The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O are re-examined. Previous reports have suggested that Zn5(OH)8(NO3)2·2H2O decomposes to ZnO via two intermediates, Zn5(OH)8(NO3)2 and Zn3(OH)4(NO3)2 whereas ZnOHNO3·H2O has been reported to decompose to ZnO via a Zn3(OH)4(NO3)2 intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn5(OH)8(NO3)2·2H2O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO3·H2O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.

Graphical AbstractTG and DTG profiles for Zn5(OH)8(NO3)2·2H2O and the corresponding reactions occurring at each step.Figure optionsDownload as PowerPoint slide