Direct Measurement Of Release-melting Transition Of Metal At M-bar And Discussion Of Transformation Kinetics

The measurement of melting-curve of metals at high pressures is an important topic in field of dynamic high-pressure science, which has been researched for several decades. But some problems are still required to be solved. At present, there are two paths to reach the melt states for metals, which include shock induced melting and unload-induced melting. In the later method, the melting temperature is deduced from the measured temperature of metal/window interface. The challenge is how to get the inierface temperature without the effects of air gap. The achievement were made at two aspects:The first was to improve the contact condition betweem the metal and window, the other was to develop the theoretical model based on heat conduct.By improving the technique of sample preparation, in this work the radiation of interface without "peak" feature of air gap is obtained with good repetition. At pressures of shock-release melting, the radiation characteristics and the temperature history of iron/sapphire interface are investigated, and the relationship between the dynamics of release melting and the time dependence of surface temperature is found. In the following aspects this work reaches new results:(1) The nearly ideal contacted interface has been prepared. The radiation without "peak" feature was obtained by refined surface polishing and reasonable target assembling at different pressure points. The repeatability of ideally contacted interface preparation was nearly achieved.(2) The characteristics of the interface temperature variation was directly observed. After the metal sample being shocked and released, if there was melting phase transition in the metal, the radiation and temperature of the metal/sapphire interface was unsteady,but if there wasn't melting phase transition in the metal, the radiation and temperature of the metal/sapphire interface was steady.This unsteady experimental signal is a new phenomenon.(3) Explained the experimental result by establish melting phase transition kinetics-heat conduct equation. This paper explained the unsteady history of radiation and temperature at the metal/sapphire interface by transformation kinetics combined with heat conduction equation. When the result of theoretical calculation was consistent with the result of experiment, the nucleation rate and nuclear growth rate under high temperature and high pressure can be confirmed.