Gleeson leads in the field of high temperature corrosion
Any industry that operates in a high- temperature environment needs structural and functional materials that can withstand heat and associated surface reactions. To help these materials resist corrosion at high temperatures, scientists have developed alloys and coatings that can naturally form a protective scale layer. While some think that research in this field is complete, Brian Gleeson, the Harry S. Tack Professor and Chair of Mechanical Engineering and Materials Science at the University of Pittsburgh, published an article in Nature Materials explaining that there is still much room for advancement and discovery.
Gleeson leads the High Temperature Corrosion Lab in Pitt’s Swanson School of Engineering where his group focuses on testing and assessing the high-temperature corrosion behavior of metallic alloys and coatings.
“From a practical standpoint, any component that is exposed to a high temperature in a reactive environment is potentially at risk of excessive surface degradation,” said Gleeson. “This includes the aerospace, power generation, metal processing, automotive, waste incineration, and chemical processing industries. For these industries, high-temperature corrosion testing and assessment is often needed to aid in material selections or to generate essential design or life-prediction data.”
Research by Gleeson and colleagues combines experiment with theory and advanced characterization to understand the complex interplay between the chemical and kinetic factors affecting protective-scale formation in single- and multi-oxidant environments. To provide extended protection, the scale that forms is typically an oxide (e.g., Al2O3, Cr2O3 or SiO2) that is both stable and adherent to the high-temperature component.
The initial stage of corrosion reaction is an area where Gleeson believes there is considerable room for discovery. It is an important part of a given oxidation process where an alloy or coating composition forms a continuous thermally grown oxide (TGO) scale. “The TGO layer is critical because it makes the material more resilient to degradation in harsh environments,” said Gleeson. “The lifetime of a particular alloy or coating is determined by the tenacity of this layer and its ability to heal or reform in the event of damage.”
Gleeson thinks that more can be done to gain a better understanding of this important step in the overall reaction. He said, “Commonly recognized oxidation theory lacks the ability to accurately predict whether a given alloy or coating composition will be able to form a continuous protective scale layer.” Researchers in the HTC Lab are probing the nature of scale formation under harsh environment conditions that mimic actual service.
Beyond understanding the formation of the TGO layer, Gleeson believes that more needs to be understood about the complex oxidizing environments during the development of these scales. The type of gas surrounding the material or the level of humidity can play a major role in the lifetime of a material.
“Water vapor, which is commonly found in these environments, is known to have a detrimental effect on the scale-forming process.” As detailed in his Nature Materials article, different scales develop on alloys oxidized in dry air than alloys oxidized in wet air containing 30 percent water vapor. “The oxidizing environment is becoming increasingly more complex and goes beyond just exposure to air. Moving forward, researchers will need to understand the role of oxidizing species, such as O2, H2O, and CO2, in affecting protective scales.”
To gain a better overall understanding of the oxidation process, including the underlying kinetic and thermodynamic factors, Gleeson encourages researchers to improve experimental and computational methods to observe and model oxidation. He said, “Researchers need to develop a multiscale predictive understanding of this initial stage and focus on the interactions and effects of alloy constituents and gaseous oxidants.”
According to Gleeson, “What largely stands in the way of advancing understanding on the kinetic and thermodynamic factors, which influence protective TGO-scale formation and maintenance in harsh service environments, is the misguided notion that high-temperature corrosion is a passé field with little room for discovery.”
Contact: Liza Allison