• 대한금속재료학회지
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• 제46권8호
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• pp.489-494
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• 2008

The effect of drawing rate on the electrochemical properties of 3003 Al alloys in 5 wt.% NaCl solution was investigated by electrochemical techniques (potentiodynamic polarization test, potentiostatic polarization test, electrochemical impedance spectroscopy (EIS)) and surface analyses (OM, SEM, EDS). Four kinds of automotive pipe materials were prepared (raw material, drawing rate = 5, 10, 15%). As the drawing rate of Al alloy tube increased, the pitting corrosion resistance increased due to the enrichment of Al oxides on the surface.

• Corrosion Science and Technology
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• 제5권1호
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• pp.15-22
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• 2006

The introduction of two-grid inside a conventional process system produces a reactive coating deposition and increases metal ion ratio in the plasma, resulting in denser and smoother films. The corrosion behaviors of TiN coatings were investigated by electrochemical methods, such as potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in deaerated 3.5% NaCl solution. Electrochemical tests were used to evaluate the effect of microstructure on the corrosion behavior of TiN coatings exposed to a corrosive environment. The crystal structure of the coatings was examined by X-ray diffractometry (XRD) and the microstructure of the coatings was investigated by scanning electron microscopy (SEM) and transmission electron spectroscopy (TEM). In the potentiodynamic polarization test and EIS measurement, the corrosion current density of TiN deposited by two grid-attached magnetron sputtering was lower than TiN deposited by conventional magnetron type and also presented higher Rct values during 240 h immersion time. It is attributed to the formation of a dense microstructure, which promotes the compactness of coatings and yields lower porosity.

• Corrosion Science and Technology
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• 제6권1호
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• pp.18-23
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• 2007

DLC coatings have been deposited onto substrate of STS 316L and Ti alloy using r.f. PACVD (plasma-assisted chemical vapor deposition) with a mixture of $C_{6}H_{6}$ and $SiH_{4}$ as the process gases. Corrosion performance of DLC coatings was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analysis (scanning electron microscopy). The electrolyte used in this test was a 0.89% NaCl solution of pH 7.4 at temperature $37^{\circ}C$. The porosity and protective efficiency of DLC coatings were obtained using potentiodynamic polarization test. Moreover, the delamination area and volume fraction of water uptake of DLC coatings as a function of immersion time were calculated using electrochemical impedance spectroscopy. This study provides the reliable and quantitative data for assessment of the effect of substrate on corrosion performance of Si-DLC coatings. The results showed that Si-DLC coating on Ti alloy could improve corrosion resistance more than that on STS 316L in the simulated body fluid environment. This could be attributed to the formation of a dense and low-porosity coating, which impedes the penetration of water and ions.

• 한국표면공학회지
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• 제39권1호
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• pp.18-24
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• 2006

Although stainless steels have the excellent corrosion resistance by passive film, they are susceptible to pitting corrosion in the environment containing halogen elements such as chloride ions. The resistance to pitting corrosion can be evaluated by measuring the critical pitting temperature (CPT). CPT values can be obtained using immersion, potentiodynamic and potentiostatic polarization test methods. Results on duplex 2205 stainless steels showed that CPT values were measured as $50^{\circ}C,\;55^{\circ}C\;and\;61^{\circ}C$, respectively for immersion, potentiodynamic and potentiostatic polarization test methods, depending upon the different test methods, even though the difference between CPT values are not much.

• 방사성폐기물학회지
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• 제8권3호
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• pp.247-260
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• 2010

한국원자력연구원 처분시스템개발과제에서는 처분용기 재료로 개발중인 저온분사코팅 구리에 대한 틈새부식(Crevice Corrosion) 시험을 실시하였다. 본 시험을 통하여 틈새에서의 부식의 발생여부와 발생되는 시점인 재부동태 전위(Repassivation Potential)를 측정하고자 하였다. 틈새부식 시험 방법으로 (1) ASTM G61-86 : Cyclic Potentiodynamic Polarization Measurements, (2) SWRI의 Potentiodynamic Polarization plus intermediate Potentiostatic Hold method, 그리고 (3) ASTM G192-08 (THE method) :Potentiodynamic- Galvanostatic -Potentiostatic Method 등의 3가지 방법을 소개하였다. 실제 저온분사 코팅구리의 부식시험에서는 ASTM G61-86에 따라서 틈새부식장치를 설치하고, 저온분사코팅구리가 KURT 지하수를 모사한 용액에서 어떻게 틈새부식이 일어나는지 살펴보았다. 전기적 부식조건으로는 Cyclic Polarization Test, Potentiostatic Polarization Test, 및 Electrochemical Impedance Spectroscopy 등을 사용하였다. 그리고 부식이 된 시편에 대해 Profilometer Measurement를 통해 실제 부식표면의 높낮이를 조사하여 틈새부식 유무를 관찰하였다. 최종적인 결론에서는 저온분사코팅구리는 틈새부식을 나타나지 않는다는 것을 확인할 수 있었다. 그리고 시험에 사용된 세종류의 구리에 대한 상대적인 부식평가를 한 결과, 부식전위를 나타내는 개방회로(Open Cell)에서의 전위는 구리의 제조방식과 상관없이 구리의 순도가 높을수록 높은 값을 보이는 것을 확인할 수 있었다. 결론적으로 KURT 심층지하수 조건에서는 구리는 틈새부식이 발생되지 않는다고 결론지었다.

• Corrosion Science and Technology
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• 제2권6호
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• pp.289-295
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• 2003

The corrosion behavior of Cr-N coated steels with different phases (${\alpha}-Cr$, CrN and $Cr_2N$) deposited by cathodic arc deposition on Hl3 steel was investigated in 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization test than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the $Cr_2N$ coating than in the other Cr-N coated steels. EIS measurements showed, for the most of Cr-N coated steels, that the Bode plot presented two time constants. Also, the $Cr_2N$ coating represents the characteristic of Warburg behavior after 72hr of immersion. The coating morphologies were examined in planar view and cross-section by SEM analyses and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, the CrN coating provided a better corrosion protection than the other Cr-N coated steels.

• 한국표면공학회지
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• 제54권2호
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• pp.71-76
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• 2021

Ag925, silver with added copper, is popular alloy due to its low price. However, it has a difficult to use because of the low corrosion resistance. In various alloys, neodymium (Nd) works as an element to improve corrosion resistance by reacting with interstitial elements in the alloy. When 1.5 wt. % Neodymium was added to Ag925, the potential on the activated polarization in a potentiodynamic polarization test was increased from -0.15 V to -0.05 V. Ag925 with added neodymium showed the passivation after activation polarization. But When the potential increased around 50 mV, the current density is increased to 3 × 10-3. Ag925 with the 1.5 wt. % Nd had the low corrosion rate.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.193-193
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• 2011

Strong adhesion of a silicon carbide (SiC) coating to a WC-Co substrate was achieved through an ion beam mixing technique and the corrosion resistance of the SiC coated WC-Co was investigated by means of a potentiodynamic electrochemical test. In a 1 M NaOH solution, the corrosion current density of SiC-coated WC-Co after heat treatment at 500$^{\circ}C$ was about 50 times lower than that for the as-received WC-Co. In addition, the corrosion resistance systematically increases with increasing the SiC coating thickness. On the other hand, for a 0.5 M H2SO4 solution, the corrosion current density for SiC-coated WC-Co was about 3 times lower than that for the as-received WC-Co. We discuss the physical reasons for the changes in the corrosion current density with the different electrolytes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1893-1896
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• 2003

This research aimed to fabricate a micro structure using micro electrochemical machining (${\mu}$-ECM). with a view to that the theory of ${\mu}$-ECM is established accurately in a different way of conventional electrochemical machining. In details, if the impedance is existed in the system, it is difficult to analyze the micro electrochemical reaction efficiently in polarization curve using a potentiodynamic test. Hence, this research investigates the relationships between impedance and electric current measuring with a potentiostatic test applying to a pair or electrode as a constant potential. And this paper examines the influence of temperature of electrolyte on polarization curve for the quantitative analysis of electrochemical reactions.

• 대한금속재료학회지
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• 제47권9호
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• pp.558-566
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• 2009

The alloying effect of a small amount of nickel on low alloy steel for application to flue gas desulfurization(FGD) systems was studied. The structural characteristics of the rust layer were investigated by scanning electron microscopy(SEM). The electrochemical properties were examined by means of potentiostatic polarization test, potentiodynamic polarization test, and electrochemical impedance spectroscopy(EIS) in a modified green death solution of 16.9 vol.% $H_2SO_4$+0.35 vol.% HCl at $60^{\circ}C$ and an acid rain solution of $6.25{\times}10^{-5}M\;H_2SO_4+5.5{\times}10^{-3}M\;NaCl$ at room temperature. It was found that as the amount of nickel increased, the corrosion rate increased in the modified green death solution, which seemed to result from micro-galvanic corrosion between NiS and alloy matrix. In acid rain solution, the corrosion rate decreased as the amount of nickel increased due to the repulsive force of $NiFe_2O_4$ rust against $Cl^-$ ions by electronegativity.