A crystallographic study of the thermal decomposition of zinc and manganese carbonates

Abstract

The thermal decompositions of zinc carbonate and manganese carbonate have been studied by X-ray diffraction using single crystal techniques. The decomposition of manganese carbonate has been studied under static atmospheric conditions and in an inert gas stream. The products differ from those previously reported. The structural and orientation relations between the carbonates and the product oxides have been determined and are discussed. A small but definite degree of topotaxy was observed in the reactions, but unlike many other topotactic reactions, retention of the closest packed oxygen framework does not occur. An inhomogeneous mechanism was shown to be inadequate to explain these results, but they can be interpreted on the basis of a recrystallisation mechanism. A previously unreported crystalline form of an oxide of manganese has been isolated. The oxide is stable in atmospheric conditions between 370° and 530°. It is tentatively named ω-MnO2 and has unit cell dimensions a = 4.48; b = 2.76 x k1 ; c = 2.38 x k2 (k1 and k2 undetermined integers)