Repassivation Of Steel Research Articles

Corrosion and Contamination of 316L Stainless Steel in Simulated HNO3-Based Spent Nuclear Fuel Reprocessing Environments with Cesium and Strontium

Austenitic 316L stainless steel is usually used as the structural material in spent fuel reprocessing facilities. However, the contamination of fission products from spent fuel (especially Cs and Sr) on the surface of facilities will greatly affect its safe decommissioning. In this study, for the first time, with the combination of characterizations of electrochemistry and laser-induced breakdown spectroscopy with two channels, the corrosion and contamination of 316L stainless steel were analyzed in simulated reprocessing environments with HNO3 concentrations of 3, 6, 8, and 12 M HNO3 containing Cs and Sr for 7, 14, 21, 30, and 60 days, respectively. The stability order of the passive film of 316L stainless steel in various environments was 12 M HNO3 > 8 M HNO3 > 3 M HNO3 > 6 M HNO3. Combined with other characterization methods, a mechanism was proposed. It was found that SrCO3, in the matrix, was the main contaminant in the initial 7 days in all environments due to a large number of holes. Then, the dissolution of contaminated steel surface led to the decrease of contaminant, and recontamination occurred after the repassivation of steel. These findings have significant implications for the development and selection of decontamination technology for the contaminated facilities made of 316L stainless steel.

Corrosion behavior of welded joints in ozonated acidic solution

The corrosion-electrochemical behavior of welded joints of steels and alloys, used as instrumental for organic synthesis processes in the presence of ozone was investigated. It was determined that welded joints in ozonated media are characterized by the increase in anodic current densities in the whole range of potentials and the shift of Е cor more negatively compared with the base metal that is associated with the decrease in active centers, on which ozone can be reduced. In ozone synthesis conditions, the alloy 06ХН28НДТ can be recommended as a structural material for reactors manufacture. In the ozone oxidation processes, it is necessary to pay attention to welded joints, especially for stainless steels such as 18-10 as wide cathodic loop formation on polarization curves indicates their tendency to intergranular corrosion (IGC). Corrosion can also proceed in dangerous areas of pitting formation and repassivation of steels under the ozone action. Welded joints of ferritic stainless steels 08Х17Т show the tendency to IGC in periodical ozone syntheses that precludes the possibility of using welding sets or requires protection of joint.

철근 부식 방식을 위한 굳지 않은/굳은 콘크리트의 전기방식 적용에 관한 연구

본 연구에서는 전기방식 종류에 따른 문헌 고찰 및 굳지 않은/굳은 상태의 콘크리트에 대해 전기방식 적용 시 방식 효과와 관련하여 연구를 실시하였다. 굳은 콘크리트의 경우 우선적으로 철근의 부동태피막 파괴를 유도하기 위하여 NaCl을 혼입한 후, 2주일동안 250, 500, $750mA/m^2$ 의 방식전류를 통전하였다. 그 후 부동태피막 복원화와 염소 이온 추출에 대해서 정량화를 실시하였다. 동시에, 굳지 않는 상태의 콘크리트에 대해서는 굳은 상태와 동일한 양의 방식전류를 타설 직후부터 동일한 기간동안 통전하여 전기방식을 실시하였다. 후광산란(Backscattered electron; BSE) 이미지를 이용하여 철근-콘크리트 계면을 관찰하였으며, 염소이온 확산에 대해서 염소이온 이동 속도와 철근 부식 저항성에 대한 콘크리트의 성질 변화에 대해 측정하였다. 결과적으로 보면, 전기 방식은 부동태피막 복원화에 매우 효육적이며, 콘크리트 내의 염소이온 중 63-73% 정도가 추출되는 것으로 확인 되었다. 굳지 않는 상태의 콘크리트에 전기방식을 적용할 경우, 철근 표면에서 $Ca(OH)_2$ 층이 조밀하게 되어 철근 부식 저항성이 향상되었다. 다만, 방식 전류에 따라 콘크리트 표면 염화물량이 증가하는 경향이 나타나는 것을 확인 할 수 있다. 【In this study, the inhibitive effect of electrochemical treatment subjected to fresh and hardened concrete and literature reviews in terms of the treatment were performed. In hardened concrete, chloride ions are mixed during casting to destroy the passivity of steel, and then the current was provided for 2 weeks with 250, 500 and $750mA/m^2$ . After completion of electrochemical treatment, the extraction of chloride ions was quantified and repassivation of steel was observed. Simultaneously, the equated levels of current density for 2 weeks were applied to fresh concrete. Steel-concrete interface in concrete was observed by BSE image analysis and the concrete properties in terms of the diffusivity of chloride ions and the resistance of steel corrosion was measured. As the result, electrochemical treatment is very effectiveness to rehabilitate the passive film on the steel surface and 63-73% of chloride ions in concrete were extracted by the treatment. As the treatment was applied to fresh concrete, the resistance of steel corrosion was improved due to the densification of $Ca(OH)_2$ layers in the vicinity of steel. However, an increase in the current density resulted in an increase in surface chloride content of concrete.】

Repassivation of steel in carbonated concrete induced by cathodic protection

AbstractThe paper discusses the peculiarities of cathodic protection applied to steel in carbonated concrete, which are strictly connected to the production of alkalinity at the steel surface. Results of a research on the application of cathodic protection to specimens with steel bars in carbonated concrete are discussed. A thin layer of concrete was realkalized within a period of 4–5 months by applying a current density of 10 mA/m2 and steel could repassivate even in the presence of small contents of chlorides. A lower current density of 5 mA/m2 could only maintain steel passive when the concrete in the vicinity of the steel had been previously realkalized through the application of a start‐up current density of 70 mA/m2 for one month. Protection mechanisms are investigated and design of cathodic protection of steel in carbonated concrete is outlined. The possibility of obtaining protection on deeper rebars is also considered.

Evaluation of steel/primer based on chestnut tannin/paint film systems by EIS

The influence of a tannin pretreatment applied to slightly rusted steel panels on the anticorrosive performance of alkyd paint systems has been investigated using electrochemical impedance spectroscopy (EIS) and open circuit potential measurements. From EIS and corrosion potential data analysis it was found that (1) there is not a significant influence of the tannin pretreatment on the anticorrosive protection level, which depends particularly on the barrier effect afforded by the applied paint system (however, as the corrosion process starts, tannins may cause the repassivation of steel); (2) the enhancement of the protection level afforded by the tannin primer was restricted to short immersion periods and corrosive media that were not very aggressive; and (3) water uptake was not significantly affected by the presence of the tannin primer.