Illustration by: Giulio D’Acunto, Lund University
Two-dimensional materials can be used as a coating to protect copper from corrosion. A recent study conducted at beamline HIPPIE shows that the onset of corrosion can be delayed from room temperature up to more than 120 degrees centigrade using graphene or hexagonal boron nitride. The different properties of the two 2D materials are reflected in the mechanism of oxidation at the critical temperature.
Copper is widely used in our society in everything from water pipes and electronic circuits to the Statue of Liberty. It is, however, a material prone to corrosion which degrades its properties over time. 2D materials have attracted a lot of scientific interest as a coating to protect the metal. The researchers studied the coated copper in an oxygen-rich environment that would accelerate oxidation.
“In our experiment, we could investigate in real-time the protective action of two-dimensional barriers towards the high-temperature corrosion of copper in an oxidising environment,” Mattia Scardamaglia, researcher at MAX IV said. “We discovered that graphene and hexagonal boron-nitride can keep the copper in the metallic state, without degradation, up to high temperature. Unprotected copper starts oxidising already at room temperature.”
Understanding the mechanism is important, as it shows any possible additional effects of the coating on for example conductivity. A certain controlled amount of oxide can also in some cases be desirable. The two coatings tested have very different material properties to start with.
“Graphene is semi-metallic while hexagonal boron nitride is an insulator. It turns out the mechanism of oxidation-protection is also different,” Scardamaglia explained. “The case of hexagonal boron nitride on copper is more straightforward – the hot copper surface is screened from oxygen very well and this prevents fast oxidation of copper. In the case of graphene on copper, oxygen starts to creep in beneath the graphene flakes and slower copper oxidation to Cu2O begins as an undercover reaction.”
The researchers used the Ambient Pressure X-ray Photoelectron Spectroscopy setup at beamline HIPPIE for their experiments. This cleverly engineered method allows for studies of surface reactions at higher gas pressures than is usually possible with X-rays.
“The experiment clearly highlights the benefit of APXPS for the study of the interfaces between real materials in realistic environments mimicking true working conditions,” said Scardamaglia. “HIPPIE is unique in terms of high photon flux, control over the sample’s environment and the electron energy analyser available there. The high photon flux together with a state-of-the-art analyser is essential to measure XPS spectra in a millibar range of gas.”
The future prospects of these types of coatings are vast.
“APXPS is a newly developed technique and the field of corrosion-protection is still largely unexplored. There are plenty of different materials and environmental conditions to be investigated with common air pollutants such as nitrogen oxides and carbon monoxides,” Scardamaglia concluded. “Furthermore, graphene has revealed to be an interesting playground where undercover reactions can happen and this opens the way to many different possible experiments involving chemical reaction in a confined environment.”
Mattia Scardamaglia, Virginia Boix, Giulio D’Acunto, Claudia Struzzi, Nicolas Reckinger, Xin Chen, Abhay Shivayogimath, Tim Booth, Jan Knudsen, Comparative study of copper oxidation protection with graphene and hexagonal boron nitride, Carbon 171, 610–617 (January 2021), DOI: 10.1016/j.carbon.2020.09.021