• 전기화학회지
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• 제12권3호
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• pp.263-270
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• 2009

레독스 흐름 전지의 전극으로 사용하기 위해 탄소펠트를 열처리와 산처리 방법으로 산화 개질하였다. 열중량 분석결과 열처리 또는 산처리에 의하여 탄소펠트의 섬유 표면에 고분자 물질이 제거되고 산소 관능기가 도입된 것을 확인할 수 있었으며 습식 방법인 산처리 방법보다 건식방법인 열처리 방법이 기계적 안정성을 유지하는데 효과적인 처리 방법으로 나타났다. XPS, 원소분석을 통하여 500$^{\circ}C$에서 4시간 열처리한 탄소펠트의 표면에 산소 관능기가 부가된 것을 확인하였으며 질소흡착실험에서 거의 없던 표면적이 96 $m^2/g$로 증가한 것을 알 수 있었다. CV실험 및 분극 실험을 수행한 결과 500$^{\circ}C$ 열처리 전극의 활성화 저항이 가장 낮게 나타났다. 산처리한 탄소펠트와 400$^{\circ}C$, 500$^{\circ}C$에서 열처리한 탄소펠트를 이용하여 바나듐 레독스 흐름 전지를 구성하고 충/방전 실험을 실시한 결과 충/방전 전압효율이 산처리 전극의 경우 86.6%, 400$^{\circ}C$ 열처리 전극의 경우 89.6%, 500$^{\circ}C$ 열처리 전극의 경우 90.6%로 500$^{\circ}C$ 열처리 전극이 가장 우수하였다.

• 대한치과보철학회지
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• 제37권1호
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• pp.1-22
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• 1999

In order to investigate various physical and biological properties of dental magnetic attachments studies on retentive characteristics, corrosion properties, cytotoxicity of different magnetic systems for dental applications were done. For the study of retentive characteristics changes of retentive force by increasing air gap, wear properties of various attachment systems and loss of magnetic force by heat treatment were measured. Forte study of corrosion property of magnet covering metal electrochemical corrosion was done in artificial saliva and 0.9% NaCl solution between $-1,000mV_{SCE}\;and\;+1,000mV_{SCE}$. Anodic polarization curves are obtained about 6 types of samples and 2 types of solution. Corroded surfaces were examined with metallurgical microscope, scanning electron microscope and surface profilometer. For the study of cytotoxicity of magnetic attachment and its field cell growth and agar overlay test were done. The results of this study were as follows. 1. In Magnetic attachments using closed circuit retentive force at zero air gap was greater than magnets using open circuit, but decrease of retentive force by increasing air gap was also greater than open systems. 2. After 40,000 cycles of wear test all mechanical attachment resulted in varing degree of retention loss but in magnetic attachments no loss of retentive force was observed. 3. The magnetic attachment using Neodymium magnet showed early loss of retentive force about $200^{\circ}C$ but attachment using Samarium magnet showed some resistance to heat treatment and complete retention loss was observed about $500^{\circ}C$. The keeper was not influenced by heat treatment in retention. 4. In electrochemical corrosion test Dyna magnetic attachment covering metal showed the highiest corrosion resistance and Shiner magnet covering metal showed the least corrosion resistance and examination of corroded surface with metallurgical microscope, scanning electron micro-scope and surface profilometer also showed same results with anodic polarization corves. 5. The result of cell culture tests on the magnet covered with metal showed least recognizable cytotoxicity.

• Asian-Australasian Journal of Animal Sciences
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• 제25권7호
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• pp.1021-1028
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• 2012

Peripheral blood mononuclear cells (PBMCs) discriminate microbial pathogens and induce T-cell responses of appropriate effector phenotype accordingly. Toll-like receptors (TLRs), in part, mediate this microbial recognition and differentiation while the development of T-cell effector functions critically depends on the release of Th1- or Th2- type cytokines. In the present study, buffalo PBMCs were stimulated under in vitro culture conditions by Bacillus subtilis cell wall petidoglycan, a TLR2 ligand, in a dose- and time- dependent manner. The expression of TLR2 as well as the subsequent differential induction of the Th1 and Th2 type cytokines was measured. Stimulation was analyzed across five doses of peptidoglycan ($10{\mu}g/ml$, $20{\mu}g/ml$, $30{\mu}g/ml$, $40{\mu}g/ml$ and $50{\mu}g/ml$) for 3 h, 12 h, 24 h and 36 h incubation periods. We observed the induction of TLR2 expression in a dose- and time-dependent manner and the peptidoglycan induced tolerance beyond $30{\mu}g/ml$ dose at all incubation periods. The correlation between peptidoglycan stimulation and TLR2 induction was found positive at all doses and for all incubation periods. Increased production of all the cytokines was observed at low doses for 3 h incubation, but the expression of IL-4 was relatively higher than IL-12 at the higher antigen doses, indicating tailoring towards Th2 response. At 12 h incubation, there was a pronounced decrease in IL-4 and IL-10 expression relative to IL-12 in a dose- dependent manner, indicating skewing to Th1 polarization. The expression of IL-12 was highest for all doses across all the incubation intervals at 24 h incubation, indicating Th1 polarization. The relative expression of TNF-${\alpha}$ and IFN-${\gamma}$ was also higher while that of IL-4 and IL-10 showed a decrease. For 36 h incubation, at low doses, relative increase in the expression of IL-4 and IL-10 was observed which decreased at higher doses, as did the expression of all other cytokines. The exhaustion of cytokine production at 36 h indicated that PBMCs became refractory to further stimulation. It can be concluded from this study that the cytokine response to sPGN initially was of Th2 type which skews, more pronouncedly, to Th1 type with time till the cells become refractory to further stimulation.

• KSBB Journal
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• 제10권1호
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• pp.63-70
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• 1995

실험실에서 자체 제작한 자유유통 전기이동 장치 에서 등전집속법을 이용한 대두 단백질의 분리를 통 해 운전 조건들이 분리에 미치는 영향을 조사하였 다. 매 실험마다 pH, 전기전도도, uv 흉광도 (280nm) 등을 측정하였고 시료의 순도는 SDS­P PAGE 분석을 통해 점검하였다. Tris와 boric acid로 처리한 대두단백질 추출액에 g glutamic acid, histidine, argmme, glycine 등 아 미노산 각 ImM과 dipeptide로 glycyl-glycine 2mM, 배경 전해액으로서 KCI ImM로 구성된 시료 의 완충액을 혼합하여 시료로 사용하였다. 분리막을 셀룰로오스 아세테이트를 사용할 경우 pH는 양극쪽에서 3, 음극쪽에서 8 정도의 값을 보였으며 2개의 변곡점을 나타내었다. 가해준 전압은 3 300V에서 lOOOV의 범위였으며 전압이 높을수록 더 나은 분리도를 얻었으나 전압을 더 높일 경우 과도한 Joule열의 발생으로 인해 한계가 있었다. 시간이 지남에 따라 단백질들은 분리조 중앙 부근에서 집속이 일어났으며 pH와 전기전도도의 변화로부터 분리 조내의 이온들이 막을 통해 전극쪽으로 이통해 가고 있음을 알 수 있었다. 완충용액의 농도를 5배로 증 가시킬 경우 300V에서 좋은 집속을 얻었으냐 10배 이상으로 농도를 높일 경우에는 분리조 입구와 출구 의 유체 온도차가 $25^{\circ}C$ 이상이 되어 단백질의 변성 이 일어날 수 있어 더 높일 수 없었다. 이온교환막을 사용할 경우 이온의 분극화현상을 일으켜 U자 형태 의 전기전도도 분포를 나타내었다. 아미노산 혼합물 대신 상용의 ampholyte를 사용하더라도 분리도에 있어 큰 차이가 없었다.

• 한국주조공학회지
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• 제31권6호
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• pp.362-365
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• 2011

In the present work, the corrosion properties of Mg-xSn (x = 1, 3, 5, 7 and 9 wt.%) alloys have been investigated. Potentiodynamic polarization and immersion tests were carried out in 3.5% NaCl solution of pH 7.2 at room temperature to measure the corrosion properties of Mg-xSn (x = 1, 3, 5, 7 and 9 wt.%) alloys. With increase of the Sn contents, the volume fraction of the $Mg_2Sn$ phase was increased. The corrosion rate of Mg-xSn alloys was increased up to 7 wt.%Sn and decreased above 9 wt.%Sn. Initiation of galvanic site during immersion mainly occurred at Mg/$Mg_2Sn$ interface and propagation went into ${\alpha}$-Mg. For this reason, corrosion properties of Mg-xSn (added from 1 wt.%Sn to 7 wt.%Sn alloys) alloys are decreased because the galvanic site was increased with increasing Sn addition. In Mg-9wt.%Sn alloy, however, the corrosion site were changed from Mg/$Mg_2Sn$ interface to ${\alpha}$-Mg/$M_2Sng$ interface in lamellar structure. Preferentially corrosion of ${\alpha}$-Mg/$M_2Sn$ interface in lamellar structure impeded corrosion propagation went into ${\alpha}$-Mg.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2013년도 춘계학술대회 논문집
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• pp.62-62
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• 2013

Magnesium alloys exhibit many attractive properties such as low density, high strength/weight ratio, high thermal conductivity, very good electromagnetic features and good recyclability. However, most commercial magnesium alloys require protective coatings because of their poor corrosion resistance. Attempts have been made to improve the corrosion resistance of the Mg alloys by surface treatments, such as chemical conversion coatings, anodizing, plating and metal coatings. Among them, chemical conversion coatings are regarded as one of the most effective and cheapest ways to prevent corrosion of Mg alloys. In this study, the effects of various $Zn^{2+}$ concentrations and pH levels on the formation of zinc phosphate conversion coatings (ZPCCs) on AZ31 magnesium alloy were investigated, and corrosion resistances of the coated samples were evaluated by immersion test and potentiodynamic polarization experiment. The corrosion resistance of the coated AZ31 samples was found to increase with increasing $Zn^{2+}$ concentration and the lowest corrosion rate was obtained for the samples coated at pH of 3.07, independent of $Zn^{2+}$ concentration. The best coatings on AZ31 were obtained at [$Zn^{2+}$] = 0.068 M and pH 3.07. At the conditions of [$Zn^{2+}$] = 0.068 M and pH 3.07, the formation and growth processes of ZPCCs on AZ31 Mg alloy are divided into four stages: formation of a dense layer, precipitation of fine crystals on the dense layer, growths of the inner and outer layers, and reorganization of outer crystalline layer.

• Journal of Advanced Marine Engineering and Technology
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• 제30권6호
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• pp.709-715
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• 2006

The effects of thermal cycle condition and applied stress on the intergranular corrosion in austenitic 316 type stainless steels were investigated. Specimens were solution-treated at 1100$^{\circ}C$ for one hour and then sensitized in the temperature range of $500{\sim}800^{\circ}C$ by holding $2{\sim}300s$ with a various applied stresses of $0{\sim}8kg/mm^2$. Degree of sensitization. DOS %, was measured through polarization curve by electrochemical DL-EPR test. Microstructural observations were also conducted DOS % increased with an increase of sensitization temperature and/or holding time. Increase of applied stress resulted in increase of DOS % and more corroded surface because of acceleration of intergranular corrosion and fine grain size due to the stress. Cr depleted zone near grain boundary was observed. The amount of depletion was profounded with an increase of sensitization temperature, holding time and applied stress. $M_{23}C_6$ carbides were precipitated discontinuously at grain boundary. However, its amount was relatively small in the thermal cycle condition of 800$^{\circ}C$, 300sec and 4kg/mm$^2$.

• Corrosion Science and Technology
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• 제2권1호
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• pp.7-11
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• 2003

Photoelectrochemical response and electrochemical impedance behavior was investigated for passive film formed on sputter-deposited Cr alloy in $0.1kmol{\cdot}m^{-3}$. Photoelectrochemical action spectrum could be separated into two components, which were considered to be derived from $Cr_2O_3$ ($E_g\sim3.6eV$) and $ Cr(OH)_3 $ ($E_g\sim2.5eV$). The band gap energy, $E_g$, of each component was almost constant for various applied potentials. polarization periods and alloying additives. The photoelectrochemical response showed negative photo current for most potentials in the passive region. Therefore, the photo current apparently exhibited p-typesemiconductor behavior. On the other hand, Mort-Schottky plot of the capacitance showed positive slope, which means that passive film formed on Cr alloy has n-type semiconductor property. These apparently conflicting results are rationally explained assuming that the passive film on Cr alloy formed in the acid solution has n-type semiconductor property with a fairly deep donor level in the band gap and forms an accumulation layer in the most of potential region in the passive state.

• 한국표면공학회지
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• 제44권2호
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• pp.44-49
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• 2011

The films formed on AZ31B magnesium alloy were prepared from alkaline solution composed of potassium permanganate and sodium hydroxide. The immersion tests were carried out at the different concentration of sodium hydroxide and pre-treatment method in 5 minute. The morphology and the phase composition of the film were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior of the film in 5.0% NaCl solution was evaluated using potentiodyanmic polarization. Open circuit potential in developing film was examined with time. The thin and transparent film was mainly composed of MgO and $Mg(OH)_2$. The film with the best corrosion resistance was obtained at $70^{\circ}C$ bath temperature, 1.6 M concentration of sodium hydroxide and chemical pre-treatment.

• 센서학회지
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• 제19권3호
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• pp.202-208
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• 2010

This study examined the dependency of crystalline orientation and electric properties of sol-gel PZT film on hydrolysis, a $PbTiO_3$ seed layer and a concentration of sol-gel solution. The PZT thin films were prepared by using 2-Methoxyethanol-based sol-gel method and spin-coating on Pt/Ti/$SiO_2$/Si substrates. The 1-${\mu}m$-thick PZT films were coated and then fired in a furnace by direct insert method. The highly (111) oriented PZT film of pure perovskite structure could be obtained. We could control the degree of orientation by various parameters such as hydrolysis, a $PbTiO_3$ seed layer and a concentration of sol-gel solution. The highest measured remanent polarization, dielectric constant and piezoelectric coefficient are $24.16\;{\mu}C/cm^2$, 2808, and 159 pC/N, respectively.