טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentPavel Bavli
SubjectMelting in HCP Lattices
DepartmentDepartment of Physics
Supervisor Professor Emeritus Polturak Emil
Full Thesis textFull thesis text - English Version


Abstract

The aim of the research was to understand the role of surfaces in the melting transition of metals having a HCP structure. The element that was chosen is magnesium, which has an HCP structure at zero external pressure conditions. It was studied by means of computer simulations using an embedded atom potential. We started by establishing the correct physical behavior of our code on a bulk system. Then we proceeded to study surface melting. Three types of samples were created, each type describing one of the three low-index facets known as the c, a and s facets. Our motivation was to answer the question whether a similar hierarchy of premelting phenomena, as that found for FCC and BCC metals, is also present in HCP metals. We found that as the temperature increases, the a facet disorders first, then the s facet, while the c facet remains stable up to the melting temperature. As the temperature increases, the disorder spreads from the surface layer into the bulk, establishing a thin quasiliquid film in the surface region. We concluded that the hierarchy of premelting phenomena is inversely proportional to the surface atomic density, being most pronounced at the a facet which has the lowest density. Furthermore, the analysis of our simulations led us to the general conclusion that the Born criterion describes both bulk and surface melting.