Search

Abstract: The composites of barium ferrite and titanium dioxide are prepared with sol–gel method. The crystalline structure, relative complex permittivity and permeability, and sublattice structure were measured with X-ray diffraction, vector network analysis and Mössbauer spectroscopy. The addition of TiO2 is shown to increase the relative complex permittivity and to improve the dielectric loss of BaFe12O19. It also decreases the ferromagnetic resonant frequency of BaFe12O19. The maximum movement of resonant frequency reaches 900MHz. Some Ti4+ ions have entered the inter space of BaFe12O19 lattice, which results in the quadrupole splitting on 4f 2 and 2a sites. The magnetocrystalline anisotropy field of BaFe12O19 is decreased, and some Fe3+ ions are converted into Fe2+ ions. [Copyright &y& Elsevier]

The nanocomposite multilayer film (NCMF) of substituted BaFe12O19 and TiO2 was prepared using sol-gel method. BaFe10.5Al1.5O19, BaFe10.1Al1.9O19 and BaFe11.4Cr0.6O19 with different absorption frequencies were selected to fabricate the multilayer film with TiO2. The morphology, crystalline structure and microwave absorption property of the NCMF were investigated with an atomic force microscopy, X-ray diffraction and vector network analyses. The results show that the NCMF is uniform without microcracks and it is an ideal microwave attenuation material with a broad frequency range. Its maximum loss efficiency is about −40 dB. The frequency range with the loss above −10 dB is more than 7 GHz. The multilayer film assembles the achievements of each layer film. Moreover, the compounding of ferrites with TiO2 is helpful to absorb more microwave energy. TiO2 particles block the growth of ferrite grains and make most of their size within nanometers. TiO2 also improves the dielectric loss efficiency of the NCMF. [ABSTRACT FROM AUTHOR]

Abstract: The chromium substituted barium hexaferrites were prepared by self-propagating combustion method. The crystalline structure, complex permittivity, complex permeability, and hyperfine parameters of BaFe12−x Cr x O19 (x varies from 0.2 to 1.0 in a step of 0.2) were measured with X-ray diffraction, vector network analyzer and Mössbauer spectroscopy. At 850°C, only a part of Cr3+ ions are permitted to enter the lattice of barium ferrite. With further calcination at 1000°C, all Cr3+ ions enter the lattice. After substitution, the complex permittivity is increased. The Cr3+ ions substitute for the Fe3+ ions on the 2a site, and simultaneously lead to a quadrupole splitting on the 4f 1 site. These changes decrease the anisotropy field, which are accordant with the spectra of μ″. In the crystalline cells of the substituted barium ferrites, some Fe2+ ions are formed. It results in a bigger dielectric loss. [Copyright &y& Elsevier]

Abstract: The composite films of barium ferrite and titanium dioxide are successfully prepared using sol–gel method. The morphology, magnetic and microwave absorption properties of the composite films with the different weight ratio of BaFe12O19 to TiO2 are investigated with atomic force microscopy, vibrating sample magnetometry and vector network analyzer. The results show that the composite films are uniform without microcracks. The grain diameters are less than 100nm. With the increase of barium ferrite, the grain diameter decreases. The composite films possess the excellent magnetic and microwave absorption properties. The specific saturation magnetization and coercivity is 18.3EMU/g and 3350Oe, respectively. The maximum microwave loss reaches 40dB when the weight ratio of BaFe12O19 to TiO2 is 3:5. [Copyright &y& Elsevier]

Abstract: In order to synthesize barium ferrite at low temperatures, a gel self-propagating combustion (GSPC) technique and a high-energy ball milling (HEBM) process are combined. After the resultants of gel combustion are milled and subsequently calcined, barium ferrite is formed. The morphologies of the milled powders are examined with transmission electron microscopy. The crystal structure of the powders during the milling and subsequent calcination is investigated with X-ray diffraction (XRD). The magnetic properties of barium ferrite powders are measured by means of vibrating sample magnetometry. The results show that the intermediate BaFe2O4 is formed during the milling at room temperature. After the powder is milled for 60h and subsequently calcined at 600°C, barium ferrite is synthesized. The powder size is decreased to 20–30nm after the powders are milled for 10h. The magnetic properties of the milled barium ferrite are improved. The coercivity is increased greatly with the maximum of 425.74kA/m. [Copyright &y& Elsevier]

Abstract: The M-type hexagonal barium ferrite powder was obtained after the calcination of precursor, which was prepared with self-propagating high-temperature synthesis. Using high-energy ball milling, the powder size was turned into nanoscale. X-ray diffraction (XRD), transmission electron microscope (TEM) and vector network analyzer were used to analyse its structure and microwave absorption property. The results indicate that the nanoscale milled barium ferrite improves microwave loss by 8 dB and broadens the frequency bandwidth with loss above −10 dB by 5.3 GHz. The mechanisms of improvement caused by nanometer size were explained. [Copyright &y& Elsevier]

Abstract: The barium ferrite particles were prepared using a self-propagating combustion method with glycine as a fuel. The process was investigated with differential scanning calorimeter and thermogravimetric analysis. The effects of the pH value of the precursor solution, the glycine dosage and calcination temperature on the morphology, the crystalline structure and the magnetic properties of the barium ferrite particles were studied by means of X-ray diffraction, infrared ray spectra, field emission scanning electron microscopy and vibrating sample magnetometry. The results show that the ignition temperature of glycine gel is lower than that of citric acid gel. The pH value of the precursor solution greatly affects the crystal structure of powders after combustion and calcination. Barium hexaferrite particles with a specific saturation magnetization of 56.1Am2/kg and a coercivity of 398.0kA/m were obtained when the pH value of the precursor solution was 7.0 and the calcination temperature was 850°C. [Copyright &y& Elsevier]

Abstract: Nanosized strontium ferrite powder was deposited with Ni–P by electroless plating under the agitation of ultrasonic wave at room temperature. The morphology, crystal structure, complex permittivity and complex permeability of the composite powder were investigated with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDS) and vector network analyzer. The results show that the imaginary part of complex permeability of the strontium ferrite powder is increased greatly by the deposited Ni–P layer. The application of the nanocomposite powder as microwave absorber is promising. [Copyright &y& Elsevier]

Abstract: The composites of barium ferrite coated on hollow ceramic microspheres were prepared using sol–gel technique. The crystal structure, morphology and microwave absorption properties of composite powders with different weight ratio of microspheres were studied with XRD, EDS, FESEM and vector network analyzer. The results show that the microwave absorption properties of composite powders are greatly improved. The maximum microwave loss of composite powders reaches 31dB with an amount of 50wt.% microspheres, and its density is only about 1.80g/cm3. The effect of hollow ceramic microspheres on the microwave absorption property is also discussed. [Copyright &y& Elsevier]