Corrosion-Resistant Coating Sets a New Benchmark

A sulfur and selenium insulator designed for flexible devices has found a new purpose as an anticorrosive coating for steel. The compound, developed by Pulickel Ajayan, a materials scientist at Rice University's materials laboratory, proved to have greater dielectric (insulating) properties than most flexible materials and greater flexibility than most dielectrics, making it a good candidate for electronic components like foldable mobile phones.

At the same time, it prompted the material's creators to think: What else can it do?

Materials scientist Muhammed Rahman, lead researcher and assistant research professor of materials science and nanoengineering at George R. Brown School, said, "Even before we reported the material for the first time, we were looking for more applications. We said, let's put it in salt water and see what happens." M.A.S.R. Saadi, a Rice graduate student and co-author, noted, "Beyond all that, we saw that the viscoelastic coating self-heals." The results of experiments at Rice and at South Dakota School of Mines and Technology, published in Advanced Materials, could be a boon for infrastructure—buildings, bridges and anything made of steel over or under water—that requires protection from the elements. The researchers noted that the sulfur-selenium compound combines the best properties of inorganic coatings like zinc and chromium-based compounds with polymer-based coatings that block moisture and chloride ions but are susceptible to microbially induced corrosion, while protecting steel against sulfate-reducing biofilms and abiotic conditions. In the material's initial test, researchers coated small mild steel plates with the sulfur-selenium alloy and exposed both to seawater for one month alongside an uncoated steel piece as a control. The coated steel showed no color change or other alteration, but the bare steel corroded significantly. The coating proved highly resistant to oxidation when submerged. To test against sulfate-reducing bacteria, known to accelerate corrosion 90 times faster than abiotic attackers, coated and uncoated samples were exposed to plankton and biofilms for 30 days. The researchers calculated a "barrier efficiency" of 99.99% for the coating. The brass compound also performed well when compared to commercial coatings of similar thickness, approximately 100 microns, and adhered easily to steel while fending off attackers. Finally, they tested the alloy's self-healing properties by splitting a film in two and placing the pieces side by side on a hot plate. The separated pieces reattached into a single film in approximately 2 minutes when heated to about 70 degrees Celsius (158 degrees Fahrenheit) and were as flexible as the original film. Pinhole defects were healed by heating at 130°C (266°F) for 15 minutes. Subsequent tests with the healed alloys proved their ability to protect both the coating itself and steel. Rahman said, "When you press on the alloy, it heals. If it needs to heal quickly, we help with heat. But over time, most thicker samples will self-correct." He said the laboratory still needs to test whether thin layers of approximately 100 microns can heal without assistance. The laboratory is modifying the material for steel varieties and investigating coating techniques. Ajayan said, "The initial target is structures, but we're aware that the electronics industry faces some problems related to corrosion. There are opportunities." Other co-authors of the paper include Sandhya Susarla, a Rice graduate now a postdoctoral researcher at Lawrence Berkeley National Laboratory, and Govind Chilkoor, a technology engineer, and Jawahar Kalimuthu, a research scientist, both from South Dakota School of Mines and Technology. Co-authors include Rice graduates Yufei Cui and Thierry Tsafack, postdoctoral researchers Anand Puthirath and Soumyabrata Roy, graduate students Samuel Castro Pardo and Morgan Barnes, and Rafael Verduzco, professor of chemistry and biomolecular engineering and materials science and nanoengineering; Pawan Sigdel and Bharat Jasthi from South Dakota School of Mines and Technology; Taib Arif, Parambath Sudeep, Aly Hassan and Tobin Filleter from University of Toronto; Leiqing Hu and Haiqing Lin from State University of New York at Buffalo; Md Golam Kibria from University of Calgary; and Santiago Solares from George Washington University. Lead co-investigators are Nikhil Koratkar from Rensselaer Polytechnic Institute and Venkataramana Gadhamshetty from South Dakota School of Mines and Technology. Ajayan is Benjamin M. and Mary Greenwood Anderson Professor of Engineering and professor of materials science and nanoengineering, chemistry and biomolecular engineering. The National Science Foundation (1454102, 1849206, 1920954) and NASA (NNX16AQ98A) supported the research. Source: Materials provided by Rice University. Journal Reference: Sandhya Susarla, Govinda Chilkoor, Jawahar R. Kalimuthu, M. A. S. R. Saadi, Yufei Cui, Taib Arif, Thierry Tsafack, Anand B. Puthirath, Pawan Sigdel, Bharat Jasthi, Parambath M. Sudeep, Leiqing Hu, Aly Hassan, Samuel Castro‐Pardo, Morgan Barnes, Soumyabrata Roy, Rafael Verduzco, Md Golam Kibria, Tobin Filleter, Haiqing Lin, Santiago D. Solares, Nikhil Koratkar, Venkataramana Gadhamshetty, Muhammad M. Rahman, Pulickel M. Ajayan. Corrosion Resistance of Sulfur–Selenium Alloy Coatings. Advanced Materials, 2021; 2104467 DOI: 10.1002/adma.202104467 Rice University. "Anticorrosion coating sets new benchmark: Engineers develop flexible, self-healing material to protect steel from the elements." ScienceDaily. www.sciencedaily.com/releases/2021/10/211018172217.htm (accessed 4 January 2022).