A self-healing coating strategy developed by Northwestern University researchers may be the latest weapon in the ongoing fight against metal corrosion in vehicles, bridges and infrastructure, Northeastern Now reported. A new material, inspired by the physical characteristics of liquids and fluids, not only acts within seconds, it also works repeatedly, 200 times in a row.
It's known that just a tiny crack or scratch can take down gigantic metal structures like pipelines, bridges and airplane fuselages. The problem is, these microscopic damages often go undetected, because the tiny dents or pinhole-sized defects are not visible to the naked eye. They're also extremely difficult to predict, prevent or repair, since many of the existing solutions up to now have been rather limited in their success.
Jiaxing Huang, who led the Northwestern research team, said that localized corrosion is "extremely dangerous," and that if left untreated, "it can lead to catastrophic failure."
A more effective self-healing coating
Huang's new patent pending system employs a novel, self-healing coating that even works on larger scratches in the millimeter range. There have been previous attempts at self-healing coatings, but they've only been effective with nanometer- to micron-sized damages. One such method, from Massachusetts Institute of Technology, relied on an ultra-thin layer of aluminum oxide to fill in cracks and gaps in a metal surface, according to MIT News.
Huang, a professor of materials science and engineering in Northwestern's McCormick School of Engineering, was inspired by how fluids naturally "heal" themselves. "When a boat cuts through water, the water goes right back together," Huang said. "The 'cut' quickly heals because water flows readily. We were inspired to realize that fluids, such as oils, are the ultimate self-healing system."
The first challenge for Huang was finding the right fluid, one that didn't just drip off the metal's surface when applied. After ruling out common oils that flowed too readily, he and his research team came up with a unique network of lightweight particles made of graphene capsules that solved the problem. The particle network "fixes" the oil coating, preventing it from dripping. The particles essentially immobilized the oil film, so that it stayed in place.
The result? The coating not only adheres to metal surfaces, it also performs extremely well under real-world conditions – even underwater and in harsh environments such as acids or chemical baths. Huang, in fact, believes that the coating could be painted onto boats, bridges or even metal structures near leaked or spilled corrosive fluids.
The coating also stands up to turbulence and sticks to sharp corners without migrating to nearby surfaces. Plus, when used underwater, the coating goes on evenly and uniformly, without trapping tiny bubbles of moisture or air that can later cause pinholes and corrosion.
According to Huang, this new corrosion-fighting system, "Self-healing microcapsule-thickened oil barrier coatings," is not limited to one specific ingredient; the coating material can be created with any hollow, lightweight material, not just graphene.