Oxidation Reactions/Reactivity of Manganese Metal in Air and Water

I am planning on doing some reactions that lead to Manganese metal and a neutral solution containing $\ce{Mn^{2+}}$ as by-products, and I wanted to try some things out with the Manganese as well.


Since Manganese has common charges of II and III, will a relatively fine, grainy form of the metal burn (and at what temperature) in air to form a mixed "$\ce{Mn(II, II)}$" oxide, $\ce{Mn3O4}$, the way Iron does as it rusts, or is $\ce{MnO}$ more predominant?


I have the same question about whether or not $\ce{Mn3O4}$ is formed in "thermite-like" reactions such as reacting $\ce{CuO}$ with $\ce{Mn}$.


As for water, I know that Manganese metal is one of the more active metals among the transition metals, so I am also concerned with whether Aluminum can be used to reduce $\ce{Mn^{2+}}$ to the metal in boiling water without the formation of any Manganese Oxide or Hydroxide side products due to the water (especially due to the fact that reducing metals like this precipitates them out as a fine powder).


$\ce{ 2Al + 3Mn^{2+} -> 2Al^{3+} + 3Mn}$




Unlike your claim, [manganese is relatively inert despite it being a little more electropositive than its neighbors in the periodic table.](https://webelements.com/manganese/chemistry.html) It is not particularly reactive to air. The surface of manganese lumps oxidize to a minor extent but when it is finely divided, it becomes pyrophoric and burns in air. It tends to form the oxide $\ce{Mn3O4}$ and the nitride $\ce{Mn3N2}$. Temperature for such reactions are reaches more than 500 °C.


$$\ce{3Mn(s) + 2O2(g) ->[\Delta] Mn3O4(s)}$$


$$\ce{3Mn(s) + N2(g) ->[\Delta] Mn3N2(s)}$$


Manganese is also said to not react with water *under normal conditions* although some sources say it reacts with water to liberate hydrogen gas.


For your thermite reaction, I haven't found any $\ce{Mn-CuO}$ reaction but I did find $\ce{Al-Mn^2+-}$ thermite reaction. You can find the details [here](https://www.nakka-rocketry.net/thermites.html).


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