The effect of crystal structure on the surface properties of a series of manganese dioxides (original) (raw)

The zero-points-of-charge for a series of manganese dioxides have been determined by both electrophoretic and coagulation-sedimentation techniques. The zpc was found to increase from pit 1.5 for the amorphous ~ form of MnO2 up to pit 7.3 for /~-MnO~, the most well-defined crystalline form. This variation is interpreted in terms of, and is shown to be in agreement with, the electrostatic field strength concept modified to describe more complex solids. The change in cation-anion spacing, as derived from the volume per unit cell per cation in the crystal lattice, corresponds to a change in the polarization of the water dipoles and their subsequent dissociation to establish the electrochemical double layer at the oxide-water interface.