Investigation of Manganese Dioxides

Abstract

The surface areas of natural ores, electrolytic, chemical, and synthetic hydrous MnO2 samples were determined by both low-temperature nitrogen gas adsorption and water vapor adsorption at 25~ using the B.E.T. adsorption isotherm relationship. These various types of manganese dioxides have distinctly different surface areas as determined by the two methods. The water content retained at ll0~ and corrected total water content were found to be surface area dependent. The synthetic hydrous MnO 2 samples occupy a unique position due to their high water content.

Cation‐Vacancy Model for MnO2

“…Depending on the spacial distribution of the four OHions, present around a vacancy, either 1, 2, or 3 OH-ions must occupy a pyramidal site. The remaining, free, accessible pyramidal sites are thus given by [0-2], = 1px -y [10] whereby p can assume values of 1, 2, or 3.…”

“…[8], all the O ~-sites are equally available, or, on the other hand, into (1px -y) 02-sites, if, according to Eq. [10], only the pyramidal oxygen sites are available for proton uptake during reduction. Neglecting interaction 2t,,,,I,,',l or, respectively…”

“…The fact that the electrochemically active forms (T-and e-MnO2) always contain in the crystal structure a considerable amount (typically 4% per weight) of "structural," "chemically bonded," or "combined" water, has been recognized for a long time (4)(5)(6)(7)(8)(9)(10)(11). This structural water appears to be distributed over a wide range of "absorption energies" and can be removed progressively by heating to increasing temperatures in the range from about 100 ~ to 400~ (12)(13)(14)(15)(16)(17).…”