• Journal of the Korean Magnetics Society
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• v.18 no.1
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• pp.32-35
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• 2008

Thermally stable diffusion barrier of tungsten carbon nitride(W-C-N) and of tungsten boron carbon nitride(W-B-C-N) thin films have studied to investigate the impurity behaviors of boron and nitrogen. In this paper we newly deposited tungsten boron carbon nitride(W-B-C-N) thin film for various $W_2B$ target power on silicon substrate. The impurities of the 100nm-thick W-C-N and W-B-C-N thin films provide stuffing effect for preventing the inter-diffusion between W-C-N or W-B-C-N thin films and silicon during the high temperature($700^{\circ}C{\sim}1000^{\circ}C$) annealing process.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2193-2199
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• 2012

A series of novel polytriazoleimides were prepared from various aromatic dianhydrides and a new kind of 1,2,3-triazole-containing aromatic diamine synthesized by the Cu (I)-catalyzed 1,3-dipolar cycloaddition reaction in DMAc, and characterized by FT-IR, $^1H$-NMR, XRD, DSC and TGA techniques. The results show the polytriazoleimides are soluble in most of strong polar solvents and have inherent viscosity values of 0.51-0.62 dL/g(DMAc). The polytriazoleimide films exhibit a tensile strength of 62.3-104.5 MPa and an elongation at breakage of 4.0-8.1%, a glass transition temperature ($T_g$) of $257-275^{\circ}C$, a decomposition temperature (at 5% weight loss) of $350-401^{\circ}C$ in $N_2$ atmosphere, and a dielectric constant of 2.47-3.01 at 10 MHz, which depend on the structure of the polymers. The polytriazoleimides perform good resistance to acid and alkali solution.

• Tribology and Lubricants
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• v.31 no.2
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• pp.42-49
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• 2015

Because of the growing need for high-speed transport options such as trains and aircraft, there is increasing demand for technology related to high-speed trains. Among them, braking systems are important in high-speed trains in terms of reliability. Especially, the disk brake system, in use in most high-speed trains, transforms kinetic energy into thermal energy and noise. Therefore, the material properties of both the friction materials and disks are expected to influence the tribological characteristics. In this paper, the tribological characteristics depend on the hardness of the brake disks between the Cu-based sintered metallic friction material and the heat-treated heat-resisting steel disks. A lab-scale dynamometer used to perform braking tests at a variety of braking speeds using dry conditions. The test results revealed that the hardness of the disks affects the friction coefficients, friction stabilities, and wear rates. Thus, the brake system using the heat-resisting steel disk requires proper heat-treatment. These differences are considered to be caused by the change in tribological mechanisms and the generation of an oxide layer on the friction surfaces. The oxide layers on the friction surfaces are confirmed to Fe₂O₃ by x-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) analysis.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.5
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• pp.220-230
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• 2018

The objective of this study is to investigate the effect of solution treatment on the microstructure and corrosion behavior of cast AZ91-4%RE magnesium alloy. In the as-cast state, microstructure of the AZ91-4%RE alloy was characterized by intermetallic ${\beta}(Mg_{17}Al_{12})$, $Al_{11}RE_3$ and $Al_2RE$ phase particles distributed in ${\alpha}-(Mg)$ matrix. After solution treatment, the ${\beta}$ particles with low melting point dissolved into the matrix, but Al-RE phases still remained due to their high thermal stabilities. It was found from the immersion and potentiodynamic polarization tests that corrosion rate of the AZ91-4%RE alloy increased after the solution treatment. On the contrary, EIS tests and EDS compositional analyses on the surface corrosion products indicated that the stability of the corrosion product was improved after the solution treatment. Examinations on the corroded microstructures for the ascast and solution-treated samples revealed that dissolution of the ${\beta}$ particles which play a beneficial role in suppressing corrosion propagation, would be responsible for the deterioration of corrosion resistance after the solution treatment. This result implies that the microstructural features such as amount, size and distribution of secondary phases that determine corrosion mechanism, are more influential on the corrosion rate in comparison with the stability of surface corrosion product.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.40-45
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• 2022

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscope, alpha step surface profiler and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.

• Polymer(Korea)
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• v.29 no.2
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• pp.190-197
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• 2005

Nanocomposites of three different polyesters with dodecyltriphenylphosphonium-montmorillonite $(C_{12}PPh-MMT)$ as an organoclay are compared with their thermal properties, mechanical properties, and morphologies. Poly (butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and poly(trimethylene terephthalate) (PTT) were used as matrix polymers in the fabrication of polyester nanocomposite fibers. The variations of their properties with organoclay content in the polymer matrix and draw ratio (DR) are discussed. Transmission electron microscopy (TEM) micrographs show that some of the clay layers are dispersed homogeneously within the polymer matrix on the nano-scale, although some clay particles are agglomerated. We also found that the addition of only a small amount of organoclay is enough to improve the thermal stabilities and mechanical properties of the polyester nanocomposite fibers. Even polymers with low organoclay contents $(<5\;wt\%)$ were found to exhibit much higher strength and modulus values than pure polyester fibers. In the cases of all polyester hybrid fibers, the values of the tensile mechanical properties were found to decrease linearly with increasing DR. However, the initial tensile modulus of the PTT hybrid fibers were found to be independent of DR.

• Journal of Applied Biological Chemistry
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• v.53 no.4
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• pp.195-201
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• 2010

A gene encoding an alanine racemase in B. pseudomycoides was cloned and one (Cys316) or both of two cysteines (Cys316 and Cys365) was (were) substituted with alanine. The cysteine (-) alanine racemases were expressed in E. coli BL21 (DE3) using a pET-21 vector. The expressed enzymes were purified through affinity chromatography using 6xHis ligand. The purified enzymes all showed major one bands by SDS-PAGE analysis, corresponding to 46 kDa. The cysteine (-) alanine racemases as well as the wild type enzyme showed alanine racemase activities, indicating that the enzyme is an alanine racemase and the cysteines in the enzyme may not be involved in the catalysis and/or substrate binding. Thermal stabilities of Cys (-) alanine racemases decreased considerably and half-lives were 26 (wild type), 21 (C316A) and 18 min (C316-365A), respectively at $60^{\circ}C$ pH 8.0, suggesting that cysteine is considerably contributive to the thermal stability of the alanine racemase.

• Food Science and Preservation
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• v.16 no.3
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• pp.392-399
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• 2009

Recent studies indicate that green tea may have anticancer, antioxidant, and antihypertensive effects, and aids body weight control and the promotion of various desirable physiological functions. However, few studies have investigated the antimicrobial effects of green tea. We sought to determine the antimicrobial activity of green tea extract against food spoilage microorganisms. The extract showed remarkable antimicrobial effects against a wide spectrum of putrefactive and food spoilage microorganisms when used at concentrations greater than $500{\mu}g/ml$. The extract showed thermal and pH stability in the range of $40{\sim}150^{\circ}C$ and pH 3.11, respectively. Green tea extract seems to be an ideal natural antimicrobial, considering both efficacy and thermal and pH stabilities. Antimicrobial substances in green tea extract were investigated using electron microscopy and a $\beta$-galactosidase assay. The data showed that the extract contains several efficacious materials, and that their activities are not synergistic but are instead independent. Our data indicate that hydrophilic antimicrobial substances in green tea extract might control food spoilage microorganisms owing to perturbation of the microbial cell membrane.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.130-131
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• 2003

The magnetic and thermal properties of NiFe/IrMn/CoFe with Mn additions have been studied. As grown CoFe pinned-layers with IrMn-Mn have dominantly larger exchange biasing field( $H_{ex}$) and blocking temperature( $T_{b}$) than when pure I $r_{22}$M $n_{78}$ is used. The magnetic properties improve, $H_{ex}$ and $T_{b}$ improve with 77-78 vol% Mn, but drop considerably with more Mn additions, losing magnetic properties of theb NiFe/IrMn/CoFe with addition 0.6 vol % Mn. The average x-ray diffraction peak ratios fcc (111)CoFe of (111)IrM $n_3$ textures for the Mn inserted total vol of 75, 77, and 79 vol% were about 1.4, 0.8, and 0.6, respectively. For the sample without Mn inserted layer, the $H_{ex}$ between I $r_{22}$M $n_{78}$ and CoFe layers is almost nothing. For two multilayer as-grown samples with ultra-thin Mn layers of 77 vol % and 79 vol %, the $H_{ex}$s are 250 Oe and 150 Oe, respectively. In case of IrMn with 77.5 vol% Mn, the $H_{ex}$ was 444 Oe up to 30$0^{\circ}C$ endured of 363 Oe at 40$0^{\circ}C$, respectively. Mn additions improve the magnetic properties and thermal stabilities of NiFe/IrMn/CoFe. Those increase the $H_{ex}$ and $T_{b}$. In applications where higher $H_{ex}$ and $T_{b}$ are accept, proper concentrations of Mn can be used.n can be used.be used.

• Polymer(Korea)
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• v.27 no.5
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• pp.470-476
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• 2003

In order to obtain high refractive plastic materials, 1,2 -ethylenedisulfanylbis(2-mercaptomethyl-1-ethanthiol) (ESTT) was newly prepared in good yield by the reaction of 1,2-ethylenedisulfanylbis(2-bromomethyl-1-ethanthiol) (ESTB) with thiourea followed by hydrolysis using an aqueous ammonia solution and characterized by $^1$H-NMR (-SH at 1.7 ppm), $\^$13/C-NMR(-CH$_2$SH at 28.4 ppm) and FT-IR (-SH at 2540 cm$\^$-1/) spectroscopy, etc. Polythiourethanes (PTU) were obtained from the combinations of ESTT with each of 4,4＇-methylenebis(phenylisocyanate) (MDI), tolyene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI), mxylene diisocyanate (XDI), and 1,6-diisocyanatohexane (HMDI) in the presence of dibutyltin dilaurylate as a catalyst, in a casting mold, and characterized by FT-IR (existence of N=C=O) spectroscopy and elemental analyzer (sulfur content). Accordingly, their thermal, mechanical and optical properties were investigated by using DSC, TGA, hardness tester and refractometer: both the melting point on DSC and crystallinity on X -ray diffraction (XRD) for specimens of PTUs were not observed. PTUs with T$\_$g/s above 110 $^{\circ}C$ showed good hardness (Shore D) in the range of 86 to 89. Thermal stabilities of PTUs obtained by using ESTT and each of diisocyanates containing aromatic rings were especially good. Also, the optical transmittances of amorphous PTUs through UV-visible source in the range of 400 to 600 nm were good. PTUs showed refractive indexes above 1.60, and their refractive indexes gradually increased with increase of sulfur contents.