Of Fe <sub> 2 </ Sub> O <sub> 3 </ Sub>-al <sub> 2 </ Sub> The O <sub> 3 </ Sub> And Fe-al <sub> 2 </ Sub> O <sub> 3 </ Sub> Nanocomposite Powder Preparation And Characterization

The Fe2O3-Al2O3 nanocomposites were prepared by sol-gel method. The reduction of the Fe2O3-Al2O3 in H2 was used to prepare Fe-Al2O3 nanocomposites. X-ray diffraction(XRD) scanning electron microscopy (SEM) transmission electron microscopy(TEM) Mossbauer spectroscopy (MS) and vibrating sample magnetometer(VSM) were used to study the structural characterization and properties of the composite materials.The results indicated: (1) The Fe2O3-Al2O3 nanocomposites with different Fe2O3 content and calcining temperature have different phases. (2) The temperature of Al2O3 transforming to a -Al2O3 decreased by the existence of a -Fe2O3 in composites. (3) In the binary system, the grain growth of Al2O3 and Fe2O3 was retarded becaused of the homogenous distribution of the two phases. (4) The composites still contained very small Fe2O3 particles (below 20nm), and showed superparamagnetism even after heating at temperature as high as 1200℃. (5) The samples prepared by different methods ,when heated at 900℃, gave obvious difference in grain size and phases construction. And these phenomena vanished as temperature rised to 1200℃. (6) The phenomenon that Fe3+ ions were partly incorporated into the structure of a -Al2O3 can be found in all samples. The solid solubility of Fe3+ ions was decreased with the increase of temperature. Contrasting with coating method, to produce samples by mixed aqueous solution of Fe(NO3)3 and A1(NO3)3 will obtain a -A12O3 with a high percentage of isolated Fe3+ ions in the lattice sites. (7) The gel made from the aqueous solution of Al + and Fe + ion was calcined at 500℃ , then the powder received were reduced in H2 atmosphere atdifferent temperature, and the Fe-Al2O3 nanocomposites will be obtained as the reducing temperature increased to 900℃ .(8) The transition phase FeAl2O4 was found during Fe2O3 was reduced to Fe. (9)The coercivity of the sample submitted to reduction at 700℃ was 488 Oe, and the magnetization was 17.8emu/g. The coercivity and the magnetization of the sample reduced at 900℃ were 2270e and 48.2 emu/g.