• Corrosion Science and Technology
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• v.17 no.3
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• pp.101-108
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• 2018

AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with $10{\mu}m$ thick $Al_2O_3$ ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.

• Membrane and Water Treatment
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• v.11 no.4
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• pp.283-294
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• 2020

This work aims at studying the feasibility of continuous removal of mixed heavy metal ions from simulated zinc plating wastewaters by coupling a microbial fuel cell and a microbial electrolysis cell in batch and continuous modes. The discharging voltage of MFC increased initially from 0.4621 ± 0.0005 V to 0.4864 ± 0.0006 V as the initial concentration of Cr⁶⁺ increased from 10 ppm to 60 ppm. Almost complete removal of Cr⁶⁺ and low removal of Cu²⁺ occurred in MFC of the MFC-MEC-coupled system after 8 hours under the batch mode; removal efficiencies (REs) of Cr⁶⁺ and Cu²⁺ were 99.76% and 30.49%. After the same reaction time, REs of nickel and zinc ions were 55.15% and 76.21% in its MEC. Cu²⁺, Ni²⁺, and Zn²⁺ removal efficiencies of 54.98%, 30.63%, 55.04%, and 75.35% were achieved in the effluent within optimum HRT of 2 hours under the continuous mode. The incomplete removal of Cu²⁺, Ni²⁺ and Zn²⁺ ions in the effluent was due to the fact that the Cr⁶⁺ was almost completely consumed at the end of MFC reaction. After HRT of 12 hours, at the different sampling locations, Cr⁶⁺ and Cu²⁺ removal efficiencies in the cathodic chamber of MFC were 89.95% and 34.69%, respectively. 94.58%, 33.95%, 56.57%, and 75.76% were achieved for Cr⁶⁺, Cu²⁺, Ni²⁺ and Zn²⁺ in the cathodic chamber of MEC. It can be concluded that those metal ions can be removed completely by repeatedly passing high concentration of Cr⁶⁺ through the cathode chamber of MFC of the MFC-MEC-coupled system.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.329-334
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• 2001

Microstructures of barrier-type oxide layers on aluminum was studied by XRD, TEM and RBS. Fer formation of oxide layer. aluminum was anodized in a boric acid solution. The thickness of the oxide film subjected to applied voltage increased linearly at ratio of 1.54nm/V. For oxide layer anodized at 300V, amorphous structure of oxide layer was not transformed after heat treatment at 50$0^{\circ}C$ , while for oxide layers anodized at higher voltages the amorphous structure crystallized into a ${\gamma}$-alumina without any heat treatment. It was also found that the amorphous structure of oxide layer formed at 100V transformed into crystalline structure by electron irradiation. The structure was identified as ${\gamma}$-alumina.

• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.238-247
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• 2021

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.3
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• pp.179-189
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• 2014

Pyroprocessing has been developed for the purpose of resolving the current spent nuclear fuel management issue and enhancing the recycle of valuable resources. An electrolytic reduction of the pyroprocessing is a process to reduce oxides into metals using LiCl as an electrolyte and requires a post-treatment process due to the inclusion of residual salt in porous metal products. A vacuum distillation has been adopted for various molten salt systems and could be applied to the post-treatment process of the electrolytic reduction. The residual salt in the metal products includes LiCl, alkali chlorides, and alkaline earth chlorides. In this paper, vapor pressures of chlorides have been estimated and the composition changes on the residual liquid during the vacuum distillation process have been calculated. A model combining a material balance and vapor-liquid equilibrium relations has been proposed under a constant vapor discharging flow rate and liquid composition changes have been calculated using the vapor pressures with respect to a dimensionless time. The behaviors have been compared with temperature and molten salt composition changes to simulate the process condition variation. The distillation of the residual salt has been dominated by LiCl which is the main component of the salt and CsCl of which vapor pressure is higher than that of LiCl would be readily removed. RbCl exhibits similar vapor pressure with LiCl and maintains its composition. However, $SrCl_2$ and $BaCl_2$ of which vapor pressures are much lower than that of LiCl are concentrated with time and expected to be possibly precipitated during the distillation when the initial compositions are increased.

• Korean Journal of Organic Agriculture
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• v.11 no.4
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• pp.93-102
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• 2003

This research was made to determine the optimum mixing ratio cattle manure and food waste investigating the effect that gets the growth and reproductive efficiency of earthworm and productivity of earthworm casts at processing process when handled cattle manure and food waste by vermicomposting, in order to establish the treatment system of organic wastes by vermicomposting. Survival ratio of earthworm was highest in the mixing ratio 80~100% : 20~0% of cattle manure and food Waste, and the increasing ratio was highest in cattle manure 100%, and the number of young worms, the weight of young worms and the productivity of earthworm casts in plots more than the mixing ratio 60% of cattle manure were significantly higher than in the other treatment plots(p<0.05). Total nitrogen and carbon contents in earthworm cast were decreased when rearing time of earthworm was increased. Carbon and nitrogen rate(C/N) of earthworm cast in plots more than the mixing ratio 80% of cattle manure was significantly higher than in the other treatment plots(p<0.05). pH in earthworm cast was higher than that in residual matter. The contents of electrolytic conductivity in the higher mixing ratio of food waste were significantly higher than those in the other treatment plots(p<0.05).

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.24-26
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• 2006

The copper foil of 10fm of thickness was prepared, and the surface treatment on the copper foil was done by the method of the electrolytic plating in the acid solution with the sulfate ion as a purpose to remove the main element of the surface contaminant of copper variously. The structure on the surface of the copper foil in this study investigated AFM with SEM the changed phenomenon according to added plating time and current. The phenomenon of the structure's of the oxide on the surface of long plating time and high current growing was confirmed.

• Microbiology and Biotechnology Letters
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• v.16 no.5
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• pp.374-378
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• 1988

Treatability and maximum no inhibitory effect concentration of benzene were measured in the synthetic wastewater medium by the activated sludge in the continuous activated sludge reactor. The maximum no inhibitory effect concentration was 1, 600mg per liter. Benzene concentration over 500mg per liter inhibited the growth of microorganims by the measurment of E/BOD, and the treatability of benzene at the maximum no inhibitory effect concentration was over 95%.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.4
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• pp.223-227
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• 2009

The feasibility of plasma electrolytic polishing technology of stainless steel was examined. The results show that austenitic stainless steel can be polished clearly using potentiostatic regimes with various concentration of ammonium sulfate ($(NH_4)_2SO_4$) solution above certain initial temperature. The equipment and deposition produces for polishing process are described and the effect of processing parameters on the characterizations polished-samples has been investigated.

• Korean Journal of Organic Agriculture
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• v.22 no.1
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• pp.183-195
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• 2014

The present study was conducted to provide basic data for environmentally friendly treatment of manure using vermicomposting by investigating the influence of physiochemical property change during the composting period on the survival of earthworms after mixing cow manure in different levels (0(CSD0), 10(CSD10), 20(CSD20), 30(CSD30), and 40%(CSD40)) with the sawdust that is used bedding in livestock pens. As composting proceeds, earthworms were able to survive in all treatments after 3 weeks. In terms of the C/N ratio by treatment groups, the sawdust mix treatment was significantly higher than the CSD0 treatment (p<0.05). The C/N ratio in the 3rdweek when earthworms started surviving was 23.26-61.05. As composting progressed, pH and electrolytic conductivity were highest in the CSD0 treatment and tended to decrease with higher proportion of sawdust in the mix. It was found that pH and electrolytic conductivity that earthworms starting to survive are 7.4-7.7 and 0.28-1.17 mS/cm respectively. To summarize, when composing cow manure with various levels of sawdust mix, all physiochemical property changes turned out to allow the survival of earthworms, but the results suggest that efficient vermicomposting requires the tests to examine growth and reproduction according to the sawdust mix ratio.