Corrosion Behavior of Weathering Steel Under Thin Electrolyte Layer at Different Relative Humidity
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JMEPEG (2018) 27:202–218 https://doi.org/10.1007/s11665-017-3101-0
Corrosion Behavior of Weathering Steel Under Thin Electrolyte Layer at Different Relative Humidity Yan Xia, Pan Liu, Jianqing Zhang, and Fahe Cao (Submitted July 11, 2017; in revised form October 29, 2017; published online December 18, 2017) The corrosion behavior of weathering steel under thin electrolyte layer (TEL) at different relative humidity (RH) was investigated by cathodic polarization, electrochemical impedance spectroscopy, electrochemical noise, SEM/EDS, XRD and Raman spectroscopy. The results indicate that during the initial stage, the corrosion rate increases as the RH decreases when the initial thickness of TEL is above 100 lm. During the middle and final corrosion stages, the corrosion behavior of weathering steel is influenced by RH, the initial thickness of TEL and corrosion product. The TEL corrosion is divided into three types, and a weathering steel corrosion model under TEL and bulk solution is also proposed. Keywords
EIS, electrochemical noise, relative humidity, thin electrolyte layer, weathering steel
1. Introduction Weathering steels are extensively used for their effective corrosion resistance to various atmospheric and environmental factors. It is well known that the enhanced corrosion resistance of weathering steel results from the formation of protective rust layer (Ref 1-3). The rust layer formed on weathering steel under atmospheric corrosion has been investigated since 1970s (Ref 1-7), and it is considered that the rust layer composed of various forms of FeOOH, such as a-FeOOH, b-FeOOH, cFeOOH, spinel type oxide and additional amorphous corrosion product. The atmospheric corrosion occurs generally according to the following reactions (Ref 8, 9). In the initial stage, the anodic and cathodic reactions of corrosion system are: Fe ! Fe2þ þ 2e
ðEq 1Þ
O2 þ 2H2 O þ 4e ! 4OH
ðEq 2Þ
Fe(OH)2 formed by the combination of the product of above reactions is extremely instable and oxidized by oxygen easily: 4FeðOHÞ2 þO2 ! 4FeOOH þ 2H2 O
ðEq 3Þ
When the supplement of oxygen is insufficient, the cathodic reaction is Fe2þ þ 8c FeOOH þ 2e ! 3Fe3 O4 þ 4H2 O
ðEq 4Þ
Yan Xia, China State Key Laboratory of Silicon Materials, Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, PeopleÕs Republic of China; and Department of Chemistry, Zhejiang University, Hangzhou 310027, PeopleÕs Republic of China; and Pan Liu, Jianqing Zhang, and Fahe Cao, Department of Chemistry, Zhejiang University, Hangzhou 310027, PeopleÕs Republic of China. Contact e-mail: [email protected].
202—Volume 27(1) January 2018
And Fe3O4 can be further oxidized by O2 2Fe3 O4 þ 1=2O2 ! 3c Fe2 O3
ðEq 5Þ
4Fe3 O4 þ O2 þ 6H2 O ! 12c FeOOH
ðEq 6Þ
It has been demonstrated that the rust layer is composed of loose outer layer and compact inner layer (Ref 10, 11) and both of the structure and composition of rust layer are determined by the
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