27Al Magic-angle spinning nuclear magnetic resonance spectroscopic study of the conversion of basic dicarboxylate aluminium(III) complexes to alumina and aluminium nitride

Abstract

The process of conversion of hydrated basic dicarboxylate aluminium(III) complexes Al(OH)(succinate)xH2O and Al(OH)(adipate)xH2O to alumina and aluminium nitride (AlN) has been investigated by 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The powdered succinate complex was calcined under various atmospheres such as N2, argon and air. The 27Al MAS NMR spectra for the calcined materials at 500C all showed three peaks at delta; 6, 33 and 63. The relative intensities of these peaks varied with increasing temperature and were also dependent on the calcination atmosphere. The 27Al NMR signal of AlN at delta; 114 was observed for the sample calcined in an N2 atmosphere at 1150C whilst in all spectra of samples calcined under an N2 atmosphere at 1150C there were no detectable signals other than those of gamma;-alumina and AlN. The finding that the ratio of the relative intensities of AlO6 and AlO4 groups in gamma;-alumina changes with temperature suggests that the carbothermal reduction and nitridation of alumina proceeds through intermediates with empirical formulae of the type AlOxNy. The degree of nitridation at each reaction temperature for the succinate complex was higher than that for the adipate complex.