I am trying to make iron-oxide through electroylsis to make thermite. I'm using nails for the iron on the positive electrode in salt water. While there definitely is a good amount of rust collecting, especially at the surface, after dissolve multiple nails, there are also these black sludge-like solids forming:

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I can pick them out of the solution if i'm careful, but they are very brittle and break up and dissolve almost immediately if I use too much force. Additionally, if I stir the up or shake the container, more of this stuff comes up from the bottom, most of it dissolved in a black-green watery, solution and you can't even see the rust anymore. If you give it time to settle, though you can see the rust again.

My question is what is this stuff, and will it make the rust impure? Do I need to get rid of it to make the thermite? Will boiling the solution to get rid of the water like I had planned be enough?

Thanks in advance.

  • $\begingroup$ If you don't know that rust isn't of much use in thermite, you shouldn't even plan such thing. Real thermites are very dangerous in use. $\endgroup$
    – Mithoron
    Aug 15, 2017 at 23:10
  • $\begingroup$ @Mithoron what do you mean? Thermite is a mixture of fine iron-oxide and aluminum particles. Or am I wrong? $\endgroup$
    – Maltysen
    Aug 15, 2017 at 23:11
  • $\begingroup$ @Mithoron the example picture on wikipedia uses iron oxide: en.wikipedia.org/wiki/Thermite#/media/File:Thermite_mix.jpg $\endgroup$
    – Maltysen
    Aug 15, 2017 at 23:13
  • $\begingroup$ sigh Oxides in rust are hydrated, and water can make the mixture useless or to kill the user. $\endgroup$
    – Mithoron
    Aug 16, 2017 at 17:26
  • 2
    $\begingroup$ Since there are safety issues here, please consult with an expert (live, not via the internet) if you have even the slightest doubt about the proper methodology. As @Mithoron mentioned, this can be extremely dangerous. $\endgroup$
    – jonsca
    Aug 17, 2017 at 2:58

1 Answer 1


The black stuff is your iron oxides. FeO and Fe3O4 are both black, Fe2O3 is red. I would guess you are making some complex iron oxide/ hydroxide/ hydrate. I have seen XRD analyses of many aqueous iron corrosion products , they are typically a complex mix.

  • $\begingroup$ Cool, thanks! So you don't think that the chlorine is messing anything up? These should be fine to use for thermite as long as they are just metal oxides, right? $\endgroup$
    – Maltysen
    Aug 16, 2017 at 0:24

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