An insulator made from sulphur and selenium that has been developed as a material for flexible devices is also found to be highly effective as an anti-corrosion coating for steel. The material was developed by researchers at the US Rice University.
The material was developed by Pulickel Ajayan, a materials scientist at Rice University. The material insulates better than most other flexible materials and is also more flexible than most other dielectrics. This makes the material very suitable for use in electronics components in foldable phones, for example.
More applications
Along with other researchers, however, Ajayan was looking for more potential applications of the new material. They therefore started experimenting with the material. "Even before we first reported on the material, we were looking for more applications," says materials researcher Muhammad Rahman, principal investigator and assistant scientist in materials science and nanoengineering at the George R. Brown School of Engineering. "So we thought: let's put it in salt water and see what happens."
PhD student and one of the authors of the research paper M.A.S.R. Saadi: "In addition, we found that the viscoelastic coating is self-healing."
Applicable to infrastructure
The researchers conducted experiments at both Rice University and the South Dakota School of Mines and Technology. These showed that the material offers opportunities for infrastructure such as buildings, bridges and other steel objects that need to be protected from the elements, among others.
According to researchers, the sulphur-selenium combination contains the best properties of inorganic coatings such as zinc- and chromium-based alloys. These alloys offer protection against moisture and chlorine ions, but not against sulphur-reducing biofilms. These properties combine the material with properties of polymer-based coatings. These coatings protect steel under abiotic conditions, but are more susceptible to corrosion by microbes.
Month immersed in seawater
The material was subjected to several tests by the researchers. For instance, they placed a coating of the material on mild steel. This combination, like an untreated piece of mild steel, was immersed in seawater for a month. During this period, the coated steel was found to show no changes. The standard soft steel, however, was significantly corroded.
Sulphur-degrading bacteria can accelerate corrosion up to 90 times compared to abiotic materials. Samples with and without coating were exposed to plankton and biofilms for a period of 30 days as a test. On this basis, the researchers report that the coating offers an inhibition efficiency of 99.99%.
The researchers also compared their coating to commercially available coatings with a similar thickness of about 100 microns. The sulphur and selenium coating was also found to perform well in this area.
Self-healing ability
Finally, the self-healing ability of the material was tested by cutting a film in two and placing the two heroes side by side on a heat plate. The separated parts bonded back together over a period of about two minutes. In the process, the material was heated to about 70 degrees Celsius and could be folded in a similar way to the original film. Small holes in the material closed in about 15 minutes if the material was heated to 130 degrees Celsius.
"If you attack the alloy, it recovers," says Rahman. "If it needs to recover quickly, we support this using heat. But over time, even the thickest samples heal on their own." In this regard, Rahman points out that it remains to be investigated whether thin layers of about 100 microns can also heal without assistance.
Possibly also applicable to electronics
The applications of the coating are presumably not limited to infrastructure. "The first target is structures. However, we are aware that the electronics industry also faces the same corrosion problems," says Ajayan. "There are opportunities."
Author: Wouter Hoeffnagel
Source photo: Pixabay / Free-Photos
