Résumé
Relationships between lattice parameters of manganese dioxides (γ/ε-MD) and their surface properties at the solid-aqueous solution interface were investigated. The studied series ranged from orthorhombic ramsdellite to tetragonal pyrolusite and encompassed disordered MD samples. The structural model used takes into account two structural defects which affect the orthorhombic network of ramsdellite: Pr (rate of pyrolusite intergrowth) and Tw (rate of microtwinning). Water adsorption isotherms showed that the cross sectional surface area of water molecules is linearly correlated to Pr: from 6.3 Å2 (Pr=0.2) to 13.1 Å2 (Pr=1). Titration of their surface charge evidenced a linear relationship between PZC and Pr starting from ramsdellite (Pr = 0, Tw = 0, PZC = 1) to pyrolusite (Pr = 1, Tw = 0, PZC = 7.3). γ-MD with intermediate values of Pr (0.2 to 0.45) have increasing PZC values. For similar Pr values (0.45), high Tw percentage (0.3 and 1) makes the PZC to increase. The experimental results are compared with data collected in the literature for dioxides of transition elements with tetragonal structure. Surface titration leads to the determination of electrochemically active surface area at alkaline pH.