Evolution of Akaganeite in Rust Layers Formed on Steel Submitted to Wet/Dry Cyclic Tests.

Haigang Xiao,Yuantai Ma,Ying Li,Xiaoping Song,Wei Ye

doi:10.3390/ma10111262

Haigang Xiao, Yuantai Ma + Show 3 more

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https://doi.org/10.3390/ma10111262

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Abstract

The evolution of akaganeite in rust layers strongly impacts the atmospheric corrosion behavior of steel during long-term exposure; however, the factors affecting the evolution of akaganeite and its mechanism of formation are vague. In this work, wet-dry cyclic corrosion tests were conducted to simulate long-term exposure. Quantitative X-ray diffraction analysis was employed to analyze variations in the relative amounts of akaganeite; scanning electron microscopy and electron probe microanalysis were used to study the migration of relevant elements in the rust layer, which could help elucidate the mechanism of akaganeite evolution. The results indicate that the fraction of akaganeite tends to decrease as the corrosion process proceeded, which is a result of the decrease in the amount of soluble chloride available and the ability of the thick rust layer to block the migration of relevant ions. This work also explores the location of akaganeite formation within the rust layer.

Highlights

Atmospheric corrosion products that form on carbon steel are composed mainly of ferric oxyhydroxides, such as goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH) and magnetite (Fe3 O4 ), and amorphous rust [1,2,3]
Sodium chloride was detected in the rust powderregardless when theof sample experienced
When there was a constant amount of salt deposited, the decline in the relative akaganeite content could be attributed to the decrease in the number of soluble chloride ions available

Summary

Introduction

Atmospheric corrosion products that form on carbon steel are composed mainly of ferric oxyhydroxides, such as goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH) and magnetite (Fe3 O4 ), and amorphous rust [1,2,3]. With a prolonged exposure time, a rust layer will experience numerous wet-dry cycles, and the corrosion products will be converted into one another during these cycles. The protective ability of a rust layer varies as the number of wet-dry cycles changes. Among all of these constituents, the presence of akaganeite in rust is considered an important cause of the severe corrosion observed in marine atmospheres [7]. Understanding the evolution of akaganeite in the rust layer during repeated wet-dry cycles would help advance our ability to interpret and predict corrosion performance in specific environments, and it may suggest a method for protection against corrosion

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