• Composites Research
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• v.16 no.1
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• pp.26-33
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• 2003

Utilizing a thermo-acoustic emission (AE) technique, a study on detection and evaluation of microfractures in cross-ply laminate composites was performed. Fiber breakages and matrix fractures formed by a cryogenic cooling at $-191^{\circ}C$ were observed with ultrasonic C-scan, optical and scanning electron microscopy. Those microfractures were monitored in a non-destructive in-situ state as three different types of thermo-AE signals classified on the basis of Fast-Fourier Transform and Short-Time Fourier Transform. Thus, it was concluded that real-time estimation of microfracture processes being formed during cryogenic cooling could be accomplished by monitoring such different types of thermo-AEs in each time-stage and then by analyzing thermo-AE behaviors for the respective AE types on the basis of the AE signal analysis results obtained during thermal heating and cooling load cycles.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.1
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• pp.179-185
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• 2000

In this study, we examined the movement of chlorophenol as a precursor of the dioxin in the after-combustion to minimize the creation and emission of dioxin in a municipal waste incinerator. The CPs was injected to the electric incinerator in temperature $300{\sim}500^{\circ}C$, using $N_2$ gas to control the reaction time, The oxygen quantity supplied into the $CP_s's$ isomer combustion was added with the value of experience formula. When the space velocity in reactor was 60~80/sec, the removal efficiency of CP was obtained in the presence of Mo-V catalyst and non catalyst. The efficiency in non-catalyst was 74% to 80% mono-CP, di-CP 55~66%, tri-CP 50~58%, while mono-CP 90~99.9%, di-CP 96~97%, tri-CP 76~99% in a catalyst. Consequently, it was shown that these were 20~30% more efficienct than those.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.1
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• pp.30-39
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• 1997

After changing the heat treating atmosphere of nitrogen gas, argon gas and vacuum, the nitrogen contents, microstructural changes, hardness and corrosion resistance of 0.25wt.%N alloyed super duplex stainless steel have been investigated in the temperature range from $1050^{\circ}C$ to $1350^{\circ}C$. The nitrogen content showed to be increased up to 0.36wt.% after heat treating the specimen in nitrogen gas at $1200^{\circ}C$, while the decrement of nitrogen content in vacuum atmosphere was shown down to 0.03wt.% at $1350^{\circ}C$. After heat treating in the mixed gas atmosphere of argon and nitrogen at $1250^{\circ}C$, the surface ${\gamma}$ phase existed as ${\alpha}+{\gamma}$ phase increased with increasing nitrogen gas content. The ${\gamma}$ single phase appeared at the surface above $80%N_2$ gas, while the surface ${\alpha}$ single phase was shown below $20%N_2$ gas. When heat treating the specimen in nitrogen gas at $1050^{\circ}C$, the hardness of austenite phases increased above Hv 40 at the surface layer compared to the hardness of the core parts, while decrement of denitriding effect caused to the hardness nearly unchanged between surface and the core parts after heat treating in vacuum atmosphere. The surface ${\gamma}$ single phase specimen showed superior corrosion resistance than the surface ${\alpha}$ single phase specimen. The surface ${\alpha}$ phase existed in the ${\alpha}+{\gamma}$ microstructure showed higher corrosion resistance after heat treating in the nitrogen gas atmosphere than the ${\alpha}$ phase heat treated in the argon gas and vacuum atmosphere.

• Journal of Adhesion and Interface
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• v.20 no.2
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• pp.53-60
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• 2019

Stable graphene dispersions in various organic solvents and in water were achieved via noncovalent functionalization of graphene surfaces using different types of commercially available surfactants. Stable dispersions were obtained in short time sonication, 3 h. In NMP, graphene with Tween and Span series, and with Pluronic surfactants showed stable dispersions. In ethanol, nitrogen based surfactants showed stable dispersions. In water and dichloromethane partially stable graphene dispersions were obtained using poly(4-vinyl pyridine) and sodium dodecyl sulfonate surfactants. Large scale productions of stable dispersions were successful using poly(4-vinyl pyridine), poly(vinyl pyrrolidone), and poly(2-(dimethylamino)ethyl methacrylate). Thus, this work will serve as a library to select the surfactants for different solvent systems.

• Journal of Soil and Groundwater Environment
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• v.28 no.6
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• pp.24-32
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• 2023

Continuous increase of domestic meat consumption has inevitably increased generation of livestock manure and caused severe environmental impacts on ecosystem and human beings. This work produced biochar from cattle manure samples with different composting aging stages and investigated the properties of the produced biochar. The result of thermogravimetric analysis showed that thermal decomposition of the manure initiated at <600℃. The biochar yield was higher for the manure with a longer pre-composting period due to the elimination of microbially metabolized carbons during composting process. The result of FT-IR analysis showed that the number of surface functional groups were reduced during pyrolysis while enhancing the graphitic structures of the carbon framework. Manure samples tended to leach out N and P in leaching tests, with its amount higher for aged one than fresh one. However, their leaching was substantially suppressed when the manure was produced into biochar. In XPS spectra, it was found that N and P in the manure incorporated into biochar surface to form N-doped graphitic carbon and P-N-moieties, respectively. The findings of this work suggest that the thermochemical process can be of a viable option to valorize into biochar for potential environmental applications as well as to alleviate undesired nutrients loading to the environment.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.8-14
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• 2024

Austenitic stainless steel 316L has been used a lot of applications because of its high corrosion resistance and formability. In addition, copper brazing is employed to create complex shape of 316L stainless steel for various engineering parts. In such system, copper-based filler metals make galvanic cell at metal/filler metal interface, and it accelerates corrosion of stainless steel. Furthermore, Cu-rich region formed by diffused copper in austenitic stainless steel can promote a pitting corrosion. In this study, we used an ammonia (NH₃) gas to nitride the 316L stainless steel for improving the corrosion resistance. The thickness of the nitride (nitrogen high) layer increased with the treatment temperature, and the surface hardness also increased. The potentiodynamic polarization test showed the improvement of corrosion resistance of 316L stainless steel by enhancing the passivation on nitride layer. However, in case of high temperature nitriding, a chromium nitride was formed and its fraction increased, so that the corrosion resistance was decreased compared to the intact 316L stainless steel.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.5
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• pp.859-867
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• 1997

In order to utilize the processing wastes of squid, chitosans were manufactured from the pens of domestic squid, Todarbdes pacificus and foreign squid, Ommastrephes bartrami and then, its rheological properties were studied. The amounts of nitrogen and minerals of the domestic squid pens were $11.4\%\;and\;0.1\%$ respectively, whereas those of its chitosan were $7.5\%\;and\;0.2\%$. In case of foreign squid pen and chitosan, the amounts of nitrogen and minerals were $12.1\%,\;0.8\%\;and\;7.8\%,\;0.2\%$ respectively. Intrinsic viscosity $([\eta]) $ of domestic and foreign squid pen chitosans were decreased with increasing pH from 3.4 to 5.4 which might be due to the reduced repulsion in inter- of intra- chitosan molecules. Intrinsic viscosity of the domestic and foreign squid pen chitosans were decreased with increasing NaCl concentration thus indicated that the domestic and foreign squid pen chitosans were polyelectrolyte molecules and stiffness of squid pen thitosans were 0.11 similar to that of k-carrageenan. Flow type of squid pen chitosan solutions were pseudoplastic fluids without yield stress by the viscosity measurement. But the squid pen chitosan solutions showed newtonian fluid up to $0.15\~0.24\%$ concentration for domestic and $0.21\~0.24\%$ concentration for foreign at $10\~50\%$. Concentration dependence of consistency index in infinitive dilute domain (Kc) were higher in the dilute domain than entangled domain. Activation energies (Ea) of the squid pen chitosans were 3.7, 6.3, 3.6, 4.0 and 4.1 Kcal/g moi for domestic and 3.2, 3.1, 3.4, 3.8 and 3.6 Kcal/g mol for foreign at 0.1, 0.15, 0.25, 0.35 and $0.5\%$, respectively.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.877-887
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• 1996

The ideal membranes for membrane-covered oxygen probes system should be selectively permeable for oxygen and chemically inert, and have good mechanical strength. Polysulfone(PSf) was selected to develop the membrane for membrane-covered oxygen electrodes system. PSf membranes have properties such as good reproducibility, good mechanical strength, chemical inertness, and high heat resistance. PSf membranes were cast from polymer solution on the glass plate at constant temperature, and casting solvents used were tetrahydrofuran(THF), methylene chloride, and N-methyl-2-pyrrolidone(NMP). Tricresyl phosphate(TCP) as plasicizer was added to PSf to increase the softness of membrane. The permeation characteristics were observed for pure oxygen and nitrogen through pure PSf membranes by variable volume method and membrane-covered electrode system. The permeability coefficients of oxygen and nitrogen measured by variable volume method were slightly decreased with increasing of upstream pressure. The permeation properties of PSf membrane using methylene choride as casting solvent were not affected by the PSf amount of polymer solution. The permeability coefficients of oxygen and nitrogen for PSf membrane containing TCP were very slightly lower than those for pure PSf membrane, but ideal separation factors were slightly higher. The flexibility of PSf membrane containing 2wt% TCP was better than that of pure PSf membrane. It was expected that this increase in flexibility would solve the difficulty of fixing the membrane to the cathode. The membrane-covered oxygen probes system was composed of anode, cathode and electrolyte. The type of the anode was Ag/AgCl half-cell, that of cathode was Ag, and the electrolyte was 4N KCl solution. The result of sampled current voltametry for PSf membrane showed the plateu region at -0.3V~-1.0V. The correlation coefficient of oxygen partial pressure versus current for PSf membrane was relatively high, 0.99949. It was concluded that PSf membrane was the good candidate for the membrane-covered oxygen probes system.

• Journal of Soil and Groundwater Environment
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• v.10 no.3
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• pp.38-45
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• 2005

The feasibility of stimulating in situ aerobic cometabolic activity of indigenous microorganisms was investigated in a trichloroethylene (TCE)-contaminated aquifer. A series of single-well natural drift tests (SWNDTs) was conducted by injecting site groundwater amended with a bromide tracer and combinations of toluene, oxygen, nitrate, ethylene and TCE into an existing monitoring well and by sampling the same well over time. Three field tests, Push-pull Transport Test, Drift Biostimulation Test, and Drift Surrogate Activity Test, were performed in sequence. Initial rate of toluene degradation was much faster than the rate of bromide dilution resulting from natural groundwater drift, indicating stimulation of indigenous toluene-oxidizing microorganisms. Transformation of ethylene, a surrogate probing overall activity of TCE transformation, was also observed, and its transformation results in the production of ethylene oxide, suggesting that some tolueneoxidizing microorganisms stimulated may express a orthomonooxygenase enzyme. Also in situ transformation of TCE was confirmed by greater retardation of TCE than bromide after the stimulation of toluene-oxidizing microorganisms. These results indicate that, in this environment, toluene and oxygen additions stimulated the growth and aerobic cometabolic activity of indigenous microorganisms expressing orthomonooxygenase enzymes. The simple, low-cost field test method presented in this study provides an effective method for conducting rapid field assessments and pilot testing of aerobic cometabolism, which has previously hindered application of this technology to groundwater remediation.

• Analytical Science and Technology
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• v.32 no.1
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• pp.17-23
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• 2019

Sources of NOx are both anthropogenic (e.g. fossil fuel combustion, vehicles, and other industrial processes) and natural (e.g. lightning, biogenic soil processes, and wildfires). The nitrogen stable isotope ratio of NOx has been proposed as an indicator for NOx source partitioning, which would help identify the contributions of various NOx sources. In this study, the ${\delta}^{15}N-NO_2$ values of vehicle emissions were measured in an urban region, to understand the sources and processes that influence the isotopic composition of NOx emissions. The Ogawa passive air sampler was used to determine the isotopic composition of $NO_2$(g). In urban tunnels, the observed $NO_2$ concentration and ${\delta}^{15}N-NO_2$ values averaged $3809{\pm}2656ppbv$ and $7.7{\pm}1.8$‰, respectively. The observed ${\delta}^{15}N-NO_2$ values are associated with slight regional variations in the vehicular $NO_2$ source. Both $NO_2$ concentration and ${\delta}^{15}N-NO_2$ values were significantly higher near the expressway ($965{\pm}125ppbv$ and $5.9{\pm}1.4$‰) than at 1.1 km from the expressway ($372{\pm}96ppbv$ and $-11.5{\pm}2.9$‰), indicating a high proportion of vehicle emissions. Ambient ${\delta}^{15}N-NO_2$ values were used in a binary mixing model to estimate the percentage of the ${\delta}^{15}N-NO_2$ value contributed by vehicular NOx emissions. The calculated percentage of the ${\delta}^{15}N-NO_2$ contribution by vehicles was significantly higher close to the highway, as observed for the $NO_2$ concentration and ${\delta}^{15}N-NO_2$.