• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.601-607
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• 2011

The study investigated the influence of current density on the corrosion-protection properties of an AZ91 Mg alloy subjected to plasma electrolytic oxidation coating. The present coatings were carried out under an AC condition at three different current densities, i.e., 100, 150, and $200mA/cm^2$. From microstructural observations, the micro cracks connecting each micro pore were pronounced on the oxide surface of the samples coated at current densities higher than $150mA/cm^2$ since increasing the current density in this study led to an increment in the relative volume fraction of the MgO compound. Based on potentio dynamic polarization and immersion tests, the sample coated at a current density of $100mA/cm^2$ showed superior corrosion resistance.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.192-193
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• 2005

Magnesium thin films were prepared on cold-rolled steel substrates by RF(Radio Frequency) magnetron sputtering technique.$^{1)}$ The crystal orientation and monitoring of the deposited films were investigated by using XRD(X-ray Diffraction) and EIS(Electrochemical Impedance Spectroscopy), respectively. The corrosion rates of Mg thin films deposited with different argon gas pressure and substrate bias voltage were monitored by AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1h immersion in 3%NaCl solution and 5h drying at 60% RH and 25$^{\circ}C$. The result of corrosion rate of Mg thin films deposited at various Ar gas pressures and substrate bias voltage under wet-dry cyclic exposure in chloride-containing solutions was showed the following conclusions. At the region I during the onset of the wet cycle, corrosion rate showed relatively low value. The increase in the Corrosion rate of region II is due to the increase in the chloride concentration. Corrosion rate of region III during the onset of the cycle zero and salt crystals remain on the metal surface.$^{2)}$

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.350-350
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• 2010

에너지 효율이 높은 LED조명을 사용하면 에너지 절감, 이산화탄소, 환경오염물질 배출 감소의 효과를 얻을 수 있다. 그러나 LED조명에서 발생하는 열은 LED조명의 수명과 에너지 효율을 감소시킨다. 따라서 LED조명을 상용화하기 위해서는 LED조명에서 발생되는 열을 효율적으로 제거하는 것이 필수적이며 LED조명 방열판의 생산단가 또한 낮아야 한다. 이러한 조건을 충족하는 LED조명용 방열판은 Al 6063이 주로 사용되고 있다. Al 6063은 열전도 특성이 우수하고 생산단가가 저렴하다. 그러나 100 W급 이상의 고출력 LED조명에 Al 6063을 사용하기 위해서는 Al 6063의 열 방출 특성을 향상시킬 필요가 있다. 금속의 열 방출 특성을 향상시키기 위해서 주로 이용되는 방법은 표면적을 극대화 시키는 것이다. 금속에 국부적인 깊이 부식을 일이키는 Pitting corrosion을 이용하면 저렴한 비용으로 Al 6063의 표면적을 극대화하여 방열판의 열 방출 특성을 향상시킬 수 있다. 실험에 사용한 기본적인 구조의 Al 6063 방열판의 크기는 $50{\times}50{\times}30(mm)$ 이며 1M HCl + 0.05M $H_2SO_4$에서 $I_a$ = +40 mA, $t_a$ = 60 ms, $I_c$ = -40 mA, $t_c$ =20 ms로 50, 100, 200 cycle AC 에칭 하였다. Pitting corrosion된 방열판은 $3W{\times}3$개의 LED모듈에서 1시간 발광 시킨 후, 열화상 카메라를 이용하여 표면온도를 측정하였다. 실험결과 AC에칭 cycle이 증가할수록 발열특성이 우수하였으며, Pitting corrosion을 이용하지 않은 방열판에 비해 최대 $5^{\circ}C$의 표면온도 감소가 이루어졌다. 본 연구를 통해, 저렴하면서도 열 방출 특성이 높은 방열판을 설계하면, 고출력 LED조명의 상용화를 앞당길 수 있을 것이다.

• Journal of the Korean Institute of Gas
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• v.5 no.4 s.16
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• pp.21-26
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• 2001

Because of the continuous growth of energy consumption, and also tile tendency to site power lines and pipelines along the same routes, the close proximity of high voltage structures and metallic pipelines has become more and more frequent. Recently, the results of assessment about a system integrity are needed in korea also when a gas pipeline is running parallel with high voltage power line in same submarine tunnel, Therefore, we analyze the system integrity(AC corrosion of pipe, melting of pipeline coating, safety of insulation flange, especially cathodic protection system which are rectifier and CI(cathodic Isolator)) resulting from the influence of high voltage power system.

• Journal of the Korean Institute of Gas
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• v.4 no.3 s.11
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• pp.26-32
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• 2000

Because of the continuous growth of energy consumption, and also the tendency to site power lines and pipelines along the same routes, the close proximity of high voltage structures and metallic pipelines has become more and more frequent. Moreover, normal steady state and fault currents become higher as electric networks increase in size and power Therefore, there has been and still is a growing concern(safety of people marking contact with pipeline, risk of damage to the pipeline coating, the metal and equipment connected to pipeline, especially cathodic protection system) about possible hazards resulting from the influence of high voltage power system on metallic structures(gas pipeline, oil pipeline and water pipeline etc.). Therefore, we analyze the interference problems when the gas pipeline is buried with power cable in the same submarine tunnel. This paper present the results of the study about interference mechanism, AC corrosion limitation of safety voltage and analysis of induction voltage.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.171-177
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• 2002

Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties, it was also highlighted as the material of frontier industry because strength, heat-resistant, corrosion-resistant and wear-resistant were superiored. In recent years, the study of metal matrix composite has increased by aluminum alloy. The study is based on the tribological properties of AC4CH that is a part of the mechanical property of metal matrix composites. Metal matrix composite that is produced from matrix material AC4CH and reinforcement SiO$_2$, Al$_2$O$_3$ and TiO$_2$ are added to the metal matrix composite fur strength so binding among the whisker can take place. Each metal matrix composite is produced using the squeeze casting method. To test for tribe a pin-on-disk machine and lubricant is used without paraffine 8.2CST at room temperature which is 40$\^{C}$. As the results of this study, the tribological properties of each specimen are more improved than AC4CH. The variation of coefficient resistance is more stable at the AC4CH and TiO$_2$, but the variation rates are higher at the inanimate binder.

• Journal of Ocean Engineering and Technology
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• v.18 no.1
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• pp.75-79
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• 2004

Organic coatings are widely used to control of the corrosion of a steel structure. The water in coatings may cause the coatings to swell, leading to the degradation of the coatings. In addition, water affects the permeation of oxygen and other corrosive agents, and consequently, the presence of such substances at coating-metal interface promotes corrosion of the metal substrate. In this study, the anticorrosive properties of 4 types of coating, such as epoxy-epoxy, epoxy-urethane, urethane-epoxy, urethane-urethane, were evaluated. The evaluation tests were conducted under cyclic water-absorption/desorption conditions, consisting of alternative exposure to diluted 0.001M-LiCl(a$H_2O$≒1) and concentrated 10M-LiCl(a$H_2O$≒0.15). The anticorrosive performance of coatings was found to decrease in the order of urethane-urethane > urethane-epoxy > epoxy-epoxy coating.

• Corrosion Science and Technology
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• v.5 no.5
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• pp.177-180
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• 2006

The anticorrosive performance of epoxy coating was examined by using the hygrothermal cyclic test and the degradation mechanism of the coating was investigated by using the AC impedance method. The relationship between the results obtained from different tests was studied. It was revealed that the hygrothermal cyclic test can be used as an effective acceleration test for the degradation of organic coating. It was also found in hygrothermal cyclic test that the epoxy coatings have the resistance to stresses at some extent. The degradation of organic coating seems to be caused by the decrease of resistance of coating and the increase of both capacitance and free volume in the organic coating.

• Korean Journal of Metals and Materials
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• v.47 no.10
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• pp.652-659
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• 2009

Many ancient and historical artifacts were made by copper and its alloys. In the case of outdoor exposure artifacts, the surface could be suffered from corrosion and tarnish by the reaction with its environment. In order to preserve the artifacts, surface treatment would be needed and BTA coating has been usually applied to tin-bronze. This paper dealt with the evaluation of the properties of BTA coated film using a linear polarization method and AC impedance measurement. On the base of corrosion rate and film resistance for the specimen formed by coating process, optimum coating conditions are as follows; 3 cycles brushing or 3 cycles spraying coatings for natural dried process and 1 cycle brushing coating or 5 cycles spraying coating for hot-air dried process.