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This question asks if the comparatively large paramagnetic susceptibility of liquid oxygen (LOX) is considered when designing rocket tank and engine systems. This comment suggests fuels such as RP-1 (kerosene-like) and liquid hydrogen (often used in liquid-propellant rockets) do not have a susceptibility as large.

I'd like to find either the approximate or even ballpark values for the magnetic susceptibility of the following four materials, or at least a source where they might be found:

  1. liquid oxygen (LOX)
  2. liquid hydrogen (LH2)
  3. RP-1 (rocket fuel), and
  4. liquid methane (LNG)

I have tried google searches of various permutations of terms, but so far no luck beyond the one value I was able to cite in that question (LOX susceptibility here).

I'm fairly sure that the susceptibility of the other three are much smaller (100× or more) than that of LOX. For example here is what I can do now:

  1. LOX: use the value reported in the link above; 3.5E-03
  2. LH2: This question links to this table which lists the susceptibility of liquid hydrogen -5.44E-06 cm³/mol. If I use a density of 0.07 g/cm³ and molar mass of 2.0 g/mol (both from here) I get approximately -1.9E-07.
  3. RP-1: decide that for paramagnetic and diamagnetic susceptibility, kerosene and crude oil are very roughly equivalent and use -1E-08 m³/kg from section I of this along with a density of order of magnitude 1000 kg/m³ to get a susceptibility of roughly -1E-05
  4. LNG: - same argument as RP-1, roughly -1E-05
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  • $\begingroup$ Liquid oxygen will be the only paramagnetic substance in this list (it has two unpaired electrons). The others are all diamagnetic. But oxygen is an oxidiser not a full and the others are all fuels. So is the question whether the oxidisers associated with the fuels are paramagnetic? $\endgroup$
    – matt_black
    Commented Mar 16, 2019 at 21:22
  • $\begingroup$ @matt_black if you look carefully you'll see I never called oxygen a fuel. I did however call it and all the rest propellants, which is the standard terminology in rocket-speak. There are some great videos in Is the Paramagnetism of Liquid Oxygen Ever Considered in Engine or Tank Design? and it's already helpful that you point out that the others propellants are likely to have much weaker responses to magnetic field than LOX, thanks! $\endgroup$
    – uhoh
    Commented Mar 16, 2019 at 23:42

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As it has been pointed out, molecular oxygen is paramagnetic. It is exceptional in that. Usually, you require either a transition metal ion, or a lanthanide ion, or a radical, for a molecule to be paramagnetic.

For most other molecules, including as far as I can tell the fuels you mention, you can safely assume that they are diamagnetic. Paramagnetism is relatively tricky and intense, diamagnetism, at least in its magnitude, is weak and comparatively straightforward to estimate.

If one wants an inexpensive, ballpark estimate of diamagnetism, many people use Pascal's constants, additive terms considering the involved atoms, with corrections for certain bonds. Rather than Pascal's original work, maybe check out the widely cited Gordon A. Bain and John F. Berry, Diamagnetic Corrections and Pascal's Constants, J. Chem. Educ. 2008, 85, 4, 532.

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