TEM characterization of nanostructured MgAl2O4 synthesized by a direct conversion process from γ-Al2O3

Nanostructured MgAl2O4 spinel was synthesized by a direct conversion process from cubic gamma-Al2O3. The effect of post-annealing temperature (300 degrees, 500 degrees, and 800 degrees C) on MgAl2O4 phase formation was investigated using transmission electron microscopy, selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS). Relative diffraction intensities as well as lattice parameter measurements from SAED revealed that MgAl2O4 spinel structure starts forming at temperatures as low as 300 degrees C. EELS and EDS spectrum images also revealed an increase in elemental homogeneity with increasing annealing temperature. The degree of ordering of Mg and Al between octahedral and tetrahedral sites has been determined from relative diffraction intensities. Results show that annealing to 800 degrees C leads to a spinel phase with an order parameter of 0.78.