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As I know, uranium and iron simply aren't mixable, which means there are no U-Fe alloys. The Google says, uranium is insoluble in molten iron.

But, if something is "insoluble", it actually means only that there is a very low maximal concentration.

What if we want to mix only 1ppm of U in molten Fe? What if 0.01 ppm? What is the maximal concentration?

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  • $\begingroup$ uranium / iron alloys do exist, they have been reported in the inorganic crystallograpic database $\endgroup$ Commented Jun 27, 2018 at 7:31

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At any temperature where the iron is liquid, uranium is also liquid and 100% miscible with it. See Chen et al.[1], from which the diagram below is taken. As with many metal pairs, the liquid phase solubility does not carry over to the solid state, where several intermetallic compounds form.

enter image description here

Reference

1. Chen, Tianyi; Smith, Travis; Gigax, Jonathan; Chen, Di; Balerio, Robert; Shao, Lin; Sencer, Bulent; Kennedy, J. (2015). "Intermetallic formation and interdiffusion in diffusion couples made of uranium and single crystal iron." Journal of Nuclear Materials 467, 82-88. https://doi.org/10.1016/j.jnucmat.2015.05.026.

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According to Uranium partitioning between liquid iron and silicate melt at high pressures: implications for uranium solubility in planetary cores

The solubility of U in liquid Fe is in the range of 0.6 to 800 ppm and increases with temperature (T) and pressure (P).

See also U solubility in Earth’s core which finds a solubility of 2 ppm at zero pressure (run number 198).

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    $\begingroup$ Hehh, you know the reason, why I asked it! Respect :-) $\endgroup$
    – peterh
    Commented May 28, 2016 at 0:19
  • $\begingroup$ There's a difference between solubility and partitioning, which is not clear from the papers you linked to (which weren't peer reviewed I guess). The solubility of U in liquid Fe is almost complete. Partitioning experiments (including the ones you linked to) show that it preferentially goes to the silicate, not the core. Read this related question in ESSE. $\endgroup$
    – Gimelist
    Commented Jun 19, 2016 at 8:01

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