MgAl2O4-γ-Al2O3 solid solution interaction: mathematical framework and phase separation of α-Al2O3 at high temperature

Although existence of MgAl2O4-γ-Al2O3 solid solution has been reported in the past, the detailed interactions have not been explored completely. For the first time, we report here a mathematical framework for the detailed solid solution interactions of γ-Al2O3 in MgAl2O4 (spinel). To investigate the solid solubility of γ-Al2O3 in MgAl2O4, Mg-Al spinel (MgO-nAl2O3; n = 1, 1.5, 3, 4.5 and an arbitrary high value 30) precursors have been heat treated at 1000°C. Presence of only non-stoichiometric MgAl2O4 phase up to n = 4.5 at 1000°C indicates that alumina (as γ-Al2O3) present beyond stoichiometry gets completely accommodated in MgAl2O4 in the form of solid solution. γ → α alumina phase transformation and its subsequent separation from MgAl2O4 has been observed in the Mg-Al spinel powders (n > 1) when the 1000°C heat treated materials are calcined at 1200°C. In the mathematical framework, unit cell of MgAl2O4 (Mg8Al16O32) has been considered for the solid solution interactions (substitution of Mg2+ ions by Al3+ ions) with γ-Al2O3. It is suggested that combination of unit cells of MgAl2O4 takes part in the interactions when n > 5 (MgO-nAl2O3).