Challenges in High-Pressure Experiments on Hydrogen in Iron Alloys - Discrepancies among Hydrogen Sources
Abstract
Hydrogen, the lightest of elements, is present in various forms in the universe. A major component of gas giants, it also easily bonds with other major elements entering the composition of rocky planets. Although prone to escape the atmosphere of planets during formation, hydrogen is likely present in significant amounts in planetary interiors, like in mantle minerals through OH bonds [1] or metallic alloys in the core [2]. The interest to study hydrogen in the high-pressure community has grown over the years. However, experimental studies involving pure H2 gas as a source comes with challenges: need for specialized gas loading facilities, diamond anvil embrittlement, and gasket weakening, which are heightened when laser-heating is involved. To alleviate these issues, paraffin has been used as a hydrogen source in diamond anvil cell studies [3], where metallic iron was found to form iron monohydrides (FeH), while studies using H2 gas [4] report the formation of polyhydrides (FeH2 and FeH3).
In an effort to investigate the effect of hydrogen on metallic alloys we studied two different systems, FeS2 and Fe2O3, together with two different hydrogen sources: H2 and paraffin. FeS2 reacted with H2 leads to the formation of polyhydrides, while FeS2 in paraffin remains unreacted. On the other hand, Fe2O3 with H2 leads to the formation of monohydrides, while polyhydrides formed for Fe2O3 in paraffin. We investigate the potential causes leading to the observed discrepancies, such as the presence of carbon in paraffin and/or different amounts of available hydrogen between paraffin and H2 gas. Our results demonstrate that the extrapolation and geophysical interpretation of experimental results should be made carefully considering the effects of different hydrogen sources. References: [1] Pearson et al., Nature, 2014 [2] Badding et al., Science, 1991. [3] Narygina et al., EPSL, 2011. [4] Pépin et al., PRL, 2014.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR21A..07P
- Keywords:
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- 3919 Equations of state;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3944 Shock wave experiments;
- MINERAL PHYSICS;
- 3994 Instruments and techniques;
- MINERAL PHYSICS