Posted on the Electrochemical Society Blog on September 22, 2017 by Amanda Staller
A new device has given scientists a nanoscale glimpse of crevice and pitting corrosion as it happens.
Corrosion affects almost everything made of metal—cars, boats, underground pipes, and even the fillings in your teeth.
It carries a steep price tag—trillions of dollars annually—not mention, the potential safety, environmental, and health hazards it poses.
“Corrosion has been a major problem for a very long time,” says Jacob Israelachvili, a chemical engineering professor at the University of California, Santa Barbara.
Particularly in confined spaces—thin gaps between machine parts, the contact area between hardware and metal plate, behind seals and under gaskets, seams where two surfaces meet—close observation of such electrochemical dissolution had been an enormous challenge. But, not any more.
Using a device called the Surface Forces Apparatus (SFA), Israelachvili and colleagues were able to get a real-time look at the process of corrosion on confined surfaces.
“With the SFA, we can accurately determine the thickness of our metal film of interest and follow the development over time as corrosion proceeds,” says project scientist Kai Kristiansen.
The researchers’ setup also allowed them to have control of the salt composition of the solution, and temperature, as well as the electric potential of the nickel surface.
Crevice and pitting corrosion isn’t the kind of widespread surface rusting you may see on the hulls of old ships exposed to the ocean. Instead, they are intense, localized attacks, where visible decay can look deceptively minor.
In fact, things appear just fine until they fail catastrophically: machines break apart, bridges buckle, seafaring ship engines malfunction, dental fillings fall out.
For the new study, that appears in the Proceedings of the National Academy of Sciences, researchers studied a nickel film against a mica surface. They focused on the initiation of corrosion—the point at which the metal surface begins to dissolve.
The degradation of the material didn’t occur in a homogenous fashion. Rather, certain areas—locations where there were likely microscale cracks and other surface defects—would experience intense local corrosion resulting in the sudden appearance of pits.