• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.109-121
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• 1995

Reaction coulples of SiC with cobalt were annealed in an Ar/4 vol% $H_2$ atmosphere at temperatures between $950^{\circ}C$ and $1250^{\circ}C$for various times between 4 and 100 h. At temperatures above $950^{\circ}C$, solid state reactions lead to the formation of various silicides with carbon precipitates. The typical reaction layer sequence was $SiC/CoSi + C/CozSi + C/CozSi/CozSi + C/{\cdot\cdot\}/CO_2Si/CO$ in the reaction zone. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was examined and discussed in terms of reaction kinetics and thermodynamic considerations. The growth of the reaction zone has a square root of time dependence. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic gowth of the reaction zone. The mechanical properties of the reaction zones were determined by the microhardness test.

• Analytical Science and Technology
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• v.16 no.6
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• pp.466-474
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• 2003

This paper describes the concentrations of total dissolved iron (tFe) and $Fe^{2+}$ in rainwater and snow, the relationship of Fe species with other metals and ions in bulk rainwater, and the $Fe^{2+}$ generation mechanism in aqueous samples in rainwater of time series collection. Volume weight mean concentrations of tFe and $Fe^{2+}$ were 3.22 and $1.25{\mu}gL^{-1}$ in bulk rainwater, and 50.1 and $43.5{\mu}gL^{-1}$ in snow, respectively. $Fe^{2+}$ was significant fraction to the tFe, accounted for 3.25-93.4% of the tFe in rainwater and 87% in snow. We also investigated temporal variations of tFe, $Fe^{2+}$, other metals and ions in rainwater of time series collection during rain event. Although the concentration range of tFe was different from those of other species, a decreasing trend of tFe from the beginning of the rain event was similar with other species. However, though $Fe^{2+}$ did not show such a decreasing trend, $Fe^{2+}$/tFe was in good correlation with solar radiation. From the results of multiple linear regression analysis and thermodynamic calculations (Mineql+), $Fe^{2+}$ in our samples may be generated from photochemical reduction of $Fe^{3+}$ species (such as $Fe(OH)^{2+}$,$Fe(OH)^{2+}$ and Fe-oxalate) at daytime.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.1
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• pp.62-72
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• 1996

The interface formation and reaction-product morphology between SiC and thin metal films were studied at temperatures between 550 and $1450^{\circ}C$ for various times. The typical reaction layer sequence was CoSi/CoSi+C/CoSi/CoSi+C/ $\cdots$ /SiC reaction at 1050 and $1250^{\circ}C$ for 2 h, while $Ni_2Si/Ni_2Si+C/Ni_2Si/Ni_2Si+C/ {\cdots} /SiC$ at 950 and 105$0^{\circ}C$ for 2 h. Carbon precipitated preferentially on the outer surface and crystallized as graphite above $1450^{\circ}C$ for SiC/Co reaction zone and $1250^{\circ}C$ for SiC/Ni. The mechanism of the periodic band structure formation with carbon precipitation behaviour was discussed in terms of thermodynamic considerations.

• Journal of Microbiology and Biotechnology
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• v.23 no.1
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• pp.7-14
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• 2013

In the Bacillus amyloliquefaciens ${\alpha}$-amylase (BAA), the loop (residues 176-185; region I) that is the part of the calcium-binding site (CaI, II) has two more amino acid residues than the ${\alpha}$-amylase from Bacillus licheniformis (BLA). Arg176 in this region makes an ionic interaction with Glu126 from region II (residues 118-130), but this interaction is lost in BLA owing to substitution of R176Q and E126V. The goal of the present work was to quantitatively estimate the effect of ionic interaction on the overall stability of the enzyme. To clarify the functional and structural significance of the corresponding salt bridge, Glu126 was deleted (${\Delta}$E126) and converted to Val (E126V), Asp (E126D), and Lys (E126K) by site-directed mutagenesis. Kinetic constants, thermodynamic parameters, and structural changes were examined for the wild-type and mutated forms using UV-visible, atomic absoption, and fluorescence emission spectroscopy. Wild-type exhibited higher $k_{cat}$ and $K_m$ but lower catalytic efficiency than the mutant enzymes. A decreased thermostability and an increased flexibility were also found in all of the mutant enzymes when compared with the wild-type. Additionally, the calcium content of the wild-type was more than ${\Delta}E126$. Thus, it may be suggested that ionic interaction could decrease the mobility of the discussed region, prevent the diffusion of cations, and improve the thermostability of the whole enzyme. Based on these observations, the contribution of loop destabilization may be compensated by the formation of a salt bridge that has been used as an evolutionary mechanism or structural adaptation by the mesophilic enzyme.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.759-769
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• 2021

For aerospace propulsion systems, Titanium Hydride Potassium Perchlorate (THPP) is a material commonly used as a pyrotechnic initiator that generates gas when energy is supplied or as a supplement charge for NASA standard initiator (NSI). However, when the energetic materials are stored for a long time, it faces the problem of 'aging'. In this study, changes in thermodynamic properties of THPP aged under various humidity environments were identified through thermal analysis and surface analysis. First, a considerable amount of cracks on the surface of the oxidant was found in the aged THPPs. Particularly, when the humidity level increased, the number and length of the cracks rapidly increased. Also, the deterioration of Viton was found only in the thermally aged sample whereas the oxidation of the fuel was more pronounced in the hygrothermally aged samples. The extracted kinetic parameters of THPP on the reaction progress vary greatly by the humidity level, indicating that moisture significantly changes the performance and combustion reaction of THPP, which may eventually result in a reduced lifespan.

• Korean Journal of Metals and Materials
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• v.46 no.12
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• pp.800-808
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• 2008

Heat treatment is an important step for tool manufacture, but unavoidably generates dimensional distortion. This study investigated the continuous dimensional change and the anisotropic behavior of STD11 tool steel during austenitizing and tempering heat treatment especially using quenching dilatometer. Dilatometric results represented that the dimensional change along longitudinal direction was larger than that along transverse direction. Anisotropic phase transformation strain was produced in forged STD11 tool steel during heat treatment. Anisotropic dimensional change increased with increasing austenitizing temperature. After tempering, anisotropic distortion was partially reduced. FactSage thermodynamic equilibrium phase simulation and microstructural observation (FE-SEM, TEM) showed that large ($7{\sim}80{\mu}m$) elongated $M_7C_3$ carbides could be formed along rolling direction. The resolution of elongated carbides during austenitizing was found to be related with the change of martensite transformation temperature after heat treatment. Anisotropic size change of STD11 tool steel was mainly attributed to large elongated carbides produced during rolling process. Using dilatometric and metallographic examination, the possible mechanism of the anisotropic size change was also discussed.

• The Journal of the Convergence on Culture Technology
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• v.8 no.5
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• pp.685-690
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• 2022

Recent research on soft adhesives has sought to understand in depth how their chemical or mechanical structures interact strongly with living tissues. The aim is to optimally address the unmet needs of patients with acute or chronic diseases. Synergy adhesion, which includes both electrostatic (hydrogen bonds) and mechanical interactions (capillary stress), appears to be effective in overcoming challenges related to long-term unstable bonds to wet surfaces. Here, we report electrostatic and mechanically synergistic mechanisms of adhesion without chemical residues. To infer the mechanism, a thermodynamic model based on custom combination adhesives has been proposed. The model supported experimental results that thermodynamically controlled swelling of hydrogels embedded in elastomeric structures improves biofluidic insensitive on-site adhesion to wet surfaces and improves detachment without chemical residues in the direction of peeling.

• The Journal of the Convergence on Culture Technology
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• v.9 no.1
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• pp.545-550
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• 2023

A pretensioner is a safety device that protects occupants by pulling the seat belt in the event of a vehicle collision. However, since the pretensioner is driven by a explosive method, it is necessary to replace not only the gas generator but also all connecting parts including the manifold after an accident. Therefore, in this paper, we propose an elastic force-based pretensioner that can be used safely and semi-permanently. After analyzing the operating mechanism of the existing pretensioner from a thermodynamic/dynamic point of view, the spring stiffness that can be deployed within an appropriate operating time was determined by converting the gas explosion energy into elastic energy. In addition, the coil spring shape that satisfies the elastic stiffness was designed in consideration of the vehicle interior installation standard. Finally, the operating performance of the pretensioner driven by elastic force was verified through fabrication.

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.237-253
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• 2022

The methyl 2-(1,3-dithietan -2- ylidene)-3-oxobutanoate (MDYO) and 2-(1,3-dithietan-2-ylidene) cyclohexane -1,3-dione (DYCD) were synthesized and tested at various concentrations as corrosion inhibitors for 316L stainless steel in 1 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface analysis techniques (SEM / EDX and Raman spectroscopy) and Functional Density Theory (DFT) was also used to calculate quantum parameters. The obtained results indicated that the inhibition efficiency of MDYO and DYCD increases with their concentration, and the highest value of corrosion inhibition efficiency was determined in the range of concentrations investigated (0.01 × 10^-3 - 10^-3 M). Polarization curves (Tafel extrapolation) showed that both compounds act as mixed-type inhibitors in 1M HCl solutions. Electrochemical impedance spectra (Nyquist plots) are characterized by a capacitive loop observed at high frequencies, and another small inductive loop near low frequencies. The thermodynamic data of adsorption of the two compounds on the stainless steel surface and the activation energies were determined and then discussed. Analysis of experimental results shows that MDYO and DYCD inhibitors adsorb to the metal surface according to the Langmuir model and the mechanism of adsorption of both inhibitors involves physisorption. SEM-EDX results confirm the existence of an inhibitor protective film on the stainless steel surface. The results derived from theoretical calculations supported the experimental observation.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.12
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• pp.2215-2226
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• 2000

Adsorption characteristics for homologous xanthates on quartz surface has been investigated by FT-IR spectroscopy to understand the adsorption mechanism in relation with verification of the influence of surfactants on the stability of hydrophilic suspended solids in aqueous system. Contact angle measurement for water droplets on quartz surface treated with xanthate was also conducted as a supplementary study for spectroscopic investigation to grant a reliability to the interpretation of experimental results. It has been observed that monolayer of ethyl xanthate was formed on quartz surface as the adsorption progressed and double layer of ethyl xanthate was formed eventually through the reverse oriented adsorption of xanthate molecules on the monolayer. Similar trend of adsorption to the case of ethyl xanthate was found for propyl and butyl xanthates and adsorption was observed to occur more rapidly as the number of carbon atom in alkyl group of xanthate homologs increased. Thermodynamic aspect of adsorption was discussed using Young's equation and the variation in adsorption rate was examined according to the concentration of ethyl xanthate. Based on the result, it has been concluded that the adsorption features of surfactant on substrate in aquatic system is governed by molecular structure and concentration of surfactant and its residual time in aqueous environment as dissolved state also influences greatly the stability of hydrophilic suspended particles.