Salamat, A. | Search NASA

DOE OSTI2023

Metallic hydrogen: Study of metastability

Metallic hydrogen (MH) has been predicted to be metastable, a high temperature superconductor, and a powerful rocket propellant. If true, MH could have an enormous impact on society. We have produced MH in a diamond anvil cell and studied its metastability. At a temperature of 5 K, the load on the metallic hydrogen was stepwise reduced until the pressure was essentially zero. While turning the load or pressure down, the sample evidently transformed to the molecular phase and escaped; the hole in the gasket containing the MH closed. We were unable to determine this value of the metastability pressure. Metallic hydrogen was not observed to be metastable at zero pressure, with no uncertainty.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Diamond and methane formation from the chemical decomposition of polyethylene at high pressures and temperatures

Abstract Polyethylene (C 2 H 4 ) n was compressed to pressures between 10 and 30 GPa in a diamond anvil cell (DAC) and laser heated above 2500 K for approximately one second. This resulted in the chemical decomposition of the polymer into carbon and hydrocarbon reaction products. After quenching to ambient temperature, the decomposition products were measured in the DAC at pressures ranging from ambient to 29 GPa using a combination of x-ray diffraction (XRD) and small angle x-ray scattering (SAXS). XRD identified cubic diamond and methane as the predominant product species with their pressure–volume relationships exhibiting strong correlations to the diamond and methane equations of state. Length scales associated with the diamond products, obtained from SAXS measurements, indicate the formation of nanodiamonds with a radius of gyration between 12 and 35 nm consistent with 32–90 nm diameter spherical particles. These results are in good agreement with the predicted product composition under thermodynamic and chemical equilibrium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗