Preparation and chemical properties of magnesium aluminium oxide solid solutions

Magnesium aluminium oxide solid solutions were prepared by thermal decomposition of hydrotalcite-like compounds, [Mg₁-xAl_x,(OH)₂](CO₃) _{x 2}·mH₂O, at 500-700°C. The Nad-type solid solutions with a cation defect structure of Mg _{2(1-x) (2+x)}Al _2x (2+x)XXX _x (2+x)O were formed in the range 0.15 ≤ Al/(Mg+Al) ≤ 0.33. Magnesium aluminium oxide hydrated and took up carbonate ion from aqueous solution to reconstruct the hydrotalcite-type structure. Phosphate was also taken up, at a rate that decreased with increasing thermal decomposition temperature from 500 to 700°C, although the nature of the product in this instance was not established. The solid solutions decomposed above 1000°C to MgO and MgAl₂O₄, which showed no capacity to take up anions.