FORMATION OF PARTIALLY INVERSE MG-AL SPINEL BY GRINDING MGO WITH GAMMA-AL2O3

Spinel (MgAl2O4) was synthesized mechanochemically (MC) by grinding MgO with gamma-Al2O3 up to 10 hours. Examination of the MC product by neutron diffraction and infrared spectroscopy showed that it has a higher degree of inversion than its thermally produced counterpart - 47% as against 10% respectively. X-ray studies showed that MgAl2O4 crystallites grow equidimensionally at a much higher rate than in the case of alpha-Al2O3. The higher degree of inversion and higher formation rate when gamma-Al2O3 is used, is attributed to similarities in oxygen framework of MgO, Al2O3 and spinel and to the higher retention of the cations coordination number. The equidimensional growth is attributed to the presence of multiple soft modes, the {111} planes.