The effect of solution chemistry on the preparation of MgAl 2O 4 by hydrothermal-assisted sol–gel processing

Abstract

Preparation of magnesium aluminate spinel powder by hydrothermal-assisted sol–gel processing from MgAl 2(OCH 2CH 2OR) 8, R CH 3 ( 1), CH 2CH 2OCH 3 ( 2), MgAl 2[OCH(CH 3) 2] 8 ( 3) and MgAl 2(O– s Bu) 8 ( 4) in toluene and parent alcohol has been investigated. Coordination status of aluminum atom in precursors was determined by 27Al NMR and correlation between coordination number of aluminum and development of spinel phase in hydrothermal-assisted sol–gel processing has been studied. The gels obtained from hydrothermal-assisted hydrolysis of magnesium-aluminum alkoxides that contain six-coordinated aluminum atom s in solution ( 1 and 2) after calcination at 700 °C resulted in the formation of pure spinel phase, whereas in similar hydrolysis and calcination processes of precursors that contain four-coordinated aluminum ( 3 and 4) spinel phase forms along with some Al 2O 3 and MgO. Selected powders obtained from hydrothermal-assisted sol–gel processing were characterized by thermal analysis (TGA/DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Results indicate that the coordination status of aluminum in the precursor is very crucial for the formation of pure phase spinel. The morphology of prepared spinels was studied by SEM and the results showed that the solvent in hydrothermal-assisted sol–gel processing has a marked effect on the morphology of the resulting MgAl 2O 4. In hydrothermal-assisted sol–gel processing of aluminum-magnesium alkoxides in hydrophobic solvent, spherical particles are formed, while in the parent alcohol, non-spherical powders are formed.