Study of the modifications of manganese dioxide

Past work on the modifications of manganese dioxide of interest in dry-cell manufacture is reviewed. New X-ray data, at both room and elevated temperatures, combined with differential heating curves lead to the conclusion that five types of manganese dioxide exist: (1) well-crystallized pyrolusite; (2) gamma manganese dioxide, a poorly crystallized pyrolusite; (3) ramsdellite; (4) cryptomelane, a form containing essential potassium or sodium; and (5) delta manganese dioxide, believed to be a poorly crystallized cryptomelane. The high-temperature X-ray diffraction data indicated the phase changes that cause the heatingcurve effects. A new crystal form of manganosic oxide (M113O4), stable above 1,170° C, w^s found to be cubic of spinel structure. Fineness determinations by both the nitrogen adsorption and the X-ray line broadening methods were made on selected samples.