Calculation Of The Condition For Synthesizing Diamond From Supercritical C-H-O Fluid And Experimental Research For Catalytic Effect Of Hydrogen

It is very important for,Geophysics and Material science to research the behavior of supercritical C-H-O fluid under high temperature and high pressure. In the past study, theoretical calculation of the formation of diamond from C-H-O system has not been done sufficiently and there was not experimental evidence of the effect of H on the formation of diamond in this system. In view of this situation, the two problems were theoretically and experimentally researched in this thesis.Theoretical calculation:1. By statistical thermodynamics methods and CHEQ code, the concentration of carbon in the system of graphite-water was calculated at 5.5-7.7GPa and 1000-2900K. Relations between the concentration or the concentration difference of carbon in water and the pressure were obtained. Thus the possible temperature sphere of the formation of diamond from C-H2O system was defined. And then, we also discussed the effects of O and H in the process of the formation of diamond. Our conclusions correspond with the experimental results published so far very well.2.Based on the general solution of Percus-Yevick equation for hard spheres, the concrete form of the pair distribution function gyy(r) was revised if n=5 and deduced if n=6.Experiments:l.With the starting material of the system of graphite and polypropylene, the behavior of it under high temperature and high pressure was studied. It was found that there is not the appearance of diamond at the three experimental points as follows: ( 6.5GPa,1300 ℃ ,30min ) ,(5.7GPa,1400 ℃ ,120min) and (5.7GPa,1300℃,120min).2.With the starting material of the system of graphite and polypropylene (or polyethylene) and micron diamond powder, its behavior was studied under high temperature and high pressure, and the sign that micron diamond powder sintered is observed. That is to say that H may act as a catalyst of diamond sintering.3.With the starting material of nanometer diamond powder or of nanometer diamond powder and polypropylene, their behavior was studied under high temperature and high pressure too. It was found that nanometer diamond powder sintered more or less at conditions of 5.8GPa,700℃,60min and the sample contained H has better character and there is no appearance of non-diamond carbon phase. It suggests that H has the action of catalyst in the process of the formation of diamond.The results of the experiments of diamond sintering above indirectly prove the catalytic action of II on the formation of diamond.