Michigan Technological University Chemists Develop Surface Analysis Technique to Monitor Early-Stage Iron Corrosion

Significance 

Corrosion is a natural process where metals are oxidized from exposure to humidity and oxidizing gases. Corrosion impacts industrial infrastructure affecting water quality and material degradation, due to the breakdown of metal protective coatings within municipal pipes leading to severe health hazards, as was observed in the Flint water crisis. Municipal water lines undergo corrosion from spontaneous electrochemical reactions and buildup layers of the inorganic scale on the surface. These scale films are produced from exposure to hard water, consisting of sulfates, carbonates, bicarbonates, and phosphates of calcium and magnesium. The growth of scale films on the internal walls acts as a physical barrier between aqueous solutions and the metal pipeline, preventing particulate dissolution into municipal water lines. However, there are still gaps into how the chemistry of these complex mixtures influences the mechanism of corrosion and scale formation.

The mechanism of corrosion begins with pitting of the surface with typically chloride ions, leading to breakdown of the native oxide surface layers, dissolution of the metal surface (acting as the anode), followed by metal oxidation, and results in the growth of inorganic mineral scale. The chemical composition of these minerals are influenced by the type of ions present in aqueous solutions and exposure to oxidizing gases, such as oxygen, water, and carbon dioxide. The presence of ions, particularly chloride, is known to accelerate or catalyze the corrosion, due to increased ionic strength affecting charge transfer in the redox reaction.

The objectives of this study were to measure how the cation affects the corrosion and oxidation of Fe interfaces to mineral films. A surface chemistry approach in three stages was used to investigate the surface mechanism and changes at the air/electrolyte/iron interface and in solution. These three stages are (1) the Fe surface in the electrolyte solution, (2) the air adsorption stage where the electrolyte solution is gradually removed to allow for exposure of the liquid/iron interface to atmospheric O2 and CO2, and (3) the oxidation stage, where the electrolyte was completely removed, allowing complete oxidation at the air/iron interface. We investigated two different chloride electrolytes, NaCl(aq) and CaCl2(aq), using PM-IRRAS to measure the interfacial oxidation and formation of minerals. The chemical compositions of the corrosion products on iron at the interfacial area and the region submerged in solution were compared using X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy.

Using a new technique, chemists at Michigan Technological University, successfully increased the detail of surface analysis during the beginning stages of corrosion. This breakthrough could transform how film growth and surface corrosion are managed, yield potential applications for monitoring air and water quality, and lead to new innovations for infrastructure maintenance. The team published its results in the Journal of Physical Chemistry A. In the right conditions, rust and corrosion can cause structural instability, environmental damage and contaminate air and water. Better data about mineral formation during the corrosion process will allow chemists to understand more about how to prevent and manage corrosion byproducts.

The authors wanted to measure and uncover chemical reactions in real environments. They have to use a high level of [surface] sensitivity in our analysis tools to get the right information back so they can really say what is the surface mechanism and how [iron] transforms. The research team investigated the surface chemistry when air, iron, solvents and water interact during the first stages of corrosion and measured byproduct output, learning more about how elements and variables impact the process. Understanding more about corrosion and mineral formation is key to managing infrastructure like bridges, tunnels and pipes and mitigating environmental concerns. This approach could result in new methods to expose sources of water pollution, reduce carbon dioxide emissions, increase infrastructure stability, and lessen environmental damage.

Michigan Technological University Chemists develop surface analysis technique to monitor early-stage iron corrosion - Advances in Engineering

About the author

Kathryn A. Perrine
Assistant Professor, Chemistry

The Perrine research group focuses on understanding reactions and processes at surfaces and interfaces, from pure metals, oxides, minerals to heterogeneous materials. We use a surface chemistry and surface science approach to connect molecular-level reactions at the gas/solid and liquid/solid interface. We also design meso- and nano-architectured materials using surface functionalization methods for next-generation heterogeneous catalysts and materials. Our aim is to understand the fundamental physical and chemical processes at interfaces to unravel surface mechanisms and transformations of materials, addressing challenges in catalysis and environmental science.

A variety of surface analysis instruments are utilized to understand surface chemistry, including vibrational spectroscopy, electron spectroscopies, mass spectrometry, scanning electron microscopy, and atomic force microscopy. Our program is multidisciplinary encompassing the fields of chemistry, physics, materials science, and engineering.

Reference

Chathura de Alwis, Mikhail Trought, Julia Lundeen, and Kathryn A. Perrine*. Effect of Cations on the Oxidation and Atmospheric Corrosion of Iron Interfaces to Minerals. J. Phys. Chem. A 2021, 125, 36, 8047–8063

Go To J. Phys. Chem.

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