Effect of liquid precursor pyrolysis on phase selection in the MgO-MgAl2O4 system

Aqueous solutions of Al and Mg nitrates have been spray pyrolysed at 673 K to synthesize powders with compositions varying between MgO and MgAl2O4. This has been carried out with the aim of studying phase selection and phase evolution in this system. The powders have been subsequently heat treated and the sequence of phases characterised by X-ray diffraction and transmission electron microscopy. Metastable extensions of the different phase fields have been calculated based on functions which predict the equilibrium phase diagram accurately. The appearance of phases is closely related to the temperature and to the non-stoichiometry in different compositional ranges of the system. The sequence of phase evolution has been correlated to the thermodynamics of nucleation in the system. (C) 1997 Elsevier Science S.A.