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.