Barium Ferrite Powders Research Articles

Surface modification of M-Ba-ferrite powders by polyaniline: Towards improving microwave electromagnetic response

A composite of polyaniline (PANI)-coated M-type hexagonal barium ferrite (M-Ba-ferrite) powder was prepared by an in situ polymerization of an aniline monomer in the presence of M-Ba-ferrite particles. The obtained composite was characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The structure and microwave response properties were investigated. The continuous coverage of polyaniline has been produced on the platelet M-Ba-ferrite particle surface, and a core–shell structure has been formed. The results show that the coverage of polyaniline has a great influence on microwave response of M-Ba-ferrite particles. A polyaniline thin layer formed on the surface of a barium ferrite particle changes the character of frequency dispersion of microwave absorption. The results indicate the existence of an interaction at the interface of polyaniline macromolecule and barium ferrite particle, which influences the physical and chemical properties of the composite. The interaction and interfacial polarization are seen as important factors contributing to the influence on microwave response of the PANI-coated ferrite composite powders.

Electromagnetic and electrical properties of coated cotton fabric with barium ferrite doped polyaniline film

AbstractIn this study, we aimed to produce fabrics with microwave absorbing properties in broad band. For this purpose, the cotton fabrics were coated with polyaniline (PAni) by using chemical oxidative polymerization method. Firstly, the type of protonic acid used, the polymerization time, the type and concentration of dopant, and the number of coating layer were varied as parameters. The effect of these parameters on resistance values of coated fabrics was investigated. We determined the most appropriate process conditions to provide the lowest resistance values. Secondly, the fabric was coated with PAni by adding barium ferrite powder as filler with different ratios. Morphological properties, electrical, and electromagnetic properties of coated fabrics were determined. As a result, we obtained 350 Ω of the minimum resistance values of coated fabric using 1M HCl, 0.5M aniline and 0.5M ammonium persulphate by chemical oxidative polymerization method for totally 4 h of polymerization time. The results of electromagnetic parameters showed that the absorption values of the fabric coated PAni was average 48% in the frequency range of 6–14 GHz. It was concluded that microwave absorber for a textile material can be successfully produced by this process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Nanosized barium ferrite powders prepared by spray pyrolysis from citric acid solution

Highly crystalline nanosized barium ferrite (BaFe 12O 19) powders were prepared by spray pyrolysis from a spray solution containing a high concentration of the metal components. The precursor powders obtained from the spray solution containing citric acid were amorphous with a porous and hollow structure. Purely crystalline and fine BaFe 12O 19 powders were obtained after post-treatment between 700 and 1000 °C and subsequent mechanical grinding in an agate mortar. The mean sizes of the powders post-treated at 700 and 1000 °C were 125 and 550 nm, respectively. The specific magnetization of the powders prepared from the spray solution containing citric acid was 57 emu/g.

Barium ferrite powders prepared by microwave-induced hydrothermal reaction and magnetic property

We have prepared barium ferrite particles by the microwave-induced hydrothermal method. The crystallization of the barium ferrite particles is promoted within a short time by microwave irradiation because the seeds of barium ferrite having large permeability are rapidly heated through the interaction of barium ferrite with the magnetic component of the microwaves. Crystals having unusually low thickness were obtained compared with the conventional hydrothermal method. The magnetic properties of barium ferrite particles are discussed.

Effect of Al-substitution on phase formation and magnetic properties of barium hexaferrite synthesized with sol-gel auto-combustion method

Al-substituted barium ferrite powders were synthesized using the sol-gel auto-combustion method according to the molecular formula BaAlxFe12−xO19 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0). Compared with non-substituted barium ferrite annealing at 1 000 °C, the vibrating sample magnetometer (VSM) measurement manifested that the optimum magnetic properties formation temperature of Al-substituted barium ferrite was 1 100 °C. The data from X-ray diffractometer (XRD) showed that with increasing x, the lattice constants (a and c) decreased as well as the unit-cell volume Vcell. Magnetic measurement of non-substituted and Al-substituted powders annealed from 900 °C to 1 200 °C exhibited that the maximum magnetization M (10 kOe), the remanent magnetization Mr and the coercivity Hc depended strongly on the chemical composition of powder as well as the annealing temperature. When annealing at 1 100 °C, BaAl0.5Fe11.5O19 of high coercivity Hc (6584 Oe) was produced. Meanwhile, M (10 kOe) and Mr were 42.83 emu/g and 25.65 emu/g, respectively.

Influence of acid catalysts on the structural and magnetic properties of nanocrystalline barium ferrite prepared by sol–gel method

BaFe 12O 19 powders with nanocrystalline size were prepared by sol–gel techniques. Nitric, hydrochloric, acetic and stearic acid were used to improve the magnetic properties. Amorphous gels were formed with Fe/Ba molar ratio of 10.5. Then powders were obtained by subsequent heat treatment at 800–1000 °C for 1 h. Barium ferrite powder was also synthesized by solid state reaction at 1210 °C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) experiments were conducted to evaluate structural properties of the samples. The value of the effective magnetic susceptibility was measured. The results show that the magnetoplumbite structure was formed in all of the powders. The TEM observation showed that the minimum particle size (20 nm) was produced with the stearic acid catalyst. The highest value of the effective magnetic susceptibility was achieved also using stearic acid.

Microwave-Assisted Synthesis of Hexagonal Barium Ferrite Powders with Nano-Particle

A novel ceramic synthesis technique, microwave-assisted process was investigated for the production of Barium Hexagonal ferrite (BaFe12O19) powders with improved physical properties. Compared to conventional syntheticroute, the new method significantly shortened synthetic steps and reaction time. This technique involves the reaction of stoichiometric amount of metal nitrates and appropriate dosage of citric acid at microwave oven and the whole process took only 15 min. The powders of BaFe12O19 were further investigated by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results showed that the formation temperature of M-type Ba hexaferrite is significant low, compared to conventional furnace heating. The X-ray diffraction analysis demonstrates that the phase purity of the microwave-processed samples were determined and compared with a conventionally processed material. SEM observations indicate that the size of the synthesized BaFe12O19 powders is small and uniform distribution. Thus, microwave irradiation is proved to be a novel, extremely facile, timesaving and energy-efficient route to the synthesis of BaFe12O19 powders.

Efeito da variação estequiométrica na formação de ferritas BaM produzidas pelo método SHS e pelo método cerâmico tradicional

As ferritas do tipo BaM são cerâmicas ferrimagnéticas, usualmente aplicadas em sistemas de gravação magnética e como magnetos duros. Possuem alta estabilidade química, resistência a corrosão e baixo custo de produção. Diante da sua crescente importância, foi estudado o efeito da contribuição do excesso de bário no processamento e formação da fase ferrita BaM por duas distintas rotas: processamento por mistura de óxidos e a síntese por reação de combustão (método SHS) com o uso de carbonato e nitrato de bário. Duas relações de concentração entre bário e ferro foram utilizadas, uma estequiométrica (n = Fe2O3/BaO = 6) e uma outra não estequiométrica (n = Fe2O3/BaO = 5,45). Os pós processados com excesso de bário resultaram na presença da fase intermediária de formação BaFe2O4, a qual permanece após altas temperaturas de calcinação e mesmo após a sinterização de compactos obtidos a partir dos pós calcinados. As conclusões foram baseadas em difratogramas de raios X das ferritas BaM em pó após calcinação e nas amostras conformadas e sinterizadas, além de imagens obtidas por microscopia eletrônica de varredura. Os resultados de medidas magnéticas indicam a diminuição da coercividade, da indução magnética remanente e dos valores de BH Máx dos pós obtidos com a contribuição do excesso de bário, provavelmente devido à presença da fase intermediária não magnética. Este efeito negativo foi mais efetivo nos pós processados pelo método SHS, chegando a uma redução de 28,8% no valor de coercividade e 35,1% no valor de BH Máx. Os pós de ferritas BaM obtidos pelo método cerâmico tradicional apresentaram maiores valores de coercividade (4,28 kOe) e BH Máx (0,87 MOe*emu/g) e a influência do excesso de bário na formulação foi menos prejudicial sobre suas propriedades magnéticas.

Influences of preheat treatment on anisotropy of BaTiCoFe10O19 magnetic powders

Ultrafine substituted M-type barium ferrite BaTiCoFe10O19 powders were synthesised successfully by the sol-gel method. The hydroxide precursor particles were formed in a gel solution containing ethanol and water at a ratio of 1 : 1 and using NaOH as a co-precipitation agent. The effects of preheat treatments on formation and anisotropy of BaTiCoFe10O19 powders were studied using XRD and SEM. The XRD analysis indicated single phase BaTiCoFe10O19 powders were formed. The average particle sizes of the powders were about 40 nm. Calculation of c/a value with XRD data indicated that the Ti-Co-substitution and preheat treatment drastically changed the atomic lattice anisotropy of hexaferrite powders. The average c/a ratio increased from 3·9347 for BaFe12O19 powders to 3·9415 for no preheat treatment and 3·9392 and 3·9432 for preheat treatment for 1 h at 300°C and 400°C, respectively. SEM analyses revealed that the particles had platelike morphology and the aspect ratio in morphology of the powders non-preheated and preheated at 400°C were larger than that of powders preheated at 300°C.

Absorbing properties and structural design of microwave absorbers based on carbonyl iron and barium ferrite

Carbonyl iron and barium ferrite powder (BaZn 1.5Co 0.5Fe 16O 27) were prepared in this work. The complex permittivity and permeability spectra for rubber radar absorbing materials employing carbonyl iron and barium ferrite powders were measured. A database describing the frequency dependence of the permittivities and permeabilities of the carbonyl iron and barium ferrite microwave absorbers with various powder percentage compositions in 2–18 GHz was created. Based on the database, the single-layer and double-layer absorbers were designed and prepared, and their microwave absorption properties were investigated. The results indicate that the carbonyl iron powder prepared via thermal decomposition of iron pentacarbonyl is single cubic iron and of spherical shape. The barium ferrite powder is single W-type ferrite and a hexagonal flake. The absorption band of the double-layer microwave absorber is obviously more than that of the single-layer absorber. The double-layer microwave absorbers with reflection loss <−13 dB over the range of 6–18 GHz and reflection loss <−8 dB over the range of 2–18 GHz were prepared. The thicknesses of the absorbers are only 3.6 and 3.7 mm, respectively.

Synthesis and Magnetic Properties of BaFe12O19 Hexaferrite Nanoparticles by a Reverse Microemulsion Technique

BaFe12O19 hexaferrite nanoparticles, containing cetyltrimethylammonium chloride (CTAC), n-hexanol, and cyclohexane, were synthesized by a reverse microemulsion technique with a combination of (NH4)2CO3 and NH3·H2O as precipitator. Barium ferrite nanoparticles with 30 nm diameter and uniform flaky structure were proved to be single magnetic domains, which have magnetic properties comparable to some of the best ever reported for fine barium ferrite powders by chemical methods. Heat-treatment conditions can significantly influence the formation of pure BaFe12O19 hexaferrite phase, where quenching and nonprecalcination would produce intermediates of α-Fe2O3 and BaFe2O4, as detected by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analyses, resulting in lower magnetic properties. High magnetocrystalline anisotropy constant K and energy barrier EA calculated from Stoner−Wohlfarth theory may also account for the high coercivity for pure BaFe12O19. The variation of electrical conductivity during ...

Synthesis and characterization of nanocrystalline BaFe 12O 19 obtained by using glucose as a fuel

Nanocrystalline BaFe 12O 19 powders are successfully synthesized by using glucose as a fuel. The effects of the calcination temperature on the morphology, crystalline structure and magnetic properties of the barium ferrite particles are characterized by thermal gravimetric/differential thermal analyzer, field emission scanning electron microscope, X-ray diffractometer and vibrating sample magnetometer. Pure barium ferrite powders with a crystal particle size of 60 nm are obtained at temperature as low as 900 °C, showing a saturation magnetization ( M s) of 53 emu/g, a coercivity ( H c) of 5.3 kOe and a squareness of 0.573.

Crystal structure and magnetic properties of barium ferrite synthesized using GSPC and HEBM

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 BaFe 2O 4 is formed during the milling at room temperature. After the powder is milled for 60 h and subsequently calcined at 600 °C, barium ferrite is synthesized. The powder size is decreased to 20–30 nm after the powders are milled for 10 h. The magnetic properties of the milled barium ferrite are improved. The coercivity is increased greatly with the maximum of 425.74 kA/m.

Microwave absorption of nanosized barium ferrite particles prepared using high-energy ball milling

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.

Complex permittivity and permeability of barium and strontium ferrite powders in X, KU, and K-band frequency ranges

This paper presents accurate results for the complex permittivity, ε=ε′−jε″ and permeability, μ=μ′−jμ″ of barium ferrite powder (BaFe12O19) and strontium ferrite powder (SrFe12O19), in the frequency range from 8.0to26.5GHz. The complex permittivity and permeability are determined via the waveguide transmission/reflection (TR) technique and the waveguide cavity resonator (CR) technique at 25°C and relative humidity &amp;lt;75%. Measurements reveal that the real permittivities of BaFe12O19 and SrFe12O19 are, respectively, 2.497&amp;lt;εBa′&amp;lt;2.678, and 2.597&amp;lt;εSr′&amp;lt;2.712. BaFe12O19 has an average real permeability μBa′=1.078 and SrFe12O19 has an average real permeability μSr′=1.063. The imaginary permittivities are respectively εBa″&amp;lt;0.081 and εSr″&amp;lt;0.077. The imaginary permeabilites are respectively μBa″&amp;lt;0.095 and μSr″&amp;lt;0.106.

Determination of the Surface Anisotropy Contribution to the Magnetic Anisotropy Field of a Nanocrystalline Barium Ferrite Powder at Various Temperatures

The temperature dependence of the average anisotropy field of a nanocrystalline barium hexaferrite powder was studied by treating remanent-magnetization curves with inclusion of thermal fluctuations. The contribution of surface anisotropy was isolated; its nonstandard temperature dependence is intimately related to the specific features of formation of near-surface regions in ultrathin particles.

Magnetic and dynamic mechanical properties of barium ferrite–natural rubber composites

High coercivity barium ferrite (BaFe 12O 19) powders have been prepared by a coprecipitation method. After removing fine powders, they were incorporated into a natural rubber matrix with different loading levels up to 120 phr (part per hundred rubber). The variations in characteristics of rubber–ferrite composites (RFCs) were evaluated as a function of ferrite loading. The results showed that the coercivity is improved and the saturation magnetization is linearly dependent on the mass fraction of the filler, while the tensile strength, strain at break and modules are highly influenced by the size, shape and volume fraction of ferrite particles. The present RFCs showed a typical characteristic of low density (2.2 g/cm 3), high stored energy (BH max = 1.18 MG Oe) and flexibility (resilience = 0.844) at 120 phr of ferrite, which are relatively high when compared to previous works.

Preparation and thermal behavior of aerosol-derived BaFe12O19 nanoparticles

Pure BaFe12O19 nanoparticles, having single magnetic domain sizes, were obtained at 700°C using a process combining the citrate precursor method and spray technique. A neutralized aqueous solution, containing Ba2+ and Fe3+ chelated by citric acid, was nebulized to undergo thermal decomposition in a flowing air with a maximum temperature of 250°C. The dried solid precursor so obtained was calcined at different temperatures and was then chemically and physically characterized. Crystalline barium hexaferrites were formed at temperatures as low as 650°C, but calcination temperatures higher than 680°C were required to produce pure barium ferrite powder. Based on the obtained experimental results, the reaction mechanism for the aerosol-derived precursor to form BaFe12O19 was proposed and discussed in this study.

Composite elastic magnet films with hard magnetic feature

Hard magnetic materials with high remnant magnetic moment, Mr, have unique advantages that can achieve bi-directional (push–pull) movement in an external magnetic field. This paper presents the results on the fabrication and testing of novel composite elastic permanent magnet films. The microsize hard barium ferrite powder, NdFeB powder, and different silicone elastomers have been used to fabricate various large elongation hard magnetic films. Three different fabrication methods, screen-coating processing, moulding processing and squeegee-coating processing, have been investigated, and the squeegee-coating process was proven to be the most successful method. The uniform composite elastic permanent magnet films range from 40 µm to 216 µm in thickness have been successfully fabricated. These films were then magnetized in the thickness direction after fabrication. They exhibited permanent magnet behaviour; for instance, the film (0.640 mm3 in volume) made of polydimethyl siloxane (PDMS) and hard barium ferrite powders is measured to give a coercive force, Hc, of 3.24 × 105 A m−1 and Mr of 1.023 × 10−5 A m2, and the film (0.504 mm3 in volume) made of PDMS and NdFeB powders gives 1.55 × 105 A m−1 Hc and 8.081 × 10−5 A m2 Mr. These composite elastic permanent magnet films' mechanical properties, like Young's modulus and deflection force, have been evaluated. To validate the films' Young's modulus, a finite-element computer simulation (ANSYS®) is used and one film is chosen whose Young's modulus (16.60 MPa) is confirmed by the simulation results with ANSYS®. The large elongation composite elastic permanent magnet film provides an excellent diaphragm material, which plays an important role in the micropump or valve. The movement of the 126 µm thick film with 4.5 mm diameter made of PDMS and NdFeB powders has been tested in a 0.21 Tesla external magnetic field. It was proven to have large deflection of 125 µm.

Synthesis and Performance of Magnetic Composite Comprising Barium Ferrite and Biopolymer

The purpose of this study was to prepare the magnetic polymer composite particles with high ferrite content by encapsulating barium ferrite powders with alginate and investigate their physical and biological properties. The magnetic Ca-alginate composite particles were manufactured by adding barium ferrite-alginate slurry dropwise to a CaCl/sub 2/ solution. The final product was then completely cleaned and dried. Average size (0.1/spl sim/1 mm in diameter) of magnetic composite particles was dependent on the ratio of barium ferrite to alginate. The degree of swelling of magnetic Ca-alginate particles was increased as pH increased in aqueous media. The magnetic polymer composite particle was found to maintain high coercivity. The saturation magnetization for the magnetic Ca-alginate composites increased with the increase in the barium ferrite/alginate ratio. The self-heating induced by hysteresis loss under an alternating magnetic field was measured as a function of barium ferrite/alginate ratio in distilled water. The agar overlay test indicated a relatively high cell viability for the L929 cell line upon contact with the magnetic composite particles.