Crystalline Aluminum Overheating Limit And Fluctuation Of Nucleation

Melting is a familiar phenomenon in the nature and an important process of phase transitions in condensed matter physics. Experiments studies indicate that supercooled liquids are commonplace in the solidification process of liquid metal, while superheated solids of metal are not commonplace in the melting process of solid metal. Since the superheating phenomenon was observed in a number of metals, to estimate the upper limit for superheating in crystals became the focus of people research.In this paper, we summarized the progress of the superheating of metal in experimental and theoretical aspect. Similar to Fecht and Johnson's isentropic limit temperature, we proposed a thermodynamic stability limit for superheated crystal in termsof a Gibbs free energy catastrophe that occurs at a critical temperature (T~G_m) when the Gibbs free energy of the superheated crystal equals that of the liquid phase. We calculate this limit temperature of Al (which is T~G_m≈1.16T_m), it is differ from other thermodynamicstability limit for superheated crystal.Superheating experiments indicate that melting is usually a process nucleated at heterogeneous nucleation sites such as grain boundaries and free surfaces. Providing heterogeneous nucleation could be avoided for melting by means of experimental techniques, crystal can be superheated above their equilibrium melting points. The stability limit of a superheated crystal would be given by a homogeneous nucleation. We think this process must be an isochoric process from the analysis of homogeneous nucleation. Calculation gave a critical temperature of homogeneous nucleation kinetics of Al (which isabout 1.11T_m).These two new superheating limit temperatures of crystal Al will be abundant the comprehension of superheated crystal.