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pourbaix diagrams to decipher precipitation conditions of Si-Fe-Mn-oxyhydroxides at the PACMANUS hydrothermal field

Acta Oceanologica Sinica 2014年第12期33卷 58-66页

作者： YANG Baoju ZENG Zhigang WANG Xiaoyuan YIN Xuebo CHEN Shuai Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of Sciences University of Chinese Academy of Sciences

Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-Mn-H2O pourbaix diagrams were constructed at 300℃and 25℃. Thepourbaix diagrams show that the main Si, Fe and Mn oxides species precipitating from the hydrothermal fluid were SiO2, Fe（OH）3, Fe3（OH）8, Mn3O4, and Mn2O3at 25℃. During mixing of hydrothermal fluid with seawater, SiO2 precipitated earlier than Fe-Mn-oxyhydroxides because of the lower stability boundary. Then Fe（OH）2 precipitated first, followed by Fe3（OH）8 and Fe（OH）3, and last, small amounts of Mn3O4 and Mn2O3 precipitated. Fe（OH）3was readily de-posited in alkaline solution with little influence by Eh. There were many Si-Fe-Mn-concentric particles in the polished sections of the massive precipitates collected from PACMANUS. In the concentric nucleus and ellipsoid, Si oxides precipitated first before the hydrothermal fluid had mixed with seawater. In the concen-tric nucleus, after the precipitation of Si oxides, the increase of pH and Eh promoted the precipitation of Mn oxides around the Si oxides. In the large ellipsoid, the precipitation of Fe was divided into two periods. In the early period, increase of pH value of hydrothermal fluid produced by low-temperature convection and an input of a small volume of seawater promoted a small amount of Fe（OH）3 to precipitate in the Si-rich core. In the late period, after complete mixing with seawater and the resultant fluid was close to neutral or slightly alkaline in pH, Fe（OH）3was easily precipitated from the solution and distributed around the Si-rich core.

关键词： Si-Fe-Mn-oxyhydroxides PACMANUS hydrothermal field pourbaix diagrams

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Efficient prediction of corrosion behavior in ternary Ni-based alloy systems:Theoretical calculations and experimental verification

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Journal of Materials Science & Technology 2023年第36期167卷 94-106页

作者： Xuelian Xiao Keke Chang Kai Xu Ming Lou Liping Wang Qunji Xue Key Laboratory of Marine Materials and Related Technologies Zhejiang Key Laboratory of Marine Materials and Protective TechnologiesNingbo Institute of Materials Technology and EngineeringChinese Academy of SciencesNingbo 315201China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China

pourbaix diagrams are calculated to describe electrochemical processes for alloys in aqueous solution.With the multi-component differentiation of alloy systems,the construction of pourbaix diagrams is fac-ing challenges,especially for non-single-phase alloy systems.In this study,the simultaneous construction of phase diagrams and pourbaix diagrams were implemented for predicting the evolution of the phases in the immune and passive regions.The CALPHAD(CALculation of PHAse Diagram)approach was used to quickly access the Gibbs free energies of various phases and the chemical potential of the elements in the phases from the thermodynamic database of the Ni-Si-Al-Y system.The corrosion behavior of two typical Ni-Al-Si and Ni-Al-Y systems was investigated.Si and Y were added to Ni-based alloys to produce the solid solutions L12-Ni_(3)(Al,Si)and L12-Ni_(3)Al+Ni_(5)Y,respectively.Calculations showed that NiO and Al_(2)O_(3)make up the passive area of the Ni_(3)Al 1 alloy.The introduction of SiO_(2)and Y(OH)3 in the passive region separately helped to minimize the alloys’susceptibility to corrosion.However,Si reduced the thermody-namical possibility of NiO for mation in the passive film,and the addition of Y caused extreme galvanic corrosion.Experiments on Ni-based alloys validated the results through electrochemical corrosion.It was also discovered that the presence of Ni_(5)Y produced galvanic corrosion and that Si reduced the oxide in the passive film,causing pitting corrosion.The corrosion prediction of the quaternary alloys indicates that the solid solution of Si in Ni_(5)Y reduces the galvanic corrosion effect and the dissolution of passive film.The current work demonstrates that phase diagrams and pourbaix diagrams may be efficiently and accurately predicted using a well-constructed thermodynamic database,which has major implications for future studies on the corrosion behavior of multi-component alloys.

关键词： pourbaix diagrams CALPHAD Ni-based alloys Passive film

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