Study On The Equation Of State And Melting Curve Of Iron

In the recent two decades, Equation of State(EOS) and melting curve of iron at high pressures has attracted much attention of scientists, since this work reflects the cross trend of multi-branches in modern science, and be applied to solve the problems in many scientific research fields such as earth's deep interior research. Despite there were many contributions to this study, but consensus data about the melting property and the EOS of iron are both lacking:(1) the melting curve determined by diamond anvil cell(DAC) techniques can't be logically connected to one determined by shock loading(SL), most pressures used in shock wave experiment are above 200GPa, it is higher than the pressure range in the Laser heated Diamond Anvil Cell (below 105GPa), so we can't directly compare the melting data from SL with the data from DAC.Indirect comparsion by extrapolation shows the melting temperature Tm data from SL experiment are higher than those from DAC technique, typically higher value is 1000-2000 K and with a tendency of increase with pressure increases. (2) Even by same methods, the melting data got from different workers are not consensus, consequently, the temperature extrapolated by the melting curve of iron to the inner core boundary (ICB, at 330GPa) is very scattered.In order to solve the above-mentioned problems, it is very necessary to construct the unified melting curve, which not only fit with melting data from SL but also fit with the data from DAC and result from theory calculation. For this purpose, in our thesis, the Hugoniot EOS data and the sound velocities curve of two groups porous irons sample with average density 6.275g/cm3 and 6.903g/cm3, have been elaborate measured by shock compression experimental; Shock-release melting temperatures of iron with two different initial density 6.175g/cm3 and 6.745g/cm3 have been measured;By combining the previous sound velocities experimental data of dense iron and Grover's thermodynamic analysis model,the pressure and temperature of metal in solid-liquid mixed region are calculated, main innovative results summarized as follows:1. In order to solve the problem such as the effects of superheating,which is not considered, or the correction parameter of superheated melting is not reasonable in previous melting temperature calculation based on sound velocities results of dense iron,a new method was deduced by combining Grover's equations of liquid metal with sound velocities results, so the melting temperature at 260GPa was recalculated, it is 5362K.2. In order to overcome the limit that only one melting pressure is found out in sound velocities measurement of dense iron, two groups porous irons sample with average density 6.275g/cm3 and 6.903g/cm3 have been measured by sound velocities experiment, two melting pressure and melting temperature are obtained, they are (135.7GPa,4062K) and (87.1GPa,3421K).Meanwhile, the Hugoniot data of two groups porous irons also been obtained. This is a great progress to measurement technique of melting curve.3. In order to get more data of melting temperature, shock-release melting temperatures of samples with two porosities have been directly measured by the technique developed by Tan.The results are (72.8GPa,3241K) and (127GPa,3683K) for samples with initial densities of 6.175g/cm3 and 6.745g/cm3 respectively.4. The melting temperature of dense iron in completely melted state (260GPa,5362K), which is of high credibility, was chosen as the standard reference point in Lindemann law, so the melting curve is abtained, the melting curve is verified by DAC melting data,SL data and results from theory calculations, and it is found not only fitting well with the SL data from 2,3 and Tan,but also fitting well with the DAC melting data from Sheng and Ma,and the results from theory calculations.Consequently, the new melting curve that sustained by DAC,SL and theory melting results was be constructed,the basic physic problem that trouble us for long time was be solved.5. based on this melting curve, we deduce the temperature at the inner core boundary (ICB, at 330GPa) is 5885±500K。This value is a very important reference data for the temperature distribution in deeper earth, and it can be applied to solve the problems in many scientific research fields such as earth's deep interior physics.