Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： none
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： none
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The corrosion behaviour of low alloy steel containing Ni and Cu was studied because it is a promising candidate canister material for the disposal of high-level radioactive waste (HLW) in China. Due to the intensely radioactive nature of HLW, the waste has to be prevented from reaching the biosphere for many tens of thousands of years. Deep geological disposal is now considered to be the most preferable option for isolating HLW and it relies on series of natural and engineered barriers, e.g. a metallic canister. However, as soon as the waste package is settled, groundwater would seep back slowly through the outer barriers and ultimately arrive at the surface of the canister. Accordingly, there comes the groundwater-induced dissolution of the canister and subsequent transport of radionuclides through the barriers. That is to say, the effectiveness of radionuclide retention and isolation depends mostly and finally on the corrosion resistance of metallic canisters in deep groundwater environments. In this work, the test solution is deaerated 0.1 mol/L NaHCO3+0.1 mol/L NaCl, simulating the deep groundwater environment. The evolution of corrosion of NiCu low alloy steel in the test solution was investigated by electrochemical measurments. XRD was used to illustrate the composition of formed corrosion products. SEM was used to observe the electrode surface morphology and the cross section of the rust layer. The electrochemical results showed that low alloy steel has a lower corrosion rate and is less prone to localized corrosion than low carbon steel. In order to understand the mechanism of alloying elements, EDS and EPMA were used to analyse the distribution of alloying elements cross-sectional. XPS and E-pH diagram were used to estimate the possible existence form of alloying elements. By means of EDS and EPMA, it was founded that Ni is concentrated in the inner rust layer while the enrichment of Cu is not so obvious. XRD, XPS and E-pH results indicated that Ni and Cu are existed in the form of NiFe2O4 and CuFeO2 respectively.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO2 due to the development of industry, and the atmosphere therefore has been changed to coastal-industrial atmosphere. The corrosion behavior and mechanism of steels in coastal-industrial atmosphere with the co-existence of SO2 and Cl- are different from that in the coastal atmosphere containing only Cl- or the industrial atmosphere containing only SO2. In addition, pH value is diverse in different coastal-industrial atmosphere. However, there are only few researches on the effect of pH value on the corrosion evolution of steels in the coastal-industrial atmosphere. Almost all the atmospheric corrosion data of steels were obtained by the field exposure test, which could not reflect the dependence of the atmospheric corrosion evolution of steels on pH value due to the difficulties in controlling the field conditions. In this work, the effect of pH value on the corrosion evolution of Q235B steel in the simulated coastal-industrial atmospheres has been investigated by the dry/wet cyclic corrosion test (CCT), XRD and EIS. The results indicate that, when the content of SO2 is lower, changing pH value has no effect on the corrosion of the steel. When the content of SO2 is higher, the corrosion rate of Q235B steel influenced by changing pH value shows an extreme phenomenon, that is, when the pH value being a certain value between the "higher" and the "lower", the corrosion rate of Q235B steel reaches the maximum value. When the SO2 content is certain, changing pH value almost has no effect on the rust composition. To some extent, the existence of SO2 inhibits the formation of b-FeOOH. With the increasing of SO2 content, the relative contents of b-FeOOH and g-FeOOH are decreasing, and g-FeOOH maybe reduced back to Fe3O4 or transform to a-FeOOH. With the corrosion process prolongs, the rust evolution shows almost the same trend. In addition, when the content of SO2 in the simulated coastal-industrial atmosphere is lower, the Q235B steel mainly follows Cl- corrosion mechanism, and the influence of pH value on corrosion behavior of the steel is not obvious. When the content of SO2 is higher, the Q235B steel also follows Cl- corrosion mechanism in the early stage; with prolonging the dry/wet cyclic corrosion test number, H2SO4 regeneration mechanism accelerates corrosion of the steel as the effect of SO2 on corrosion increasing significantly.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： High level radioactive waste (HLW) is an extremely dangerous by-product of the global nuclear industry. Due to its intensely radioactive nature and ultra long half-life, HLW has to be safely managed and disposed for thousands of years, isolated from the biosphere. Deep geological repository (DGR) is considered to be the most feasible option worldwide because of its operability, stability, durability, environmental protection and so on. Basically, DGR relies on a multibarrier system and it consists of metallic canisters, backfill materials and a stable geologic formation. Since radionuclides could be moved into the biosphere by action of groundwater, both the geologic formation and backfill materials have to be of very low hydraulic permeability and metal canisters have to be corrosion resistant and prevent contact between the groundwater and the radioactive waste for as long as possible. Low carbon steel has been selected and studied as a candidate canister material in many countries because its long industrial experience, high-strength, low cost and it is less prone to localized corrosion than materials that passivity, but its larger corrosion rate may also set an insuperable barrier for the practical application. Recently, our studies revealed that NiCu low alloy steel is a more promising candidate for the canister material compared with the popular one, low carbon steel, since the former performs a more acceptable corrosion rate without increasing much cost and has better resistance to localized corrosion in environments with high concentration of Cl- . In this work, effects of SO42-, another ubiquitous species in deep groundwater, on the corrosion behavior of NiCu low alloy steel during immersion in simulated deep groundwater environments were investigated by in situ electrochemical measurements and surface analysis techniques. Results show that the addition of SO42- can promote the substrate dissolution during the initial stage of immersion. In the later stage, SO42- weakens the protectiveness of formed films and consequently, active dissolution prevails on the electrode surface rather than the prepassivation. Concentrated SO4 2- and HCO3 - can both promote the formation of Fe6(OH)12CO3. The main components of corrosion products are a-FeOOH, Fe3O4 and Fe6(OH)12CO3, and uniform corrosion is observed.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：在HCO3-浓度为0.08mol/L，不同浓度配比的SO42-和Cl-混合溶液中，用循环极化的电化学测试方法和扫描电子显微镜的观察手段，对Cu工作电极的循环极化行为和点蚀表面形貌进行了系统的研究。结果表明，SO42-和Cl-促进Cu的阳极溶解。Cl-降低Cu电极的腐蚀电位，增强其电化学活性。在点蚀敏感区域图中，Cu发生点蚀的临界Cl-浓度为0.02mol/L。当Cl-为低浓度时，SO42-对点蚀敏感性无影响。当Cl-为中浓度时，SO42-抑制点蚀。当Cl-为高浓度时，SO42-先提高后降低点蚀敏感性。无论SO42-浓度的高低，Cl-都能促进点蚀。蚀坑的自催化效应受阴离子影响较大。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：NiCu低合金钢是极具应用前景的高放废物地质处置罐的候选材料。本文对其在模拟深层地下水环境，即除氧0.1 mol/L NaHCO3 + 0.1 mol/L NaCl溶液中，原位监测NiCu低合金钢在长时间浸泡条件下的开路电位变化曲线及阻抗谱的演化，研究电极表面的腐蚀演化规律，并与相同条件下低碳钢的腐蚀行为进行比较。结果表明，NiCu低合金钢在本实验溶液中的耐蚀性要显著优于低碳钢，尤其是其耐局部腐蚀的能力。合金元素Ni富集在内锈层中，可能以NiFe2O4的形式存在，而合金元素Cu的富集不明显，可能的存在形式考虑为CuFeO2。
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