Study On Physical Properties Of RDX Under High Temperature And High Pressure

Temperature and pressure are two important physical parameters that can control the structure and properties of materials.They are also key parameters to analyse the detonation of energy materials.The microstructure and chemical kinetics of energetic materials can be changed under external stimulation,such as temperature and pressure.These changes directly affect and determine the basic properties and macroscopic properties of energetic materials,and ultimately affect the detonation and safety of energetic materials.The shockwave generated in the detonation process of energy materials propagates rapidly.It is extremely difficult to perform the dynamic analysis of energy materials.However,the experiments under static high temperature and high pressure make it possible to analysis the physical properties of energy materials.The distance between atoms/molecules of energetic materials can be effectively shorten under high pressure,which result in the changes of intermolecular interaction,structure and properties of energy materials.Temperature is a physical parameter that can not only change the structure of the energetic material,but also contribute to the activation of energetic materials and accelerate the process of physical and chemical reactions.In this thesis,the phase transition and chemical decomposition reaction of 1,3,5-Trinitrohexahydro-s-triazine(RDX)were systematically studied under high temperature and high pressure conditions.There are six chapters in the full text,as follows:In the first chapter,we briefly introduced the research progress of high-pressure science and technology,high-pressure technology application fields and energetic materials under high pressure.In the second chapter,single-crystal particles of 1,3,5-trinitrohexahydro-s-triazine(RDX)crystallized in the ? phase have been successfully obtained by sublimation-recrystallization method.The sublimation temperature,deposition time and selection of hydrophobicity/hydrophilicity of the substrates were three important parameters to obtain single-crystal particles of ?-RDX with higher purity.Lower sublimation temperature,shorter deposition time and hydrophilic substrates were favorable for the growth of ?-RDX with the AAA conformation.In the third chapter,the structural evolution of ?-RDX under static high pressure was studied.A phase transition of ?-RDX was observed at pressure of 3?9 GPa.Moreover,this phase transition is obviously different from the irreversible phase transition from?-RDX to a-RDX by mechanical stimulation.The phase transitions in our experiments were reversible when the pressure was subsequently released to ambient pressure.However,the recovery of the distortion in CH2 group require a pressure threshold of about 20 GPa.In the fourth chapter,pressure induced phase transitions of RDX were systematically studied under different compression conditions.Precise phase transition points were obtained based on the high-quality Raman spectra.With helium as pressure transmitting medium(PTM),a-RDX immediately transformed into y-RDX under 3.5 GPa due to hydrostatic conditions and possible interaction between the penetrating helium molecules and RDX.While with other PTMs,such as argon,4:1 methanol:ethanol solution and RDX itself,the first phase transition started at 2 GPa and completed at around 4.3 GPa.This study confirms that ?-RDX is independent of PTM and exists under non-hydrostatic conditions.Evidence for a new phase(?)was found at about 28 GPa.Moreover,all the phase transitions in our experiments were reversible when released to ambient pressure.In the fifth chapter,phase transition and chemical decomposition of RDX under high temperature and high pressure conditions were investigated.Under the non-hydrostatic pressure condition with RDX itself as PTM,the phase transition temperatures and chemical decomposition temperatures of RDX were significantly higher than those under the hydrostatic pressure condition with argon as PTM.Furthermore,the P-T phase diagram of RDX was obtained under non-hydrostatic pressure condition.In addition,the structure changes of high temperature and high pressure phase(?-RDX)under high pressure were studied.The molecular structure of ?-RDX showed rearrangement or distorted under high pressure.In the sixth chapter,the research results in the previous chapters were summarized.