Oxide und Oxidhydroxide des drei- und vierwertigen Mangans

Abstract

The cryptocristalline manganese oxides and oxidehydroxides have been investigated by means of focusing X ray cameras, electron microscopy, electron diffraction, thermoanalysis and classical analytical methods. Morphology, structure and reactivity of these products were compared.
The authors find that only two true MnO₂ modifications (mineral species) exist, namely, ramsdellite (no greek sign attributed), and pyrolusite (= polianite, β-MnO₂).
All other products do not have the analytical composition MnO_2,000, or they are varieties of the two modifications mentioned to which they can be attributed by means of MoK_α radiation patterns. A common series is known as the mineral nsutite (γ-MnO₂) which forms large deposits e.g. in Nsuta (Ghana).
Another group, known hitherto as “δ-MnO₂” or birnessite may be attributed to a layer structure hydroxide of the analytical composition Mn₇O₁₃, 5 H₂O which differs distinctly from the mentioned true MnO₂ modifications. Disperse varieties approach the composition MnO_≈2 and may, incidentally, appear amorphous though they are not.
A third group may be distinguished from the second in that Na⁺ ions are lattice constituants and cause a distortion of the basically hexagonal densest oxygen packing to at least orthorhombic structure. Disperse varieties may look similar to those of the second group, in terms of powder patterns, but are by far more stable towards, e.g., organic reducing agents, or thermal decomposition, or when subject to a vacuum.