• Corrosion Science and Technology
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• 제9권1호
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• pp.20-28
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• 2010

According to the bipolar model, ion selectivity of some species in the passive film is important factor to control the passivation. An increase of cation selectivity of outer layer of the passive film can stabilize the film and improves the corrosion resistance. Therefore, the formation and roles of ionic species in the passive film should be elucidated. In this work, two types of solution (hydrochloric or sulfuric acid) were used to test high N and Mo-bearing stainless steels. The objective of this work was to investigate the formation of oxyanions in the passive film and the roles of oxyanions in passivation of stainless steel. Nitrogen exists as atomic nitrogen, nitric oxide, nitro-oxyanions (${NO_x}^-$), and N-H species, not nitride in the passive film. Because of its high mobility, the enriched atomic nitrogen can act as a reservoir. The formation of N-H species buffers the film pH and facilitates the formation of oxyanions in the film. ${NO_x}^-$ species improve the cation selectivity of the film, increasing the oxide content and film density. ${NO_x}^-$ acts similar to a strong inhibitor both in the passive film and at active sites. This facilitates the formation of chromium oxide. Also, ${NO_x}^-$ can make more molybdate and nitric oxide by reacting with Mo. The role of Mo addition on the passivation characteristics of stainless steel may differ with the test environment. Mo exists as metallic molybdenum, molybdenum oxide, and molybdate and the latter facilitates the oxide formation. When nitrogen and molybdenum coexist in stainless steel, corrosion resistance in chloride solutions is drastically increased. This synergistic effect of N and Mo in a chloride solution is mainly due to the formation of nitro-oxyanions and molybdate ion. Oxyanions can be formed by a 'solid state reaction' in the passive film, resulting in the formation of more molybdate and nitric oxide. These oxyanions improve the cation selectivity of the outer layer and form more oxide and increase the amount of chromium oxide and the ratio of $Cr_2O_3/Cr(OH)_3$ and make the film stable and dense.

• Corrosion Science and Technology
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• 제14권3호
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• pp.140-146
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• 2015

The commercialization of aluminum had been delayed than other metals because of its high oxygen affinity. Anodizing is a process in which oxide film is formed on the surface of a valve metal in an electrolyte solution by anodic oxidation reaction. Aluminum has thin oxide film on surface but the oxide film is inhomogeneous having a thickness only in the range of several nanometers. Anodizing process increases the thickness of the oxide film significantly. In this study, porous type oxide film was produced on the surface of aluminum in sulfuric acid as a function of electrolyte temperature, and the optimum condition were determined for anodizing film to exhibit excellent cavitation resistance in seawater environment. The result revealed that the oxide film formed at $10^{\circ}C$ represented the highest cavitation resistance, while the oxide film formed at $15^{\circ}C$ showed the lowest resistance to cavitation in spite of its high hardness.

• Tribology and Lubricants
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• 제28권5호
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• pp.233-239
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• 2012

The engine of a large ship operates under wet conditions using a fuel such as bunker C oil, which includes sulfur and many impurities. A cylinder liner made of cast iron is very susceptible to damage such as scuffing on the surface. This scuffing can reliably be attributed to the destruction of the oil film and the corrosion wear caused by water and sulfur included in the fuel, along with abrasion impurities and poor lubricants. In this study, a reciprocating friction and wear test was carried out with a cast iron specimen, which was used to simulate an engine cylinder in a corrosive environment. Base-oil and stirred oil containing distilled water, NaCl solution, and dilute sulfuric acid were used as lubricants. The friction surface was analyzed using a microscope and EDAX, and the friction coefficient was measured using a load-cell under each experimental condition. We then attempted to investigate the damage to the cylinder liner using the results.

• 한국융합학회논문지
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• 제8권11호
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• pp.307-312
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• 2017

산업계에서는 희생양극의 원리를 이용한 아연도금이 사용되고 있다. 순수아연도금보다 내식성을 증가시키기 위한 방안의 하나로 Zn-Ni 합금도금이 개발되었다. 합금 도금층은 순 아연 도금층에 비하여 4-5배의 내식성을 가지고 있어서 도금 단가가 높음에도 불구하고 고내식성을 요구하는 자동차 부품 등에 적용이 증가되고 있다. Zn-Ni 합금도금액은 황산욕, 염화욕, 알칼리욕과 암모니아욕 등이 사용되고 있다. 여기에서는 염화욕에서 합금도금의 조성에 미치는 전해조건의 영향을 조사하였다. 그 결과는 음극 과전압 및 확산계수에 의해 설명하였다. 일반적으로 음극의 과전압이 증가함에 따라 활성화분극보다 농도분극이 중요하게 된다. 농도분극은 확산 층 내의 원소 확산에 의해 결정된다. 즉 음극의 과전압이 증가함에 따라 확산계수가 큰 Zn 함량이 증가한다.

• 한국분말재료학회지
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• 제21권2호
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• pp.114-118
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• 2014

In this study, an aluminum oxide layer for sealing treatment of nano-diamond powder was synthesized by anodizing under constant current. The produced pore size and oxide thickness were investigated using scanning electron microscopy. The pore size increased as the treatment time increased, current density increased, sulfuric acid concentration decreased, which is different from the results under constant voltage, due to a dissolution of the oxide layers. The oxide layer thickness by the anodizing increased as temperature, time, and current density increased. The results of this study can be applied to optimize the sealing treatment process of nano-diamond particles of 4-10 nm to enhance the resistances of corrosion and wear of the matrix.

• 한국정밀공학회지
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• 제23권4호
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• pp.146-152
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• 2006

In micro electrochemical machining (ECM), electrodes should be prevented from unfavorable oxide and Passive layer formation on the machined surface or overall corrosion of the entire surface. Generally, metal electrodes corrode, passivate or dissolve in the electrochemical cell according to the electrode potential. Therefore, each electrode must maintain its stable potential. Tn this paper, the stable electrode potentials of tool and workpiece were determined using the potentiodynamic polarization test and verified experimentally considering machining stability and surface quality. Stable workpiece electrode potentials of two different passive materials of 304 stainless steel and nickel were determined in the 0.1 M sulfuric acid. Experimental results show good machined surface and fast machining rate using the determined electrode potentials.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.197-203
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• 1999

Stainless steels in general has passive film having strong corrosion resistance on surface. Therefore it must be necessarily removed by etching in mixing solution of sulfuric and chloric acid before Nitriding treatment. But in the ion nitriding, nitride layer was easily formed because passive film was removed without difficult by sputtering effect. The removal extent of these passive films was greatly effected by gas mixing ratios and pressure and holding times of pre sputtering factors in pre sputtering stage. As a results of experiment it has been known that pre sputtering pressure and holding time was not nearly effective on the formation behavior of nitride layer. But when A/H2 gas mixing ratios was 1/2 (vol%) was the most effective of the all pre sputtering conditions. It was resulted from the combination of mechanical reaction byArgon bombardment and chemical reaction by reduction of hydrogen on the passive film.

• 보존과학회지
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• 제29권2호
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• pp.187-196
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• 2013

본 연구는 해저 환경 내에서의 철제유물 부식인자 중 황화물에 의한 부식상태 및 출수 후 대기 중 고습 상태에서의 손상 현상에 대한 것이다. 이를 위하여 충청남도 태안 마도해역 뻘층에서 출수된 철제유물 4점에서 생성된 부식생성물을 대상으로 황화물의 존재 여부를 확인하고자 SEM-EDS 및 XRD 분석을 실시하였다. 분석 결과, 해저퇴적토 내에서 형성된 부식생성물은 주요 성분이 황(S)이며 화합물로서 황화철(FeS)이 형성되었고, 해저면에 노출된 상태에서 형성된 부식생성물은 일부 결과를 제외하면 표면을 덮고 있는 응결물(concretion)의 영향으로 뚜렷한 부식 양상이 나타나지 않았다. 출수 후 고습 상태에서 철제유물의 손상 현상을 확인하기 위해 부식생성물을 고습 제습환경에 노출시키는 실험을 실시하였다. 실험 결과, 고습 환경에서 황화철 부식생성물의 산화는 황산철($FeSO_4$)과 함께 황산($H_2SO_4$)을 생성하여 철제유물을 2차적으로 부식시킬 수 있음을 확인하였다. 따라서 해저 환경에서 출수된 철제유물의 황화철 부식생성물은 반드시 제거하고 유물의 보존 환경도 제습된 상태가 유지되어야 할 것으로 판단된다.

• Tribology and Lubricants
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• 제40권3호
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• pp.71-77
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• 2024

Hydrogen has emerged as an eco-friendly and sustainable alternative to fossil fuels. However, the utilization of hydrogen requires high-pressure compression, storage, and transportation, which poses challenges to the durability of compressor components, particularly the diaphragm. This study aims to improve the durability of 304 stainless steel diaphragms in hydrogen compressors by optimizing their surface roughness and corrosion resistance through wet etching. The specimens were prepared by immersing 304 stainless steel in a mixture of sulfuric acid and hydrogen peroxide, followed by etching in hydrochloric acid for various durations. The surface morphology, roughness, and wettability of the etched specimens were characterized using optical microscopy, surface profilometry, and water contact angle measurements. The friction and wear characteristics were evaluated using reciprocating sliding tests. The results showed that increasing the etching time led to the development of micro/nanostructures on the surface, thereby increasing surface roughness and hydrophilicity. The friction coefficient initially decreased with increasing surface roughness owing to the reduced contact area but increased during long-term wear owing to the destruction and delamination of surface protrusions. HCl-30M exhibited the lowest average friction coefficient and a balance between the surface roughness and oxide film formation, resulting in improved wear resistance. These findings highlight the importance of controlling the surface roughness and oxide film formation through etching optimization to obtain a uniform and wear-resistant surface for the enhanced durability of 304 stainless steel diaphragms in hydrogen compressors.

• 마이크로전자및패키징학회지
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• 제17권1호
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• pp.63-68
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• 2010

CNT-퍼멀로이 복합도금을 실시하였다. CNT를 더 작게 분쇄하기 위하여 전처리를 하였다. 볼밀링과 같은 물리적인 처리보다 산처리와 같은 화학적인 처리가 CNT 분쇄에 더 효과적이었다. 10 M 질산과 10 M 황산이 사용되었으며 황산이 질산보다 CNT의 입체적인 구조를 줄이는데 있어서 더 효과적이었다. 산처리 과정만을 거친 CNT를 $10{\sim}40\;mA/cm^2$의 전류밀도 하에서 복합전기도금시킨 후 FESEM을 통하여 표면을 관찰하였다. 분산제를 사용하여 CNT 분산을 하였다. 분산제의 종류로는 Sodium Dodecyl Sulfate(SDS)와 Triton-X 100, Poly Acrylic Acid(PAA)를 사용하였다. PAA를 사용하여 도금한 경우 다른 분산제를 사용한 것에 비하여 더 많은 CNT가 공침되었다. PAA 2 g/L를 이용하여 분산시킨 CNT를 $10{\sim}80\;mA/cm^2$의 전류밀도 하에서 도금되었으며 FESEM으로 표면을 관찰하였다. 전류밀도가 $20\;mA/cm^2$인 경우 표면에 균열을 발생시키지 않는 도금층을 얻었다. 도금된 표면의 결정화 정도를 XRD로 관찰하고 표면 경도를 측정하였으며 분극 거동을 통해 내식성을 비교하였다. CNT의 첨가로 인한 경도의 변화는 없었으며 내식성의 향상도 관찰되지 않았다.