• Journal of Soil and Groundwater Environment
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• v.26 no.4
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• pp.1-7
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• 2021

The removal of PCBs (Polychlorinated biphenyls) in aqueous phase was investigated in the ultraviolet (UV) process, ultrasonics (US) process and ultraviolet/ultrasonic (UV/US) process using PCB No.7 and Aroclor 1260. For PCB No.7 relatively high removal efficiency over 90% was obtained during 20 min in the UV process and UV/US process. On the other hand, lower removal efficiency of 50 - 70% was achieved for it consisted of individual congeners of PCBs containing 3~8 of chlorine atom. It was found that the dechlorination reaction (the photolytic cleavage of C-Cl bond) was considered as a main removal mechanism in the UV process while PCBs were removed by cavitation-induced radical reaction in the US process. No significant dechlorination occurred in the US process. Consequently, it was suggested that the UV process or UV/US process was applicable for the removal of PCBs in aqueous phase in terms of the removal efficiency and operation time. In addition, the application of saturating gas such as Ar and Air could be considered to control redox condition and enhance the severity of acoustic cavitation for the removal of PCBs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.2 s.245
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• pp.170-176
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• 2006

A spark discharge aerosol generator using air as a carrier gas has successfully been applied to silver nanoparticle production. The spark discharge between two silver electrodes, which was periodically obtained by discharging the capacitor, produced sufficient high temperatures to evaporate a small fraction of the silver electrodes. The silver vapor was subsequently supersaturated by rapid cooling and condensed to silver nanoparticles by nucleation and condensation. The morphology of the generated particles observed by transmission electron microscope was spherical. The element composition of the nanoparticles was silver, which was determined by energy dispersive X-ray spectroscopy. The crystal phase of the particles spark-generated under air atmosphere was composed of silver and silver oxides phase, which was determined by Xray diffraction analysis. While the nanoparticles generated under nitrogen atmosphere had only silver phase. This XRD data indicates that some fraction of the evaporated silver vapor could be oxidized in air atmosphere by the reaction with oxygen. A stable operation of the spark discharge generator has been achieved. The size and concentration of the particles can be easily controlled by altering the repetition frequency, capacitance, gap distance and flow rate of the spark discharge system.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.4
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• pp.545-550
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• 2016

Demilitarization involves the disposal and recovery of obsolete explosives or ammunition. Cyclotol has been used as a military explosive along with RDX and HMX. A limited number of processes exist for safe disposal due to their sensitivity to thermal shock. Rotary kilns are widely used for thermal decomposition in many countries due to cost effectiveness and simplicity compared with supercritical oxidation. Phase change as well as condensed phase reactions(CPRs) and gas phase reactions(GPRs) with rates described by the Arrhenius equation of cyclotol has been considered in this work. Changes in gas fraction, reaction rate and mass of explosives were predicted at 490, 505 and 575 K. A maximum temperature of 2062 K has been predicted within the reactor at an initial temperature of 575 K due to GPRs. From this research, Thermal decomposition in the rotary kiln is plausible for demilitarization.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.6
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• pp.674-681
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• 2008

Silver as a metal catalyst has been used to remove odorous compounds. In this study, silver particles in nano sizes ($5{\sim}30nm$) were prepared on the surface of $NaHCO_3$, the supporting material, using a sputtering method. The silver nano-particles were dispersed by dissolving $Ag-NaHCO_3$ into water, and the dispersed silver nano-particles in the aqueous phase was applied to remove inorganic odor compounds, $NH_3$ and ${H_2}O$, in a scrubbing reactor. Since ammonia has high solubility, it was removed from the gas phase even by spraying water in the scrubber. However, the concentration of nitrate (${NO_3}^-$) ion increased only in the silver nano-particle solution, implying that the silver nano-particles oxidized ammonia. Hydrogen sulfide in the gas phase was rapidly removed by the silver nano-particles, and the concentration of sulfate (${SO_4}^{2-}$) ion increased with time due to the oxidation reaction by silver. As a result, the silver nano-particles in the aqueous solution can be successfully applied to remove odorous compounds without adding additional energy sources and producing any harmful byproducts.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.303-307
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• 2000

The crystal structure of ZnS fabricated by gas-liquid phase reaction was obtained by XRD and refined by RIETAN near R$_{wp}$ factor 10%. The increasement of HCP phase depended on extra H$_2$S gas and the lattice parameter and crystalline size changed by the relative ratio of multiphase. Using ZnS of the different multiphase ratio and crystalline size, sintered ZnS:Cu, Al green phosphor and the CL property resulted optimum luminescence in the range of 91~94% and 150~190$\AA$, respectably, FCC/HCP ratio and crystalline size. As changing of structure ratio, the reason of different luminescence property is now studying. As well as, after XRD pattern of TiO$_2$powder fitted by RIETAN and the structure factor using MEED method simulated about each atom of (002) plane. Additionally, we proposed RIETAN and MEED were the methods of the study of luminescence mechanism for many phosphor materials.s.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.5
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• pp.421-428
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• 2012

The Sulfur-Iodine (SI) thermochemical hydrogen production process is one of the most promising thermochemical water splitting technologies. In the integrated operation of the SI process, the $O_2$ produced from a $H_2SO_4$ decomposition section could be supplied directly to the Bunsen reaction section without preliminary separation. A $HI_x$ ($I_2+HI+H_2O$) solution could be also provided as the reactants in a Bunsen reaction section, since the sole separation of $I_2$ in a $HI_x$ solution recycled from a HI decomposition section was very difficult. Therefore, the Bunsen reaction using $SO_2-O_2$ mixture gases in the presence of the $HI_x$ solution was carried out to identify the effect of $O_2$. The amount of $I_2$ unreacted under the feed of $SO_2-O_2$ mixture gases was little higher than that under the feed of $SO_2$ gas only, and the amount of HI produced was relatively decreased. The $O_2$ in $SO_2-O_2$ mixture gases also played a role to decrease the amount of a impurity in $HI_x$ phase by only striping effect, while that in $H_2SO_4$ phase was hardly affected.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.77-83
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• 2006

Anodic overpotential has been investigated with gas composition changes in a $100cm^2$ class molten carbonate fuel cell. The overpotential was measured with steady state polarization, reactant gas addition (RA), inert gas step addition (ISA), and electrochemical impedance spectroscopy (EIS) methods at different anodic inlet gas compositions, i.e., $H_2:CO_2:H_2O=0.69:0.17:0.14\;atm\;and\;H_2:CO_2:H_2O=0.33:0.33:0.33\;atm$, at a fixed $H_2$ flow rate. The results demonstrate that the anodic overpotential decreases with increasing $CO_2\;and\;H_2O$ flow rates, indicating the anode reaction is a gas-phase mass-transfer control process of the reactant species, $H_2,\;CO_2,\;and\;H_2O$. It was also found that the mass-transfer resistance due to the $H_2$ species slightly increases at higher $CO_2\;and\;H_2O$ flow rates. EIS showed reduction of the lower frequency semi-circle with increasing $H_2O\;and\;CO_2$ flow rate without affecting the high frequency semi-circle.

• Clean Technology
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• v.29 no.1
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• pp.39-45
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• 2023

To investigate the effects of Mg addition at different aging times and temperatures, Cu/MgO/Al₂O₃ catalysts were synthesized for the low-temperature water gas shift (LT-WGS) reaction. The co-precipitation method was employed to prepare the catalysts with a fixed Cu amount of 30 mol% and varied amounts of Mg/Al. Synthesized catalysts were characterized using XRD, BET, and H₂-TPR analysis. Among the prepared catalysts, the highest CO conversion was achieved by the Cu/MgO/Al₂O₃ catalyst (30/40/30 mol%) with a 60 ℃ aging temperature and a 24 h aging time under a CO₂-rich feed gas. Due to it having the lowest reduction temperature and a good dispersion of CuO, the catalyst exhibited around 65% CO conversion with a gas hourly space velocity (GHSV) of 14,089 h-1 at 300 ℃. However, it has been noted that aging temperatures greater or less than 60 ℃ and aging times longer than 24 h had an adverse impact, resulting in a lower surface area and a higher reduction temperature bulk-CuO phase, leading to lower catalytic activity. The main findings of this study confirmed that one of the main factors determining catalytic activity is the ease of reducibility in the absence of bulk-like CuO species. Finally, the long-term test revealed that the catalytic activity and stability remained constant under a high concentration of CO₂ in the feed gas for 19 h with an average CO conversion of 61.83%.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.10-16
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• 2008

Numerical simulations of freely propagating premixed flames burning mixtures of methane and chlorinated hydrocarbons in fuel are performed at atmospheric pressure in order to understand the effect of chlorinated hydrocarbons on the formation of nitrogen oxide. A detailed chemical reaction mechanism is used, the adopted scheme involving 89 gas-phase species and 1017 elementary forward reaction steps. Chlorine atoms available from chlorinated hydrocarbons inhibit the formation of nitrogen oxides by lowering the concentration of radical species. The reduction of NO emission index calculated with thermal or prompt NO mechanism is not linear and is probably related to the saturation effect as $CH_3Cl$ addition is increased, In the formation or consumption of nitrogen oxide, the $NO_2$ and NOCl reactions play an important role in lean flames while the HNO reactions do in rich flames. The molar ratio of Cl to H in fuel has an effect on the magnitude of NO emission index.

• Journal of the Korean Chemical Society
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• v.25 no.3
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• pp.145-151
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• 1981

The intrinsic reactivity of $S_N2$reaction in the gas phase was discussed MO theoretically (CNDO/2). We investigated the changes in geometry and electronic structure by means of the partial geometry optimization for reactantes, transition states, and products with various nucleophiles and leaving groups. We found that it was possible to discuss qualitatively the reactivity of $S_N2$ reaction with CNDO/2 MO calculation and the reactivity was controlled by basicity and of induced polarizability.