Third CorroZoom Season 3 Webinar- Roger Newman
Third CorroZoom Season 3 Webinar - Roger Newman
2 March 2023 at 0800 US Eastern
The effect of alloy composition on molten salt corrosion- Dealloying, but not as we know it
University of Toronto, Canada
This talk will be based mainly on the recent PhD research of Dr. Touraj Ghaznavi, with other comparison material as required. Molten salt corrosion is topical in several technologies, including small modular molten-salt nuclear reactors. Our research has been focused on NiFe and NiCrFe alloys, but the general principles should be applicable to other solid-solution alloy systems that show dealloying, with the formation of nano- or micro-porous dealloyed layers.
There are two kinds of dealloying threshold, or parting limit, that are familiar at ambient temperatures in aqueous electrolytes. One is in the 50-60 at.% range of less-noble (LN) metal content (example: AuAg). The other is close to 20 at.% LN content (example: CuZn). Both these compositions have a meaning within percolation theory, as discussed by Artymowicz et al. . It is recognized that increasing kinetics of surface diffusion of the more-noble (MN) metal (or surface exchange of MN metal and its ions, as in the brass example) reduce the parting limit by exposing otherwise inaccessible paths rich in LN metal. With this background, we can expect a further reduction in the parting limit at the high temperatures where we get molten salt corrosion. We can also expect that with sufficient increase in temperature, lattice diffusion of alloying elements will start to affect the kinetics and/or the morphology of the dealloyed material. Both these expectations have been realized in Dr. Ghaznavi’s work using molten chloride salts, but with several surprises along the way.
 D.M. Artymowicz, J. Erlebacher, and R.C. Newman, Relationship between the parting limit for de-alloying and a particular geometric high-density site percolation threshold, Philosophical Magazine 89(21) (2009) 1663-1693.
Roger Newman is Professor and UNENE Research Chair in the Department of Chemical Engineering and Applied Chemistry at the University of Toronto (UofT). Before joining UofT in 2004, he spent 20 years in the Corrosion and Protection Centre, UMIST, Manchester, UK. Prior to that, he spent several years at Brookhaven National Laboratory in the US. His main research interests have been localized corrosion, stress corrosion cracking, passivity, and dealloying. He also has an active program in metallic nanomaterials. He has ongoing research with the nuclear power, nuclear waste management, and natural gas (GTL) industries. Some decades ago, he was very active in corrosion issues in the pulp and paper industry, and oil and gas production.