• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.53-59
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• 2019

Solid fuel reacts with an oxidizer during combustion of a propellant to increase performance. Representative solid fuels are aluminum, cyclotrimethylenetrinitramine (RDX) and octahydro-1, 3,5,7-tetra nitro-1,3,5,7-tetrazocin (HMX). During combustion, these compounds generate white smoke by reacting with moisture and produce materials that are harmful to the environment, such as carbon monoxide, carbon dioxide, and methane gas. This study prepared a high-nitrogen-containing energetic material, hydrazinium 5-aminotetrazolate (HAT), which could be applied as a solid fuel. The compound was characterized by nuclear magnetic resonance (NMR) spectroscopy, and a thermal analysis was measured by differential scanning calorimetry (DSC). Also, the specific impulses and volumes of detonation gases were calculated using the EXPLO5 program.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2290-2295
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• 2018

An acceleration stress test (AST) was performed to evaluate the durability of a polymer membrane in a polymer electrolyte membrane fuel cell (PEMFC) for 500 hours. Previous studies have shown that hydrogen crossover measured by linear sweep voltammetry (LSV) increases when the polymer membrane deteriorates in the AST process. On the other hand, hydrogen crossover of the membrane often decreases in the early stages of the AST test. To investigate the cause of this phenomenon, we analyzed the MEA operated for 50 hours using the AST method (OCV, RH 30% and $90^{\circ}C$). Cyclic voltammetry and transmission electron showed that the electrochemical surface area (ECSA) decreased due to the growth of electrode catalyst particles and that the hydrogen crossover current density measured by LSV could be reduced. Fourier transform infrared spectroscopy and thermogravimetric/differential thermal analysis showed that -S-O-S- crosslinking occurred in the polymer after the 50 hour AST. Gas chromatography showed that the hydrogen permeability was decreased by -S-O-S- crosslinking. The reduction of the hydrogen crossover current density measured by LSV in the early stages of AST could be caused by both reduction of the electrochemical surface area of the electrode catalyst and -S-O-S- crosslinking.

• Advances in nano research
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• v.10 no.1
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• pp.25-42
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• 2021

In this article, the vibration behavior of embedded Functionally Graded Nanoplate (FGNP) employing nonlocal Kirchhoff's plate theory has been investigated under hygrothermal environment. The FGNP is considered to be supported by Winkler-Pasternak foundation. The Eringen's differential theory is used for size effect on the vibration of the FGNP. Rayleigh-Ritz method with orthogonal polynomials are employed for the governing equations and edge constraints. The advantage of this method is that it overcomes all the drawbacks of edge constraints and can easily handle any combinations of mixed edge constraints. The coefficients viz. moisture expansion, thermal expansion and elastic coefficients are considered to be transversely graded across the FGNP. The similarity of the calculated natural frequencies is examined with the previous research, and a good concurrency is seen. The objective of this article is to analyze the parameters' effect on the nondimensionalized frequency of embedded FGNP under hygrothermal environment subjected to all possible edge constraints. For this, uniform and linear rise of temperature and moisture concentration are considered. The study highlights that the nonlocal effect is pronounced for higher modes. Moreover, the effect of the Pasternak modulus is seen to be prominent compared to the Winkler modulus on non dimensionalized frequencies of FGNP.

• Advances in nano research
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• v.12 no.1
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• pp.101-115
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• 2022

Some researchers pointed out that the nonlocal cantilever models do not predict the dynamic softening behavior for nanostructures (including nanobeams) with clamped-free (CF) ends. In contrast, some indicate that the nonlocal cantilever models can capture the stiffness softening characteristics. There are substantial differences on this issue between them. The vibration analysis of porosity-dependent functionally graded nanoscale tubes with variable boundary conditions is investigated in this study. Using a modified power-law model, the tube's porosity-dependent material coefficients are graded in the radial direction. The theory of nonlocal strain gradients is used. Hamilton's principle is used to derive the size-dependent governing equations for simply-supported (S), clamped (C) and clamped-simply supported (CS). Following the solution of these equations by the extended differential quadrature technique, the effect of various factors on vibration issues was investigated further. It can be shown that these factors have a considerable effect on the vibration characteristics. It also can be found that our numerical results can capture the unexpected softening phenomena for cantilever tubes.

• Journal of Powder Materials
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• v.30 no.4
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• pp.332-338
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• 2023

Thermite welding is an exceptional process that does not require additional energy supplies, resulting in welded joints that exhibit mechanical properties and conductivity equivalent to those of the parent materials. The global adoption of thermite welding is growing across various industries. However, in Korea, limited research is being conducted on the core technology of thermite welding. Currently, domestic production of thermite powder in Korea involves recycling copper oxide (CuO). Unfortunately, controlling the particle size of waste CuO poses challenges, leading to the unwanted formation of pores and cracks during thermite welding. In this study, we investigate the influence of powder particle size on thermite welding in the production of Cu-thermite powder using waste CuO. We conduct the ball milling process for 0.5-24 h using recycled CuO. The evolution of the powder shape and size is analyzed using particle size analysis and scanning electron microscopy (SEM). Furthermore, we examine the thermal reaction characteristics through differential scanning calorimetry. Additionally, the microstructures of the welded samples are observed using optical microscopy and SEM to evaluate the impact of powder particle size on weldability. Lastly, hardness measurements are performed to assess the strengths of the welded materials.

• Current Research on Agriculture and Life Sciences
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• v.33 no.1
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• pp.1-5
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• 2015

This study investigated the chelation of a sorghum bran extract using iron (Fe) as a new natural colorant. The composition of the sorghum bran extract and chelation conditions were both examined. The thermal properties of the chelated colorants were analyzed using differential scanning calorimetry (DSC) and a thermal analyzer system(TGA). The sorghum bran extract solution showed a maximum absorbance at 281 nm based on UV/Vis spectrophotometry. According to the chelation pH conditions, pH 7.5 was the most effective. The chelation of the sorghum bran extract increased rapidly when increasing the iron concentration up to 2 mg/L, with no further chelation at a higher concentration. The particle size distribution curve for the chelated tannin revealed four groups: $4.5{\sim}17{\mu}m$, $20{\sim}42{\mu}m$, $45{\sim}80{\mu}m$, and $83{\sim}160{\mu}m$. In a DSC analysis, endothermic peaks attributed to the pyrolysis of the extract and chelated tannin were found at $318^{\circ}C$ and $415^{\circ}C$, respectively. In a TGA analysis, the chelation was shown to increase the final degradation temperature from $253^{\circ}C$ to $382^{\circ}C$, confirming that the chelation improved the thermal stability.

• Elastomers and Composites
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• v.34 no.2
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• pp.135-146
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• 1999

The thermal degradation kinetics of SBR and tire were studied using a conventional thermogravimetric analysis in the stream nitrogen at a heating rate of 5, 10, 15, $20^{\circ}C/min$, respectively. Thermogravimetric curves and their derivatives were analyzed using various analytical methods to determine the kinetic parameters. The degradation of the SBR and tire was found to be a complex process which has multi-stages. The Friedman method gave average activation energies for the SBR and tire of 247.53kJ/mol and 230.00kJ/mol, respectively. Mean-while, the Ozawa method Eave 254.80kJ/mol and 215.76kJ/mol. It would appear that either. Friedman's differential method or Ozawa's integral method provided satisfactory mathematical approaches to determine the kinetic parameters for the degradation of the SBR and tire. Approximately 86% and 55% of oil products were obtained at a final temperature of $700^{\circ}C$ and a heating rate of $20^{\circ}C/min$ for the SBR and tire respectively.

• Composites Research
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• v.30 no.6
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• pp.379-383
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• 2017

A study on the low Earth orbit (LEO) space environment have been conducted as a use of composites have increased. Among the LEO environmental factors, atomic oxygen is one of the most critical factors because atomic oxygen can react and erode a surface of polymer-based composite materials. POSS (Polyhedral Oligomeric Silsesquioxane) materials have been widely studied as an atomic oxygen-resistant nanomaterial. In this study, nanocomposites, which are composed of OG (Octaglycidyldimethylsilyl) POSS nanomaterials and DGEBA/DDM epoxy, were fabricated to find out its thermal and mechanical properties. FT-IR results showed that the nanocomposites were fully cured and contained OG POSS enough. Thermogravimetric analysis and differential scanning calorimetry were performed to measure the thermal properties of the nanocomposites. The initial mass loss temperature and char yield were increased through the filling of OG POSS. As the content of OG POSS increased, glass transition temperature tended to increase to 5 wt.% of OG POSS, but the temperature decreased significantly at 10 wt.% of OG POSS. The tensile test results showed that the content of OG POSS did not affect tensile strength and tensile stiffness.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.976-980
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• 2010

A series of arylacetylene resins with siloxane units were synthesized by the condensation reactions of m-diethynylbenzene magnesium reagents with various $\alpha,\omega$-bis(chloro)dimethylsiloxanes. These resins are liquids and are miscible with common organic solvents at room temperature. The structures of the resins were characterized by FT-IR, $^1H$ NMR, $^{13}C$ NMR, $^{29}Si$ NMR, and gel permeation chromatography (GPC). The thermal behaviors of the resins were examined with differential scanning calorimetry (DSC). These resins have good processability. They can be thermally cross-linked through the ethynyl groups to produce cured resins. The thermal and thermooxidative stabilities of the cured resins were studied by thermogravimetric analysis (TGA). The cured resins possess high thermal and thermooxidative stability. Their decomposition occurs at above $500^{\circ}C$ in both $N_2$ and air. With increasing the length of siloxane units in the resins, the thermal stability of the cured resins decreases in $N_2$. When the cured resins were sintered above $1450^{\circ}C$ under argon, hard and glassy SiOC ceramics were obtained. These SiOC ceramics have the decomposition temperatures at 5% weight loss above $800^{\circ}C$ in air.

• Journal of Sericultural and Entomological Science
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• v.48 no.1
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• pp.11-15
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• 2006

Antheraea yamamai silk fibroin powder was prepared by treatment with HCl. The prepared A. yamamai fibroin hydrolysate was characterized by gel filtration chromatography, amino acid analysis, X-ray diffractometry, circular dichroism analysis, differential thermal analysis, and thermogravimetry. The average molecular weight of A. yamamai powder was about 430 and the major amino acids composed of the powder were Ala and Ser. According to XRD analysis, A. yamamai silk powder showed sharp diffraction peaks at $2{\theta}=20.34^{\circ}\;and\;31.5^{\circ}$. CD spectrum showed a peak around 220 nm and a should 215 nm, assigned to ${\alpha}-helix\;and\;{\beta}-sheet$ structure, respectively. DSC and TGA showed that the maximum degradation temperature of powder was around $250{\sim}270^{\circ}C$. Moreover, no harmful heavy metal was contained in the A. yamamai silk fibroin hydrolysate.