November 25th, 2021
Researchers at Rice University in Houston, TX, have recently developed an anticorrosive and self-healing coating for steel. The National Science Foundation and N.A.S.A supported the research.
The development stems from research conducted by Pulickel Ajayan, a scientist at the Rice lab of materials, who created a compound composed of sulphur and selenium, which was shown to be more insulating than most flexible materials and more flexible than most dielectrics.
“Even before we reported on the material for the first time, we were looking for more applications,” said materials scientist Muhammad Rahman, principal investigator on the study and an assistant research professor of materials science and nanoengineering in the George R. Brown School of Engineering. “So we thought, let’s put it in saltwater and see what happens.”
The experiment, published in Advanced Materials, was joint researched between Rice and the South Dakota School of Mines and Technology.
The lightweight sulphur-selenium alloy “combines properties of inorganic coatings like zinc- and chromium-based compounds that bar moisture and chlorine ions but not sulphate-reducing biofilms, and polymer-based coatings that protect steel under abiotic conditions but are susceptible to microbe-induced corrosion.”
The lab also exposed these samples to plankton and biofilms for thirty days, simulating sulphate-reducing bacteria that accelerate corrosion. The inhibition efficiency for the coating was calculated as 99.99 percent.
According to the release, the compound performed well compared to commercial coatings with a similar thickness of about one hundred microns.
“Atop all that, we found the viscoelastic coating is self-healing,” said Rice graduate student and co-lead author M.A.S.R. Saadi.
Scientists placed small slabs of mild steel treated with the coating alongside plain steel in seawater for a month. According to Rice, the coated steel showed no discolouration or other change, but the bare steel rusted significantly.
If you give the alloy a poke, it recovers,” Rahman said. “If it needs to recover quickly, we assist it using heat. But over time, most thick samples will recover on their own.”
The researchers cut a film in half and placed it on a hotplate to test the self-healing properties. The pieces reportedly reconnected in about two minutes when heated to about 70 Celsius (158 Fahrenheit) and could be folded just like the original film. Pinhole defects were healed by heating them at 130 Celsius (266 Fahrenheit) for fifteen minutes.
“The first target structures, but we’re aware the electronics industry faces some of the same problems with corrosion,” Ajayan said. “There are opportunities.”
In March, scientists from the Helmholtz Centre for Materials and Coastal Research in Geesthacht, Germany, developed a magnesium alloy that was reported to have elevated resistance to corrosion.
The alloy was reported to have a lower corrosion rate than ultra-high-purity magnesium. The scientists claimed to approach stainless magnesium through alloying pure magnesium with tiny amounts of calcium.
A team of scientists added tiny amounts of calcium to the magnesium alloy, careful to retain the material’s purity. The calcium reduces the cathodic water reduction kinetics, which makes the magnesium more resistant to corrosion and allows for the development of a protective surface film. The calcium additive also stabilizes impurities (such as iron and silicon) within the alloy.
Earlier this month, a study found that biochar nanoparticles (BCN), or graphene oxide, derived from spruce wood and wheat straw can improve corrosion resistance in zinc-rich epoxy coatings. The study, published in Progress in Organic Coatings, suggests a more sustainable option for the coatings industry.
Four kinds of coatings were prepared for analysis:
- Pure zinc-rich coating (0-ZRC);
- Graphene oxide-based zinc-rich coating (GO-ZRC);
- Sulfonated multiwall carbon nanotube-based zinc-rich coating (SM-ZRC); and
- SM-GO-based zinc-rich coating (SG-ZRC).
The coatings were then studied via open circuit potential (OCP), electrochemical impedance spectroscopy (E.I.S.), a salt spray test, 3D confocal microscope and electro scanning electron microscope (S.E.M.). Researchers found that coatings with the presence of G.O. increased the shielding effect of zinc particles, improving corrosion resistance.
The study also found that biochar increases the interlayer spacing of coatings. The galvanic corrosion of G.O. is relatively weak, and that carbon nanotube should not be used to modify G.O. in zinc-rich coatings.
