Herstellung und Reaktion von Gliedern der Hollandit-Gruppe MxMn8O16 (M = K, Rb, Cs, Ca, Sr, Pb; x = 1 und M = Na; x = 1.9)

Abstract

Hollandite, cryptomelane, manjiroite, and coronadite were synthesized by hydrothermal methods at 500 °C and 2 kbar in order to determine their unit cell dimensions and analytical composition from fully crystalline samples. Analyses, X-ray diffraction, and electron microscopy have shown that the tunnel structure accommodates 1 K, Rb, Cs, Ca, Sr, or Pb but ca. 2 Na per unit Mn₈O₁₆. Crystalline samples show no conceivable ion exchange nor are they attacked by concentrated nitric acid at room temperature. Finely divided cryptomelane, however, is attacked by conc. HNO₃. The unit cell dimensions as well as the relations between ionic radius of the tunnel ion, symmetry, and composition are discussed.