2016 Van Horn Distinguished Lectures: 2 (thermodynamics of interfaces)
1,676 views · Published 29 September 2016 · 1:16:51 · Indexed 19 October 2026
Channel: bhadeshia123 · 2016 · Education
The Kent R. van Horn Lectureship is an endowed Lectureship at the Case Western Reserve University and dates from 1974. It honours Kent R. van Horn, an alum, who had a distinguished career as a metallurgist, director of research, and ultimately corporate vice-president of Alcoa. Three lectures on varied topics are to be delivered over three successive days. The 2016 lectures were delivered by Professor Wayne Kaplan of the Department of Materials Science and Engineering Technion – Israel Institute of Technology. This one is about the thermodynamics of interfaces. These videos are reproduced courtesy of the Materials Science and Engineering Department of Case Western Reserve University. http://engineering.case.edu/emse/node/121 http://www.phase-trans.msm.cam.ac.uk Abstract: Since the 1980s it has been recognized that the structure of grain boundaries in polycrystalline ceramics can have a diffuse nature, characterised by a ~1 nm thick nominally amorphous film. More recently, the structure of grain boundaries has been described following diffuse interface theory, stating that the structure and chemistry of grain boundaries, interfaces and surfaces can go through two dimensional transitions between thermodynamic states (sometimes termed complexions). As an example, surface reconstruction is a first order complexion transition, equivalent to a discontinuous change in the level of adsorbed excess. As such complexions for interfaces are analogous to phases in bulk, although they are not bulk phases. In the past these conclusions had been reached based on structural characterisation of grain boundaries and interfaces correlated with mechanical and electrical properties, and more recently it has been shown that specific complexions can have a significant influence on grain boundary mobility, and thus the morphology of an evolving microstructure. To date, almost all of these studies have been conducted at grain boundaries in single phase polycrystalline systems, which by definition are not at equilibrium, and in some cases it is not even clear if the identified complexions are at steady-state. Similar questions have been raised for studies focusing on metal-ceramic interfaces from thin film studies, where the deposition process used to form the samples may be very far from equilibrium. This presentation will focus on an experimental approach to address the structure, chemistry and energy of (metal-ceramic) interfaces which are fully equilibrated, from which it can be demonstrated that formation of a distinct structural and chemical state at equilibrium minimises interface energy. This will be compared with solid-liquid interfaces, where a region of ordered liquid exists adjacent to the interface at equilibrium, and the details of a reconstructed solid-solid interfaces where the reconstructed interface structure accommodates lattice mismatch for a nominally incoherent interface. These three systems will be compared to known reconstructed solid surfaces, which can also be described within a more generalised Gibbs adsorption isotherm.
