KINETICS OF SOLID-STATE SPINEL FORMATION - EFFECT OF CATION COORDINATION PREFERENCE

Formation of the spinels MgAl2O4, NiAl2O4, and ZnAl2O4 from α-alumina and MgO, NiO, or ZnO was studied at several temperatures by measuring the fraction of reaction completed as a function of time. Apparent activation energies (in kJ mole-1) were MgAl2O4, 185; NiAl2O4, 300; and ZnAl2O4, 230. At 1373 K, the rates of spinel formation followed the sequence MgAl2O4 < ZnAl2O4 < NiAl2O4. The results are discussed in terms of coordination preference of the involved divalent cations. © 1994 Academic Press, Inc.