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Control of magnesia–alumina properties by acetic acid in sol–gel synthesis

1997; Elsevier BV; Volume: 210; Issue: 2-3 Linguagem: Inglês

10.1016/s0022-3093(96)00168-8

1873-4812

Saloua Rezgui, Bruce C. Gates,

Magnesium Oxide Properties and Applications

Sol–gel synthesis was used to prepare oxides of aluminum and magnesium from mixtures of Al(O–s-Bu)3 and Mg(O–Et)2, with the atomic ratio of Al to Mg being 4. The hydrolysis and condensation reactions were controlled by acetic acid in the absence of added water; the ratio R of acetic acid to aluminum alkoxide (R=[CH3COOH]/[Al(O–s-Bu)3]) was varied from 1 to 6. The products were characterized by differential thermal analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. For R>1, gelatinous precipitates formed as relatively large amounts of acetate species in the form of crystalline layered materials, which upon calcination lost their acetate ligands and formed a crystalline material composed of a mixture of amorphous alumina and crystalline spinel syn MgAl2O4. The excess alumina is inferred to have remained amorphous and highly dispersed in this relatively ordered material. For R=1, however, a gel formed, and the material was less crystalline than the gelatinous precipitates because of the relatively low concentration of acetate. When the gel was calcined, a mixture of crystalline spinel syn MgAl2O4 and amorphous alumina formed, with the alumina being separate from the spinel and not highly dispersed so that, after calcination at temperatures higher than 750°C, a heterogeneous mixture of crystalline phases of magnesium–aluminum oxide and aluminum oxide formed.