Research On High Pressure Melting Curve Of Typical Metal

Melting is a common phase transition. The melting temperature of a certain material usually changes with pressure. The relationship between melting temperature and pressure of solids is crucial for research in many fields, such as material science, high pressure physics, and geophysics, etc. This thesis focused on metal elements. We made some tentative research of melting curve through theoretical calculation and experiments.In theoretical calculation, ab initio calculation method was employed to determine the potential function and the unknown parameters in pair-potential-based mean field model for metals. The mean field was constructed from the potential functions, and the vibrant free volumes of atoms at melting points were evaluated. Then the free volume theory of high pressure melting was tested. In the following, We proposed a modified free volume theory and using it to calculate melting temperature of metals. The calculation results of Al, Cu, Ni, Na and K indicate that the widely used hypothesis--- the ratio of vibrant free volume to the primitive cell volume of atoms in melting curve is a constant--- is not universal valid. The model we proposed here can be used to obtain much more accurate results of melting curve.In experiments, we measured the melting curve of Sn at 1.33～4.77 GPa using large volume high-pressure cell by the method of sound velocity measurement. Some relatively good results have been obtained. The experiment results can also be described by our theoretical calculation method.