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We report the effects of MgSiO3 addition on the crystal growth and characteristics of type Ⅰb diamonds synthesized in Fe-Ni-C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385-1405℃, and duration of 23.1 h. As MgSiO3 increases from 0.0 wt.% to 3.0 wt.%, the diamond growth temperature increases from 1385℃ to 1405...
Citations
... 28 Adding silicate such as MgSiO 3 and basalt into the FeNi−C system slows down the growth rate of synthetic diamond. 29,30 The nucleation efficiency of diamonds can be significantly improved when the water content in the silicate−H 2 O−C system increases. 16 Besides, the addition of water in the Fe− Ni−C system gradually changes the morphology of diamonds from {111} to {111} dendrites, {110} rhombic dodecahedron, and {110} dendrites. ...
... Our previous work has confirmed that the addition of silicate has no obvious effects on the decreased N total and evolved morphology of diamonds. 30,63 Therefore, H 2 O is speculated to account for these crystal characteristics. We think that the formation of −CH 3 , −CH 2 , and R1−CH(R2)−OH groups terminates the extension of the three-dimensional network structure of the C−C bond, resulting in the reduction of crystal growth rate. ...
... On this basis, the growth processes and characteristics of diamond in metal-silicate-C and metal-silicate-C-H 2 O systems have been studied. The addition of silicate and H 2 O may affect the morphology and nitrogen content of the synthesized crystal (Chepurov et al., 2020;Ding et al., 2020;Lu et al., 2020;Palyanov et al., 2012). MgSiO 3 and coesite were detected when Mg 2 Si 3 O 8 ⋅5H 2 O was added into the Fe 70 Ni 30 -C system, but the reaction mechanism has not been explained clearly (Ding et al., 2020). ...
... The experimental data of diamond synthesized in the metal-silicate- H 2 O-C system by predecessors and this paper allow us to discuss the influences of silicate and H 2 O on the diamond synthesis and its implication to natural diamond grown partly in the reducing metal melt environment at the upper mantle (Ding et al., 2020;Lu et al., 2020). We propose the model diagram of diamond growth in the metalsilicate-H 2 O-C system at HPHT conditions shown in Fig. 10. ...
The detailed phase composition and characteristics of diamond crystals grown in the metal-silicate-H2O-C system at 5.5 GPa and 1385 °C are reported in this paper. The conversion efficiency of the graphite-to-diamond in the metal-silicate-C system is lower than that in the metal-C system, which significantly decreases the growth rate of crystal. As the Mg2Si3O8·5H2O content increases to 1.5 wt%, growth pits and the {110} related features of trigonal pyramids, skeletal structure, rhombic dodecahedron, and {110} dendrites exhibit in sequence. Simultaneously, the content of graphite and metal inclusions inside the crystal increases. These systematic changes were accompanied by the appearance of CH, CO, and CO bonds and a decrease of nitrogen content from ⁓210 ppm to ⁓60 ppm. It is speculated that H2O will further decompose and bond with carbon atoms and finally enter the diamond structure. The formation of CH and CO bonds will terminate the extension of the three-dimensional network of CC bonds. These defects will accumulate along the [111] direction and form {110} related characteristics. These chemical bonds also compete with the nitrogen in the system during entering into the diamond lattice. Our experimental model may provide implications for the morphology and formation environment of natural diamonds.
Studying the influence of oxygen on the growth and properties of diamond has research significance. In this paper, we created an oxygen-rich environment by adding Ni2O3 to the Fe-Ni-C system....
