Trace quantities of water can cause a reaction at the interface between iron and the fluid, prompting the formation of corrosive chemicals.
FREMONT, CA: The iron that rusts in water should theoretically not corrode when it comes into contact with an "inert" supercritical carbon dioxide fluid. However, it does. Materials experts have yet to figure out why, but a team from Rice University has a notion that could help develop new techniques to protect the iron from rust.
Theorists discovered through atom-level simulations that when the iron is exposed to supercritical CO2 (sCO2) and trace amounts of water, it promotes the formation of reactive species in the fluid that return to attack it. The research concluded that Thin hydrophobic layers of 2D materials like graphene or hexagonal boron nitride might be used as a barrier between iron atoms and the reactive constituents of sCO2.
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Supercritical fluids are materials kept between phases at a temperature and pressure roughly between liquid and gas. According to the researchers, the qualities of sCO2 make it a perfect working fluid because it is "basically inert," noncorrosive, and low-cost. As the dominant impurity in sCO2, water forms a hydrogen bond network that triggers interfacial interactions with CO2 and other pollutants like nitrous oxide, comprising corrosive acid that is harmful to iron.
The simulations also revealed that iron functions as a catalyst, decreasing the reaction energy barriers at the iron-sCO2 interface, resulting in various corrosive species such as oxygen, hydroxide, carboxylic acid, and nitrous acid.
According to the researchers, the work demonstrates the power of theoretical modelling to handle complex chemical problems, such as forecasting thermodynamic reactions and corrosion rates at the interface between iron and sCO2. They also demonstrated that traces of water in the superfluid could speed up the corrosion process.
Through UT-Battelle LLC, the research was funded by the US Department of Energy's Fossil Energy Program, Branch of Crosscutting R&D and Systems Integration.
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