Synthesis of nanocrystalline Mn-oxides by gas condensation

The preparation of nanocrystalline (n-) Mn-oxides has been investigated. The oxides were obtained by oxidation of n-Mn metal, prepared by inert gas condensation, in air and in oxygen at different temperatures and times. Differential thermal analysis revealed a broad exothermic peak with a maximum at 596 °C, while thermogravimetry showed the adsorption of O₂ between 580 and 700 °C. XRD diffractograms, performed after annealing at lower temperatures in air (T<400 °C) for 1 h, revealed the formation of MnO and Mn₃O₄ as main crystalline phases. After oxidizing between 400 and 600 °C the presence of Mn₅O₈ and Mn₂O₃ has been detected, while at higher temperatures (T≥600 °C) Mn₂O₃ as single phase was observed. After oxidation the average particles size increased from 27 to 43 nm but no further changes of the crystalline phases was observed.