• Journal of Korean Society of Environmental Engineers
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• v.30 no.2
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• pp.155-160
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• 2008

In this study, the nitrate removal efficiency was examined under a variety of operating conditions, such as different doses of the reducing agent, different electrode types, different HRTs(hydraulic retention times), and different current densities, using the multistep electrochemical process. The nitrate removal efficiency increased and the input energy decreased when the reducing agent was used, and almost no difference was found between the electrode types in terms of their nitrate removal efficiency and current efficiency. So that the Zn reducing agent could be recovered, though, the B-type electrode was chosen(step 1: Pt-Zn; step 2: Pt-Zn; step 3: Pt-Zn; step 4: Pt-Zn). HRT experiments were carried out on constant electric current density unrelated HRTs and various electric current density related HRTs: the constant amount of electric current per unit volume. As a result, HRT and the electric current density caused concentration polarization and the lack of an applied current. That is to say,the lower the HRT, the greater the decrease in concentration polarization and in the amount of applied current per unit volume. Therefore, optimal conditions were found through the experiments that were conducted on HRT and electric current density. When a spacer was installed in the process, the nitrate removal efficiency and energy efficiency increased even more because the diffusion likewise increased.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.73-79
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• 1999

The superstructured $Li_{4/3}Ti_{5/3}O_4$ was prepared by sol-gel process using a mixed solution of lithium acetate (LA) and titanium n-butoxide (TNB). The gel phase was obtained by adding ammonia water ($NH_4OH/TNB$ mole ratio of 0.35) and water ($H_2O/TNH$ mole ratio of 3.5) into the clear sol that was prepared after mixing TNB/LA mole ratio of 5/4 with AA/TNB mole raio of 0.125. It was found that the most suitable $Li_{4/3}Ti_{5/3}O_4$ was obtained by heat treatment of xerogel at $600^{\circ}C$ for 30 hrs. The synthesized $Li_{4/3}Ti_{5/3}O_4$ showed an initial discharge capacity of 174 mAh/g and the capacity loss of about 27.3% during 25 cycles in Li/1M $LiClO_4(in\;PC)/Li_{4/3}Ti_{5/3}O_4$ at current density of $0.15mA/cm^2$ and the voltage range of 0.5~3.0 V.

• Applied Chemistry for Engineering
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• v.28 no.2
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• pp.153-157
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• 2017

Gel type internal electrolytes were synthesized by varying hydroxyethyl-cellulose (HEC) amounts and their durability and conductivity were measured. The ionic conductivity decreased as the content of HEC increased thus the internal electrolyte containing more than 12% of HEC could not be used as a reference electrode. Based on durability test results, as the HEC amount decreased carrier density resulting in increasing of the amount of KCl coming out of the porous membrane. Therefore in order to use long time at ballast water treatment systems, we selected 10% HEC for gel type internal electrolyte. The resolution test for total residual oxidants (TRO) was carried out using the TRO sensor and the gel type reference electrode made of 10% HEC. A 50 mV potential was applied to the TRO sensor for 30 sec and changes in the current were measured. It was confirmed that the TRO concentrations ranging from 0 to 15 mg/L could be separated at salinity conditions of 0.2~30 PSU. The results indicated that the TRO concentration at sea water and at fresh water was successfully measured by the TRO sensor constructed with the reference electrode using gel-type internal electrolyte of HEC.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.240-245
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• 2013

Electrochemical surface treatment is commonly used to form a thin, rough, and porous oxidation layer on the surface of titanium. The purpose of this study was to investigate the formation of nanotubular titanium oxide arrays during short anodization processing. The specimen used in this study was 99.9% pure cp-Ti (ASTM Grade II) in the form of a disc with diameter of 15 mm and a thickness of 1 mm. A DC power supplier was used with the anodizing apparatus, and the titanium specimen and the platinum plate ($3mm{\times}4mm{\times}0.1mm$) were connected to an anode and cathode, respectively. The progressive formation of $TiO_2$ nanotubes was observed with FE-SEM (Field Emission Scanning Electron Microscopy). Highly ordered $TiO_2$ nanotubes were formed at a potential of 20 V in a solution of 1M $H_3PO_4$ + 1.5 wt.% HF for 10 minutes, corresponding with steady state processing. The diameters and the closed ends of $TiO_2$ nanotubes measured at a value of 50 cumulative percent were 100 nm and 120 nm, respectively. The $TiO_2$ nanotubes had lengths of 500 nm. As the anodization processing reached 10 minutes, the frequency distribution for the diameters and the closed ends of the $TiO_2$ nanotubes was gradually reduced. Short anodization processing for $TiO_2$ nanotubes of within 10 minutes was established.

• Journal of the Korean institute of surface engineering
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• v.41 no.6
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• pp.292-300
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• 2008

Dental implant system is composed of abutment, abutment screw and implant fixture connected with screw. The problems of loosening/tightening and stability of abutment screw depend on surface characteristics, like a surface roughness, coating materials and friction resistance and so on. For this reason, surface treatment of abutment screw has been remained research problem in prosthodontics. The purpose of this study was to investigate the stability of TiN and WC coated dental abutment screw, abutment screw was used, respectively, for experiment. For improving the surface characteristics, TiN and WC film coating was carried out on the abutment screw using EB-PVD and sputtering, respectively. In order to observe the coating surface of abutment screw, surfaces of specimens were characterized, using field emission scanning electron microscope(FE-SEM) and energy dispersive x-ray spectroscopy(EDS). The stability of TiN and WC coated abutment screw was evaluated by potentiodynamic, and cyclic potentiodynamic polarization method in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The corrosion potential of TiN coated specimen was higher than those of WC coated and non-coated abutment screw. Whereas, corrosion current density of TiN coated screws was lower than those of WC coated and non-coated abutment screw. The stability of screw decreased as following order; TiN coating, WC coating and non-coated screw. The pitting potentials of TiN and WC coated specimens were higher than that of non-coated abutment screw, but repassivation potential of WC coated specimen was lower than those of TiN coated and non-coated abutment screws due to breakdown of coated film. The degree of local ion dissolution on the surface increased in the order of TiN coated, non-coated and WC coated screws.

• Journal of Conservation Science
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• v.30 no.1
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• pp.95-101
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• 2014

Silver objects tarnish with black from reaction with sulfurous acid or hydrogen sulfide of atmospheric. Blackening of silver objects results from formation of silver sulfide($Ag_2O$) on the surface. Silver sulfide usually is usually removed by conservation treatment. There are several cleaning methods such as chemical, electrochemical and micro-abrasion cleaning, but all of them consume silver. This study investigated the safe and effective parameter of laser cleaning by test on silver coupons. Laser cleaning is a selective process for the removal of specific substances. At first, laser cleaning applied to plain silver coupons, which were not corroded, to find out the safe range of laser energy density. From results, plain silver coupons were not changed at 1064nm below $4.00J/cm^2$ and at 532nm below $2.39J/cm^2$. The corrosion layer(silver sulfide) of artifical corroded silver coupons was removed at 1064nm with $2.39J/cm^2$ by 5~10 pulses and at 532nm with $1.19J/cm^2$ by 5~10 pulses. The removal thickness of corrosion layer was about 13-25nm per a laser pulse using AES analysis. In addition, laser cleaning tested the tarnish silver rings based on the results of silver coupons. As a result of test, the black surface were clean successfully and gave luster of silver, which showed the application possibility of laser cleaning for silver objects.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.398-402
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• 2000

Three kinds of $Al_3Ti-Cr$ alloys, namely, $Al_{67}Ti_{25}Cr_8,\;Al_{66}Ti_{24}Cr_{10}\;and\;Al_{59}Ti_{26}Cr_{15}$, were prepared by induction melting followed by the thermomechanical treatment. The corrosion behavior in 3.5% NaCl solution and the high-temperature oxidation behavior at 1000, 1100 and $1200^{\circ}C$ for the prepared alloys were investigated. Electrochemical results indicated increased resistance to localized corrosion with increasing Cr content. Cr additions were found to prevent passive film from undergoing brittle fracture. XPS results revealed the passive films of $Al_3Ti-Cr$ alloys were composed mainly of $Al_2O_3$ that coexisted with $TiO_2$ and $Cr_2O_3$. The overall oxidation resistance of the prepared alloys were excellent. Specifically, the oxidation resistance increased in the order of $Al_{59}Ti_{26}Cr_{15},\;Al_{66}Ti_{24}Cr_{10}\;and\;Al_{67}Ti_{25}Cr_8$. As the Al content in the base alloys increased, the $Al_2O_3$ formation was facilitated leading to the increased oxidation resistance.

• Analytical Science and Technology
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• v.13 no.5
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• pp.630-635
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• 2000

The concentration of neurotransmitters in rat brain was determined by HPLC-ECD (electrochemical detection) method and the effects of methanol extracts of some crude drugs, such as Polygala Radix, Myristicae Semen, Zizyphi Semen, Acori graminei Rhizoma, Visci Herba, Liriopsis Tuber, Myrrha on the concentration of neurotransmitters in the ethanol-treated rat brain were investigated. By the administration of ethanol, dopamine (DA), 3, 4-dihydroxyphenyl acetic acid (DOPAC) and serotonin (5-HT) levels in frontal cortex and 5-HT level in hippocampus were significantly increased compared with the neurotransmitter levels in the brain of saline-treated rats. The ${\gamma}$-aminobutyric acid (GABA) level in frontal cortex was decreased by the same treatment. There was a tendency that the DA level in frontal cortex and striatum of ethanol-treated rats were increased by the administration of crude drug extracts. Especially, Myrrha and Visci Herba significantly increased the DA level of frontal cortex in ethanol-treated rats, while they significantly decreased the 5-HT level in the same region of the brain. GABA level in striatum of ethanol-treated rats was significantly decreased by Myristicae Semen, Visci Herba and Myrrha. These results suggest that the tested crude drug extracts have selective interaction with neurotransmitters in specified region of central nervous system.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.25-29
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• 2012

$TiO_2$ nanotubes are prepared from rutile prticles via an alkaline hydrothermal synthesis and the consequent heat treatment at $300{\sim}500^{\circ}C$. The physical and electrochemical properties of the $TiO_2$ nanotubes are characterized for use as a anode material of rechargeable lithium battery. In particular, the microscale dusts as an impurity component occurred in the purification step after the hydrothermal reaction are completely removed to yield $TiO_2$ nanotube with a higher specific surface area and more obvious crystalline phases. As the annealing temperature increases, the specific surface area is slightly decreased due to some aggregation between the isotropically dispersed nanotubes. Highest initial discharge capacity of 250 mAh $g^{-1}$ is achieved for the $TiO_2$ nanotube annealed at $300^{\circ}C$, whereas the $400^{\circ}C$ $TiO_2$ nanotube shows the superior cycle performance and high-rate capability.

• Journal of the Korean Chemical Society
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• v.55 no.1
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• pp.57-62
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• 2011

Sometimes inhabitants in remote areas have inadequate or no access to modern medicines or medical services. They can get benefit in term of the treatment against malaria by cultivating selected breeding of A. annua and making teas or decoctions from the plant materials following the proper way of tea preparation. In order to have the maximum extraction efficiency for artemisinin, different ways of tea preparations of A. annua were investigated by applying the developed DPP method and described in this article. Tea was prepared by three different ways (cooking, without cooking with/without shaking and microwave oven) with different times. From the results, it has been found that higher concentration of artemisinin (84.7%) can be attained by following the approach for tea preparation without cooking with shaking for 15 minutes (R.S.D. 2.34%). The concentration of artemisinin decreases with cooking more than 1.5 min in microwave oven. The utmost extraction (88.9% of artemisinin) is possible to extract by shaking with boiled 5% ethanol in distilled water (R.S.D. 2.28%).