Formation Region of Cryptomelane with Different K-Ion Occupancy and Elutriation of K-Ion with Water

Abstract

Cryptomelanes [Kx(Mn3+, Mn4+)8O16(1.1≤x≤2.0)] with different occupancies (55% to 100%) of K-ion in the one-dimensional tunnels were synthesized by solid state reaction. The critical formation temperatures of cryptomelanes with low occupancy are lower than those with high occupancy. Cryptomelanes with low occupancy change to those with high occupancy accompanied with bixbyite (Mn2O3) during the heating. The deformation temperature measured by DTA is a function of the K-ion occupancy. A certain amount of K-ions of cryptomelane is elutriated quickly from the tunnels by water. The K-ion occupancy can be determined from the functional relationship between the deformation temperature and the K-ion occupancy, based on the deformation temperature measured by DTA.