MTU Studies Early-Stage Rust Surface Chemistry

MONDAY, DECEMBER 13, 2021


Researchers at the Michigan Technological University recently announced that they have developed a more precise method to observe early-stage iron mineral corrosion like rust with water and oxygen.

The study, “Effect of Cations on the Oxidation and Atmospheric Corrosion of Iron Interfaces to Minerals,” was recently published in The Journal of Physical Chemistry A. Researchers hope that a better understanding of this process will aid with carbon dioxide capture, uncover polluted water systems and improve infrastructure for structures like bridges and pipes.

According to MTU, the case’s main finding is that cation in solution, like positively charged sodium or calcium ions, influences the type of carbonate films grown when exposed to air. With gradual exposure to oxygen and carbon dioxide, the carbonate films produced are specific to the cation, and different shapes and morphologies of iron hydroxides are exposed without gradual air exposure, not specific to the cation.

The Research Process

The MTU team, which focuses on surface chemistry, was lead by Assistant Professor of Chemistry Kathryn Perrine.

Rust typically consists of iron oxides and iron hydroxides, but corrosion can lead to iron carbonate and other mineral formation. Different environments and variables can cause corrosion, so the study wanted to better understand the conditions to prevent or grow it.

Perrine said environmental issues, like the Flint Water Crisis, are an example of how something simple like rust can cause more complicated, unwanted results.

“We want to measure and uncover chemical reactions in real environments,” Perrine said. “We have to use a high level of [surface] sensitivity in our analysis tools to get the right information back so we can really say what is the surface mechanism and how [iron] transforms.”

The new technique is a three-stage process, assessing changes to the electrolyte composition and using oxygen and carbon dioxide from air as a reactant, to observe real-time formation of the different minerals like rust observed at the air-liquid-solid interface.

When exposed to electrolyte solutions, the polished iron formed iron carbonate and calcium carbonate films when also exposed to oxygen and a heterogeneous mixture of platelets. To analyze the process, the research team used four surface-sensitive techniques:

  • Polarized modulated-infrared-reflection-absorption spectroscopy (PM-IRRAS);
  • Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy;
  • X-ray photoelectron spectroscopy (XPS); and
  • Atomic force microscopy (AFM). 

“The spectroscopy tells us the chemistry; the microscopy tells us the physical changes,” Perrine said. “It’s really difficult to [image] these corrosion experiments [in real-time with AFM] because the surface is constantly changing, and the solution is changing during corrosion.”

In a video recorded by the lab, corrosion is shown on the surfaces over time. Perrine added that since iron is abundant in environmental systems, slowing down and closely observing mineral formation comes down to adjusting the variables in how it transforms in different solutions and exposure to air.

“We can watch the corrosion and film growth as a function of time. The calcium chloride [solution] tends to corrode the surface faster, because we have more chloride ions, but also has a faster rate of carbonate formation,” Perrine said.

   

Tagged categories: Asia Pacific; Colleges and Universities; Corrosion; EMEA (Europe, Middle East and Africa); Latin America; Microscopy; North America; Program/Project Management; Research; Research and development; Rust; Z-Continents

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