• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.80-80
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• 2017

Titanium and its alloys that have a good biocompatibility, corrosion resistance, and mechanical properties such as hardness and wear resistance are widely used in dental and orthopedic implant applications. However, they do not form a chemical bond with bone tissue. Plasma electrolytic oxidation (PEO) that combines the high voltage spark and electro-chemical oxidation is a novel method to form ceramic coatings on light metals such as tita-nium and its alloys. This is an excellent re-producibility and economical, because the size and shape control of the nano-structure is relatively easy. Silicon (Si), manganese (Mn), and magne-sium (Mg) have a useful to bone. Particularly, Si has been found to be essential for normal bone, cartilage growth, and development. Mn influences regulation of bone remodeling be-cause its low content in body is connected with the rise of the concentration of calcium, phosphates and phosphatase out of cells. Pre-studies have shown that Mg plays very im-portant roles in essential for normal growth and metabolism of skeletal tissue in verte-brates and can be detected as minor constitu-ents in teeth and bone. In this study, Electrochemical behavior of plasma electrolytic oxidized films formed in solution containing Mn, Mg and Si ions were researched using various experimental in-struments. A series of Si-Mn-Mg coatings are produced on Ti dental implant using PEO, with the substitution degree, respectively, at 5 and 10%. The potentiodynamic polarization and AC impedance tests for corrosion behav-iors were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV. Also, AC impedance was performed at frequencies anging from 10MHz to 100kHz for corrosion resistance.

• 한국산학기술학회논문지
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• 제14권9호
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• pp.4117-4123
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• 2013

본 연구에서는 해수용 열교환기의 코팅에 따른 해수 부식특성을 조사하기 위해 실험이 수행되었다. 코팅은 테플론, 전착, 세라믹+실리콘 3종을 선정하였고, 코팅되지 않은 알루미늄 부식과 비교하였다. 해수부식을 가속시키기 위하여 $70^{\circ}C$ 고온의 농도 3.5% 인공해수를 제작하여 9주 동안 침지부식을 시켰다. 침지기간에 따른 코팅의 부식특성 변화를 관찰하기 위하여 임피던스 분광법과 SEM을 이용하였다. Bode 선도에서 얻어진 분극저항으로부터 코팅재질의 내부식성을 확인하였다. 이중코팅은 4주 이후에도 코팅의 내부식성을 유지하였다. 또한 침지기간에 따라서 금속모재와 점착된 코팅면 사이에 블리스터가 발생할 수 있음을 확인하였다.

• 한국자기학회지
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• 제18권4호
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• pp.154-158
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• 2008

역 스피넬 구조(Inverse Spinel structure)를 갖는 마그네타이트($Fe_3O_4$) 나노입자에서 거대 자기저항(Giant Magneto-Resistance, GMR) 거동을 주의 깊게 관찰하였다. 이 연구 결과로부터 MR 현상이 100%의 스핀 분극 값을 갖는 마그네타이트 전자기적 특성뿐만 아니라 입자들의 표면에 형성된 절연체 터널 장벽(tunnel barrier)의 특성에 영향을 받음을 확인할 수 있었다. 이는 박막형태의 터널 접합소자에서 터널링 특성이 벌크가 아닌 자성 층과 산화 층 사이의 계면 특성에 매우 큰 영향을 받는다는 연구 결과와 일치한다. 따라서 나노입자의 I-V 특성을 측정하여 박막의 터널 접합에 대한 이론 모델 중 하나인 Brinkman 이론을 적용하여 입자 표면의 심층적 분석을 시도하였다. 한편 GMR을 측정하기에 앞서 입자의 구조와 자기적 특성의 상호작용에 대한 연구 또한 진행되었다.

• 한국표면공학회지
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• 제34권3호
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• pp.195-205
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• 2001

The surface characteristics of Ti/TiN films coated on sintered stainless steels (SSS) by electron beam physical vapour deposition (EB-PVD) were investigated. Stainless steel compacts containing 2, 4, and 10wt%Cu were prepared by the electroless Cu-plating method, which results in increased homogenization in the alloying powder. The specimens were coated with Ti and TiN with a 1.0$\mu\textrm{m}$ thickness respectively by EB-PVD. The microstructures were investigated using scanning electron microscopy (SEM). The corrosion behaviors were investigated using a potentiosat in 0.1 M $H_2$$SO_4$, and 0.1M HCl solutions and the corrosion surface was observed using SEM and XPS. The Ti coated specimens showed rough surface compared to Ti/TiN coated specimens. Ti and Ti/TiN coated SSS revealed a higher corrosion and pitting potential from anodic polarization curves than that of Ti and Ti/TiN uncoated SSS. In addition, Ti/TiN coated SSS containing 10wt% Cu exhibited good resistance to pitting corrosion due to the formation of a dense film on the surface and the decrease in interconnected porosity by electroless coated Cu.

• Corrosion Science and Technology
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• 제16권3호
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• pp.128-140
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• 2017

Aluminum alloy matrix may be used for manufacturing lighter automobiles. However, galvanic corrosion may occur between the rivet joint combining aluminum alloy matrix and a CFRP (carbon fiber reinforced plastic) laminate. The possibility of galvanic corrosion may be investigated by measuring galvanic couple currents. Two types of galvanic current measuring methods were used. One method is to use potentiodynamic polarization curves and the other is the ZRA (zero resistance ammeter) method. For galvanic corrosion experiments graphite, a major component of CFRP, was used with carbon steel (rivets) and 6061 aluminum alloys. Regardless of carbon steel, Ni deposited carbon steel, and 316L stainless steels we also investigated the possibility of reduction in galvanic corrosion. Results revealed that even though Ni deposited carbon steel or 316L stainless rivet may slightly increase galvanic current density between those and Al matrix, substitute rivets for carbon steel may be considerably useful for reducing overall galvanic corrosion.

• 대한기계학회논문집A
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• 제29권7호
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• pp.930-937
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• 2005

One of the useful technology for light-weightening of components required in the automobile and machine industry is to use of high strength materials. To improve material properties, carbonizing treatment, nitrifying treatment, and shot-peening method are representatively applied, However, the shot-peening method is generally used to remove the surface defect of steel and to improve the fatigue strength on surface. Benefits by shot peening are to make increase resistance against fatigue, stress corrosion cracking, fretting, galling, erosion and closing of pores. In this paper, investigated the effect of shot peening on the corrosion of SUP-9 steel immersed in $3.5\%$ NaCl solution and corrosion characteristics by the heat treatment during shot peening process. The immersion test was performed on the four kinds of specimens. Corrosion potential, polarization curve, residual stress and etc. were investigated from the experimental results.

• 한국표면공학회지
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• 제50권3호
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• pp.147-154
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• 2017

This research was conducted to investigate the electrochemical properties of the thin air-formed oxide film-covered AZ31 Mg alloy. Native air-formed oxide films on AZ31 Mg alloy samples were prepared by knife-abrading method and the changes in the electrochemical properties of the air-formed oxide film were investigated in seven different electrolytes containing the following anions $Cl^-$, $F^-$, $SO{_4}^{2-}$, $NO_3{^-}$, $CH_3COO^-$, $CO{_3}^{2-}$, and $PO{_4}^{3-}$. It was observed from open circuit potential (OCP) transients that the potential initially decreased before gradually increasing again in the solutions containing only $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions, indicating the dissolution or transformation of the native air-formed oxide film into new more protective surface films. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) showed that there was growth of new surface films with immersion time on the air-formed oxide film-covered specimens in all the electrolyte. The least resistive surface films were formed in fluoride and sulphate baths whereas the most protective film was formed in phosphate bath. The potentiodynamic polarization curves illustrated that passive behaviour of AZ31 Mg alloy under anodic polarization appears only in $CO{_3}^{2-}$, or $PO{_4}^{3-}$ ions containing solutions and at more than $-0.4V_{Ag/AgCl}$ in $F^-$ ion containing solution.

• Membrane and Water Treatment
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• 제7권2호
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• pp.127-141
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• 2016

Electrodialysis (ED) is known to be a useful membrane process for desalination, concentration, separation, and purification in many fields. In this process, it is desirable to work at high current density in order to achieve fast desalination with the lowest possible effective membrane area. In practice, however, operating currents are restricted by the occurrence of concentration polarization phenomena. Many studies showed the occurrence of a limiting current density (LCD). The limiting current density in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Therefore, its reliable determination is required for designing an efficient electrodialysis plant. The purpose of this study is the development of a predictive model of the limiting current density in an electrodialysis process using response surface methodology (RSM). A two-factor central composite design (CCD) of RSM was used to analyze the effect of operation conditions (the initial salt concentration (C) and the linear flow velocity of solution to be treated (u)) on the limiting current density and to establish a regression model. All experiments were carried out on synthetic brackish water solutions using a laboratory scale electrodialysis cell. The limiting current density for each experiment was determined using the Cowan-Brown method. A suitable regression model for predicting LCD within the ranges of variables used was developed based on experimental results. The proposed mathematical quadratic model was simple. Its quality was evaluated by regression analysis and by the Analysis Of Variance, popularly known as the ANOVA.

• Corrosion Science and Technology
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• 제15권5호
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• pp.217-225
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• 2016

Linear polarization resistance (LPR) testing of soils has been used extensively by a number of water utilities across Australia for many years now to determine the condition of buried ferrous water mains. The LPR test itself is a relatively simple, inexpensive test that serves as a substitute for actual exhumation and physical inspection of buried water mains to determine corrosion losses. LPR testing results (and the corresponding pit depth estimates) in combination with proprietary pipe failure algorithms can provideauseful predictive tool in determiningthe current and future conditions of an asset. Anumber of LPR tests have been developed on soil by various researchers over the years1), but few have gained widespread commercial use, partly due to the difficulty in replicating the results. This author developed an electrochemical cell that was suitable for LPR soil testing and utilized this cell to test a series of soil samples obtained through an extensive program of field exhumations. The objective of this testing was to examine the relationship between short-term electrochemical testing and long-term in-situ corrosion of buried water mains, utilizing an LPR test that could be robustly replicated. Forty-one soil samples and related corrosion data were obtained from ad hoc condition assessments of buried water mains located throughout the Hunter region of New South Wales, Australia. Each sample was subjected to the electrochemical test developed by the author, and the resulting polarization data were compared with long-term pitting data obtained from each water main. The results of this testing program enabled the author to undertake a comprehensive review of the LPR technique as it is applied to soils and to examine whether correlations can be made between LPR testing results and long-term field corrosion.

• 콘크리트학회논문집
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• 제21권6호
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• pp.689-696
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• 2009

최근 들어 균열 치유 향상도의 가속화 방안으로서 전기 화학적 전착 기법을 활용한 인공 균열 치유방법에 관한 실험연구가 수행되고 있다. 이 연구에서는 고내구성 콘크리트의 설계 및 유지관리를 위한 방안으로서 혼합콘크리트의 사용에 따른 인공 균열 치유방법상의 부식방식 모니터링의 비교 및 균열 치유향상도의 분석을 수행하였다. 이를 위해 철근콘크리트내로의 가압전류의 특성분석, 가용 전해질의 특성분석, 갈바닉 전류 모니터링, 선형분극저항측정 비교, 균열 치유 전/후의 치유향상도의 사진화상분석등을 통해 혼합 콘크리트의 인공 균열 치유기법 적용에 따른 치유 향상도를 실험적 연구로서 수행하였다. 실험결과로부터, 인공균열치유에 의한 가압전류 측면에서 20,000 min의 통전시간에 따라 점차적으로 가압전압값이 증가하면서 2.9 V로 물/시멘트비에 관계없이 수렴하고 있음을 알수 있었고, 갈바닉전류 모니터링에 따른 부식지연성은 W/C의 경우에 0.4 $>$ 0.5 $>$ 0.6의 순서로, 결합재별 비교에 있어서는 OPC $>$ 60%GGBS $>$ 10%SF $>$ 30% PFA의 순서로 나타남을 알 수 있었다. 한편 전기화학적 전착기법에 의한 치유후 기존 균열면적의 76.47%가 치유됨을 확인하였다.