DESIGN AREA SEMINAR November 15, 2006 3:30 pm ME 256 F.D. Fischer Institute of Mechanics, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700 Leoben, Austria "On the Role of Surface Energy and Surface Stress in Phase-Transforming Nanoparticles" Abstract The role of surface energy and surface stresses has been a topic in thermodynamics and physics since the seminal work by Gibbs. Since both quantities take the same values for liquids this may have given rise to misconceptions in the community in the case of solids. Terms such as surface tension have been applied with a double meaning as a surface stress state or surface energy. These considerations are of special importance for phase transforming nanoparticles (precipitates, transforming or melting/solidifying single particles). A review on the relevant literature is presented showing that the findings from continuum mechanics, esp. the concept of configurational forces (stresses), are often either not known or not accepted. Therefore, the progress report gives a rather detailed introduction into the continuum mechanics and thermodynamics of a moving surface. The relevant literature is referenced and the main findings are reported. Then the terms "surface energy", "surface tension" and "surface stress" and their relations are discussed. A global transformation condition for a sudden phase-transforming nanoparticle is explained. The concept of configurational forces is applied to derive a local transformation condition in a material point at the phase interface. In this case the transformation process is controlled by a moving phase interface. Four different cases for nanoparticles (growing precipitate, growing solid nucleus in liquid, melting particle, solidifying particle) are studied in detail. It can be shown that the surface energy and the surface stress contribute to the thermodynamic force in different ways. The role of both terms is quantified in detail and compared with the case of a sudden transformation of the nanoparticle. Brief Bio Dr. Fischer received his PhD at the Technical University of Vienna, Austria, in 1965. From 1965 to 1983 he held various positions in industry. He was appointed as a Lecturer in Technical Mathematics in 1976 and Lecturer in Technical Mechanics in 1981 both at the Technical University of Vienna. Since 1983 he has been Professor of Mechanics at the Montanuniversität Leoben, Austria. He is a Senior Fellow of the Christian-Doppler-Forschungsgesellschaft Vienna, Austria, a Guest Professor at the Erich Schmid Institute of the Austrian Academy of Sciences (2002-05) and recently received the Erwin Schrödinger Prize of the Austrian Academy of Sciences (2005). He is Head of the Christian Doppler Laboratory of Micromechanics of Materials. He is Author and co-author of more than 450 scientific publications in International Journals and Conference Proceedings. His current research interests include Multicomponent diffusion in multiphase systems; non-equilibrium thermodynamics; Transformation Induced Plasticity; the deformation behaviour of Ti-Al Intermetallics; Constitutive laws for phase-transforming materials; Damping control of structures by means of shape memory alloy devices; Fully three-dimensional modelling of stable ductile crack growth in heterogeneous materials; Straightening of rails - residual stresses and optimal strategy; Microstructure of the running surface of rails. -- ------------------------------------------------------------------------ Annie Cheever, Area Secretary School of Electrical and Computer Engineering acheever@purdue.edu Purdue University Birck Nanotechnology Center, Room 2027 1205 West State Street West Lafayette, IN 47907-2057 Phone: 765-496-8327 Fax: 765-496-6443 http://www.nano.purdue.edu/ ------------------------------------------------------------------------