The nanoworld of corrosion

Feb 09, 2006
The nanoworld of corrosion
Structural model of the ultrathin passivation layer resulting from the fit to the X-ray diffraction data. Au atoms are represented by yellow spheres, and Cu atoms by red spheres. The ABC stacking of the substrate is inverted in the single crystalline overlayer. The two topmost layers are only partially occupied. A schematic view of the in situ X-ray diffraction cell is included.

The effect of corrosion has an impact on about 3% of the world's Gross Domestic Product. From a positive point of view, however, chemical attack of metal surfaces may result into surface nano-structures with very interesting technological applications such as catalysts and sensors. Therefore, a better understanding of corrosion processes is required to both prevent it and make the most of it.

Scientists from Germany and the European Synchrotron Radiation Facility (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 authors publish their results in Nature this week.

The nanoworld of corrosion
Ex situ atomic force microscope image (1 µm x1 µm) after applying a potential of 450 mV versus Ag/AgCl; in this potential regime the formation of 2–3 nm-thick pure Au islands was observed in the X-ray diffraction experiments, which is a typical corrugation of the surface.

Researchers from Max Planck Institute, the University of Ulm (Germany), and the ESRF used the European synchrotron light source to reproduce in situ the onset of the corrosive process in a gold-copper alloy. Gold is a very noble metal, which doesn't corrode, whilst copper is less noble and, thus, more prone to chemical attack. 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: "Understanding and controlling the formation of the first layer and the nano-islands may help to produce nano-materials with specific properties", explains Jorg Zegenhagen, one of the authors of the paper.

In order to carry out these experiments, researchers placed the samples in an electrochemical cell filled with sulphuric acid, in which voltage can be applied, and monitored the early corrosion process. "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, first author of the paper.

These new insights can be applied to a variety of different alloys used in corrosive environments and to materials that can exploit such degradation to form porous metals of technological interest. Although understanding the process of corrosion in gold-copper alloy has only become possible now, the process itself is many centuries old. Ancient Incas metal-smiths stretched their supplies of precious gold by mixing it with copper, and then surrounding the alloy with salty substances. This created an acidic environment that dissolved the copper from the top layer, leaving a gold-rich surface ready for polishing.

Source: European Synchrotron Radiation Facility

Explore further: Simulations provide new insight into emerging nanoelectronic device

add to favorites email to friend print save as pdf

Related Stories

Evolving robot brains

3 hours ago

Researchers are using the principles of Darwinian evolution to develop robot brains that can navigate mazes, identify and catch falling objects, and work as a group to determine in which order they should ...

Facebook fends off telecom firms' complaints

3 hours ago

Facebook founder Mark Zuckerberg fended off complaints on Monday that the hugely popular social network was getting a free ride out of telecom operators who host its service on smartphones.

Scientists find clues to cancer drug failure

3 hours ago

Cancer patients fear the possibility that one day their cells might start rendering many different chemotherapy regimens ineffective. This phenomenon, called multidrug resistance, leads to tumors that defy ...

Glass coating improves battery performance

3 hours ago

Lithium-sulfur batteries have been a hot topic in battery research because of their ability to produce up to 10 times more energy than conventional batteries, which means they hold great promise for applications ...

Recommended for you

Graphene meets heat waves

26 minutes ago

EPFL researchers have shed new light on the fundamental mechanisms of heat dissipation in graphene and other two-dimensional materials. They have shown that heat can propagate as a wave over very long distances. ...

When temperature goes quantum

4 hours ago

A UA-led collaboration of physicists and chemists has discovered that temperature behaves in strange and unexpected ways in graphene, a material that has scientists sizzling with excitement about its potential ...

Buckybomb shows potential power of nanoscale explosives

Mar 05, 2015

(Phys.org)—Scientists have simulated the explosion of a modified buckminsterfullerene molecule (C60), better known as a buckyball, and shown that the reaction produces a tremendous increase in temperatur ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.