THERMAL-DECOMPOSITION OF COBALT(II) ACETATE TETRAHYDRATE STUDIED WITH TIME-RESOLVED NEUTRON-DIFFRACTION AND THERMOGRAVIMETRIC ANALYSIS

The thermal decomposition of cobalt acetate tetrahydrate has been studied using time-resolved powder neutron diffraction. By using selectively deuterated samples, the loss of water or the breakdown of the acetate group can be identified by following the decrease in the incoherent background of the diffraction pattern as the hydrogen atoms are lost. The results suggest that by 150-degrees-C dehydration is complete and a glass-like phase is formed. Crystallization of this anhydrous acetate occurs at 200-degrees-C. Further heating initiates a two-stage decomposition of the anhydrous acetate terminated by the formation between 275-310-degrees-C of a tetrahedrally co-ordinated cubic zinc blende form of CoO. This transforms at 310-degrees-C to a rock-salt structure. The neutron diffraction data have been complemented by thermogravimetric and chemical analyses from which we have been able to propose some possible intermediate decomposition products and suggest an explanation for the formation of the unusual zinc blende form of CoO.