Study On Synthesis Of Large Diamond Single Crystals In Fe-Ni-C-S(O) System At High Temperature And Pressure

Diamond is an extremely important earth mineral,not only because of its important value,but also because its internal inclusions carry mineralogical information from deep in the mantle.Due to the variability of the growth location of natural diamond,its internal inclusions can provide effective information such as mineralogy and mantle chemistry at different depths of the earth.Through the study of diamond and its internal inclusions,we can determine the temperature and pressure of diamond growth,the material composition of the growth environment,and the growth time of diamond.At the same time,due to the characteristics of diamond itself,it can preserve the high-pressure phases of some minerals,and these high-pressure phases cannot exist stably under normal pressure.This is important for researchers to explore the phases of different minerals at different earth depths.significance.Nevertheless,there is still no widely accepted answer to the key question about how diamond is formed.In order to explain the crystallization process of this natural diamond,the relationship between natural diamond and its mineral inclusions is very important.Due to a series of geological activities such as mantle convection,carbon cycle,plate subduction,etc.,the ratio of elements in different regions of the earth's interior is complex and changeable.Every element and substance in the growth environment of natural diamond has special significance for its nucleation and growth.Because the material composition in the growth environment of natural diamond cannot be collected,the researchers established different growth models based on the inclusions inside the diamond.The researchers explored the effects of sulfur and oxygen in different synthesis systems on the characteristics of diamond and the growth conditions of diamonds,including Fe-Ni-C-S system,C-H-O-N system,Fe-Ni-C-O system,FeS-C system,MgCO3-SiO2-AlO3-FeS system,etc.However,the synthesis of large-size diamond single crystals with FeS and Fe₃O₄ as additives has not received sufficient attention.FeS and Fe₃O₄ are common sulfide and oxide inclusions in natural diamonds,and their role in the growth of natural diamonds has not yet been effectively explained.Therefore,using FeS and Fe₃O₄ as additives to synthesize large diamond single crystals in a growth environment similar to natural diamonds is extremely important for us to explore the causes of natural diamonds.At the same time,pressure is also one of the indispensable conditions for natural diamonds.Therefore,exploring the influence of pressure on the characteristics of diamonds has important research value for us to explore the causes of natural diamonds.In this paper,China-type largevolume cubic high-pressure apparatus(SPD-6×1200)is used as the high-pressure equipment to provide the pressure and temperature required for the synthesis of diamond.The temperature gradient method is used to successfully synthesize FeS and Fe₃O₄ as additives in the Fe/Ni-C system.Sulfur doped and oxygen doped diamond single crystals.Because FeS and Fe₃O₄ are all natural minerals that exist in the earth,they will not introduce other elements into the synthetic system at the same time.Observe the surface morphology of diamond by electron microscope(OM),use Raman spectroscopy(Raman)to characterize the crystal quality of diamond,use Fourier infrared absorption spectroscopy(FTIR)to detect the nitrogen content inside diamond,and use photoelectron spectroscopy(XPS)study the bonding form and content of impurity elements in diamond,and use X-ray diffractometer(XRD)to detect the characteristics of carbon source,metal solvent and synthetic crystal after high temperature and high pressure(HPHT)experiment.The main research contents and results are as follows:1.The sulfur-containing diamond single crystal was successfully synthesized with FeS as the dopant in the Fe/Ni-C system.The scanning electron microscope of the crystal shows that the {100} plane of the crystal is rougher than the {111}.This phenomenon is related to the number of dangling bonds on different crystal planes.Mapping was used to detect the residue on the surface of the crystal,and the results showed that it was a compound of iron sulphur and nickel sulphur.FeS will decompose in the synthesis system,and the decomposition products are Fe and S2.The XPS spectra of the crystal showed that S was successfully incorporated into the diamond lattice by two bonding methods of C-S-O and C-S-SO2-C,and the peak intensity was strong.The infrared spectrum shows that the N content in the crystal gradually increases with the increase of the doping ratio.Raman spectroscopy analysis shows that the sulfur-doped Ib-type diamond single crystal still has a high-quality sp3 structure even when the doping concentration is high,and the half-width of the crystal gradually widens with the increase of the doping ratio.2.The oxygen-containing diamond single crystal was successfully synthesized with Fe₃O₄ as the dopant in the Fe/Ni-C system.OM showed that with the increase of the doping ratio,the crystal growth rate slowed down and crystal cracks appeared.XPS spectra show that O successfully enters the diamond lattice in the form of C=O and C-O bonding under high concentration doping conditions.The infrared spectrum shows that the N content in the crystal gradually increases with the increase of the doping ratio,and increasing the pressure under the same doping condition will reduce the N content in the crystal.Raman spectroscopy analysis shows that Fe₃O₄ doped type ?b diamond single crystal has a high-quality sp3structure,and with the increase of the doping ratio,the half-value width of the crystal gradually becomes wider.The Raman peak of the doping ratio appears red-shifted.Raman spectroscopy shows that increasing the pressure under the same doping concentration is beneficial to increase the crystallinity of the crystal.When Fe₃O₄ was added to the catalyst,XRD detection of diamond containing inclusions revealed that it was reduced to FeO.3.In the Fe/Ni-C system,FeS is used as the dopant to study the causes of diamond cracking.Use OM,SEM,XPS,FTIR,Raman to characterize the crystal.The OM of the crystal shows that crystal cracks will appear as the doping ratio increases,and increasing the pressure is beneficial to alleviate the cracking phenomenon.The XPS spectrum of the crystal shows that under high concentration doping conditions,S successfully enters the diamond lattice in three bonding methods:C-SO2-C6H5,C-S-SO2-C and C-S.The infrared spectrum showed that the N content in the crystal showed a decreasing trend as the doping ratio increased.Raman spectroscopy analysis shows that the multi-S-doped type ?b diamond single crystal has a high-quality sp3structure,and with the increase of the doping ratio,the half-value width of the crystal gradually widens,and the Raman peak position appears red shift.Raman spectroscopy shows that increasing the pressure under the same doping concentration is beneficial to increase the crystallinity of the crystal.4.In the Fe/Ni-C-N system and in the Fe/Ni-C system,change the synthesis pressure to explore its influence on the nitrogen content and the form of nitrogen in the diamond.The results of FTIR spectroscopy and XPS spectroscopy show that increasing the pressure in the nitrogen-doped system will result in a decrease in the nitrogen content in the diamond.The increase of pressure will increase the proportion of A-center nitrogen in nitrogen-doped diamond,which plays an important role in exploring the formation of natural ?a diamond.Raman spectroscopy and XRD spectroscopy analysis show that type ?b diamond single crystal has high-quality sp3 structure.Increasing the pressure in the nitrogen-doped system will shift the Raman peak position of the synthesized crystal to the right,and the Raman FWHM of the crystal will decrease.