Study of magnesium aluminate spinel formation from carbonate precursors

The aim of the presented work was to study formation of magnesium aluminate spinel precursor powder during the co-precipitation of magnesium and aluminium nitrate with ammonium carbonate and its thermal transformation to spinel powder. After precipitation, the only crystalline phase is NH4Al(OH)2CO3·H2O (ammonium dawsonite). The second one, Mg6Al2(CO3)(OH)16·4H2O (hydrotalcite) appears during ageing. As found by DTA-MS and HT-XRD measurements, co-existence of both phases in very close contact results in their easier decomposition. On the base of the results obtained the scheme of phase transformations of co-precipitated precursor leading to formation of MgAl2O4 is proposed.