No abstract

In the present study, graphite/alumina composites are fabricated via reductive sintering of gel-casted green bodies with structurally controlled cross-linked epoxy polymers for the first time. The cross-linking degrees of polymers are tuned by the amount ratio of epoxy monomer/polyvinyl alcohol cross-linker utilized in gel-casting process. Superior electrical properties with respect to 5-fold enhanced electrical conductivity and 2-fold higher carrier mobility are successfully achieved in graphite/alumina composite fabricated from cross-linked epoxy polymer, whose phenomenon is attributed to the excellent conductive path in ceramic matrix established by highly uniform network with improved graphitization degree.

Preparation of spinel Mn-doped Fe(Al 1−x Mn x ) 2 O 4 (0 ≤ x ≤ 0.9) ferrite powders, in which B-site Al 3+ were replaced partially by Mn 3+ , has been tried via a modified citric acid route. Fe and Al nitrate salts and fine MnO 2 powder were used as starting materials. Homogeneous mixed solutions containing Fe 3+ , Al 3+ ions and MnO 2 were added to the mixed solution of citrate acid (CA) and ethylene glycol (EG) at room temperature with stirring. After boiling and continuous drying, thus obtained precursors were heated in air to burn out the organic substances and calcined at 1173 K (900°C) for 7.2 × 10 3 s (2 h) under nitrogen atmosphere with a small amount of hydrogen to control the valances of Fe and Mn in the ferrite powders. Single spinel B-site Mn-doped Fe(Al 1−x Mn x ) 2 O 4 powders with the compositions of x = 0.0, 0.2, and 0.6 ~ 0.9 have been obtained. With increasing x value, the magnetic property of spinel powder changed from paramagnetism (x = 0) to ferrimagnetism (x = 0.2, 0.6 ~ 0.9) at room temperature. Neutron-diffraction analysis measured at room temperature proved that some of Mn ions occupied B-site and on the contrary Fe did A-site. Magnetic properties also supported this configuration determined by XRD and NRD.