Nanotextured Surface Boosts Corrosion Resistance of Stainless Steel

An untreated SS sample (right) and a sample (left) that was electrochemically treated to create a nanotextured surface. Photo by Rob Felt, Georgia Tech University.

Using an electrochemical etching process, researchers at Georgia Tech University (Atlanta, Georgia, USA) created a nanotextured surface on a Type 316L (UNS S31603) stainless steel (SS) alloy that could improve its corrosion resistance.

The researchers initially sought to create a superhydrophobic SS surface to repel liquids and bacteria. But it became clear that a superhydrophobic surface required the use of a coating. Researchers then proposed an alternative that employed a nanotextured surface to control bacterial adhesion.

They experimented with varying levels of voltage and current flow in an electrochemical process that applied current to the SS surface submerged in a nitric acid (HNO3) etching solution. The current moved electrons from the metal surface into the electrolyte, thereby altering its texture. Typically, these processes polish SS, but the researchers used it to roughen the surface.

“Under the right conditions, you can create a nanotexture on the grain surface structure,” says Dennis Hess, a professor and Thomas C. DeLoach, Jr. Chair at the Georgia Tech School of Chemical and Biomolecular Engineering. “This texturing process increases the surface segregation of chromium and molybdenum and thus enhances corrosion resistance, which is what differentiates stainless steel from conventional steel.”

Microscopic examinations showed protrusions 20 to 25 nm above the surface. Researchers believe the protrusions allowed the treated surface to interact with bacterial cell membranes, which killed the bacteria. Because the process appears to rely on a biophysical rather than chemical process, the bacteria shouldn’t be able to develop resistance to it.

Source: Georgia Tech University, www.gatech.edu