Study On Phase Transition Of Pyridine And Pyridine Mixed With Water Under Extreme Conditions With Laser Irradiation

High pressure can shorten the interatomic distance in matter,enhance the intermolecule interaction,and then change the structure and physical properties of the matter.Pressure combined with temperauture ans laser irradiation can further modify the structure and properties of the materials.Under high temperature,high pressure and laser irradiation,the crystal structures,energy bands and electronic orbitals of aromatic organic compounds should undergo complex changes,resulting in some new phenomena and new substances that canot appear at ambient conditions.Pyridine is a simple aromatic hydrocarbon compound second only to benzene and is the starting reactant for the synthesis of a range of products including pharmaceuticals,energetic materials,dyes and adhesives,etc.Recent studies on pyridine under high pressure and low temperature have shown that the phase structure of pyridine is very sensitive to the loading path of pressure and temperature,and is affected by factors such as the precision of pressure increment and the range of low-frequency Raman characterization.The previous research results(Definition of pyridine phase,solidification pressure point,number of pyridine phases under high pressure,pressure threshold of pyridine chemical reaction,product definition of pyridine chemical reaction)are contradictory each other.Under high temperature and high pressure exploring the phase structures of pyridine and its aqueous solutions has an insight into the mechanism of the growth of pyridine derivatives,provides the new synthetic routes for pyridine derivatives.In this paper,we mainly studied the structural transformation of pyridine and pyridine aqueous solution under high pressure and laser irradiation,as well as the chemical reactions and products under high pressure.The thesis contains seven chapters and the content is briefly given as follows:In the first chapter,the research progress of aromatic???婜??訚??労媱耞晜??浍偛????覀e conditions and the existing problems of pyridine under high pressure are introduced.The second chapter describes the high-pressure technology and its application in related fields;the high-pressure research methods and characterization techniques related to this paper are also briefly provided.In the third chapter,the phase structure and pressure dependent properties of pyridine near the solidification pressure were studied by in-situ three-stage Raman spectroscopy using a self-bulit loading device and fine-tuning pressure technique.Phase Ⅰ of pyridine was observed by Raman spectroscopy for the first time.The number of cycles of loading and unloading pressure determines the evolution of pyridine phase.The loading paths of pyridine from phase Ⅰ to phase Ⅱ and then to phase Ⅲ were determined.Two low density and high density phase Ⅱ under high pressure were identified.It is found that the transition of pyridine from solid state to amorphous state can be achieved by pressurizing pyridine in high density phase Ⅱ.The solidification pressure of 2.1 GPa at room temperature was accurately measured by the third-order Raman low wave number.The liquid-solid transition point of pyridine is about 2.0 GPa,but the solid-liquid pressure point of pyridine solution is about 0.7 GPa.In fourth chapter,we verified the phase transitions of pyridine at 1.0,2.5,10.9 and 17.1 GPa.In addition,loading up to 59 GPa,the products of laser-induced chemical reaction for pyridine under high pressure were compared with those of chemical reaction without laser irradiation under pressure.The results show that the products induced by laser irradiation are the same as those obtained by chemical reaction without the irradiation under pressure,and the final products are CN nanotubes.The reaction pressure of heterocyclic aromatic pyridine at room temperature can be reduced to 1.5 GPa from 26 GPa under pressure under high pressure and laser irradiation.We try to induce pyridine chemical reaction with different laser wavelengths of 785,633,514.5 and 325 nm laser,but only 325 nm laser can induce pyridine chemical reaction.In addition,low/high temperature and high pressure experiments were carried out on pyridine.It was found that pyridine remained stable at low temperature.Under high temperature and high pressure,high temperature can effectively reduce the pressure threshold of pyridine chemical reaction,but the product has not been analyzed.The follow-up work will continue in the future.In fifth chapter,the structure evolution behavior of pyridine water mixture under high pressure and the effect of laser irradiation on the mixture are studied.The hydrogen bond exists between pyridine and water.When the pressure reaches about 16 GPa,the hydrogen bond breaken and the ring opening reaction of pyridine can only occur with the 325 nm laser irradiation.Under high pressure water and pyridine mixed solution form eutectic system,and this system is more stable than pyridine.In addition,the physical properties of the mixture of pyridine and water at low temperature were studied.It was found that the mixture of pyridine and water remained stable at low temperature without phase transition.In the sixth chaper,the structure of the mixture of pyridine and water under high pressure was studied by in-situ third-order Raman spectroscopy.During the decompression for the mixture of pyridine and water,solid-liquid equilibrium was achieved at 0.8 GPa and room temperature.In the recrystalization process,pyridine and water were separated with the increase of the pressure.With the increase of pressure,part of pyridine recrystallized.Some phase transitions were obtained at 1.8 GPa,2.3 GPa and 4.7 GPa,respectively.The isolated pyridine was studied under light irradiation.In the seventh chapter,the research results of the previous chapters are summarized.