Manganese dioxide structural effects on its thermal decomposition

In this work, the influence of the structure, composition and morphology on the amount of mass lost from gamma-MnO2 during heat treatment, and the activation energy for this process (from iso-conversional kinetic analysis), was determined using a statistical approach. It was found that the differential thermogravimetric (DTG) data for electrolytic manganese dioxide (EMD) samples typically show two regions of mass loss; water bound to surface sites and structural water at or near the surface removed between similar to 120 and 200 degrees C, and bulk hydroxyl groups lost in the range similar to 200-400 degrees C. The composition and morphology had the greatest effect on the amount of mass lost; namely, BET surface area and percentage Mn(III) for the first process (r(2) = 0.92) and percentage Mn(IV), percentage Mn(III) and cation vacancy fraction for the second (r(2) = 0.89). The activation energy for the first processes was most affected by BET surface area, c(o) and crystallite size in the (221) direction (r(2) = 0.89). Relatively poor correlations were found between the amount of water lost and the activation energy for the second process and the material properties measured in this work. This likely relates to the slow kinetics of the first mass loss which complicates the relationships existing for the second. (C) 2011 Elsevier B.V. All rights reserved.