Third CorroZoom Season 2 Webinar - Karl Sieradzki
22 Feb 2022 at 0800 US Eastern
Percolation, Chemical Short-Range Order and Passivation
The Fulton School of Engineering
Arizona State University
Tempe, Arizona USA 85287
In this presentation, I will describe the results of recent modeling of aqueous passivation of Fe-Cr, Ni-Cr and Cu-Rh alloys. These metals form excellent nanometer-thick protective passive oxide films that have the ability to self-heal with little accompanying metal dissolution; a key criterion for good passive behavior. The presentation is organized as follows. First, I briefly describe the alloy passivation models of Uhlig, McCafferty and Marcus that have been developed over the past 70 years. This will also include a description of Sieradzki and Newman’s 1986 model of passivation and the motivation for using percolation concepts to describe alloy passivation. Next, I provide the necessary background from percolation theory required to understand our new model. Importantly, this includes the concept of chemical short-range order in alloys, which characterizes atomic-scale nearest-neighbor identities. The new percolation theory of passivity is based on the concept that a system of finite thickness, h, may be coarse-grained or “renormalized” to a two-dimensional (2D) system, resulting in a series of h-dependent 2D percolation thresholds. Here h corresponds to the depth of dissolution required for passivation to occur. Next, I describe results of kinetic Monte Carlo simulations and electrochemical experiments which are compared to predictions of the model. Density functional theory is used to examine how the dissociative heat of dioxygen adsorption varies with the size of Cr atom clusters on Fe (110) and (100) surfaces. Finally, I will show how our new theory provides a quantitative path forward for designing corrosion resistant alloys that minimizes the requisite metal dissolution for passive film formation in aqueous electrolytes.
Karl Sieradzki is a professor of materials science and engineering in the School for Engineering of Matter, Transport and Energy at Arizona State University. He earned his PhD in Solid-State/Materials Science and Engineering from Syracuse University in 1978. Prior to joining Arizona State University in 1994, he held positions at Iowa State University/Ames Laboratory (joint), Brookhaven National Laboratory and Johns Hopkins University. His current research interests are in fracture of solids, thermodynamics of surfaces and interfaces, dealloying, nanoporous metals, stress-corrosion cracking and modeling of various processes associated with aqueous corrosion and the high temperature oxidation of alloys.