Thermal behaviors of cryptomelane with various occupancy of K-ions.

Thermal behaviors of cryptomelane (KxMn8O16 ; 0≤x≤2) have been examined with DTA and TGA. The differences in thermal decomposition of various cryptomelanes depend on the K-ions occupancy in its one-dimensional tunnels. Arising temperature from 630°C to 860°C, cryptomelane with lower occupancy is gradually converted to one with higher occupancy accompanied by producing bixbyite (Mn2O3) . After the tunnels are filled up with K-ions at 860°C, the cryptomelane is converted to bixbyite and K2Mn4O8 phase. Subsequently, the bixbyite is transformed to hausmannite (Mn3O4) . According to the above fact, cryptomelanes with various occupancies have been obtained by means of solid state reaction. [J. Cryst. Soc. Jpn. 26, 278 (1984) ] .