The wonderful nanoworld of corrosion
Do you know that chemical corrosion affects about 3% of the world's gross domestic product? But this impact is not exclusively negative. European researchers have studied the nanoworld of corrosion and found that "chemical attack of metal surfaces may result into surface nano-structures with very interesting technological applications." They also observe for the first time corrosion of a gold-copper alloy at the atomic level. Their discoveries could be applied to other alloys used in corrosive environments or to a better understanding of the formation of porous metals.
Here is the introduction of this European Synchrotron Radiation Facility (ESRF) news release.
Scientists from the Max Planck Institute, the University of Ulm (Germany), and the ESRF have highlighted a self-organization process on the surface of a metal alloy, which is of crucial importance in determining the response to corrosion of this material.
In fact, this study, providing a structural description with atomic-scale resolution thanks to the X-rays from the ESRF synchrotron, unvealed the chemical composition and structure of a protective surface layer which hinders further corrosion.
The researchers concentrated their efforts on a gold-copper alloy because these two metals are quite different: one is noble and doesn't corrode while the other one is common and easily attacked.
At the first moments of corrosion, the copper-gold alloy develops a mechanism to protect itself with an extremely thin gold-rich layer. This layer has an unexpected crystalline and well-ordered structure. When the corrosion process proceeds, this alloy layer transforms into gold nano-islands of 20 to 1.5 nanometres. These islands eventually develop into a porous gold metal layer, which may have technological applications
"We found a vast amount of detail on structural evolution and chemical information by combining detailed 3D analysis of the structure with additional anomalous scattering experiments before more severe corrosion happened", explains Frank Renner of ESRF.
Now here are some of illustrations about the experiments done by the researchers. First is an image of the "structural model of the ultrathin passivation layer resulting from the fit to the X-ray diffraction data" (Credit: ESFR).
And here is an "ex situ atomic force microscope (AFM) image (1 µm x1 µm) after applying a potential of 450 mV versus Ag/AgCl" (Credit: ESFR).
This research work has been published by Nature under the title "Initial corrosion observed on the atomic scale" (Volume 439, Number 7077, Pages 707-710, February 9, 2006). Here are two links to the abstract and to the Editor's summary. Here is an intriguing excerpt of it.
Among other structural insights, their work reveals the formation of a thin layer involved in passivation, a previously rather mysterious mechanism by which the surface of the material is rendered inactive.
And if you want even more information, you'll find other illustrations in the Figures and Tables section of the Nature article.
And where will this research lead to? Probably to nanomaterials with specific properties, such as alloys used in corrosive environments.
Sources: European Synchrotron Radiation Facility news release, via EurekAlert!, February 9, 2006; and various web sites
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