Tailoring oxidation resistance of Super304H by controlling Mn content

Ha, Heon-Young,Lee, Chang-Geun,Jang, Min-Ho,Kang, Jun-Yun,Young Park, Jun,Lee, Tae-Ho,Hong, Hyun-Uk Elsevier 2019 Corrosion science Vol.146 No.-

<P><B>Abstract</B></P> <P>The effects of Mn on oxidation resistance of Fe-18Cr-8.5Ni-3.5Cu-0.5Nb-0.1C-0.1 N-(0.08–2.05 wt%)Mn alloys were investigated by isothermal oxidation in ambient air at 700 °C for up to 8 weeks. The Mn addition up to 0.44 wt% increased the oxidation resistance, but further addition decreased it, thus the best oxidation resistance was obtained in the alloy with 0.44 wt% Mn. Mn promoted the internal oxidation and changed the Mn and Cr concentrations of the inner oxide layer. The best oxidation resistance of the alloy with 0.44 wt% Mn was attributed to the improved protectiveness of the inner oxide layer having the highest Cr content.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of Mn (0–2 wt%) on oxidation resistance of Super304H were examined. </LI> <LI> Addition of Mn up to 0.44 wt% increased the oxidation resistance. </LI> <LI> Further addition of Mn up to 2.05 wt% accelerated the oxidation. </LI> <LI> The best oxidation resistance was obtained in the alloy with 0.44 wt% Mn. </LI> <LI> Alloying Mn changed Mn and Cr contents of the internal oxide layer. </LI> </UL> </P>

Chromium Speciation in Cr(III) Oxidation by Mn-Oxides: Relation to the Oxidation Mechanism

정종배,Chung, Jong-Bae 한국응용생명화학회 1998 Applied Biological Chemistry (Appl Biol Chem) Vol.41 No.1

크롬의 산화는 자연계에 존재하는 여러 가지의 Mn-oxide에 의해 일어나며 산화과정에 존재하는 크롬 화학종들은 반응계 내에서 흡착, 침전 현상을 유발할 수 있고 결과적으로 산화반응을 조절할 수 있을 것이다. 본 연구에서는 birnessite와 pyrolusite에 의한 크롬의 산화에서 크롬 화학종이 반응에 미치는 영향을 조사하였다 Mn-oxide는 그 종류에 따라 크롬 산화력에서 큰 차이를 보였으며 용액의 pH와 초기 3가 크롬 첨가량도 산화반응에 큰 영향을 미쳤다. 동일 표면적당의 산화력을 비교하면 pyrolusite의 산화력은 birnessite의 5% 정도에 불과하였다. 이는 pyrolusite 의 결정도에 크게 기인하며 또한 양으로 하전된 표면 특성 때문에 반응물인 3가 크롬의 접근이 어렵고 반응산물인 6가 크롬의 흡착 등에 기인하는 것으로 보인다. Birnessite에 의한 산화반응에서 pH 3에서는 oxide의 표면에서의 크롬 화학종들의 흡착이나 침전 현상은 발견되지 않았으며 pyrolusite의 경우 일부 6가 크롬의 흡착이 나타났으나 침전현상은 발견되지 않았다. 따라서 pH 3의 경우 산화반응은 Mn-oxide의 특성에 따라 결정된다. Mn-oxide에 의한 크롬의 산화는 열역학적으로 용액의 pH가 높아질수록 더 진행되어야 한다. Birnessite의 경우 pH 5에서 오히려 산화반응이 현저히 저해되었는데 이는 birnessite의 표면에 형성되는 3가 크롬의 침전이 반응표면을 감소시킴으로써 나타나는 현상으로 판단된다. Pyrolusite의 경우 pH 3보다 pH 5에서 크롬의 산화는 더 일어나나 초기 3가 크롬의 첨가량이 많아지면서 반응이 억제된다. 일부 3가와 6가 크롬의 흡착이 일어나나 이 경우도 역시 pyrolusite의 표면에 형성되는 3가 크롬의 침전이 반응을 조절하는 주 요인으로 생각된다. Mn-oxide의 표면에 형성되는 3가 크롬의 침전은 산화가 일어날 수 있는 반응표면을 감소시키고 또한 반응물의 농도를 낮춤으로써 용액의 pH가 높고 3가 크롬의 첨가량이 많아질 때 크롬의 산화반응을 억제하는 주 요인이 되는 것으로 판단된다. Various Mn-oxides can oxidize Cr(III) to Cr(VI). Behaviors of chromium species in the oxidation system, especially on the oxide surface, are expected to control the reaction. During Cr(III) oxidation by birnessite and pyrolusite, Cr species in the reaction system were determined to elucidate their effects on the oxidation. Capacities of Cr oxidation of the two Mn-oxides were quite different. Solution pH and initial Cr(III) concentration also had significant effects on the Cr(III) oxidation by Mn-oxides. Chromium oxidation by pyrolusite was less than 5% of the oxidation by birnessite. The high crystallinity of pyrolusite could be one of the reasons and the difficulty of Cr (III) diffusion to the positive pyrolusite surface and Cr(VI) and Cr(III) adsorption seems to be other controlling factors. At pH 3, adsorption or precipitation of Cr species on the surface of birnessite were not found. Small amount of Cr(VI) adsorption was found on the surface of pyrolusite, but arty Cr precipitation on the oxide surface was not found. Therefore Cr(III) oxidation at pH 3 seems to be controlled mainly by the characteristics of Mn-oxides. Chromiun oxidation by Mn-oxides is thermodynamically more favorable at higher solution pH. However as solution pH increased Cr oxidation by birnessite was significantly inhibited. For Cr oxidation by pyrolusite, as pH increased the oxidation increased, but as Cr(III) addition increased the reaction was inhibited. Under these conditions some unidentified fraction of Cr species was found and this fraction is considered to be Cr(III) precipitation an the oxide surface. Chromium(III) precipitation on the oxide surface seems to play an important role in limiting Cr(III) oxidation by armoring the reaction surface on Mn-oxides as well as lowering Cr(III) concentration available for the oxidation reaction.

Fe-22%Cr-5.8%Al 합금의 고온 산화 거동

김송이(Song-Yi Kim),최성환(Sung-Hwan Choi),윤중열(Jung-Yeul Yun),공영민(Young-Min Kong),김병기(Byoung-Kee Kim),이기안(Kee-Ahn Lee) 한국표면공학회 2011 한국표면공학회지 Vol.44 No.1

This study investigated the high temperature oxidation behavior of Fe-22%Cr-5.8%Al alloy and the oxidation kinetics of the alloy were discussed. Bulk samples were prepared by VAM (vacuum arc melting) and hot forging. High temperature oxidation testes were isothermally conducted up to 100 hours in 79%N₂+ 21%O₂ environment at three different temperatures (900℃, 1000℃, 1100℃). The weight gain was measured after oxidation according to oxidation time (2, 4, 6, 8, 10, 15, 20, 25, 30, 60, 80, 100 hours). The weight gain significantly increased with increasing oxidation temperature. As the temperature increased, the oxidized samples showed sequential formation of Al₂O₃, Cr-rich oxide, Fe-rich oxide. The activation energy of high temperature oxidation was obtained as 306.63 KJ/㏖. Al₂O₃ were developed on the surface in the early stage of oxidation, representing protective role of oxidation. However, Fe-based and Cr-based oxides leaded to breakaway of oxide layer, thus resulted in the significant increase of additional oxidation.

Ni-Cr-Co-Al-Mo-Ti-Re-Ta-W-Ru 단결정의 대기중 1000 o C에서의 산화

한준희,XIAO XIAO,이동복 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.4

Three kinds of Ni-based single crystals with the compositions of 63.8Ni-7.5Cr-5.1Co-4.8Al-1.9Mo- 0.9Ti-3Re-11.8Ta-1.2W, 61.4Ni-7.4Cr-5Co-4.8Al-1.8Mo-0.9Ti-3.1Re-11.6Ta-4W, and 60.9Ni-7.5Cr-5Co-4.8Al- 2Mo-1Ti-2.9Re-10.9Ta-1.2W-3.8Ru, in wt%, were cast in a Bridgman furnace. In the cast alloys, Cr, Co, Re, Mo, W, and Ru became microsegregated in dendrites consisting of γ-Ni, while Ni, Ta, and Al microsegregated in interdendrites consisting of eutectic γ/γ . The cast alloys were oxidized at 1000 o C up to 275 h in air to study the effect of alloying elements on high-temperature oxidation. The oxide scales consisted primarily of CrTaO4, with some NiCr2O4, NiO, and α-Al2O3. The oxidation resistance was dependent on the formation and continuity of the α-Al2O3 scale. Ta and W were beneficial, while Ru was harmful in improving the oxidation resistance. The selective oxidation of Al in dendrites led to the formation of thin, uniform α-Al2O3 scales, i.e., uniform oxidation. The competitive oxidation of active elements such as Al, Ti, and Ta in interdendrites led to the formation of porous, crack-susceptible oxide nodules, i.e., nodular oxidation. Less active elements such as Ru, Re, Ni, Co, Mo, W, and Cr tended to enrich in the vicinity of the oxide nodules. The oxidation progressed through the outward diffusion of cations and the inward diffusion of oxygen. This inward diffusion formed internal alumina islands, beneath the oxide scale.

Oxidation behaviour of an Alloy 617 in very high-temperature air and helium environments

Jang, C.,Lee, D.,Kim, D. Applied Science Publishers ; Elsevier Science Ltd 2008 The International journal of pressure vessels and Vol.85 No.6

The oxidation characteristics of Alloy 617, a candidate structural material for the key components in the very high-temperature gas-cooled reactor (VHTR), were investigated. High-temperature oxidation tests were conducted at 900 and 1100<SUP>o</SUP>C in air and helium environments and the results were analysed. Alloy 617 showed parabolic oxidation behaviour at 900<SUP>o</SUP>C, but unstable oxidation behaviour at 1100<SUP>o</SUP>C, even in a low oxygen-containing helium environment. The SEM micrographs also revealed that the surface oxides became unstable and non-continuous as the temperature or the exposure time increased. According to the elemental analysis, Cr-rich oxides were formed on the surface and Al-rich discrete internal oxides were formed below the surface oxide layer. After 100h in 1100<SUP>o</SUP>C air, the Cr-rich surface oxide became unstable and non-continuous, and the matrix elements like Ni and Co were exposed and oxidized. Depletion of grain boundary carbides as well as matrix carbides was observed during the oxidation in both environments. When tensile loading was applied during high-temperature oxidation, the thickness of the surface oxide layer, the internal oxidation, and decarburization were enhanced because of the increase in diffusion of oxidizing agent and gaseous reaction products. Such enhancement would have detrimental effects on the high-temperature mechanical properties, especially the creep resistance of Alloy 617 for the VHTR application.

Oxidation of Fe-(5.3-29.8)%Mn-(1.1-1.9)%Al-0.45%C Alloys at 550-650 oC

Soon Yong Park,Xiao Xiao,Min Ji Kim,Geun Taek Lee,Dae Ho Hwang,Young Ho Woo,Dong-BokLee 한국부식방식학회 2022 Corrosion Science and Technology Vol.21 No.1

Alloys of Fe-(5.3-29.8)%Mn-(1.1-1.9)%Al-(0.4-0.5)%C were oxidized at 550 oC to 650 oC for 20 h to understand effects of alloying elements on oxidation. Their oxidation resistance increased with increasing Mn level to a small extent. Their oxidation kinetics changed from parabolic to linear when Mn content was decreased and temperature was increasing. Oxide scales primarily consisted of Fe2O3, Mn2O3, and MnFe2O4 without any protective Al-bearing oxides. During oxidation, Fe, Mn, and a lesser amount of Al diffused outward, while oxygen diffused inward to form internal oxides. Both oxide scales and internal oxides consisted of Fe, Mn, and a small amount of Al. The oxidation of Mn and carbon transformed γ-matrix to α-matrix in the subscale. The oxidation led to the formation of relatively thick oxide scales due to inherently inferior oxidation resistance of alloys and the formation of voids and cracks due to evaporation of manganese, decarburization, and outward diffusion of cations across oxides.

Long-time Oxidation of Ti3(Al,Si)C2 Carbides at 400-800 oC

한준희,박상환,이동복 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.3

Quarternay carbides of Ti3AlxSi1-xC2 (x=0.3, 0.5, and 0.7) were oxidized at 400, 600, and 800 °C for 0.5-6 months in order to study their long-time oxidation behavior in air. When they were oxidized at 400- 600 oC for 0.5-3 months, oxidation proceeded relatively slowly with moderate weight gains. However, further oxidation at 400-600 oC for 6 months resulted in the oxidation-induced microcracking of oxide scales due to large volume expansion and large stress induced owing to the formation of Al2O3, SiO2. TiO3, and TiO2 in oxide scales. However, at 800 oC, microcracking of oxide scales, which could lead to pulverization of Ti3AlxSi1-xC2, did not occur due to stress relaxation in oxide scales. Instead, at 800 oC, Ti3AlxSi1-xC2 oxidized rapidly to form thick, somewhat porous oxide scales, which consisted primarily of an outer TiO2 layer with some Al2O3, an intermediate Al2O3 layer with some TiO2, and an inner TiO2 layer with some (SiO2+Al2O3). The overall longtime oxidation resistance of Ti3AlxSi1-xC2 at 400-800 °C was considered to be poor. Factors that determined the oxidation rates of Ti3AlxSi1-xC2 were; (1) How fast titanium oxidized to semi-protective titanium oxides, (2) How fast Al and Si oxidized to Al2O3 and SiO2 barrier oxides, and (3) Whether oxidation-induced microcracking occurred in oxide scales or not. The ratio of Al/Si in Ti3AlxSi1-xC2 and the matrix grain size were apparently not dominant factors, because the basic oxidation mode of Ti3Al0.3Si0.7C2, Ti3Al0.5Si0.5C2, and Ti3Al0.7Si0.3C2 was similar under the identical oxidation condition.

Pseudotsuga menziesii의 Monoterpenoid가 질화작용에 미치는 효과

김종희,Jean H. Langenheim 한국생태학회 1994 Journal of Ecology and Environment Vol.17 No.3

Nitrification potential bioassay and terpenoid analyses were performed to determine the roles of terpenoid as an inhibitor of nitrification in the Douglas fir (Pseudotsuga menziesii) forests. The effect of terpenoids in the forest floor was also tested by adding $10{\mu}g/ml$ of four terpenoids(${\alpha}-pinene,{\beta}-pinene,{\gamma}-terpinene, and terpinolene) to mineral soils. The amount of terpenoids in the litter was higher than that in the soil and varied over time, but the amount of terpenoids in the soils was relatively constant. The correlation between the amount of terpenoids in the litter and ammonium oxidation was in inverse proportion to that in the mineral layers $(r^2=0.678)$. Inhibition of ammonium oxidation by terpenoids in the litter was always higher than in the mineral layer, but nitrite oxidation was different from the ammonium oxidation. The fact that there was greater nitrate production from ammonium in the mineral layer than in the forest floor layer seems to be due to the less amounts of terpenoids in the mineral layer. The result of the experiment in which four terpenoids were added to the mineral layer suggests that, after some lag time, the four terpenoids were effective in inhibiting ammonium oxidation. However, nitrite oxidation did not appear to be affected by the four terpenoids. Accordingly, all of our results suggested that terpenoids in Douglas fir forests apparently would act as a part of the inhibitors of nitrification. Pseudotsuga menziesii 임상에서 질화작용의 억제제로서의 monoterpenoids의 역할을 연구하고자 토양에서의 질화작용과 식물체잎, 낙엽 및 무기토양에서의 monoterpenoids의 함량을 분석하였다. Pseudotsuga menziesii잎이나 임상에서 분석된 monoterpenoids는 대략 16종 이었으며, 그 중 ${\alpha}$-pinene, ${\beta}$-pinene, ${\gamma}$-terpinene 그리고 terpenolene이 대표적인 것들이었다. 임상에 있는 monoterpenoids의 양은 무기토양층에 비해 항상 많았으며, 계절적 변이가 있었으나 토양층은 항상 일정하였다. 질화작용 과정 중 ammonium oxidation 과정은 낙엽층이 보다 더 많은 저해를 받았으나, nitrite oxidation 과정은 두층별간 별 차이가 없었다. 또한 4가지 monoterpenoids(${\alpha}$-pinene, ${\beta}$-pinene, ${\gamma}$-terpinene, terpenolene)를 인위적으로 첨가한 토양에서의 질화작용에 역시 am-monium oxidation 과정은 심히 저해를 받는 반면 nitrite oxidation 과정은 저해를 받지 않는 것으로 나타났다. 이 같은 모든 결과들은 Pseudotsuga menziesii 임상에 있는 monoterpenoids의 영향으로 질화작용에 관여하는 미생물, 특히 Nitrosomonas europaes의 증식이 억제되어 am-monium oxidation 과정이 저해되었음을 시사한다.

Passivation performance improvement of ultrathin ALD-Al₂O₃ film by chemical oxidation

Cha, Hamchorom,Chang, Hyo Sik Elsevier 2018 Vacuum Vol.149 No.-

<P><B>Abstract</B></P> <P>We investigated the passivation performance improvement of ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> tunnel oxide by chemical oxidation. The thickness of the Al<SUB>2</SUB>O<SUB>3</SUB> tunnel oxide deposited by atomic layer deposition (ALD) was about 1 nm. The surface treatment was prepared as a function of chemical-oxidation time before ALD-Al<SUB>2</SUB>O<SUB>3</SUB> growth. The Al<SUB>2</SUB>O<SUB>3</SUB> films on surface-treated wafers showed improved passivation performance compared with the Al<SUB>2</SUB>O<SUB>3</SUB> films on untreated wafers. The electrical characteristics showed that the surface-treated films, due to their enhanced initial ALD growth, enabled a low-interface-state defect and high film quality. In terms of tunneling and passivation performance, the optimal time of chemical oxidation was 2.5 min. The values of open-circuit voltage and carrier lifetime for the passivated tunnel oxide under this surface condition were 645 mV and 1 ms, respectively. A 1 nm ALD-Al<SUB>2</SUB>O<SUB>3</SUB> films on surface treatment are applicable for passivated tunnel oxide.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Passivation performance improvement of ultrathin Al<SUB>2</SUB>O<SUB>3</SUB> film by chemical oxidation. </LI> <LI> Passivation performance was strongly dependent on the chemical oxidation time. </LI> <LI> Optimal of chemical oxidation time for the tunnel-oxide ALD-Al<SUB>2</SUB>O<SUB>3</SUB> was 2.5 min. </LI> <LI> Chemical oxidation of 1-nm-thick Al<SUB>2</SUB>O<SUB>3</SUB> film is useful for passivated-tunnel oxide. </LI> </UL> </P>

Suggesting Simplified Reactions for Pyrite and Copper(I) Oxidation to Predict Corrosion Environments in Deep Geological Repository

Nakkyu Chae,Samuel Park,Seungjin Seo,Richard I. Foster,Shuang Liu,Sungyeol Choi 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Chemical environments of near-field (Engineered barrier and surrounded host rock) can influence performance of a deep geological repository. The chemical environments of near-field change as time evolves eventually reaching a steady state. During the construction of a deep geological repository, O2 will be introduced to the deep geological repository. The O2 can cause corrosion of Cu canisters, and it is important predicting remaining O2 concentration in the near-field. The remaining O2 concentration in the near field can be governed by the following two reactions: oxidation of Cu(I) from oxidation of Cu and oxidation of pyrite in bentonite and backfill materials. These oxidation reactions (Cu(I) and pyrite oxidation) can influence the performance of the deep geological repository in two ways; the first way is consuming oxidizing agents (O2) and the second way is the changing pH in the near-field and ultimately influencing on the mass transport rate of radionuclides from spent nuclear fuel (failure of canisters) to out of the engineered barrier. Hence, it is very important to know the evolution of chemical environments of near-field by the oxidation of pyrite and Cu. However, the oxidation kinetics of pyrite and Cu are different in the order of 1E7 which means the overall kinetics cannot be fully considered in the deep geological repository. Therefore, it is important to develop a simplified Cu and pyrite oxidation kinetics model based on deep geological repository conditions. Herein, eight oxidation reactions for the chemical species Cu(I) were considered to extract a simplified kinetic equation. Also, a simplified kinetics equation was used for pyrite oxidation. For future analysis, simplified chemical reactions should be combined with a Multiphysics Cu corrosion model to predict the overall lifetime of Cu canisters.