Structure and Thermal Decomposition of K_xMnO₂・yH₂O Prepared by Sol-Gel Method

抄録

The birnessite-type K_0.28MnO₂ hydrates with the average crystalline size of about 10-20 nm have been prepared by a sol-gel method using KMnO₄ and glucose aqueous solutions. Their crystal structure and thermal stability have been investigated by XRD, TG-DTA, and TEM-EDX. The dehydration reaction occurs at around 180℃. The samples heated in between 600 and 800℃ transform into a cryptomelane-type phase with 2×2 tunnel type structure. Not so much change in the crystalline size due to the above phase transformation was observed. The heating at above 900℃ causes the decomposition reaction into the tetragonal spinel-phase Mn₃O₄ and the layered K-rich birnessite, K_0.31MnO₂, accompanied with the release of oxygen and the 4 times increase in the crystalline size.