Sonochemical synthesis and characterization of iron oxide coated on submicrospherical alumina: A direct observation of interaction between iron oxideand alumina

Coating of iron oxides on submicrospheres of alumina was carried out by the sonochemical method. Three kinds of alumina were used, namely, the as-prep ared, 700 and 1000 degrees C heated-alumina. TEM results reveal various coa ting effects on different heat-treated substrates. The optimum coating is o btained on as-prepared amorphous alumina, in which most of the iron oxide p articles are adhered to alumina spheres tightly, while in the sample coated on crystallized alumina heated at 1000 degrees C, most of the iron oxide p articles remain separate from the alumina spheres. The strong interaction b etween iron oxides and alumina substrate was directly observed by XRD, TEM, and IR and magnetic measurements. Owing to the strong interaction between adhered iron particles and alumina substrate, the complete transformation o f gamma-Fe2O3 to alpha-Fe2O3 was retarded to higher than 700 degrees C; con versely, the presence of haematite can induce the formation of alpha-Al2O3 at the high temperatures. TEM images clearly show the changes of particle s ize and morphology for samples at the different heating stages and the comb ination degree of iron oxide with alumina substrate. At a low temperature, IR results show that iron or iron carbonyl compound is interacted with the isolated OH groups on alumina surface. At high temperatures, the iron ions can incorporate into the defect sites of alumina and form a solid solution at the interface. Magnetization measurements show the existence of elementa l iron in as-prepared sample coated on crystallized alumina.