Study of the modifications of manganese dioxide

Abstract

P ast work on the modificat ion s of manganese dioxide of in terest in dry-cell manu facture is r evie wed. New X-ray da ta, at bo th room and elevaLcd te mperat ures, combined ' with differen t ial hea t ing curves lead to t he co ncl usion that five type of m anga nese dioxide exi t : (1) well-crystallized p yrolu site ; (2) gamm a m a nganese di ox ide, a p oorly crystalli zed pyrol u-site; (3) ramsd ellite ; (4) cryp tomelane, a form co n taining esse nt ial p otassium or sodi ulll.; a nd (5) delta m angan ese dioxide, belie ved to be a p oorly crystalli ze d cryptom ela ne. The high-t empera ture X-r ay diffraction da ta indicate d t he phase cha nges t h at ca use th e heating-cur ve effects. A new cr ystal fo rm of man gan osic oxide (Mn30 4), stable a bove 1,170 0 C, w ~ s fo und t o be cubic of spinel structure. Fincness dcten n in aLion by b oth t hc ni t rogen a dsorp-t ion and Lhe X-ray line broadening m e thod s were m ad e on selected sam p les.