Compression of Fe–Si–H alloys to core pressures

Abstract

We examined the compression behavior of hexagonal‐close‐packed (hcp) (Fe0.88Si0.12)1H0.61 and (Fe0.88Si0.12)1H0.79 (in atomic ratio) alloys up to 138 GPa in a diamond anvil cell (DAC). While contradicting experimental results were previously reported on the compression curve of double‐hcp (dhcp) FeHx (x ≈ 1), our data show that the compressibility of hcp Fe0.88Si0.12Hx alloys is very similar to those of hcp Fe and Fe0.88Si0.12, indicating that the incorporation of hydrogen into iron does not change its compression behavior remarkably. The present experiments suggest that the inner core may contain up to 0.47 wt % hydrogen (FeH0.26) if temperature is 5000 K. The calculated density profile of Fe0.88Si0.12H0.17 alloy containing 0.32 wt % hydrogen in addition to geochemically required 6.5 wt % silicon matches the seismological observations of the outer core, supporting that hydrogen is an important core light element.

Chemical Reactions Between Fe and H2O up to Megabar Pressures and Implications for Water Storage in the Earth's Mantle and Core

“…Experimental and theoretical studies of FeHx suggest that such an iron hydride can satisfy the density and sound velocity of the Earth's core (Hirao et al, 2004;Mao et al, 2004;Sakamaki et al, 2016;Shibazaki et al, 2012;Tagawa et al, 2016). A primary mechanism for including hydrogen into the Earth's core might be through reaction between iron and water during core formation.…”

The effects of ferromagnetism and interstitial hydrogen on the equation of states of hcp and dhcp FeHx: Implications for the Earth's inner core age

“…Isaev et al, 2007;Elsässer et al 1998;Pépin et al, 2014), melting temperature (e.g. Yagi and Hishinuma, 1995;Okuchi, 1998;Sakamaki et al, 2009;Shibazaki et al, 2011;, density and elastic properties (Caracas, 2015;Hirao et al, 2004;Mao et al, 2004;Pépin et al, 2014;Shibazaki et al, 2012;Tagawa et al, 2016;Umemoto and Hirose, 2015). The maximum abundance of hydrogen has been estimated to be 0.3  x  0.5 (in atomic ratio) for the Earth's core (Okuchi, 1997;Narygina et al, 2011;Umemoto and Hirose, 2015).…”

“…The maximum abundance of hydrogen has been estimated to be 0.3  x  0.5 (in atomic ratio) for the Earth's core (Okuchi, 1997;Narygina et al, 2011;Umemoto and Hirose, 2015). Furthermore, recent experimental study on hcp Fe-Si-H ternary alloys suggests that the abundance of alloying hydrogen is x = 0.17 (Tagawa et al, 2016). These results rely on our knowledge of non-stoichiometric phases such as FeH x .…”

Ferrous Iron Under Oxygen‐Rich Conditions in the Deep Mantle

“…Therefore, reactions between iron and water are likely even at lower mantle conditions and the present study on FeOOH transformations is relevant for modeling these interactions at depth. Iron hydride FeH x indeed satisfies density and sound velocities constraints in the Earth's core (e.g., Tagawa et al, 2016). Pyrite-structured FeO 2 H x was indeed reported to result from the reaction of water with metallic iron Mao et al, 2017;Yuan et al, 2018), a reaction that may have taken place during core formation resulting in the delivery of hydrogen to the Earth's core (Yuan et al, 2018).…”

“…Pyrite-structured FeO 2 H x was indeed reported to result from the reaction of water with metallic iron Mao et al, 2017;Yuan et al, 2018), a reaction that may have taken place during core formation resulting in the delivery of hydrogen to the Earth's core (Yuan et al, 2018). Iron hydride FeH x indeed satisfies density and sound velocities constraints in the Earth's core (e.g., Tagawa et al, 2016). In addition, dehydration melting of transition zone materials swept down to the lower mantle by mantle convection or melting of dense hydrous magnesium phases in subducting slabs that are stagnating near 660-km seismic discontinuity could produce deep hydrous melts at the top of the lower mantle.…”