• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.9-15
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• 2005

In order to know the electrochemical decomposition characteristics of ammonia to nitrogen, this work has studied several experimental variables on the electrolytic ammonia decomposition. The effects of pH and chloride ion at $IrO_2$, $RuO_2$, and Pt anodes on the electrolytic decomposition of ammonia were compared, and the existence of membrane equipped in the cell and the changes of the current density, the initial ammonia concentration and so on were investigated on the decomposition. The performances of the electrode were totally in order of $RuO_2{\approx}IrO_2>Pt$ in the both of acid and alkali conditions, and the ammonia decomposition was the highest at a current density of $80mA/cm^2$, over which it decreased, because the adsorption of ammonia on the electrode surface was hindered due to the evolution of oxygen. The ammonia decomposition increased with the concentration of chloride ion in the solution. However, the increase became much dull over 10 g/l of chloride ion. The $RuO_2$ electrode among the tested electrodes generated the most OH radicals which could oxidized the ammonium ion at pH 7.

• Clean Technology
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• v.14 no.3
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• pp.184-192
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• 2008

Fluoride-type cleaning agents such as 2,2,2-trifluoroethanol (TFEA) and hydrofluoroethers (HFEs) do not destroy ozone in the stratosphere and have low global warming potential compared to hydrofluorocarbons(HFCs) and hydrochlorofluorocarbons (HCFCs). Especially, HFEs which have no flash point are paid attention as next generation type of cleaning agents for chlorofluorocarbons (CFCs) since they are safe in handling and have excellent penetration ability compared to hydrocarbon cleaning agents with low flash point. Here, the physical properties and cleaning abilities of fluoride-type cleaning agents such as TFEA, HFE-7100, HFE-7200, HFE-476mec, HFE-449mec-f, AE-3000 and AE-3100E and silicide-type cleaning agents such as trifluoroetoxytrimethylsilane (TFES) and hexamethyldisilazane (HMDS) were measured and compared with those of ozone destruction substances such as CFC-113 and 1,1,1-trichloroethane. They were also compared with toxic methylene chloride (MC) and isopropyl alcohol (IPA) which are now being used as an alternative cleaning agents. As a result, TFEA and HFEs had lower cleaning ability for removal of various soils compared to chloride-type cleaning agents, but they showed excellent cleaning ability fur fluoride-type soils. TFES and HMDS also showed excellent cleaning ability for silicide-type soils.

• Journal of Conservation Science
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• v.28 no.4
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• pp.403-410
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• 2012

The brine treatment applied during the fabrication of forged high tin bronze objects is considered effective at the removal of surface oxide layers developed at elevated temperatures. There is not much information, however, available for the understanding of its exact effect and purpose. This work performed laboratory experiments to characterize the effect brine treatments produce on the surface of bronze objects during fabrication. Specimens were first made in the bronze shop of the Yongin folk village under varying conditions of brine treatments, and the results obtained were then used in the following laboratory experiments where the effect of brine treatments were investigated in terms of brine concentrations, alloy compositions and thermo-mechanical treatments. The results show that oxide layers generated at high temperature are easily removed by the brine treatment. It was found that the element, chlorine, played a key role in the removal of such oxide layers as opposed to the other constituent of the brine, sodium, makes no notable contribution. In bronze alloys containing 22% tin, this brine effect is obtained regardless of the application of forging as long as the brine concentration is over 0.5% based on weight. In alloys containing lead, however, no brine effect is observed due to the molten lead that emerges from inside the hot bronze specimen and forms a thin layer on its surface.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.7
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• pp.549-556
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• 2009

In situ chemical oxidations (ISCO) are technologies for destruction of many contaminants in soil and groundwater, and persulfate has been recently studied as an alternative ISCO oxidant. Trichloroethylene (TCE) and tetrachloroethylene (PCE) were chosen for target organic compounds. The objective of this study is to demonstrate the influence of initial pH (3, 6, 9, 12), oxidant concentrations (0.01, 0.05, 0.1, 0.3, 0.5 M), and contaminants concentrations (10, 30, 50, 70, 100 mg/L) on TCE/PCE degradation by persulfate oxidation. The maximum TCE/PCE degradation occurred at pH 3, and the removal efficiencies with this pH condition were 93.2 and 89.3%, respectively. The minimum TCE/PCE degradation occurred at pH 12, and the removal efficiencies were 55.0 and 31.2%, respectively. This indicated that degradation of TCE/PCE decreased with increasing the initial pH of solution. Degradation of TCE/PCE increased with increasing the concentration of persulfate and with decreasing the concentration of contaminants (TCE/PCE). The optimum conditions for TCE/PCE degradation were pH 3, 0.5 M of persulfate solution, and 10 mg/L of contaminant concentration. At these conditions, the first-order rate constants ($k_{obs}$) for TCE and PCE were 1.04 and 1.31 $h^{-1}$, respectively.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.3
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• pp.211-221
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• 2016

Waste salt generated from a pyro-processing for the recovery of uranium and transuranic elements has high volatility at vitrification temperature and low compatibility in conventional waste glasses. For this reason, KAERI (Korea Atomic Energy Research Institute) suggested a new method to de-chlorinate waste salt by using an inorganic composite named SAP ($SiO_2-Al_2O_3-P_2O_5$). In this study, the de-chlorination behavior of waste salt and the microstructure of consolidated form were examined by adding $B_2O_3$ and $Fe_2O_3$ to the original SAP composition. De-chlorination behavior of metal chloride waste was slightly changed with given compositions, compared with that of original SAP. In the consolidated forms, the phase separation between Si-rich phase and P-rich phase decreases with the amount of $Al_2O_3$ or $B_2O_3$ as a connecting agent between Si and P-rich phase. The results of PCT (Product Consistency Test) indicated that the leach-resistance of consolidated forms out of reference composition was lowered, even though the leach-resistance was higher than that of EA (Environmental Assessment) glass. From these results, it could be inferred that the change in the content of Al or B in U-SAP affected the microstructure and leach-resistance of consolidated form. Further studies related with correlation between composition and characteristics of wasteform are required for a better understanding.

• Clean Technology
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• v.24 no.4
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• pp.339-347
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• 2018

In order to cope with environmental problems and climate change caused by fossil fuels, renewable energy supply is increasing year by year. Currently, waste energy accounts for 60% of renewable energy production. However, waste has a lower calorific value than fossil fuels and contains various harmful substances, which causes serious problems when applied to power generation boilers. In particular, the chlorine in the waste fuel increases slagging and fouling of boiler heat exchangers, leading to a reduction in thermal efficiency and the main cause of high temperature corrosion, lowering facility operation rate and increasing operating cost. In this study, the high temperature corrosion experiments of superheater materials (ASME SA213/ASTM A213 T2, T12 and T22 alloy steel) by alkali chlorides were conducted, and their corrosion characteristics were analyzed by the weight loss method and SEM-EDS. Experiments show that the higher the temperature and chloride content, the more corrosion occurs, and KCl further corrodes the materials compared to NaCl under the same condition. In addition, the higher the chromium content of the material, the better the corrosion resistance to the alkali chlorides.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.327-337
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• 2017

A continuous low temperature ($510^{\circ}C{\sim}530^{\circ}C$) pyrolysis experiment in a pilot-scale of 85.3 kg/hr was carried out by the mixed feedstock of half dried digested sewage sludge and waste plastics. As a result, the amount of pyrolysis gas generated was maximum 68.3% of input dry mass and scored $40.9MJ/Nm^3$ of lower heating value (LHV), and the percentage of air inflow caused by continuous pyrolysis was 19.6%. The oil was produced 4.2% of the input dry mass, and the LHV was 32.5 MJ/kg. The sulfur and chlorine contents, which could cause corrosion of the facility, were found to be 0.2% or more respectively. The carbide generated was 27.5% of the input dry mass which shows LHV of 10.2 MJ/kg, and did not fall under designated waste from the elution test. The concentration of carbon monoxide, sulfur oxides and hydrogen cyanide of emitted flu gas from pyrolysis gas combustion was especially high, and dioxin (PCDDs/DFs) was within the legal standards as $0.034ng-TEQ/Sm^3$. Among the 47 water pollutant contents of waste water generated from dry flue gas condensation, several contents such as total nitrogen, n-H extract and cyanide showed high concentration. Therefore, the merge treatment in the sewage treatment plants after pre-treatment could be considered.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.4
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• pp.385-389
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• 2005

To understand the pollution level by polychlorinated biphenyls (PCBs) in ambient air of industrial area, PCBs concentrations were measured at Sihwa and Banwol industrial region, Korea. The concentrations of total PCB and WHO-TEQ ranged from 2,080 to $5820\;pg/m^3$ (median value is 2,760) and from 0.19 to $1.01\;pgTEQ/m^3$ (median value is 0.42), respectively. In terms of homologues composition the fraction of highly chlorinated biphenyls(from hexa-CB to deca-CB) were higher than the air samples of other regions such as jeonju and yokohama area. The cluster analysis was conducted to study the relation between the air samples and sources such as incinerator flue gases and Aroclor samples. The isomer fractions in the homologue were used as input variables. Based on the results, the industrial ambient air samples were divided from source samples with long Euclidian distance. This suggest that the ambient air samples of Sihwa and Banwol were not on the influence of Aroclor and incinerators. Therefore, further investigation on systematical air monitoring will be required to estimate the sources of PCBs in the above industrial areas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.132-137
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• 2018

Although the number of chemical accidents has been declining since the Chemical Control Act of 2015, there have been repeated occurrences of similar types of accidents at printed circuit board (PCB) manufacturing facilities. These accidents were caused by the overflow of hydrochloric acid and hydrogen peroxide, which are toxic chemicals used in the printed circuit board manufacturing process. An analysis of the $Cl^-$ content to identify the cause of the accident showed that in the mixed route of hydrochloric acid and hydrogen peroxide, which are accidental substances, the $Cl^-$ concentration was 66.85 ppm in the hydrogen peroxide sample. Through reaction experiments, it was confirmed that the deformation of a PVC storage tank and generation of chlorine gas, which is a toxic gas, occurred due to reaction heat occurring up to $50.5^{\circ}C$. This paper proposes a facility safety management plan, including overcharge, overflow prevention, leak detection device, and separation tank design for mixing prevention in printed circuit board manufacturing facility etch process. To prevent the recurrence of accidents of the same type, the necessity of a periodic facility safety inspection and strengthening of the safety education of workers was discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.134-134
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• 2015

최근 액체 플라즈마에 대한 주된 이슈는 방전에 의해 발생하는 히드록실라디칼(OH-)과 버블이다. 액체 플라즈마를 이용한 다양한 응용분야에서는 히드록실라디칼에 주목하고 있다. 액체 플라즈마는 그래핀 파생물의 용액 친화도 향상을 위해 이용될 수 있다. 흑연이 포함된 과산화수소(H2O2) 용액에서 전기적인 방전으로 만들어진 히드록실라디칼로 그래핀 파생물의 용액 친화도를 향상시킨다. 이는 잠재적인 프린팅(printing) 기술 발전에 기대된다. 그리고 이 라디칼은 폐수에서 발암성의 트라이클로로아세트산(CCl3COOH)을 탈 염소하고 분해하는 역할을 하여 액체 플라즈마가 새로운 수처리 기술로 부상되고 있다. 또한 인체에서는 살균 작용을 하는 것 뿐만 아니라 단백질 고리를 끊는 역할을 하여 전립선 수술과 같은 인체수술에 적용될 수 있다. 최근 액체 플라즈마를 이용한 돼지 각막 임상수술에서 레이저와 필적할 정도로 매우 정밀하게 수술된 연구결과가 발표되어 인체 각막수술 적용에 기대된다. 이처럼 액체 플라즈마를 이용한 대부분의 응용분야에서 히드록실라디칼의 역할이 중요하다. 액체 플라즈마의 또 다른 이슈인 버블은 2가지의 역할을 한다. 첫 번째로 방전소스의 역할이다. 액체 속에 담긴 얇은 전극에 전압을 인가하면 전극 주변에서 강한 전기장의 발생으로 줄열(joule heating)에 의해 버블이 생성된다. 전극에서 버블이 생성되었을 때, 서로 다른 유전율을 가진 두 물질로 나누어진다. (버블 안은 공기로 상대 유전율 ${\varepsilon}r{\fallingdotseq}=1$, 용액은 ${\varepsilon}r{\fallingdotseq}=80$이다.) 시스템에 인가된 전압이 항복 전압(breakdown voltage)을 넘어서면 유전율이 상대적으로 낮은 버블내부에 강한 전기장이 걸리게 되어 방전이 일어난다. 만약 버블이 존재하지 않는다면 방전을 위해서 매우 높은 전압이 필요하다. 따라서 버블은 플라즈마 방전의 소스역할을 한다. 두번째로 버블은 전극의 부식을 방지하는 역할을 한다. 전극 부식은 주로 전기분해로 인한 산화반응에 의해 발생하는데 버블을 전극에 오래 머무르게 하면 부식을 방지할 수 있다. 이처럼 액체 플라즈마 시스템에서 버블의 역할들은 상당히 중요하다. 일반적으로 버블은 시스템에 인가하는 전원, 전극 극성 그리고 전압크기에 따라 거동이 달라진다. 시스템에 AC파워를 인가하면 버블은 주파수가 높을수록 전극에서 떨어지는 속도가 빨라지는 특성을 보인다. 핀 전극 극성이 음극일 때는 양극일 때보다 버블이 더 잘 생성된다. 또한 인가전압크기에 따라 거동이 달라지며 시스템에 같은 전압을 인가하여도 크기가 항상 같지 않고, 거동도 일관성을 보이지 않은 랜덤적인 모습을 보인다. 본 연구에서는 이 랜덤적인 버블의 거동을 정리하고 응용분야에서 중요하게 여기는 히드록실라디칼 생성에 대해 공부하기 위해 염류 용액(saline solution)에 핀(pin)-면(plane) 전극 구조를 설치하여 10Hz 주파수(1% duty cycle)를 가진 0-600V 구형펄스로 실험하였다. 실험을 통한 결과로서 랜덤적인 버블의 거동을 전극에서 버블이 떨어지는 속도와 플라즈마 특성에 따라 슈팅모드(shooting mode)와 유지모드(keeping mode) 2가지 모드로 분류하였다. 슈팅모드에서는 버블이 핀 전극에서 성장하지 못하고 빠른 속도로 떨어지는 모드로 플라즈마 방전이 잘 이루어지지 않는다. 반면 유지모드에서는 버블이 핀 전극에서 떨어지지 않고 지속적으로 성장한다. 이 모드에서는 펄스 시간 동안 하나의 버블로 연속적인 방전이 가능하다. 방전이 일어날 때 발생하는 히드록실라디칼의 생성은 버블 내부의 쉬스와 관련이 있다. 이 라디칼을 만들기 위해서는 높은 에너지가 요구되기 때문에 버블 내부의 쉬스(sheath)에서 만들어진다. 펄스 동안 쉬스는 주로 핀 전극 주변에서 유지되며 히드록실라디칼은 이곳에서 주로 만들어진다. 따라서 버블과 함께 쉬스도 성장하는 버블유지모드에서 슈팅모드보다 히드록실라디칼이 더 많이 생성된다.