Despite being bathed in supercritical fluids of carbon dioxide, iron can react with trace amounts of water to produce corrosive chemicals. This reaction is shown in atomistic simulations at Rice University. Credit: Rice University.
Iron that rusts in water should not be in contact with a supercritical fluid of carbon dioxide. It does.
A team at Rice University has a theory that could contribute to new strategies to protect iron from the environment.
Boris Yakobson and his colleagues at Rice's George R. Brown School of Engineering found that iron's role in the formation of reactive species was due to its exposure to supercritical CO2 and trace amounts of water.
In their research, published in the Cell Press journal Matter, they conclude that thin hydrophobic layers of 2D materials like graphene or hexagonal boron nitride could be used as a barrier between iron atoms and the reactive elements of sCO2.
The paper is co-authored by a graduate student and a research scientist. The Rice assistant research professor is a co-author.
Supercritical fluids are materials at a temperature and pressure that keep them between phases. According to the researchers, sCO2 is an ideal working fluid because of its low cost and noncorrosive properties.
As the government prepares to invest heavily in infrastructure, it's on a lot of people's minds as to how to eliminate corrosion. "Iron is a pillar of infrastructure from ancient times, but only now are we able to get an atomistic understanding of how it corrodes."
The devil's in the details are revealed in the simulations. The presence of bulk water and other contaminants in the superfluid isn't necessarily the reason for the increase in corrosion.
Li said that water is the primary impurity in sCO2 and that it provides a hydrogen bond network to cause interfacial reactions with CO2 and other impurities.
The simulations showed that the iron itself acts as a catalyst, lowering the reaction energy barriers at the interface between iron and sCO2, ultimately leading to the formation of a host of corrosive species.
The study shows the power of theoretical modeling to solve complicated chemistry problems, in this case predicting thermodynamic reactions and estimates of sCO2 rates at the interface between iron and sCO2. All bets are off if there is more than a trace of water in the superfluid.
Initio dynamics insights: How impurities matter, was written by Qin-Kun Li and his colleagues. Thematt is a journal.
The journal has information about Matter.
Simulations show that iron oxidizes carbon dioxide.
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