Abnormaly phase change by thermal on some pyrolusites

Abstract

Pyrolusites from two localities in southwestern Hokkaido, Japan, were studied by means of DTA, thermo-balance and high temperature X-ray analysis. From the thermal behavior of the first endothermic reaction generally pyrolusite seems to deoxidize abruptly at about 680°C transforming into α-Mn₂O₃. A specimen from Hanaishi, however, shows double peaks by endothermic reaction at about 710°C and 773°C. The first endothermic peak at 710°C of this specimen shows transformation into α-Mn₂O₃ and γ-Mn₂O₃. γ-Mn₂O₃ phase is an unstable from at high temperature. The second peak at about 773°C of this pyrolusite is due to the following endothermic reaction: α-Mn₂O₃+γ-Mn₂O₃→α-Mn₂O₃+Mn₃O₄. Two types of pyrolusite, one with a single peak and the other with double peaks can be distinguished from DTA and thermo-balance curves.