Effect of agglomeration during coprecipitation: Delayed spinellization of magnesium aluminate hydrate

Precipitation of magnesium aluminate hydrate with faster addition of ammonia at desired pH causes agglomeration. Agglomerated powder, without any further treatment, on calcination forms intermediate compounds at low temperatures (≤ 900°C). The intermediate compounds on further heat treatment (≥ 1000°C) decompose into MgO, MgAl₂O₄ and α-Al₂O₃. Effect of agglomeration and absorption of foreign ions such as Cl⁻, SO₄²⁻, and NH₄⁺ in complex compounds probably cause loss of Al³⁺ and Mg²⁺ ions during heat treatment, and stoichiometry changes. Powders prepared by continuous method with better control of process parameters than batch process yields better spinellization.