The composition of the fluid phase in inclusions in synthetic HPHT diamonds grown in system Fe–Ni–Ti–C

Abstract

Diamonds grown by high pressure high temperature process (HPHT) are usually characterized by yellow color and high contents of nitrogen. Introduction of Ti decreases nitrogen content in diamond. Understanding the formation of nitrogen-poor diamond is very important not for the progress of HPHT process only, but because these diamond varieties represent the rare natural stones, although their crystallization conditions have not been clarified yet. Here we studied the composition of fluid phase in synthetic diamonds. The experiments were performed using a high-pressure apparatus BARS at pressures 5.5–6.0 GPa and temperatures 1350–1400 °C. It was found that introduction of metallic Ti leads to concentration of nitrogen mainly as nitrogenated hydrocarbons. The hypothesis that elucidates the formation of low-nitrogen diamond in Fe–Ni is proposed: the presence of Ti leads to an increase of hydrogen fugacity in the metal melt which drastically reduces the nitrogen solubility. As a result, nitrogen concentrates in the form of complex hydrocarbon compounds, while diamond grows colorless and characterized by very low nitrogen content. It is suggested that the proposed mechanism acts the same way in the presence of other metals which are strong reducing agents.

Characterization of the nitrogen state in HPHT diamonds grown in an Fe–C melt with a low sulfur addition

“…The reliability of this mechanism was recently confirmed by experiments on growth of nitrogen-poor diamonds in an Fe–Ni melt with addition of titanium. 59…”

Impact of Solid Hydrocarbon on the Composition of Fluid Phase at the Subduction (Experimental Simulation)

“…Volatiles from the samples were analysed using the pyrolysis-free coupled gas chromatography-mass spectrometry (GC-MS) method on a Focus GC/DSQ II Series Single Quadrupole MS analyser (Termo Scientifc, Austin, TX, USA) at the V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk [32,[46][47][48][49]. The gas mixture was released from the fluid and melt inclusions of the samples by means of shock mechanical crushing in a custom-designed crusher.…”

Thermal Annealing Effect on the Thermoluminescence Properties of Commercial High‐Pressure High‐Temperature Diamond Powders

“…The commercial HPHT microdiamond (MD) samples exhibit different morphologies, mainly cubic, octahedron, and cube octahedron, as shown in Figure 1, which are consistent with conventional HPHT diamonds manufactured with Mg-Si-C and Fe-Ni-Ti-C systems. [24,25] The morphological differences among the samples can be related to the initial growing conditions in HPHT synthesis, such as the alloy metal systems used, primarily Fe-C, Fe-Si-C, FeAl-C, Fe-Ni-C, and the use of silicates, adamantanes, C 6 H 8 O 7 , and Ni 2 O 3 as additives employed in the synthesis. [26][27][28][29][30][31] To evaluate the diamond quality, the samples were characterized by Raman and photoluminescence (PL) spectroscopy.…”