Amorphou Phase Transformation Dynamics Behavior Of Sulfur

Up to now, there are three kinds of preparation methods of amorphous solid sulfur (a-S) have been reported. The first one is quenching melt of sulfer. e.g. rapidly ejecting the molten sulfur into liquid nitrogen. The second is high pressure induced amorphization of crystal sulfur, and then amorphous-amorphous phase transition under higher pressure. The a-S phases obtained through above two methods recrystallized easily even at high pressure and low temperature. The third method is rapid compressing melt of sulfur, in such method prepared bulk amorphous sulfur has a high glass transition temperature and a wide supercooled liquid region, showing very high thermostability. DSC thermal analysis shows clearly that this amorphous sulfur has a broad exothermic peak in the temperature range of373.8-414.9K, the peak value is about399.5K, and then an endothermic peak about441.5K, the two events caused by temperature are marked as phase transition â…  and â…¡ in this thesis respectively. In this work we have studied mainly dynamic behavior of the two phase transitions with different heating rate under atmospheric pressure and high pressure.All samples of bulk amorphous sulfur have been prepared through the method of rapid pressuring caused solidification in our unique device.Under atmospheric pressure, the phase transition temperatures of the amorphous sulfur were measured by a series of differential scanning calorimeter (DSC) conditions at different heating rate. Results showed that temperature of phase change I is sensitive to heating rate, increases with the increase of heating rate, but temperature of the phase change II is almost stable at around433K, no obvious increase could been observed with the increase of heating rate.High pressure experiments were carried out by employing a slide-tepy large volume high pressure apparatus with cubic anvils. The phase transition temperatures of amorphous sulfur were measured directly at several high pressure and different heating rate. Results showed that the temperatures of phase transition â…  and â…¡ both increase with the pressure rise under the heating rate of10K/min, and the temperature of phase change I rises with the heating rate, while the temperature of phase change â…¡ was almost unchanged under0.9GPa.Finally, analyzed and sorted the experimental data, we attempted to make a dynamic phase diagram (PTTT figure) of amorphous sulphur with pressure, time and temperature within high pressure of2.5GPa, and so essentially presented an experimental method to establish dynamic phase diagram for general materials.