Computer Models Reveal Chloride’s Role in Corrosion

Surface structural changes to iron passive films caused by the adsorption of OH and/or Cl. (a) Fe(OH)3, (b) Fe(OH)2Cl, (c) Fe(OH)Cl2, (d) FeCl3. The location of the edge Fe atom prior to the adsorption is shown with an orange dashed line. Atoms types indicated by white (H), royal blue (Cl), large pink (Fe) and small red (O) spheres. Image courtesy of OSU College of Engineering.

A research team from Oregon State University’s (OSU) College of Engineering (Corvallis, Oregon, USA) recently conducted a study that used supercomputer simulations to monitor the corrosive effects of chloride on various materials, including structural steels. The results of the study were published inMaterials Degradation, a Nature partner journal.

The detailed models used in the study were produced by high-performance computers at the San Diego Supercomputer Center (SDSC) at the University of California (UC) San Diego (San Diego, California, USA) and the Texas Advanced Computing Center (TACC) at the University of Texas at Austin (Austin, Texas, USA). Through this study, the researchers gained new insights into the effects of chloride induced corrosion on structural metals, including economic and environmental impacts.

“Steels are the most widely used structural metals in the world and their corrosion has severe economic, environmental, and social implications,” says Burkan Isgor, an OSU civil and construction engineering professor and co-author of the study. “Understanding the process of how protective passive films break down helps us custom design effective alloys and corrosion inhibitors that can increase the service life of structures that are exposed to chloride attacks.”

Along with Isgor, the research team included OSU School of Engineering professor Líney Árnadóttir, as well as graduate students Hossein DorMohammadi and Qin Pang. Árnadóttir’s chemical engineering work often uses computational methods to study chemical processes on surfaces with applications in materials degradation.

“We frequently collaborate with experimental groups and use experimental surface science tools to complement our computational methods,” says Árnadóttir. “For this study we relied on allocations from the National Science Foundation’s (NSF) Extreme Science and Engineering Discovery Environment (XSEDE) so that we could use Comet and Stampede2 to combine different computational analyses and experiments applying fundamental physics and chemistry approaches to an applied problem with potentially great societal impact.”

Using a method called density functional theory (DFT), the OSU team investigated the structural, magnetic, and electronic properties of the molecules involved. Their simulations were also corroborated by others using reactive molecular dynamics (Reax-FF MD), which enabled the OSU team to accurately model the chemistry-based nanoscale processes that lead to chloride-induced breakdown of iron passive films.

“Modeling degradation of oxide films in complex environments is computationally very expensive, and can be impractical even on a small local cluster,” says Isgor. “Not only do Comet and Stampede2 make it possible to work on more complex, more realistic, and industrially relevant problems, but also these high-performance computers let us do so within a reasonable timeframe, moving knowledge forward.”

Source: UC San Diego News Center, https://ucsdnews.ucsd.ed.