# Iron and copper oxide for thermite

I recently successfully made thermite from iron oxide powder and aluminum powder. However, I have a couple of questions about copper and iron oxides.

The kind of iron oxide that is made by electrolyzing iron in a salt water bath. You rinse the solution well to get some of the salt out then boil off/dry the remaining sludge. What is left is a red powder. What kind of iron oxide is this? (II,III)

Lastly, if I repeated the same process with copper, would I get copper(I) oxide or copper(II) oxide?

Apologies for my lack of knowledge in chemistry.

• Iron(I) and iron(IV) oxides do not exist. The only iron oxide with a reddish color is iron(III) oxide $\ce{Fe_2O_3}$. Iron(II) oxide FeO is not stable in air. It gets quickly transformed into iron(III) oxide. The thermite reaction works well with aluminum powder and iron(III) oxide. – Maurice Jul 12 '20 at 19:44
• Copper oxides are nowhere near as stable as aluminum oxides. – Jon Custer Jul 13 '20 at 18:15
• @Maurice $\ce{FeO}$ oxidizes to black $\ce{Fe3O4}$, not to red/brown $\ce{Fe2O3}$, as the former is the most stable at low/medium temperatures. So does $\ce{Fe2O3}$ converts to $\ce{Fe3O4}$ when heated enough. Note that these oxides as many oxides of transition metals are not fully stoichiometric. – Poutnik Jul 23 '20 at 13:07
• @ Poutnik. Thank you for the complementary information. – Maurice Jul 23 '20 at 15:52