The Research Of N-hexane And N-pentane Under High Pressure

Pressure is a parameter for substance as independent of temperature and chemical compositions, and it can effectively change the performance. The effect of pressure may reduce Physical volume, which leads to change the freedom and structure morphology.High-pressure physics intersected with many disciplines, it provides many important information for biology, origin of life, geophysical exploration, high-pressure physics is very important in many fields and does an irreplaceable role, to promote the knowledge innovation and technological innovation and to boost the progress of science.With the development of high-pressure physics, some biological big molecules are used to do high pressure experiment. N-hexane and n-pentane are simple saturated hydrocarbons as the key component of petroleum, and they are extensively studied for their chemical stability and special structure. In general, the n-alkanes exhibit different kinds of conformational isomers in the liquid state.At present, the atmosphere study of N-hexane and n-pentane has been reported earlier, but research about the high pressure is less, and the pressure point has been reported in experiment are very low.High-pressure studies of n-hexane and n-pentane would then give an insight into the structural changes of simple saturated hydrocarbons.It would also help in understanding the generation and retention of petroleum.This thesis studies on the phase transition and conformational changes of n-hexane and n-pentane under high pressure, the main work is done by Raman spectrum and synchrotron radiation X-ray diffraction to achieve the in-situ high pressure experiment. The high pressure cell used in this experiment is Diamond Anvil Cell,and the ruby fluorescence technique is used to calibrate the pressure applied on the sample. Obtaining the results thereinafter, the main conclusion as follows:First, By the high pressure Raman spectrum studying the phase transition and conformational changes of n-hexane, the experiment on n-hexane has been carried out up to 33.5GPa for the first time. The liquid n-hexane exhibits different kinds of conformational isomers,but the pressure breaks original conformation balance because application of hydrostatic pressure to the molecular system causes a change in the interatomic distances, following a reduction in bond lengths and atomic distances with pressure. Before the crystallization point 1.78GPa n-hexane is liquid, which is called phaseâ… .We observe a liquid-solid transition from phaseâ… to phaseâ…¡at 1.78GPa with crystallizing. We observe a solid-solid transition from phaseâ…¡toâ…¢at 8.7 GPa, and the methy end group of n-hexane is random freezing above 12.6 GPa. The conformation of n-hexane transform into all-trans conformation which has the lowest energy in high pressure,and in the end all conformation is all-trans. Second, by EDXRD studying the high-pressure features of n-hexane, my results are large according with the ones of Raman spectrum studying.After solidification the slope of d-p figure is not articularly evident in each phase transition. In the phase transition after solidification the change of long-range order in internal structure is unconspicuous, but some change in short-range order.So the curve of performance is not obviousThird,by the high pressure Raman spectrum studying of n-pentane, we find out two new phases under different pressures. We observe a liquid-solid transition from phase I to phase II at 1.88GPa with crystallizing, with a solid-solid transition from phase II to III at 13.08 GPa later.But a gauche conformer is still present in high pressure in the case of n-pentane, which is different from other straight-chain paraffins.