<Original Papers>Studies of the System Ba-Mn-O.(I) : Preliminary Results of the Phase Equilibria in the System BaO-Manganese Oxide in Air, with the Thermal Transformation of Hollandite

The hollandites (Ba_ Mn_8 O_・nH_2O) from Miyazaki mine, Miyagi Prefecture and Funakozawa mine, Iwate Prefecture were heat-treated at various temperatures for 24 hours in air and examined by X-ray powder method. After being heated to about 1,000℃, both specimens show an X-ray pattern arising mainly from the tetragonal Mn_3O_4 (hausmannite). Also, some extra lines are present and these most probably represent the unknown compound belong the system BaO-manganese oxide. Subsolidus relation of the manganese rich region in the system BaO-manganese oxide were examined using air atmosphere and the quenching technique. The BaMnO_3,"X" phase (probably BaO・2Mn_2O_3) and tetragonal Mn_3O_4 were confirmed in the temperature range (from 900 to 1,100℃) presently investigated