The Influence of the Active Surface on the Cathodic Reduction of MnO[sub 2]

Abstract

The surface area of samples of manganese dioxide is shown to be an important factor in influencing its behavior. Four samples of MnO~ of widely different origins, electrolytic, activated, natural ore, and synthetic pyrolusite, with total surface area values of 52.8, 50.5, 7.4, and 1.6 mS/g, respectively, are used as examples. The rates of the recuperation reaction at temperatures of 21~ 50~ are shown to be related to the total surface area of the oxides by a complex relation, dependent on temperature and other factors. The product of the reaction MnOOH develops on the surface and in the pores of the original MnO~ particle, thus increasing the diameter and resulting in reduced pore volume, respectively. The MnOOH made under these conditions, from all four starting materials, appears as rod-shaped units in electron micrographs.

Investigation of Manganese Dioxides

“…The results clearly indicate that the surface area depends on the type of MnO2, a conclusion drawn by various authors (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The various groups of MnO2 samples, with the exception of synthetic hydrous MnO2, have distinctly different surface area values and the deviation in the surface areas within the group is small.…”

“…In the latest work Wagner, Lawless, and Gwathmey (10) measured the kinetics of the oxidation of several carefully prepared surfaces parallel to low index planes on an iron single crystal using interference colors. However, due to the formation of at least two oxide phases on iron, this optical technique may not be satisfactory for the estimation of total oxide film thickness (11). Furthermore it is desirable to determine the relative amounts of the various phases present in the oxide film, as well as the total thickness.…”