Physico-chemical characterization of thermal decomposition course in zinc nitrate-copper nitrate hexahydrates

Abstract

This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO3)(2)center dot 4H(2)O, Cu(NO3)(2)center dot 4H(2)O and their mixtures of known compositions in the temperature range 30-1200 degrees C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0-60 degrees C. The mixture with composition 0.85Zn(NO3)(2)center dot 6H(2)O+0.15Cu(NO3)(2)center dot 6H(2)O showed single melting peak at 29 degrees C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu2O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl2 center dot 2H(2)O into the mixture 0.85Zn(NO3)(2)center dot 6H(2)O+0.15Cu(NO3)(2)center dot 6H(2)O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO3)(2)center dot 6H(2)O+0.15Cu(NO3)(2)center dot 6H(2)O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.