# How to convert Mn2O3 to Mn3O4?

I was preparing $$\ce{Mn3O4}$$ but it was when characterized by XRD, a $$\ce{Mn2O3}$$ phase existed. Now how can I convert $$\ce{Mn2O3}$$ to $$\ce{Mn3O4}$$?

You may need a good lab oven.

Manganese(II,III) oxide on Wikipedia

### Preparation

$$\ce{Mn3O4}$$ formed when any manganese oxide is heated in air above 1000 °C. Considerable research has centred on producing nanocrystalline $$\ce{Mn3O4}$$ and various syntheses that involve oxidation of $$\ce{Mn^{II}}$$ or reduction of $$\ce{Mn^{VI}}.$$

As @Poutnik has answered, heating manganese oxides at elevated temperature results in forming of $$\ce{Mn3O4}$$, research paper suggest that the reaction gets affected not only temperature but the partial pressure of oxygen and further heating at 1400 °C results in formation of $$\ce{MnO}$$. Here is an excerpt from a research paper [1] (emphasis mine):

TG and DTA curves of $$\ce{γ-MnO2}$$ have been obtained in nitrogen, air and oxygen. The reactions $$\ce{MnO2 → Mn2O3}$$ and $$\ce{Mn2O3→ Mn3O4}$$ were observed in the ranges 450° to 600° and 750° to 1100° respectively, and the decomposition temperatures are affected by the partial pressure of oxygen. The endotherm at ~1200° is unaffected by the atmosphere and is not accompanied by weight loss. It is, therefore, due to a polymorphic transformation of $$\ce{Mn3O4}$$ rather than formation of $$\ce{MnO}$$.

Another process is carbothermic reduction [2], i.e. reduction of manganese oxides with the help of carbon or carbon monoxide. It requires high carbon monoxide/carbon dioxide pressure and precise change of pressure w.r.t. to temperature. The following reactions depicts how the standard energy of formation varies with temperature:

\begin{align} \ce{3 Mn2O3 + C &->[T = \pu{1100 °C}] 2 Mn3O4 + CO} &\quad ∆G^\circ &= -0.25 - 0.17T\\ \ce{3 Mn2O3 + CO &->[T = \pu{1100 °C}] 2 Mn3O4 + CO2} &\quad ∆G^\circ &= -170.71 - 0.004T\\ \end{align}

References

1. Tinsley, D. M.; Sharp, J. H. Thermal Analysis of Manganese Dioxide in Controlled Atmospheres. Journal of Thermal Analysis 1971, 3 (1), 43–48. https://doi.org/10/bvwj2v.