Solvent-free synthesis of hexagonal barium ferrite (BaFe12O19) particles

M-type barium ferrite (BaFe₁₂O₁₉) particles, from a mixture of barium nitrate, ferric nitrate, cetyltrimethylammonium bromide (CTAB), and ammonium carbonate, have been successfully prepared through simple grinding and calcination in the absence of any solvent. The products are characterized by X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer, whose results indicate that they have well crystalline phase of BaFe₁₂O₁₉, typically hexagonal platelet-like structure, large saturation magnetization, even submicrometer particle size under the optimum condition. Meanwhile, the effects of Fe/Ba ratio, CTAB, and ammonium carbonate are also investigated. It has been found that the proper Fe/Ba ratio could suppress the intermediate phase such as α-Fe₂O₃ and BaFe₂O₄, CTAB could promote the crystallinity of BaFe₁₂O₁₉ and produce hexagonal crystal structure, and ammonium carbonate was the key for forming BaFe₁₂O₁₉ phase. This facile method may be helpful for the preparation of other multicomponent functional materials.     

Preparation of high quality,single domain BaFe12O19 particles by the citrate sol–gel combustion route with an initial Fe/Ba molar ratio of 4

BaFe₁₂O₁₉ particles have been synthesized by citrate sol–gel combustion route in a wide temperature range between 800 and 1200 °C with initial Fe/Ba molar ratios between 12 and 2. Structural, morphological and magnetic properties of the powders have been investigated by XRD, FT-IR, SEM and magnetization measurements. It was observed that both coercivity and specific saturation magnetization increase with annealing at temperatures up to 1100 °C, where a transition from single to multi domain structure occurs. To prevent formation of the hematite phase (α-Fe₂O₃), samples with different Fe/Ba molar ratios between 12 and 2 have been prepared and an intermediate phase, BaFe₂O₄, which may occur in Ba-rich samples has been removed by etching the powders in diluted hydrochloric acid. In this way, it was shown that single domain barium hexaferrite particles having high saturation magnetization, close to the theoretical value, and high coercivity can be synthesized with the initial Fe/Ba molar ratio of 4 in the sol–gel method. The chemical composition of this sample was determined as BaFe_11.80O_19.45 by the EDS analysis and Ba_1.05Fe_11.54O_18.4 using an ICP-MS device. Both are very close to the theoretical formula.     

Effect of Trivalent Ion Substitution on the Physical Properties of M-Type Hexagonal Ferrites

Aluminum-substituted barium hexagonal ferrite particles BaAl _x Fe_12-x O₁₉ with 0 ≤ x ≤ 3.5 have been prepared by solid state reaction method. The qualitative phase analysis of studied powder samples and the morphology of powders after milling were determined using the x-ray diffraction method and scanning electron microscopy, respectively. The barium hexagonal ferrite phase appeared to be the main component of the samples. The crystal size of BaFe₁₂O₁₉ phase is above 25 nm. The scanning electron microscopy images showed irregular shape and size of powder particles. According to the analytical method findings, the type of crystal lattice was confirmed to be hexagonal and the parameters of unit cell volume and x-ray density were determined. It is shown that such parameters decrease with increasing Al substitution from 699.019 to 696.702 Å³ and 5.258 to 4.828 gm/Cm³, respectively. The values of lattice parameters, grain size, microstrain, and dislocation density of all samples were calculated. The c/a value obtained from the x-ray indicates that notable changes of the atomic lattice anisotropy were induced by the Al-substitution and preheat treatments. Characteristics such as the interchain distance and interplanar distance parameter, which were obtained in the analytical method calculations, decrease with increasing Al substitution, in addition to the fact that they are related to the binding energy.     

Synthesis and Magnetic Properties of Barium Hexaferrite Powders Using Organic Acid Precursor Method

An investigation of the synthesis of BaFe₁₂O₁₉ powders by the organic acid precursor method is reported by acidic and neutral media. X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) are utilized to study the effect of organic precursor type and annealing temperature on the crystal structure, crystallite size, microstructure and magnetic properties of the formed powders. The XRD analysis showed that the crystalline BaFe₁₂O₁₉ phase was obtained at 1200 °C for 2 h using different carboxylic acids in acidic medium. However, pure BaFe₁₂O₁₉ was achieved at low annealing temperature 1000 °C in neutral medium. SEM micrographs showed that the particles were strongly influenced by type of carboxylic acid and the annealing temperature. VSM study indicated that the saturation magnetization was increased with increasing annealing temperature to 1200 °C as the result of formation of single barium hexaferrites phase. High saturation magnetization (M _s =66.5 emu/g) was achieved for the formed powders in neutral medium using tartaric acid as organic precursor. Wide coercivities of the formed powders (H _c =259–5114 Oe) were obtained.     

Thermally activated crystalline phase restoration in disordered barium ferrite powder prepared by ball milling

Depending on milling conditions (air or vacuum) for the same milling time, a different level of decomposition and structure disorder in BaFe₁₂O₁₉ ferrite powders can be obtained by ball milling. Air-milled material has a tendency to form a gas-saturated disordered structure (superoxide) and to transform into simple oxides (reduction process through oxygen-saturated disordered phase) as opposed to the vacuum-milled powder where a highly disordered phase occurs. Both powders have a different morphology (particle size and distribution). Annealing processes produce crystalline barium ferrite phase with interesting magnetic properties, but in the present paper only structural transformations are analysed. Scanning electron microscopy, X-ray diffraction and thermal analysis techniques were applied to study the effects of heat treatment (10 h at 773 or 1273 K) in disordered BaFe₁₂O₁₉ ferrite powders prepared by 1000 h ball milling in air and vacuum.     

Synthesis and characterization of nano crystalline BaFe12O19 powders by low temperature combustion

Nano crystalline BaFe₁₂O₁₉ powders have been prepared at a relatively low calcination temperature by a gel combustion technique using citric acid as a fuel/reductant and nitrates as oxidants. The effects of processing parameters, such as Ba/Fe ratio, citric acid/nitrates ratio, reaction temperature on the powder characteristics and magnetic properties of the resultant barium ferrites were investigated. By controlling the molar ratio of citric acid to metal nitrates, nano crystalline BaFe₁₂O₁₉ powders with different particle sizes have been obtained. Phase attributes, microstructures and magnetic properties of the powders were characterized using X-ray diffraction analysis, X-ray line-broadening technique, Fourier transform infrared spectroscopy measurements, transmission electron microscopy and vibrating sample magnetometer. The maximum saturation magnetization value and intrinsic coercivity value for the obtained barium hexaferrites are 59.36 emu/g and 5540 Oe.     

Preparation of core-shell structured hollow glass microspheres/BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/Ag composites with excellent microwave absorbing properties

Hollow glass microspheres/barium ferrite (HGM/BaFe₁₂O₁₉) was first prepared via co-precipitation reaction, which was then performed to fabricate the HGM/BaFe₁₂O₁₉/Ag composites by chemical plating method. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM) were utilized to characterize the structures, morphologies and properties of the resultant composites. Results showed that a homogeneous and complete BaFe₁₂O₁₉ shell was coated on the surface of the HGM, and HGM/BaFe₁₂O₁₉ composites were also fully covered with Ag particles. The conductivity of the HGM/BaFe₁₂O₁₉/Ag composites was 1.24?×?10² S/cm, whereas the saturation magnetizations of the composites was reduced to 12.76 emu/g. The microwave absorption properties of the HGMs/BaFe₁₂O₁₉/Ag composites were significantly improved compared with those of HGMs/BaFe₁₂O₁₉ composites and BaFe₁₂O₁₉ particles. The reflection loss (R) showed that the bandwidth of reflection loss of HGM/BaFe₁₂O₁₉/Ag less than ?10 dB (90% absorption) was 2.1 GHz (from 10.3 to 12.4 GHz), herein, the minimum loss value was ?19.7 dB at 12.4 GHz.     

A novel approach for synthesis of M-type hexaferrites nanopowders via the co-precipitation method

M-type hexaferrites; barium hexaferrite BaFe₁₂O₁₉ and strontium hexaferrite SrFe₁₂O₁₉ powders have been successfully prepared via the co-precipitation method using 5 M sodium carbonate solution as alkali. Effects of the molar ratio and the annealing temperature on the crystal structure, crystallite size, microstructure and the magnetic properties of the produced powders were systematically studied. The results indicated that a single phase of barium hexaferrite was obtained at Fe³⁺/Ba²⁺ molar ratio 12 annealed at 800–1,200 °C for 2 h whereas the orthorhombic barium iron oxide BaFe₂O₄ phase was formed as a impurity phase with barium M-type ferrite at Fe³⁺/Ba²⁺ molar ratio 8. On the other hand, a single phase of strontium hexaferrite was produced with the Fe³⁺/Sr²⁺ molar ratio to 12 at the different annealing temperatures from 800 to 1,200 °C for 2 h whereas the orthorhombic strontium iron oxide Sr₄Fe₆O₁₃ phase was formed as a secondary phase with SrFe₁₂O₁₉ phase at Fe³⁺/Sr²⁺ molar ratio of 9.23. The crystallite sizes of the produced nanopowders were increased with increasing the annealing temperature and the molar ratios. The microstructure of the produced single phase M-type ferrites powders displayed as a hexagonal-platelet like structure. A saturation magnetization (53.8 emu/g) was achieved for the pure barium hexaferrite phase formed at low temperature 800 °C for 2 h. On the other hand, a higher saturation magnetization value (M _s = 85.4 emu/g) was obtained for the strontium hexaferrite powders from the precipitated precursors synthesized at Fe³⁺/Sr²⁺ molar ratio 12 and thermally treated at 1,000 °C for 2 h.     

Synthesis and magnetic properties of conventional and microwave calcined barium hexaferrite powder

Single phase nanoparticles of barium hexaferrite (BaFe₁₂O₁₉–BaF) were synthesized by sol–gel method using metal nitrates as source and d-Fructose as a fuel. The prepared precursors were calcined by two different calcination techniques, using conventional furnace and microwave furnace. The samples are characterized using powder X-ray diffraction, theromogravimetric analysis and vibration sample magnetometer. Thermal analysis studies showed exothermic and endothermic reaction peaks from room temperature to 1,200 °C. X-ray diffraction studies established the formation temperature of single phase BaFe₁₂O₁₉. HR-SEM results showed the dispersed particles of hexagonal structure in platelet form. The broad hysteresis loop showed that the barium hexaferrite powder was in good crystalline nature.     

Barium hexaferrite nanoparticles: morphology-controlled preparation,characterization and investigation of magnetic and photocatalytic properties

In this paper, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized via a simple co-precipitation route. Six chelating agents such as three amino acids (proline, alanine, aspartic acid) and three surfactants (SDBS, PVP, and EDTA) were used. The result showed that the amino acids decrease the particle size and the best result was observed for alanine. Besides, the photocatalyst activity of as-prepared BaFe₁₂O₁₉ nanoparticles was evaluated by degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 200 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 30 emu/g.     

Preparation and characterisation of magnetically ordered columnar structures of barium ferrite particles

In this study, we report on the columnar structures of barium ferrite particles that were prepared from water suspensions by applying a magnetic field during drying. Commercial barium ferrite (BaFe₁₂O₁₉) monodomain particles were used, and the surfaces of the particles were treated with an organic surfactant to reduce their agglomeration. The columnar structures were obtained by drying the water suspensions of BaFe₁₂O₁₉ particles on Al₂O₃ substrates under an applied magnetic field of 1?T. After the degradation of the organic components, the samples were sintered at 1350°C. X-ray powder diffraction, scanning electron microscopy and magnetic measurements were used to characterise the samples. When the magnetic field was applied perpendicularly to the sample plane, the as-deposited sample exhibited a higher coercivity (H _c?=?5434?Oe) and a higher squareness ratio (SQR?=?0.76) than the sintered sample (H _c?=?625?Oe, SQR?=?0.58). However, the sintered sample showed a higher anisotropy of the magnetic behaviour than the as-deposited sample.     

Controlled synthesis and photocatalytic activities of barium hexaferrite nanoparticles and examine decolorization methyl orange on liver of rats

The controlled morphological of magnetic nanoparticles have gained great importance in a wide variety of applications due to their promising physico-chemical properties. Therefore, in this study, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were prepared with the simplest and most efficient chemical route, the two-step sol–gel method, in the presence of seven different and widely used surfactants. The aim of this research is to investigate the influence of the different surfactants on the morphology and particle size of the BaFe₁₂O₁₉ nanoparticles; therefore, different techniques were employed in order to elucidate the composition and structure of the BaFe₁₂O₁₉ nanoparticles such as XRD, SEM, FT-IR, and EDX. The magnetic properties were investigated by measuring the hysteresis loops. In order to investigate the role of BaFe₁₂O₁₉ nanoparticles as the photocatalysts, decolorization of methyl orange under ultraviolet light irradiation was also evaluated. In addition, the purity of decolorized water was examined by investigating its effect on the health condition of liver of rats.     

Synthesis of <Emphasis Type="Italic">c</Emphasis>-Axis Barium Hexaferrite Puck for Communication Application

Recent progress and needs by telecommunication industries require thick barium ferrite film with excellent magnetic properties for microwave monolithic integrated circuit applications. In the present work we show a novel barium hexaferrite (BaFe₁₂O₁₉, or BaM) composite material, BaFe₁₂O₁₉ nanopowder mixture with epoxy, as a low-cost solution to fabricate thick BaM films. The mix is used to fabricate thick puck of BaM within an alumina substrate. The resulting barium hexaferrite thick pucks have good magnetic properties with a magnetization saturation 4πMs between 2000 and 2500 Gauss, a perpendicular coercivity of 3800 to 4000 Oe and a close to 0.9 squareness. In addition, we have successfully fabricated and tested a self-biased microwave circulator by depositing and patterning copper contact lines on the alumina substrate and the BaM thick puck.     

Highly aluminium doped barium and strontium ferrite nanoparticles prepared by citrate auto-combustion synthesis

Aluminium doped barium and strontium hexaferrite nanoparticles BaAl_xFe_(12−x)O₁₉ and SrAl_xFe_(12−x)O₁₉ were synthesised via a sol-gel route using citric acid to complex the ions followed by an auto-combustion reaction. This method shows promise for the synthesis of complex ferrite powders with small particle size. It was found that around half of the iron could be substituted for aluminium in the barium ferrite with structure retention, whereas strontium aluminium ferrites could be produced with any aluminium content including total substitution of the iron. All synthesised materials consisted of particles smaller than 1 μm, which is the size of a single magnetic domain, and various doping levels were achieved with the final elemental composition being within the bounds of experimental error. The materials show structural and morphological changes as they move from iron to aluminium ferrites. Such materials may be promising for imaging applications.     

Sol–gel synthesis of Ce-substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Ce-substituted BaFe₁₂O₁₉ (BaCe _x Fe_12−x O₁₉, x = 0, 0.01, 0.03, 0.05) was prepared by citrate sol–gel method. The thermal decomposition process of precursor was investigated by TG-DSC. The phase composition of the BaCe _x Fe_12−x O₁₉ was characterized by X-ray powder diffraction analysis (XRD) which reveals that the BaCe _x Fe_12−x O₁₉ crystallizes in a hexagonal structure. The lattice parameter of BaCe _x Fe_12−x O₁₉ increases slightly when Ce was substituted into BaFe₁₂O₁₉. The average crystallite size calculated from the XRD line broadening is about 30–33 nm and no intermediate phases are detected in the XRD patterns. The transmission electron microscope (TEM) analysis indicates that the particles of samples obtained are the rod-like morphology.     

Barium hexaferrite nanoparticles: Synthesis and magnetic properties

Carbon combustion synthesis is applied to rapid and energy efficient fabrication of crystalline barium hexaferrite nanoparticles with the average particle size of 50-100 nm. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm with a surface area of 80 m²/g generates a self-propagating thermal wave with maximum temperatures of up to 1000 °C. The thermal front rapidly propagates through the mixture of solid reactants converting it to the hexagonal barium ferrite. Carbon is not incorporated in the product and is emitted from the reaction zone as a gaseous CO₂. The activation energy for carbon combustion synthesis of BaFe₁₂O₁₉ was estimated to be 98 kJ/mol. A complete conversion to hexagonal barium ferrite is obtained for carbon concentration exceeding 11 wt.%. The magnetic properties H_c∼3000 Oe and M_s∼50.3 emu/g of the compact sintered ferrites compare well with those produced by other synthesis methods.     

Microwave absorption properties of substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/TiO<Subscript>2</Subscript> nanocomposite multilayer film

The nanocomposite multilayer film (NCMF) of substituted BaFe₁₂O₁₉ and TiO₂ was prepared using sol-gel method. BaFe_10.5Al_1.5O₁₉, BaFe_10.1Al_1.9O₁₉ and BaFe_11.4Cr_0.6O₁₉ 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.     

Topochemical Memory Effect in the Formation of Barium Hexaferrite

The topochemical memory effect in Ba(NO₃)₂ : Fe₂O₃ = 1 : 6 reaction mixtures containing -Fe₂O₃ with different particle sizes was studied at low (540–630°C; the main reaction product BaFe₂O₄) and high (900–930°C; the main product, BaFe₁₂O₁₉) reaction temperatures. The results indicate that the particle size of Fe₂O₃ has a significant effect on the BaFe₂O₄ yield in the low-temperature solid-state reaction (<585°C), in contrast to the liquid-assisted reaction (>585°C). In the subsequent high-temperature solid-state reaction (900–930°C), the BaFe₁₂O₁₉ yield depends on the particle size of Fe₂O₃, regardless of the initial reaction temperature. It is shown that, to achieve a high BaFe₁₂O₁₉ yield, the process conditions should be optimized in both the low- and high-temperature stages.     

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe₁₂O₁₉) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe₁₂O₁₉) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H₂O₂ decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.     

Poly(vinyl phosphonic acid) (PVPA)–BaFe12O19 Nanocomposite

We present a method for the fabrication of PVPA/BaFe₁₂O₁₉ nanocomposite by in-situ polymerization of vinyl phosphonic acid, VPA in the presence of synthesized BaFe₁₂O₁₉ NPs. Nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, SEM, TEM, VSM, and conductivity techniques for structural and physicochemical characteristics. Nanoparticles, identified as BaFe₁₂O₁₉ from XRD analysis, were successfully coated with PVPA and the linkage was assessed to be via P?CO bonds. Electron microscopy analysis revealed aggregation of BaFe₁₂O₁₉ particles and dominantly platelet morphology upon composite formation. TGA analysis revealed the composition of the nanocomposite as 65% BaFe₁₂O₁₉ and 35% polymer. Magnetic evaluation revealed that adsorption of PVPA anions during the preparation of the nanocomposite strongly influenced the magnetic properties resulting in much lower saturation magnetization values. DC conductivity measurements were used to calculate activation energy of PVPA/BaFe₁₂O₁₉ nanocomposite and it was obtained as 0.37?eV.