Simulations show that iron catalyzes corrosion in ‘inert’ carbon dioxide

Rusting iron can be its own worst enemy

Iron (blue) can react with trace amounts of water to produce corrosive chemicals despite being bathed in “inert” supercritical fluids of carbon dioxide. Atomic simulations performed at Rice University show how this reaction occurs. Credit: Evgeni Penev / Rice University

Iron rusting in water should theoretically not corrode in contact with an “inert” supercritical fluid of carbon dioxide. But it does.

The cause has so far eluded materials researchers, but a team at Rice University has a theory that could contribute to new strategies to protect iron from the environment.

Materials theorist Boris Yakobson and his colleagues at Rice’s George R. Brown School of Engineering found through atomic level simulations that iron itself plays a role in its own corrosion when exposed to supercritical CO2.2 (sCO2) and trace amounts of water by promoting the formation of reactive species in the fluid that return to attack it.

In their research, published in the journal Cell Press Fabric, they conclude that thin hydrophobic layers of 2D materials such as graphene or hexagonal boron nitride could be used as a barrier between iron atoms and the reactive elements of sCO2.

Rice graduate student Qin-Kun Li and researcher Alex Kutana are co-lead authors of the paper. Rice Assistant Research Professor Evgeni Penev is a co-author.

Supercritical fluids are materials at a temperature and a pressure that keep them roughly between phases – for example, not all liquid, but not yet all gas. The properties of sCO2 makes it an ideal working fluid because, according to the researchers, it is “essentially inert”, non-corrosive and inexpensive.

“Eliminating corrosion is a constant challenge, and it’s on the minds of many people right now as the government prepares to invest heavily in infrastructure,” said Yakobson, professor of materials science and nanotechnology at Karl F. Hasselmann and professor of chemistry. “Iron is a pillar of infrastructure from ancient times, but only now are we able to gain an atomistic understanding of how it corrodes.”

The rice lab’s simulations reveal the devil’s details. Previous studies have attributed corrosion to the presence of bulk water and other contaminants in the supernatant, but this is not necessarily the case, Yakobson said.

“Water as the primary impurity in sCO2, provides a hydrogen bonding network to trigger CO interface reactions2 and other impurities such as nitrous oxide and to form corrosive acid to the detriment of iron, “Li said.

The simulations also showed that the iron itself acts as a catalyst and lowers the reaction energy barriers at the iron-sCO interface2, which ultimately leads to the formation of a host of corrosive species: oxygen, hydroxide, carboxylic acid and nitric acid.

For the researchers, the study illustrates the strength of theoretical modeling to solve complicated chemistry problems, in this case predicting thermodynamic reactions and estimates of corrosion rates at the iron-sCO interface2. They also showed that all bets are off if there is more than one trace of water in the superfluid, accelerating corrosion.


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More information:
Qin-Kun Li et al., Iron corrosion in the “inert” supercritical CO2, ab initio dynamic insight: How impurities matter, Fabric (2022). DOI: 10.1016 / j.matt.2021.12.019

Provided by Rice University

Citation: Simulations show that iron catalyzes corrosion in ‘inert’ carbon dioxide (2022, January 21) retrieved January 22, 2022 from https://phys.org/news/2022-01-simulations-iron-catalyzes-corrosion-inert. html

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