Synthesis of Mg–Al spinel powder via precipitation using ammonium bicarbonate as the precipitant

A precursor for Mg–Al spinel has been synthesized via the precipitation method, using ammonium bicarbonate as the precipitant. The precursor was composed of crystalline ammonium dawsonite hydrate [NH4Al(OH)2CO3·H2O] and hydrotalcite [Mg6Al2(CO3)(OH)16·4H2O] phases. The precursor converted to pure spinel phase at ∼900°C via two steps upon calcination: (i) decomposition of hydrotalcite at lower temperatures (400–800°C) and (ii) solid-state reaction between MgO (decomposed from hydrotalcite) and γ-Al2O3 (derived from NH4Al(OH)2CO3·H2O) at higher temperatures (>800°C). The effect of calcination temperature on particle morphology and sinterability of the resultant spinel powders were investigated.