Chemical Reaction Between Silicon Carbide and Water and its Implication for the Stability of Carbide Exo-Planets
Abstract
Astrophysical observations have shown that some stars have sufficiently high carbon-to-oxygen ratios that planets they host would be mainly composed of carbides. However, it has been known that SiC reacts with water to form silica and gasses at temperatures as low as 700 K at very low pressure [1]. We have examined if this reaction proceeds under the pressure and temperature conditions relevant to planetary interiors in both laser-heated diamond anvil cell (LHDAC) and large volume press (LVP). LHDACs were loaded with powder of either the 6H or 3C polymorphs of SiC, and then H2O was injected as a medium. The samples were compressed to pressures of 20 and 40 GPa and then heated to temperatures between 1400 K and 1800 K while collecting in situ X-ray diffraction (XRD) patterns. For LVP samples, SiC-6H powder was loaded with H2O into a Pt capsule, then compressed to 19 GPa and heated to 1200 K for one hour. XRD patterns from the LHDAC samples showed the transformation of SiC into SiO2 stishovite. Raman spectroscopy confirmed these phases, as well as showing the presence of hydrocarbons. Raman measurements of the MAP sample confirmed the transformation into stishovite, while electron probe microanalysis showed very little carbon remained. This result indicates that the SiC + H2O → SiO2 + CH4 reaction also proceeds at high pressures and temperatures. It also implies that in the presence or with delivery of water, a carbide exoplanet would oxidize and turn into a silicate/oxide (therefore Earth-like) planet. However, in the case of carbide planets, the byproducts, specifically reduced carbon, could represent a metabolic source for biochemical reactions necessary to support life.
References: [1] Yoshimura M. et al. JMR, 1986.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR41B0044A
- Keywords:
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- 1042 Mineral and crystal chemistry;
- GEOCHEMISTRY;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3999 General or miscellaneous;
- MINERAL PHYSICS;
- 3620 Mineral and crystal chemistry;
- MINERALOGY AND PETROLOGY;
- 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGY;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 7208 Mantle;
- SEISMOLOGY