Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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MP welcomes submissions of Up Front articles. Please send photos and information to Ben DuBose, NACE International; tel: +1 281-228-6414; email: ben.dubose@nace.org. 9 MATERIALS PERFORMANCE: VOL. 58, NO. 6 JUNE 2019 Certificate: 3612.01 www.galvotec.com anodes@galvotec.com Sales Office: 181 Grefer Lane | Harvey, LA 70058 | Tel.: (504) 362-7776 | Fax: (504) 362-7440 Headquarters: 6712 S. 36th Street | McAllen, TX 78503 | Tel.: (956) 630-3500 | Fax: (956) 630-3595 Setting the Standard! Cathodic Protection Corrosion Vertical Tension Anodes Pin Brazing Aluminum Anodes Zinc Anodes Magnesium Anodes Specialty Magnesium Products Superior Quality Excellence Beyond Compare ISO Certified Accredited Efficient Anode F CE Certified Technicians Technologists Specialists Leader Since 1984 INNOVATION W Offshore On Shore Retrofit QU PRODUCTS Metal Oxide Deforms into Liquid-Like Anticorrosion Coating Researchers found a solid oxide protective coating for metals that can, when applied in sufficiently thin layers, deform as if it were a liquid. This allows it to fill any cracks and gaps as they form. Image by Christine Daniloff, MIT. An academic research team recently discov- ered that aluminum oxide (Al 2 O 3 ), a chemi- cal compound commonly used as a protec- tive coating for metals, can deform into a thin, liquid-like substance to fill cracks and prevent leakage of corrosive or radioactive materials. The team consisted of researchers from the Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts, USA), Xi'an Jiaotong University (Shaanxi, China), and Brookhaven National Laboratory (Upton, New York, USA). Their work was supported by the National Science Founda- tion (Alexandria, Virginia, USA). Most metals tend to oxidize when exposed to air and water, resulting in cracks and long-term structural failure, the researchers explain. However, aluminum is one of three elements (along with silicone and chromium) that produce an oxide that can protect metals against abrasion and corrosion. With that in mind, the research- ers wanted to determine why Al 2 O 3 and sili- con dioxide (SiO 2 ) offer such strong corro- sion resistance. The researchers used an environmental transmission electron microscope (E-TEM) to examine how samples of these oxides would react on metal surfaces that are exposed to an oxygen environment and placed under stress. The microscope enabled researchers to study the effects of certain gases or liquids on the samples to see if they would exhibit signs of stress cor- rosion cracking (SCC). Whereas other metals corrode quickly under SCC, the researchers found that Al 2 O 3 was not only able to protect the metal sur- face, but could also penetrate between the metal grains, thereby preventing deep-set corrosion. Because it had been impossible to observe how metal oxides behave at room temperature, it was assumed they were too brittle to assume a flowing, crack- resistant form. But thanks to the E-TEM donated by Brookhaven—one of only ~10 such devices in the world—the team learned that Al 2 O 3 can, even at room temperature, be made into a liquid-like layer ~2 to 3 nm thick. As a result, a flowing layer of aluminum oxide coated onto an aluminum surface protects it from structural failure. According to Ju Li, an MIT professor, an oxide-coated portion of aluminum "forms a very uniform conformal layer that protects the surface" and can be stretched to more than twice its length without signs of crack- ing. He adds that the liquid-like properties of the self-healing Al 2 O 3 coating and its abil- ity to prevent the intrusion of cracks or grain boundaries could make it a viable material in numerous potential applications. For more information, visit news.mit.edu.

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