Formation of MgSO4-Al-2(SO4)(3) solid solution and thermal decomposition into the spinel solid solution

Solid solution of MgSO4 and Al-2 (SO4)(3) was prepared from mixed aqueous s olutions by rapid dry using micro-wave heating. The Mg2+ ion is soluble int o the anhydrous aluminum sulfate crystal lattice over a wide range up to ne ar the equimolar composition of MgSO4 and Al-2(SO4) (3) The anhydrous alumi num sulfate solid solution, at first, thermally decompose into the mixture of eta-Al2O3 and MgSO4. The crystalline spinel phase appears at the second step of the thermal decomposition. The lattice parameters of the spinel cha nges linearly with the Mg content ranging from 0.5 to 0.8 at the fraction o f MgAl2O4/ (MgAl2 O-4 + Al2O3) The produced nonstoichiometric spinel solid solutions must be metastable because the stable region of the composition o f the spinel solid solutions is very narrow at the heating temperature empl oyed to the thermal decomposition.