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

The surface area of samples of manganese dioxide is shown to be an important factor in influencing its behavior. Four samples of 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 m 2 /g, respectively, are used as examples. The rates of the recuperation reaction at temperatures of 21°–50°C 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 develops on the surface and in the pores of the original particle, thus increasing the diameter and resulting in reduced pore volume, respectively. The made under these conditions, from all four starting materials, appears as rod‐shaped units in electron micrographs.