Uniformity of Droplet of Eutectic NaCl-MgCl2 System for Corrosion Test of Coating Layer

Wonseok Lee,Wonseok Yang,Jihun Kim,Hyeongbin Kim,Taeho Jang,Sungyeol Choi 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Corrosion-related challenges remain a significant research topic in developing next-generation Molten Salt Reactors (MSRs). To gain a deeper understanding of preventing corrosion in MSRs, previous studies have attempted to improve the corrosion resistance of structural alloys by coating surfaces such as alumina coating. To conduct a corrosion test of coating alloys fully immersed in molten salt, it’s important to ensure that the coating application process is carefully carried out. Ideally, coating all sides of the alloy is necessary to avoid gaps like corners of the alloy, while only applying a one-sided coating alloy can lead to galvanic corrosion with the base metals. Using the droplet shape of eutectic salt applied to only one side of the coating alloy would avoid these problems in conventional corrosion immersion tests, as corrosion would occur solely on the coating surface. Although the droplet method for corrosion tests cannot fully replicate corrosion in the MSRs environment, it offers a valuable tool for comparing and evaluating the corrosion resistance of different coating surfaces of alloys. However, the surface area is important due to the effect of diffusion in the corrosion of alloy in molten salt environments, but it is difficult to unify in the case of droplet tests. Therefore, understanding the droplet-alloy properties and corrosion mechanism is needed to accurately predict and analyze these test systems’ behavior highlighting unity for corrosion tests of different coating surfaces of alloys. To analyze the molten salt droplet behavior on various samples, pelletized eutectic NaCl-MgCl2 was prepared as salt and W-, Mo-coating, and base SS316 as samples. At room temperature, the same mass of pelletized eutectic NaCl-MgCl2 was placed on different samples under an argon atmosphere and heated to a eutectic point of 500°C in a furnace. After every hour, the molten droplets were hardened by rapid cooling at room temperature outside the furnace. The mass loss of salts and the contact area of the samples were measured by mass balance and SEM. The shape, surface area to volume ratio, and evaporation of the droplets of NaCl-MgCl2 per each coating sample and hour were analyzed to identify the optimal mass to equalize the contact coating surface of alloys with salts. Furthermore, We also analyzed whether their results reached saturation of corrosion products through ICP-MS. This will be significant research for the uniformity of the liquid-drop shape corrosion test of the coating sample in molten eutectic salts.

스테인리스 강의 부식 측정방법의 이용과 전망

최용선(Yongseon Choi),이재원(Jaewon Lee),박은옥(Eunoak Park),이기영(Kiyoung Lee) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.6

As the number of cases of performance degradation owing to corrosion of plant during processing in industries increases, the cost of maintaining industrial factory is increasing year by the year. Most of the materials of the facilities are consist of stainless steel (SS) such as austenite SS, ferrite SS, martensite SS, and duplex SS. Among them austenite SS is cheap and has excellent corrosion resistance and heat resistance. Corrosion is the consumption and change of metals by altering chemical and electrical reactions. The types of SS corrosion include pitting corrosion, crevice corrosion, galvanic corrosion, stress corrosion cracking, and thermal corrosion. The corrosion of SS is not only investigated various environmental factors but also the measurement of the corrosion rate. Therefore, it aims to understand comprehensive corrosion rates in various environments using qualitative, quantitative and electrochemical methods.

부식 환경에 따른 출토 청동 유물의 부식 특성

장준혁,배고운,정광용 국립문화재연구원 2020 헤리티지:역사와 과학 Vol.53 No.1

In excavated bronze artifacts, corrosion products of various shapes and colors are observed due to multiple corrosion factors coexisting in the burial environment, and these corrosion products can constitute important data not only in terms of long-term corrosion-related information, but also in connection with preservation of artifacts. As such, scientific analysis is being carried out on the corrosion layer and corrosion products of bronze artifacts, and the corrosion mechanism and the characteristics of corrosion products elucidated, which is essential for interpreting the exposed burial environment and its association with corrosion factors inside the burial environment. In this study, after classifying excavated bronze artifacts according to alloy ratio and fabrication technique, comprehensive analysis of the surface of corrosion artifacts, corrosion layer, and corrosion products was carried out to investigate the corrosion mechanism, formation process of the corrosion layer, and characteristics of corrosion products. The study designated two groups according to alloy ratio and fabrication technique. In Group 1, which involved a Cu-Sn-Pb alloy and had no heat treatment, the surface was rough and external corrosion layers were formed on a part, or both sides, of the inside and the outside, and the surface was observed as being green or blue. α+δ phase selection corrosion was found in the metal and some were found to be concentrated in an empty space with a purity of 95 percent or more after α+δ phase corrosion. The Cu-Sn alloy and heat-treated Group 2 formed a smooth surface with no external corrosion layer, and a dark yellow surface was observed. In addition, no external corrosion layer was observed, unlike Group 1, and α corrosion was found inside the metal. In conclusion, it can be seen that the bronze artifacts excavated from the same site differ in various aspects, including the formation of the corrosion layer, the shape and color of the corrosion products, and the metal ion migration path, depending on the alloy ratio and fabrication technique. They also exhibited different corrosion characteristics in the same material, which means that different forms of corrosion can occur depending on the exposure environment in the burial setting. Therefore, even bronze artifacts excavated from the same site will have different corrosion characteristics depending on alloy ratio, fabrication technique, and exposure environment. The study shows one aspect of corrosion characteristics in specific areas and objects; further study of corrosion mechanisms in accordance with burial conditions will be required through analysis of the corrosive layer and corrosive product characteristics of bronze artifacts from various regions.

Corrosion of Copper in Anoxic Ground Water in the Presence of SRB

( L. Carpen ),( P. Rajala ),( M. Bomberg ) 한국부식방식학회(구 한국부식학회) 2018 Corrosion Science and Technology Vol.17 No.4

Copper is used in various applications in environments favoring and enabling formation of biofilms by naturally occurring microbes. Copper is also the chosen corrosion barrier for nuclear waste in Finland. The copper canisters should have lifetimes of 100,000 years. Copper is commonly considered to be resistant to corrosion in oxygen-free water. This is an important argument for using copper as a corrosion protection in the planned canisters for spent nuclear-fuel encapsulation. However, microbial biofilm formation on metal surfaces can increase corrosion in various conditions and provide conditions where corrosion would not otherwise occur. Microbes can alter pH and redox potential, excrete corrosion-inducing metabolites, directly or indirectly reduce or oxidize the corrosion products, and form biofilms that create corrosive microenvironments. Microbial metabolites are known to initiate, facilitate, or accelerate general or localized corrosion, galvanic corrosion, and intergranular corrosion, as well as enable stress-corrosion cracking. Sulfate-reducing bacteria (SRB) are present in the repository environment. Sulfide is known to be a corrosive agent for copper. Here we show results from corrosion of copper in anoxic simulated ground water in the presence of SRB enriched from the planned disposal site.

Corrosion Cost and Corrosion Map of Korea -Based on the Data From 2005 to 2010

( Y. S. Kim ),( H. K. Lim ),( J. J. Kim ),( W. S. Hwang ),( Y. S. Park ) 한국부식방식학회(구 한국부식학회) 2011 Corrosion Science and Technology Vol.10 No.2

Corrosion of metallic materials occurs by the reaction with corrosive environment such as atmosphere, marine, soil, urban, high temperature etc. In general, reduction of thickness and cracking and degradation are resulted from corrosion. Corrosion in all industrial facilities and infrastructure causes large economic losses as well as a large number of accidents. Economic loss by corrosion has been reported to be nearly 1-6% of GNP or GDP. In order to reduce corrosion damage of industrial facilities, corrosion map as well as a systematic investigation of the loss of corrosion in each industrial sector is needed. The Corrosion Science Society of Korea in collaboration with 15 universities and institutes has started to survey on the cost of corrosion and corrosion map of Korea since 2005. This work presents the results of the survey on cost of corrosion by Uhlig, Hoar, and input-output methods, and the evaluation of atmospheric corrosion rate of carbon steel, weathering steel, galvanized steel, copper, and aluminum in Korea. The total corrosion cost was estimated in terms of the percentage of the GDP of industry sectors and the total GDP of Korea. According to the result of Input/output method, corrosion cost of Korea was calculated as 2.9% to GDP (2005). Time of wetness was shown to be categories 3 to 4 in all exposure areas. A definite seasonal difference was observed in Korea. In summer and fall, time of wetness was higher than in other seasons. Because of short exposure period (12 months), significant corrosion trends depending upon materials and exposure corrosion environments were not revealed even though increased mass loss and decreased corrosion rate by exposure time.

Effect of Heat Treatment on the Grooving Corrosion Resistance of ERW Pipes

Lee, Jongkwon,Lee, Jaeyoung,Lim, Soohyun,Park, Jihwan,Seo, Bomin,Kim, Seonhwa 한국부식방식학회 2002 Corrosion Science and Technology Vol.31 No.3

The v-sharp grooving corrosion of ERW(electrica1 resistance welding) steel pipes limited their wide application in the industry in spite of their high productivity and efficiency. The grooving corrosion is caused mainly by the different microstructures between the matrix and weld that is formed during the rapid heating and cooling cycle in welding. By this localized corrosion reaction of pipes, it evolves economic problems such as the early damage of industrial facilities and pipe lines of apartment, and water pollution. Even though the diminishing of sulfur content is most effective to decrease the susceptibility of grooving corrosion, it requires costly process. In this study, improvement of grooving corrosion resistance was pursuited by post weld heat treatment in the temperature range between 650℃ and 950℃. Also, the effect of heat input in the welding was investigated. By employing chromnoarnperometry and potentiodynarnic experiment, the corrosion rate and grooving corrosion index(α) were obtained. It was found that heat treatment could improve the grooving corrosion resistance. Among them, the heat treated at 900°C and 950℃ had excellent grooving corrosion resistance. The index of heat treated specimen at 900℃ and 950℃ were 1.0, 1.2, respectively, which are almost immune to the grooving corrosion. Potential diffmnce after the heat treatment between base and weld metal was decreased considerably. While the as-received one measured 61 - 71 ㎷, that of the 900℃ heat treated steel pipe measured only 1O㎷. The results were explained and discussed.

탄소강 및 해드필드강의 파이프 조관에 따른 침식부식 거동에 대한 비교연구

김성진,윤덕빈,박진성,이상철,최종교,황중기 한국부식방식학회 2022 Corrosion Science and Technology Vol.21 No.3

Erosion-corrosion behaviors of Hadfield steel under a neutral aqueous environment with fine SiO2 particles were examined and compared with those of conventional carbon steel. A range of electrochemical experiments (potentiodynamic polarization, linear polarization, and impedance), immersion test, and slurry pot test (i.e., erosion-corrosion test) were performed. Results showed that the Hadfield steel composed of austenitic matrix with (Fe,Mn)-based carbide had lower corrosion potential and higher corrosion current density than carbon steel with a typical ferrite/pearlite structure. In addition, pipe forming increased total corrosion rates (i.e., pure corrosion and erosion-enhanced corrosion rates). Nevertheless, the erosion-corrosion rate of Hadfield steel was much smaller. Morphological observation showed that local damage in the form of a crater by erosion-corrosion was more noticeable in carbon steel. The higher resistance of Hadfield steel to erosion-corrosion was attributed to its lower total erosion rates (i.e., pure erosion and corrosion-enhanced erosion rates) highly depending on surface hardness. This study suggests that Hadfield steel with higher resistances to flowing erosion-corrosion in an aqueous environment can be applied widely to various industrial fields.

Corrosion Resistance of Cr-bearing Rebar in Macrocell Corrosion Environments Due to Different Concentrations of Chloride Ions

Tae, Sung-Ho,Noguchi, Takafumi,Ujiro, Takumi Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.10

<P>Reinforced concrete specimens were prepared by embedding 10 types of Cr-bearing reinforcing bars having different Cr contents and supplying saltwater from the upper surfaces to allow chloride ions to penetrate into concrete, thereby forming macrocells, with the aim of developing Cr-bearing rebars having corrosion-preventing properties required under macrocell-corrosion conditions due to differences in the chloride concentrations. The time-related changes in the macrocell corrosion current density, soluble chloride ion content of concrete, and half-cell potential were then measured during corrosion-accelerating test up to eight months. Also, the corrosion area and corrosion loss of anodic and cathodic bars were measured at the end of the 8-month corrosion-accelerating test to investigate the corrosion-inhibiting property of Cr-bearing rebars in macrocell corrosion environments due to chloride ion concentration in concrete.As a result, the Cr content required for corrosion inhibition was found to be more than 7% in macrocell corrosion environments with a difference in soluble chloride ion concentrations of not more than 2.4 kg/m<SUP>3</SUP>.</P>

무기성 PCM 혼합물에 의한 에너지저장용기재료의 방식특성

송희열,성현숙 건국대학교 산업기술연구원 2000 건국기술연구논문지 Vol.25 No.-

This is the experimental study on the effects of PCM (Phase Change Material) mixture and anti-corrosion additives on the metal for energy storage container. Aluminum, copper, steel, and SUS 304 were used as metal materials. Experiments were carried out at constant temperature above the melting point of the corresponding PCM submerging test metal specimens into the PCM mixture and anti-corrosion additives contained PCM mixture for 30 days. Aluminum showed the significant corrosion against all the PCM mixture and copper was not corroded against DSP only as the PCM mixture. Steel was corroded against GS with rust, ST with black color and not corroded against DSP, SA. SUS 304 seems to be corrosion-resistant material due to the anti-corrosiveness and no decrease of weight. Hexamethylene tetramine as anti-corrosion additive showed unsuitable anti-corrosion effects on aluminum against all the PCM mixture, but other additives showed suitable one against ST only, Mono quarternary ammonium chloride seems to be suitable additive for the anti-corrosion on copper against GS, DSP, SA and especially all the anti-corrosion effects on copper against DSP. N-methymorpholine and adipic acid showed insignificant anti-corrosion effects against PCM mixture except DSP and the other additives showed unsuitable anti-corrosion effects. All the anti-corrosion additives showed good anti-corrosion effects on SUS 304.

Magnesium Corrosion Mechanisms

Song, G. L.,Atrens, A. 한국부식방식학회 2002 Corrosion Science and Technology Vol.31 No.2

This paper provides an overview of the corrosion mechanisms of magnesium alloys based on our recent research and the literature. Magnesium is a very reactive metal. Thus galvanic cmosian is very important. Galvanic corrosion is associated with (1) impurities, particularly Fe, Ni & Cu (2) second phases, eg β, and (3) coupling with a less active metal. Magnesium alloys exposed without galvanic coupling have a corrosion resistance that, in general, is not as good as that of aluminium alloys. When magnesium is passive, then the corrosion rates are low. But the range of environmental conditions for passivity for magnesium is less than for aluminium; ie passive films are not very stable. Corrosion is typically important as localised corrosion such as pitting & SCC. There is the expectation that SCC failures will increase with increased use of Mg alloys in load bearing applications. Corrosion of AZ91 is by "pitting" in IN NaCI. The corrosion potential, Ecorr is above the "pitting" potential. Corrosion of cast AZ91 has the following morphologies, (1) preferential attack of primary α, (2) preferential attack of eutectic α & undermining of β. The β phase is more stable than α, and β is a better cathode. There is corrosion protection and low corrosion rates if there is a significant fraction of finely divided continuous β. Otherwise β accelerates corrosion. Corrosion acceleration is significant if there are large blocks of interconnected β. Corrosion acceleration may be small if β is small and finely divided.