Corrosion is a long-standing problem, and it is estimated to cost about $ 1 trillion per year, accounting for about 5% of US gross domestic product. Corrosion of metals is complex, but fortunately metals are often protected from catastrophic damage by naturally forming ultra-thin oxide films.
Traditionally these protective films have been considered simple oxides of the expected compounds, but new research by scientists from Northwestern University, University of Virginia and Wisconsin-Madison University has revealed compelling new insights.
Using the most advanced experimental techniques and theoretical models, scientists can analyze oxide films at the atomic level and decipher the arrangement of atoms in the oxide. This indicates that the development of a new structure and composition of the protective film depends on the growth rate of the oxide film.
Scientists say their findings could provide clues on how to produce good or even excellent protective films. This could be a breakthrough in everything from nuts and bolts to high-tech batteries and turbine engines.
"This changed our understanding of these oxide films and opened up new ways to protect metals," said Laurence Marks, a professor in the Department of Materials Science and Engineering at Northwestern's McCormick School of Engineering and leader of the study. "We now know how many This method can predict the chemical composition of these films, so we can use these methods to extend the life of the protective film. "Scientists published their findings in" Physical Review Letters ".
"We now have more ways to control and regulate oxides to protect materials than ever before," said John Scully, a professor, head of the department and one of the authors of the Department of Materials Science and Engineering at the University of Virginia.
"This research provides less critical information on how new materials can be designed to make them corrode," said Peter Voorhees, professor of Northwestern engineering materials science and engineering and another author of the paper.
The research team has studied oxides formed on alloys consisting of nickel and chromium, which are used in a wide range of products from heating elements for home toasters to aircraft engines.
These oxides can also be used in the presence of water, such as in dental implants. It is well known that these oxides are both heat resistant and resistant to oral corrosion due to the formation of chromium oxides. It is speculated that nickel forms a separate oxide that is soluble in the body in some cases. But the research team discovered something unexpected-the oxides included not only chromium and oxygen, but also a large number of nickel atoms.
It was shown that nickel atoms did not have time to escape from the oxide and were trapped inside. The number of captured parts depends on the speed of oxide growth. If it grows slowly, nickel atoms can escape. If it grows fast, they can't.
This happens when the metal reacts with oxygen in the air at high temperatures and when it reacts with water on board or in dental implants. Scientists say that atoms trapped in the oxide affect many properties of the film.
These findings suggest that we can intentionally trap atoms in these oxides in new ways, altering their performance.
"As a case, we are close to the limit we can do with aircraft engines." John Perepezko, a professor of materials science and engineering at Wisconsin-Madison and another author of the paper, said: "This new vision for protective oxide formation can Develop many new ways to make better engines. "