Formation and characterization of magnetic barium ferrite hollow fibers with high specific surface area via sol-gel process

The magnetic barium ferrite (BaFe12O19) hollow fibers with a high specific surface area about 22-38 m(2) g(-1), diameters around 1 mu m and a ratio of the hollow diameter to the fiber diameter estimated about 1/2-2/3 have been prepared by the gel-precursor transformation process. The precursor and resulting ferrite hollow fibers were analyzed by thermo-gravimetric and differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy and X-ray diffraction. The specific surface area was measured by the Brunauer-Emmett-Teller method. The gel formed at pH 5.5 has a good spinnability. A pure barium ferrite phase is formed after calcined at 750 degrees C for 2 h and fabricated of nanograins about 38 nm with a hexagonal plate-like morphology, which are increased to about 72 nm with the calcination temperature increased up to 1050 degrees C. The barium ferrite hollow fibers obtained at 750 degrees C for 2 h have a specific surface area 38.1 m(2) g(-1) and average pore size 6.5 nm and then the specific surface area and average pore size show a reduction tendency with the calcination temperature increasing from 750 to 1050 degrees C owing to the particle growth and fiber densification. These barium ferrite hollow fibers exhibit typical hard-magnetic materials characteristics and the formation mechanism for hollow structures is discussed. (C) 2010 Elsevier Masson SAS. All rights reserved.