Particle Growth, Melting and Nucleation at the Nanoscale

When: Monday, January 27, 2014 at 10:30 am
Where: DG 50
Speaker: Professor JJ Hoyt
Organization: Chair, Department of Materials Science and Engineering, MCMaster University, Hamilton, ON
Sponsor: Distinguished Lecture in Nanotechnologies through Materials Innovation, Co-hosted by Mechanical and Industrial Engineering, Chemical Engineering, and Physics Departments

In this seminar various aspects of first order phase transitions at the nanoscale will be discussed. First, the growth velocity of plate-like precipitates in alloys is investigated, where the close analogy with dendritic solidification is emphasized. The concentration field in the matrix phase during growth is formulated by a boundary integral technique, which correctly accounts for the nanoscale step-terrace structure of the advancing precipitate, and, by examining the conditions at the plate tip and by using a stability argument for the plate thickness, a modified Ivantsov relationship is established between the growth velocity, the radius of curvature of the plate tip and the supersaturation. Results of the boundary integral formulation will be compared with experiment. Second, the concept of premelting at surfaces and internal interfaces will be reviewed and a molecular dynamics simulation method for extracting the so-called disjoining potential will be described. Preliminary results on the premelting of Au nanoparticles will be presented with particular emphasis on the suppression of the melting point in these nanoscale systems. Finally, molecular dynamics simulations of nucleation of the body centered cubic phase from the face centered cubic phase in a model of pure Fe will be presented and comparison of the simulation results with the classical theory of solid-solid nucleation will be described.