It's hard to believe that even the tiniest cracksin metal one day can lead to the destruction of entire structures. However, there is no need to go far after the examples - falling bridges, breaking through pipelines and many other catastrophic consequences are often the effect of corrosion formed in tiny cracks, scratches and dents that are very difficult to detect. The most common method of dealing with corrosion is the application of protective coatings that isolate the metal surface from the damaging effects of the environment. The problem is that with the violation of this coating its effectiveness is lost.
A group of scientists from Northwestern Universityunder the direction of Jiaxing Huang, she developed a coating for metal that, if damaged, can repair itself in seconds, preventing these barely noticeable defects from turning into local corrosion, which in turn can cause the entire structure to collapse. The new material is resistant to extreme environmental conditions and can be applied even under water.
“Local corrosion is very dangerous. It is difficult to predict, prevent and detect, but it can lead to disastrous consequences, ”says Jiaxing Huang.
According to the developers, their patentedThe coating has the most optimal flow properties and self-healing capabilities. In the course of the experiments, the researchers demonstrated that the metal coated with this substance restored its structure 200 times after repeated damage and did not corrode in hydrochloric acid solution.
A new development is reported in the Research journal article. A summary of the study was published in a press release on the website of the Northwestern University.
There are already several options on the market.self-repairing coatings, but all of them, the researched notes, are generally suitable for repairing damage no larger than a few nanometers in size. To address the issue of larger damage a few millimeters in size, scientists turned to the properties of a fluid.
"After the boat" cuts "the water surface,fluid restores its original state. The "cut" quickly "heals" due to the property of fluidity of water. We decided that the most effective core for self-repairing coating would be liquid, so we decided to use silicone oil (polymerized siloxane), ”comments Huang.
The scientist adds that low viscosity allowsthe material recovers quickly, however, such liquids are poorly retained on the metal surface. Too viscous coatings are either not able to recover at all, or they do it very slowly. The ability to combine these two contradictory properties in a new coating was made possible by a combination of silicone oil (responsible for fluidity) of the coating and microcapsules of reduced graphene oxide, which are responsible for the viscosity of the substance. Graphene micro-capsules, absorbing the oil, form a coherent structure. In case of its violation, the oil leaves the capsules and restores the connection between the damage. According to Huang, they decided to use graphene, but any light particles would be suitable as a binder.
The inventors have noted that even a smallthe concentration of binding particles can significantly increase the viscosity of the oil - five mass percent of the microcapsules increased it a thousand times. Particles do not make the fluid heavier, so it does not even flow down from a vertical surface. It can be applied to the surface with any geometry and even in water, without trapping any air bubbles or the liquid itself. In addition, the stability of oil with graphene microcapsules to mechanical damage was also tested in acid. Its effectiveness was at the same high level.
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