Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion： an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones.Samples of ground Alloy 690 TT showed superior resistance to intergranular attack（IGA）.
To explore the usage of monolayer graphene as an anti-oxidation barrier in simulated primary water of pressurized water reactors（PWRs）,we transferred the monolayer graphene synthesized by low pressure chemical vapor deposition（LPCVD） on Cu foil to Alloy 690 TT.After a 500 h immersion,strong oxidation resistance was obtained from the graphene coated Alloy 690 TT sample,indicating that the transferred monolayer graphene can act as an effective barrier to protect the substrate from oxidation in simulated primary water of PWRs.
Hongliang MingSiyan WangZhiming ZhangJianqiu WangEn-Hou HanWei Ke
Initial corrosion kinetics of X52 anti-H2S pipeline steel exposed to 90 ℃/1.61 MPa H2S solutions was investigated through high temperature and high pressure immersion tests. Corrosion rates were obtained based on weight loss calculation. The corrosion products were analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and electron probe micro-analysis （EPMA）. The initial corrosion kinetics was found to obey the exponential law. With increasing immersion time, the main corrosion products changed from iron-rich mackinawite to sulfur-rich pyrrhotite. The corrosion films had two layers： an inner fine-grained layer rich in iron and an outer columnar-grained layer rich in sulfur. The corrosion film formed through the combination of outward diffusion of Fe2＋ ions and inward diffusion of HS^- ions. The variation of the corrosion products and compaction of the corrosion layer resulted in a decrease in the diffusion coefficient with increasing immersion time. The double-layered corrosion film formed after long time immersion acted as an effective barrier against diffusion.
Multilayer graphene as a potential anti-oxidation barrier to protect nickel foils from oxidation was studied in simulated primary water of pressurized water reactors （PWRs）. The results show that after immersion for 1000 h, the structure of the multilayer graphene remains unchanged and no obvious oxide film formed on the graphene coated nickel foils, indicating multilayer graphene can effectively act as the anti-oxidation barrier to protect the substrate from oxidation and hence can improve the heat transfer efficiency of the substrate in simulated primary water of PWRs.
Hongliang MingJianqiu WangZhiming ZhangSiyan WangEn-Hou HanWei Ke
The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves, electrochemical impedance spectra （EIS）, scanning electron microscopy （SEM）, X- ray photoelectron spectroscopy （XPS） and transmission electron microscopy （TEM）. The corrosion rate of Alloy 690 reaches a local maximum at 250℃. The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200-300 ℃. A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.
Jiazhen WangJianqiu WangHongliang MingZhiming ZhangEn-Hou Han
Effect of ethanolamine （ETA） on Alloy 690 in simulated pressurized water reactor （PWR） secondary cooling water was studied by electrochemical impedance spectroscopy （EIS）, potentiodynamic polarization, atomic force microscopy （AFM）, Fourier transform infrared spectroscopy-attenuated total reflectance （FTIR-ATR）, X-ray photoelectron spectrometer （XPS） and time of flight secondary ion mass spectrometry （ToF-SIMS）. The results show that moderate addition of ETA can enhance the corrosion resistance of Alloy 690 in high-temperature pressurized water and the optimum additive value is 2 mg/L. The addition of ETA contributes to the formation of oxide rather than hydroxide in the film on the surface of Alloy 690. The corrosion resistance of Alloy 690 at 320 ℃ with the addition of ETA is better than that at 280 ℃.
The influence of conductivity on corrosion behavior of 304 stainless steel （SS） in high temperature water was investigated by using in-situ potentiodynamic polarization curves, electrochemical impedance spectra （EIS） at 300 ℃, and ex-situ scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and X-ray pho- toelectron spectroscopy （XPS）. The structures of oxide films formed on 304 SS change with different conductivities at 300 ℃. With the increase in conductivity, the passive current density increases while the resistances of oxide films decrease. But the resistances do not decrease lineally with the increase in conductivity. A modified double-layer model for oxide structure was proposed to explain the influence mechanism of conductivity on the oxide films on 304 SS in high temperature water. Improving the 10B enrichment level can reduce the conductivity of primary water and increase the corrosion resistance of 304 SS.
In high-temperature and high-pressure water, traditional anticorrosion approaches are not suitable to be used to protect structural materials from oxidation and corrosion. In this study, monolayer graphene was explored as a barrier to protect the materials from degradation. The oxidation and corrosion rate of the monolayer-graphene-coated copper is much lower than that of the bare copper, suggesting that the monolayer graphene can effectively protect the copper from oxidation and corrosion in the simulated primary water of pressurized water reactors.
Hong-Liang MingSi-Yan WangZhi-Ming ZhangJian-Qiu WangEn-Hou HanWei Ke
