• Korean Chemical Engineering Research
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• v.51 no.6
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• pp.700-708
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• 2013

Pyroprocessing has been developed for the purpose of resolving the current spent nuclear fuel management issue and enhancing the recycle of valuable resources. Pyroprocessing has been developed with the dry technologies which are performed under high temperature conditions excluding any aqueous processes. Pyro-processes which are based on the electrochemical principles require pretreatment processes and a voloxidation process is considered as a pretreatment step for an electrolytic reduction process. Various kinds of gas conditions are applicable to the voloxidation process and the understanding of Cs behavior during the process is of importance for the analyses of waste characteristics and heat load on the overall pyroprocessing. In this study, the changes of chemical compounds with the gas conditions were calculated by analyzing gas-solid reaction behavior based on the chemical equilibria on a Cs-Te-O system. $Cs_2TeO_3$ and $Cs_2TeO_4$ were selected after a Tpp diagram analysis and it was confirmed that they are relatively stable under oxidizing atmospheres while it was shown that Cs and Te would be removed by volatilization under reducing atmosphere at a high temperature. This work provided basic data for predicting Cs behavior during the voloxidation process at which compounds are chemically distributed as the first stage in the pyroprocessing and it is expected that the results would be used for setting up material balances and related purposes.

• Journal of the Korean Chemical Society
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• v.50 no.6
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• pp.454-463
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• 2006

refractory organic compounds in aqueous solution are not readily removed by the existing conventional wastewater treatment process. In recent years, the sonolysis and electrochemical oxidation process had been shown to be promising for wastewater treatment due to the effectiveness and easiness in operation. This study was performed to investigate the characteristics of sonolytic and electrolytic decomposition as the basic data for development of the wastewater treatment process. Trichloroethylene(TCE) and 2,4- dichlorophenol(2,4-DCP) were used as the samples, and their destruction efficiency were measured with various operating parameters, such as initial solution concentration, initial solution pH, reaction temperature, sonic power and current density. Also, the decomposition mechanism conformed indirectly with the effect of NaHCO3 as a radical scavenger on the decomposition reaction. Thermal decompositon reaction is predominant for TCE but thermal and radical decompositon reactions were dominant for 2,4-DCP. Results showed that the destruction efficiencies of all samples were above 65% within 120 minutes by sonolysis and electrolysis at the same time, and were increased with increasing initial concentration, sonic power and current density. Destruction efficiency of TCE was high in the acidic solution, but 2,4-DCP showed high destruction efficiency in basic solution.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.32-38
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• 2011

Galvanized steel has gone through a chemical process to keep it from corroding. The steel gets coated in layers of zinc because rust will not attack this protective metal. For countless outdoor, marine, or industrial applications, galvanized steel is an essential fabrication component. The reduction of the corrosion rate of zinc is an important topic. In the past, a very popular way to reduce the corrosion rate of zinc was to use chemical conversion layers based on $Cr^{+6}$. However, a significant problem that has arisen is that the use of chromium salts is now restricted because of environmental protection legislation. Therefore, it is very important to develop new zinc surface treatments that are environmentally friendly to improve the corrosion resistance of zinc and adhesion with a final organic protective layer. In this study, a Urethane solution (only Urethane 20 wt.%; S-700) and an organic/inorganic solution with Si (Si polysilicate 10 wt.% + Urethane 10 wt.%; LRO-317) are used. Based on the salt spray test of 72 h, S-700 and LRO-317 had a superior effect for the corrosion resistance on EGI and HDGI, respectively.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.67-74
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• 2010

Chromate conversion coating is a coating technique used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, tin, and their alloys to slow corrosion. The process uses various toxic chromium compounds, which may include hexavalent chromium. The industry is developing less toxic alternatives in order to comply with substance restriction legislation, such as RoHS. One alternative is to develop a Cr-free coating solution. In this study, eco-friendly, Cr-free solutions (urethane solution S-700, organic/inorganic solution with Si LRO-317) were used. Test specimens were dried in a drying oven at $190^{\circ}C$ for 3, 5, 7, and 9 minutes. Corrosion resistance was evaluated using a salt spray test for 72 hours. The results show that the optimum corrosion resistance was achieved at $190^{\circ}C$ for five minutes for EGI and three or five minutes for HDGI, respectively. The adhesive properties of the two types of coating solutions were superior regardless of drying time.

• Journal of Microbiology and Biotechnology
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• v.28 no.3
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• pp.432-438
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• 2018

Microalgae hold promise as a renewable energy source for the production of biofuel, as they can convert light energy into chemical energy through photosynthesis. However, cost-efficient harvest of microalgae remains a major challenge to commercial-scale algal biofuel production. We first investigated the potential of electrolytic water as a flocculant for harvesting Tetraselmis sp. Alkaline electrolyzed water (AEW) is produced at the cathode through water electrolysis. It contains mineral ions such as $Na^+$, $K^+$, $Ca^{2+}$, and $Mg^{2+}$ that can act as flocculants. The flocculation activity with AEW was evaluated via culture density, AEW concentration, medium pH, settling time, and ionic strength analyses. The flocculation efficiency was 88.7% at 20% AEW (pH 8, 10 min) with a biomass concentration of 2 g/l. The initial biomass concentration and medium pH had significant influences on the flocculation activity of AEW. A viability test of flocculated microalgal cells was conducted using Evans blue stain, and the cells appeared intact. Furthermore, the growth rate of Tetraselmis sp. in recycled flocculation medium was similar to the growth rate in fresh F/2 medium. Our results suggested that AEW flocculation could be a very useful and affordable methodology for fresh biomass harvesting with environmentally friendly easy operation in part of the algal biofuel production process.

• Journal of the Korean Applied Science and Technology
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• v.35 no.3
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• pp.612-621
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• 2018

In this study, $TiO_2$ nanotube plate and metal electrodes(Copper, Nickel, Stainless Steel, Aluminum, Tin, Titanium) were compared on cathodic reduction of nitrate ($NO_3{^-}-N$) during electrolysis. The electrochemical characteristics were compared based on electrochemical impedance spectroscopy (EIS). The surface morphology was obtained using scanning electron microscopy (SEM) method. Brunauer-Emmett-Teller (BET) method was implemented for the specific surface area analysis of the cathodes. To study kinetics, 90 minute batch electrolysis of nitrate solution was performed for each cathodes. In conclusion, under the condition of relatively low ($0.04 A\;cm^{-2}$) current density, $TiO_2$ nanotube plate showed no surface corrosion during the electrolysis, and the reaction rate was measured the highest in the kinetic analysis.

• Korean Journal of Materials Research
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• v.14 no.11
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• pp.813-820
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• 2004

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which is a chemically aggressive environment that is very corrosive for typical structural materials. So, it is essential to choose the optimum material for the process equipment handling molten salt. In this study, corrosion behavior of Haynes 263, 75, and Inconel X-750, 718 in molten salt of $LiCl-Li_{2}O$ under oxidation atmosphere was investigated at $650^{\circ}C\;for\;72\sim360$ hours. At $3\;wt\%\;of\;Li_{2}O$, Haynes 263 alloy showed the highest corrosion resistance among the examined alloys, and up to $8\;wt\%\;of\;Li_{2}O$, Haynes 75 exhibited the highest corrosion resistance. Corrosion products were formed $Li(Ni,Co)O_2,\;LiNiO_2\;and\;LiTiO_2\;and\;Cr_{2}O_3$ on Haynes 263, $Cr_{2}O_3,\;NiFe_{2}O_4,\;LiNiO_2,\;Li_{2}NiFe_{2}O_4,\;Li_{2}Ni_{8}O_10$ and Ni on Haynes 75, $Cr_{2}O_3,\;(Al,Nb,Ti)O_2,\;NiFe_{2}O_4,\;and\;Li_{2}NiFe_{2}O_4$ on Inconel X-750 and $Cr_{2}O_3,\;NiFe_{2}O_4\;and\;CrNbO_4$ on Inconel 718, respectively. Haynes 263 showed local corrosion behavior and Haynes 75, Inconel X-750, 718 showed uniform corrosion behavior.

• Korean Journal of Materials Research
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• v.15 no.3
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• pp.155-160
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• 2005

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is very corrosive fir typical structural materials. So, it is essential to choose the optimum material f3r the process equipment handling molten salt. In this study, the corrosion behavior of Al-Y coated Haynes 263 in a molten salt of $LiCl-Li_2O$ under oxidation atmosphere was investigated at $650^{\circ}C$ for $72\~168$ hours. The corrosion rate of Al-Y coated Haynes 263 was low while that of bare Haynes 263 was high in a molten salt of $LiCl-Li_2O$. Al-Y coated Haynes 263 improved the corrosion resistance better than bare Haynes 263 alloy. An Al oxide layer acts as a protective film which Prohibits Penetration of oxygen. Corrosion Products were formed $Li(Ni,Co)O_2$ and $LiTiO_2$ on bare Haynes 263, but $LiAlO_2,\;Li_5Fe_5O_8\;and\;LiTiO_2$ on Al-Y coated Haynes 263.

• Korean Journal of Materials Research
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• v.16 no.9
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• pp.557-563
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• 2006

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. So, it is essential to choose the optimum material for the process equipment handling molten salt. In this study, corrosion behavior of Inconel 713LC, MA 754, X-750 and 718 in the molten salt $LiCl-Li_2O$ under an oxidizing atmosphere was investigated at $650^{\circ}C$ for $72{\sim}216$ hours. Inconel 713LC alloy showed the highest corrosion resistance among the examined alloys. Corrosion products of Inconel 713LC were $Cr_2O_3,\;NiCr_2O_4$ and NiO, and those of Inconel MA 754 were $Cr_2O_3\;and\;Li_2Ni_8O_{10}$ while $Cr_2O_3,\;NiFe_2O_4\;and\;CrNbO_4$ were produced from Inconel 718. Also, corrosion products of Inconel X-750 were found to be $Cr_2O_3,\;NiFe_2O_4\;and\;(Cr,Nb,Ti)O_2$. Inconel 713LC showed local corrosion behavior and Inconel MA 754, 718, X-750 showed uniform corrosion behavior.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.562-565
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• 2013

The high purity Al foil, which has an enlarged surface area by electrochemical etching process, has been used as an anode for an aluminum electrolytic capacitor. Etch pits are randomly distributed on the surface because of the existence of surface irregularities such as impurity and random nucleation of pits. Even though a large surface area was formed on the tunnel-etched Al, its applications to various fields were limited due to non-uniform tunnel morphologies. In this work, the selective electrochemical etching of aluminum was carried out by using a patterned mask fabricated by photolithographic method. The formation of etch pits with uniform distribution has been demonstrated by the optimization of experimental conditions such as current density and etching solution temperature.