Self-healing metal oxides can protect against corrosion

Researchers at the Massachusetts Institute of Technology (MIT) have discovered that a solid protective layer of metal oxide, when used as a thin, medium layer, is capable of deforming as a liquid and filling all traces cracks and openings appear.

This special thin coating works to prevent leakage of small molecules to penetrate through most materials such as hydrogen gas used to power the cell or radioactive tritium fuel cells ( heavy form of hydrogen formed inside the core of nuclear power plants.

Most metals except gold tend to oxidize when exposed to air and water. This reaction produces rust on the iron, stains on silver and rust on the copper, which can weaken the metal over time and lead to cracks or structural failure. However, there are 3 types of metal oxides including aluminum oxide, chromium oxide and silicon oxide in fact that can be used as a protective layer to prevent oxidation.

This special thin coating works to prevent the leakage of small molecules.

The research team, led by graduate student Yang Yang, used special tools to examine the metal surface in detail with these oxides to observe what happens when they are exposed to the lips. oxygen field and under stress conditions. Although most transmission electron microscopes (TEM) require placing samples into a vacuum, the team used a modified microscope called Transmission Electron Microscope. via the environment (E-TEM ) allows to study samples in the presence of gases or liquids. This device is used to study the process that leads to cracking, which is caused by stress corrosion.

The metal under the impact of the inside of the reactor tank and exposed to a slightly overheated environment can be quickly corroded if not protected. Even through solid protection, cracks will form, allowing oxygen to penetrate the surface of the inert metal, namely the interface points between the metal particles constituting large metal materials, causing produce stronger corrosion and damage the structure.

Yang said that before, people thought that metal oxide was brittle and prone to cracking and no one had proven it because it was difficult to observe material behavior in real conditions. Now, the team has for the first time observed within the resolution range almost at the atomic level. This method has proved that aluminum oxide is often very brittle, so it will be broken under the impact of stress, when produced in ultra-thin form, it is almost as deformed as a thin, thicker aluminum metal layer. When aluminum oxide is coated on the surface of a large piece of aluminum, the flow is like a liquid that keeps aluminum covered with a protective layer.

Researchers have demonstrated that within E-TEM, aluminum coated with oxide can be stretched more than twice its original length without causing any cracks. Oxides form a uniform coating that protects the surface without the boundary between particles or any cracks, even when stretched. Technically, the material is a type of glass, but it moves like a liquid and covers the surface as long as it is in a thin form.

Ju Li, a professor of engineering and nuclear science and co-author of the study, said: "With the advantage of soft surface and no cracks or boundaries between particles to penetrate inside the object whether, self-healing coating has many potential applications ".