Microscopic structure of Fe-Ni and Fe-Ni-S molten alloys of geophysical interest

Abstract

The static $S(Q)$ liquid structure factors for binary ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x},$ $x=0.90,$ 0.85, and ternary ${\mathrm{Fe}}_{0.85}{\mathrm{Ni}}_{0.05}{\mathrm{S}}_{0.15}$ molten alloys are investigated by means of the concurrent use of neutron diffraction and reverse Monte Carlo simulations. The measured $G(r)$ radial distributions reveal atomic orderings varying from that present in the ${\mathrm{Fe}}_{0.90}{\mathrm{Ni}}_{0.10}$ alloy, reminiscent of the ideal bcc structure of solid Fe, to a far more open structure found in ${\mathrm{Fe}}_{0.85}{\mathrm{Ni}}_{0.05}{\mathrm{S}}_{0.15}.$ From data at hand no clear evidence of the clustering of sulfur within the Fe-Ni matrix is found. In contrast, the addition of sulfur leads to significant changes in structural and some dynamical properties that can be inferred from knowledge of the static structure factors. Such dynamical changes seem to arise as a result of a strong decrease of the elastic moduli of the alloys resulting from interactions with a light element rather than from a density effect.