On the thermal decomposition of Zn(NO3)2·6H2O and its deuterated analogue

Abstract

The thermal dehydration and decomposition of Zn(NO3)2·6H2O (I) were studied via DTA, TG and DSC, quantitative analysis and IR spectroscopy, and compared with those of Zn(NO3)2·6D2O (II). The following phase transitions were observed: melting of the salts; partial dehydration to tetrahydrate; formation of basic nitrate-hydrate; and formation of ZnO. The sum of the enthalpies of dehydration and thermal decomposition for I was 286 kJ/mol, while that for II was 299 kJ/mol (data from DSC). The probable mechanisms were determined from the TG curves and the formal kinetic parameters were calculated for the two stages of thermal decomposition. Calculations with an equation of the accelerating-type exponential law gave for the formation of basic zinc nitrate-hydrateE *=59 kJ/mol for I andE *=64 kJ/mol for II. For the decomposition of the basic salt, the equation for bidimentional diffusion yieldedE *=127 kJ/mol for I andE *=138 kJ/mol for II.