A wet-chemical process yielding reactive magnesium aluminate spinel (MgAl2O4) powder

Ammonium carbonate was used as the precipitant to synthesize Mg–Al spinel precursors from a mixed solution of magnesium and aluminum nitrates. The precursor, composed of crystalline ammonium dawsonite hydrate [NH4Al(OH)2CO3·H2O] and hydrotalcite [Mg6Al2(CO3)(OH)16·4H2O] phases, transformed to pure spinel at ∼900°C via the decomposition of hydrotalcite at ∼400–800°C and a solid-state reaction between MgO (decomposed from hydrotalcite) and γ-Al2O3 (derived from NH4Al(OH)2CO3·H2O) at ∼800–900°C. Sinterability of the resultant spinel powders was evaluated by the constant-rate-of-heating sintering method. The effect of calcination temperature on particle morphology and sinterability of the resultant spinel powders was investigated. Spinel ceramics of ∼99% dense were produced by vacuum sintering at 1550°C for 2 h from the powder calcined at 1100°C for 2 h.