ENERGETICS OF SOLID/SOLID AND LIQUID/SOLID INTERFACES

The main thrust of this research was to develop better understanding of the interfacial energetics of crystalline particles of one phase confined (or embedded) in matrices of another phase. Much of the work that motivated this research had been performed on Pb particles embedded in Al. Furthermore, significant contributions to that body of knowledge had emerged from collaborative work between Dr. U. Dahmen of the National Center for Electron Microscopy at LBNL and Prof. E. Johnson of the Neils Bohr Institute of the University of Copenhagen. Thus, the work performed under this Grant benefited from significant input into the design of the research from Dr. Dahmen and Prof. Johnson, who were officially listed as collaborators on the grant. Beyond interest in interfacial energies, there were several intriguing observations on Pb particles embedded in Al for which understanding was lacking. These included observations of large melting point elevation, or superheating, of embedded Pb particles. The melting temperature of these particles was found to increase with decreasing particle size, and to rise several tens of degrees above the bulk melting temperature for nano-scale particles. Since nucleation phenomena play an important role in melting and freezing, it was clear that the difficulties of interpreting superheating during melting could not readily be addressed without knowledge of the interfacial energies that enter into the formalism used to predict nucleation effects. The approaches taken in the studies included computer simulations, experimental studies and analytical modeling. Although about half of the work focused on Pb particles embedded in Al, other systems and issues were also addressed