High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion

Abstract

Diamond formation in polystyrene (C 8 H 8 ) n , which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606-611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa. V

Measurement of diamond nucleation rates from hydrocarbons at conditions comparable to the interiors of icy giant planets

“…For the samples at ambient conditions, the diffraction signatures of both the amorphous polystyrene (the blue line-out subtracting the sharp Al Bragg peaks) as well as the thin aluminum coatings (Bragg peaks in the blue line-out) can be observed. In the driven case, the formation of compressed diamond crystallites is clearly visible, as demonstrated by the appearance of the corresponding (111) powder diffraction ring above a broader diffraction signature of a remaining warm dense CH liquid [7]. Complying with the assumption that diamond crystallites are formed in quasi-steady-state conditions after the second shock wave has passed, we do not find evidence for a preferred orientation of the crystallites.…”

“…The first compression wave (e.g., ∼60 GPa, ∼4000 K, for the intermediate drive) takes ∼7.5 ns to reach the sample rear side. The second compression wave that creates the high-pressure, high-temperature conditions required for diamond formation is launched 6 ns after the initial shock and traverses the precompressed sample volume within ∼1 ns [6,7]. Therefore, there were on average t D = 500 ps to form diamonds at the moment when the two compression waves overlap at the sample rear side.…”

“…Structural changes could be observed by in situ x-ray diffraction (XRD) with the LCLS pulses of 8. discussion of the pressure and temperature conditions reached in the experiment, can be found in Refs. [6,7].…”

“…This material mix likely undergoes chemical reactions and structural transitions due to the high-pressure, high-temperature conditions deep inside the planets' interiors [3][4][5]. A prominent example of such a reaction is the possible carbon-hydrogen dissociation and the subsequent phase separation that results in the formation of diamonds [6][7][8]. The diamonds are denser than the surrounding fluid and therefore precipitate towards the planetary centers [3].…”

High Pressure Hydrocarbons Revisited: From van der Waals Compounds to Diamond

“…Dynamic compression experiments on hydrocarbons are used to probe their properties at combined high-pressure and -temperature conditions [33][34][35][36][37][38][39][40], both to investigate their potential decomposition, but also to better understand a critical ablator material used in inertial confinement fusion experiments. The thermal equation of state of hydrocarbons has therefore been a subject of several ab initio molecular dynamics studies [41][42][43][44][45][46].…”