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?

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

2 Answers 2


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.

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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.


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).

  • 1
    $\begingroup$ 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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