumene phase. For example, the thermal expansion coefficient of $Li_2O$ 10 wt% glass-ceramics was $20\times10^{-7}$, which is enough for application in various heat-resistance fields. But above 20 wt% $Li_2O$, the thermal coefficient expansion of glass-ceramics, on the contrary, was higher than that of the same composition glass, due to formation of mullite.

• Applied Biological Chemistry
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• v.29 no.1
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• pp.44-50
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• 1986

Two fractions of ${\beta}-glucanase$(CMCase), two fractions of filter paper degradation enzyme (FPase) and one ${\beta}-glucanase$ fraction were partially purified from Fusarium moniliforme and applied to recovery process of red bean starch. Red bean were incubated with the fractions of CMCase and FPase at $50^{\circ}C$ for 2 hours and the starch granules are separated. Maximal sedimentation rate of red bean starch granules was obtained with treatment of the mixture solution of 0.004 units/ml of FPase and 0.3 units/ml of CMCase. In the enzyme treated process percent recovery of red bean starch granule increased about 7% and suspended solid in waste water was reduced about 40%, compared with those of control. The results indicated that red bean cell treated with cellulase fractions absorbed water more rapidly and specific gravity of starch granule increased.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3665-3670
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• 2012

Metal-p-$NH_2$-Bn-DOTA (paraammionobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid: ABDOTA) complex was synthesized and purified for bio-tagging to quantify biological target materials using laser ablation (LA)-ICP-MS. Since the preparation of a pure and stable tagging complex is the key procedure for quantification, magnetic particles were used to purify the synthesized metal-ABDOTA complex. The magnetic particles immobilized with the complex attracted to a permanent magnet, resulting in fast separation from free un-reacted metal ions in solution. Gd ions formed the metal-complex with a higher yield of 64.3% (${\pm}3.9%$ relative standard deviation (RSD)) than Y ions, 52.3% (${\pm}2.5%$ RSD), in the pH range 4-7. The complex bound to the magnetic particles was released by treatment with a strong base, of which the recovery was 81.7%. As a reference, a solid phase extraction (SPE) column packed with Chelex-100 resin was employed for separation under similar conditions and produced comparable results. The tagging technique complemented polydimethylsiloxane (PDMS) microarray chip sampling in LA-ICP-MS, allowing determination of small sample volumes at high throughputs. For application, immunoglobulin G (IgG) was immobilized on the pillars of PDMS microarray chips and then tagged with the prepared Gd complex. IgG could then be determined through measurement of Gd by LA-ICP-MS. A detection limit of 1.61 ng/mL (${\pm}0.75%$ RSD) for Gd was obtained.

• Bulletin of the Korean Chemical Society
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• v.25 no.9
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• pp.1331-1335
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• 2004

Angiogenesis is essential for the growth and persistence of solid tumors. Their metastases, anti-angiogenesis could lead to the suppression of tumor growth. One of the main strategies of cancer treatment is developing molecules of anti-angiogenic activity. In this study, two angiogenic inhibitors, Ang3 (KLFDF) and Ang4 (XLFDF) derived from KLYDY, which is the sequence of angiostatin active sites kringle 5, were designed and synthesized. Previously we reported the activities and structures of two inhibitors, Ang1 (KLYDY) and Ang2 (KLWDF). In order to investigate the effect of Phe substitution, Ang3 was designed with a sequence of KLFDF. In order to reduce conformational flexibility of side chain in Lys, Ang4 was designed with a sequence of XLFDF, where X has amino substituted phenyl ring. Solution structures of those inhibitors were investigated using NMR spectroscopy and their activities as angiogenesis inhibitors were studied. Ang1 and Ang2 show angiogenic activities, while Ang3 and Ang4 have no activities and have extended structures compared to Ang1 and Ang2. Therefore, Phe rings do not have effective hydrophobic interactions with other aromatic residues in Ang3 and Ang4. The representative structure of Ang2 has a stable intramolecular hydrogen bond. Therefore, intramolecular hydrogen bonding might be more important in stabilizing the structure than the hydrophobic interactions in these inhibitors. More rigid structure, which can be expected to have higher activities and better match with the receptor bound conformations, can be obtained with a constrained cyclic structure. Further peptidomimetic approaches should be tried to develop angiogenesis inhibitors.

• Journal of Biomedical Engineering Research
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• v.22 no.6
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• pp.511-518
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• 2001

In vitro corrosion resistance of the commercially used 76.5wt.%Pd-17.6%Cu-7.2%Ga and 77.3%Pd-6.0%Ga dental Prostheses high-Palladium system alloys in cast, degassing and porcelain-firing heat treatment conditions were evaluated by the potentiodynamic polarization technique in the de-aerated 0.9%NaCl and a modified Fusayama electrolyte. From the corrosion rate experimental results, we found that there is a small difference in the corrosion resistance depending on the microstructure. However. it was so small that there is no significant problem as a dental material. The 77.3%Pd-6.0%Ga showed better corrosion resistance than the 76.5%Pd-11.6%Cu-7.2%Ga dental Prostheses high-palladium system alloys. These experimental observations in 76.5%Pd-11.6%Cu-7.2%Ga alleys are mainly due to a rapid quenching and Cu in the alloy which accelerate the eutectic reaction with a segregation and Precipitates in the microstructure. On the ocher hand, 77.3%Pd-6.0%Ga alloys, which are solid-solution matrix, show much better col·lesion resistance compared with that of 76.5%Pd-11.6%Cu-7.2%Ga alloys.

• Journal of Powder Materials
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• v.27 no.4
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• pp.311-317
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• 2020

In this study, the effects of Co content on the microstructure and Charpy impact properties of Fe-Cr-W ferritic/martensitic oxide dispersion strengthened (F/M ODS) steels are investigated. F/M ODS steels with 0-5 wt% Co are fabricated by mechanical alloying, followed by hot isostatic pressing, hot-rolling, and normalizing/tempering heat treatment. All the steels commonly exhibit two-phase microstructures consisting of ferrite and tempered martensite. The volume fraction of ferrite increases with the increase in the Co content, since the Co element considerably lowers the hardenability of the F/M ODS steel. Despite the lowest volume fraction of tempered martensite, the F/M ODS steel with 5 wt% Co shows the highest micro-Vickers hardness, owing to the solid solution-hardening effect of the alloyed Co. The high hardness of the steel improves the resistance to fracture initiation, thereby resulting in the enhanced fracture initiation energy in a Charpy impact test at - 40℃. Furthermore, the addition of Co suppresses the formation of coarse oxide inclusions in the F/M ODS steel, while simultaneously providing a high resistance to fracture propagation. Owing to these combined effects of Co, the Charpy impact energy of the F/M ODS steel increases gradually with the increase in the Co content.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.995-1000
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• 2011

The microstructure of Cu-24 wt.%Ag filamentary nanocomposite fabricated by a thermo-mechanical process has been investigated by transmission electron microscopy (TEM) observations. This study is focused on the stability of Ag filaments formed by cold drawing; the effects of thermal treatment on the precipitation behavior and distribution of Ag-rich precipitates were also investigated. The Ag filaments elongated along the <111> orientation were observed in Cu-rich ${\alpha}$ phase of the as-drawn specimen and the copper matrix and the silver filament have a cube on cube orientation relationship. Annealing at temperatures lower than $200^{\circ}C$ for the as-drawn specimen caused insignificant change of the fibrous morphology but squiggly interfaces or local breaking of the elongated Ag filaments were easily observed with annealing at $300^{\circ}C$. When samples were annealed at $400^{\circ}C$, discontinuous precipitation was observed in supersaturated Cu solid solution. Ag precipitates with a thickness of 7-20 nm were observed along the <112> direction and the orientation relationship between the copper matrix and the Ag precipitates maintained the same orientation relationship in the as-drawn specimen. The interface between the copper matrix and the Ag precipitates is parallel to {111} and micro-twins were observed in the Ag precipitates.