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).
Volume 42 | Issue 6
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