Радиопоглощающие свойства феррит-полимерных композитов поливиниловый спирт/Ni-Zn феррит

The electromagnetic and radio-absorbing characteristics of ferrite-polymer composites with conductive inclusions based on polyvinyl alcohol are investigated. The Ni-Zn spinel ferrite powder of 2000NN grade with composition Ni0.32Zn0.68Fe2O4 was used as filler. It is shown that the obtained composites are effective absorbers in the frequency range of 2⸺5 GHz with peak reflection loss less than –20 dB. Through the analysis of the permittivity spectra and permeability spectra, as well as the calculated reflection loss spectra, critical factors of the electromagnetic wave absorption in obtained composites are established.

Effect of milling time on microstructure of cobalt ferrites synthesized by mechanical alloying

Purpose: of this paper is to determine the effect of manufacturing conditions, especially milling time, on the microstructure and phase composition of CoFe2O4 cobalt ferrite. Design/methodology/approach: Cobalt ferrite (CoFe2O4) has been synthesised from a stoichiometric mixture of CoCo3 and α-Fe2O3 powders in a high energy planetary mill. Annealing at 1000°C for 6 hours after milling was used to improve the solid-state reaction. Calcinated samples were analysed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The relationship between the milling time of powders, their microstructure, as well as their properties were evaluated. Particles size distribution and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) examination were also made. Findings: CoFe2O4 ferrites were successfully synthesized by mechanical alloying of α-Fe2O3 and CoCO3 powders. The powder particles had undergone morphological changes with the increasing milling time. However, the milling time does not affect the ferrite formation rate. It is expected that the improvement of fabrication parameters can further enhance the properties of cobalt ferrite presented in this work. Research limitations/implications: Contribute to research on the structure and properties of cobalt ferrites manufactured by mechanical alloying. Practical implications: The reactive milling and subsequently annealing is an efficient route to synthesise cobalt ferrite powder. However, using steel milling equipment risks powder contamination with iron and chromium from the vials and balls. Originality/value: The results of the experimental research of the developed ferrite materials served as the basis for determining material properties and for further investigation.

Diagnostic of Structural Changes in Ferromagnetic Powders during Milling in Beater Mill

Problem of obtaining fine powders of strontium hexa-ferrite is actual because of its wide applications. The paper provides the results of studies of particle size distribution and structural characteristic changes of strontium hexa-ferrite powder (SrFe12O19) during milling in impact mill and after its consequent annealing. Mechanical processing of coarse particulate system was carried out in the mill for 120 minutes without electromagnetic effect and with creation of magneto fluidized bed, formed by perpendicular constant and alternating magnetic field with induction gradient of 210 mT/m, providing reciprocating motion of particles and aggregates with sizes of 3 – 4 mm. It was shown that milling of coarse strontium hexa-ferrite with average particle size 1558.5 μm and the most possible size 1500 μm in magneto fluidized bed allowed to intensify milling process and to provide a significant increase of powder particle sizes uniformity. It was found out, that milling in magneto fluidized bed leads to a great decrease of coherent scattering regions sizes and an increase of lattice micro-deformations and relative dislocation density. Consequent annealing of the powder for 2 hours at 850°C refined structural characteristics significantly. The carried out research allows to choose the optimal milling duration for solution of practical problems of powder metallurgy.

Dynamical magnetic behavior of anisotropic spinel-structured ferrite for GHz technologies

We have fabricated a high quality magnetic Ni0.5Zn0.5Fe2O4 ferrite powder/polymer composite sheet consisting of common and environmentally friendly elements only. The sheet was then tested for its dynamic permeability by irradiating with electromagnetic waves with frequencies up to 50 GHz. Two different originally developed methods were used for the high-frequency permeability measurements, a short-circuited microstrip line method and a microstrip line-probe method. It is challenging to measure the dynamic permeability of magnetic thin films/sheets beyond 10 GHz because of the low response signal from these materials. However, the two methods produced essentially equivalent results. In the frequency dependent permeability profile, the maximum position of the profile, $$\mu ^{\prime \prime }_{max}$$ μ max ″ , shifted towards higher frequencies upon increasing an applied (strong) static external magnetic field, $$H_{dc}$$ H dc . A linear relationship between $$\mu^ {\prime \prime }_{max}$$ μ max ″ and $$H_{dc}$$ H dc for the entire range of $$H_{dc}$$ H dc was observed even at small $$H_{dc}$$ H dc . In general, the spinel-structured Ni-based ferrites exhibit low magnetic anisotropy, but the present sample showed a uniaxial-anisotropic behavior in the parallel direction of the sheet. Our Ni0.5Zn0.5Fe2O4 powder/polymer composite sheet thus exhibits high performance at GHz frequencies, and should be applicable e.g. as an anisotropic electromagnetic wave-interference material.

Operational lifetime increase of the pumping equipment when pumping-out contaminated groundwater

Purpose. Solving the problem of increasing the pumping equipment operational lifetime when pumping-out contaminated groundwater in the iron-ore industry by extracting the hard, abrasive part, using magnetic filters based on permanent ferrite magnets. Methods. To produce spherical hard-magnetic ferrite elements that catch finely-dispersed magnetic and weakly-magnetic abrasive particles when pumping-out contaminated groundwater in the iron-ore industry, barium ferrite powder BaО∙6Fe2O3 is applied, which is usually used for obtaining hard-magnetic ferrites. Spherical elements for filling a magnetic filtering installation are obtained by the method of spheroidizing the barium ferrite powder in a dragee machine. Sintering of spherical granules obtained from barium ferrite powder is conducted in a high-temperature atmospheric electric box furnace. The sintered spherical elements made of hard-magnetic barium ferrite are magnetized using a magnetic pulsed toroidal-shaped setup in a pulsed constant magnetic field. Findings. For continuous pumping-out and purification of contaminated groundwater from magnetic, weakly-magnetic and non-magnetic highly abrasive particles with the help of magnetic filters, a scheme of a filtering installation of two sections is pro-posed. A technology for producing spherical permanent magnets from barium ferrite powder has been developed for a filtering installation, which includes a coarse purification column with hollow-spherical permanent magnets of 16-17 mm in diameter and a fine purification column with full-bodied spherical barium ferrite magnets of 6-7 mm in diameter. Originality.The term of pumping equipment operation is doubled if to eliminate abrasive wear due to the filtering two-section installation by filling with barium ferrite spherical magnets. In the case of changing the filter, idle time is reduced by using the supplementary auxiliary column. The possibility of processing filtration products and their use in the field of construction and metallurgy without environmental pollution is substantiated. Practical implications. The scheme of magnetic groundwater purification in the iron-ore industry is proposed, consisting of a filtering column of coarse and fine purification from abrasive particles. A technology for producing spherical magnets with different diameters has been developed to ensure the quality of the process. The research results allow to increase the operational lifetime of pumping equipment by eliminating abrasive wear, which will lead to significant savings in the replacement and repair of centrifugal pumps. Keywords: pumping equipment, groundwater, wear, barium ferrite, spherical magnet, filter, iron-ore industry

Fabrication and Electromagnetic wave absorption Properties of Co-Cu-substituted Ni-Zn Spinel Ferrite-epoxy Composites

Spinel ferrites (Ni0.5Zn0.5)1-<i>x-y</i>Co<i>x</i>Cu<i>y</i>Fe2O4, (<i>x</i> = 0 and <i>y</i> = 0, <i>x</i> = 0.2 and <i>y</i> = 0, <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0 and <i>y</i> = 0.2) were prepared by sol-gel method and post-annealed at 1100 ^oC. The grain growth of the sample is very sensitive to the Cu substitution <i>y</i>. The average grain size of the non-doped sample (<i>x</i> = 0, <i>y</i> = 0) was ~400 nm and it increased to ~3 μm at the sample with <i>x</i> = 0 and <i>y</i> = 0.2. The real and imaginary parts of permittivities (<i>ε', ε"</i>) and permeabilities (<i>μ', μ"</i>) were measured on the spinel ferrite powder-epoxy (10 wt%) composite samples by a network vector analyzer in the frequency range of 0.1 ≤ <i>f</i> ≤ 15 GHz. The <i>μ'</i> and <i>μ"</i> depend on Co substitution <i>x</i> and the <i>ε'</i> is sensitive to Cu doping <i>y</i>. Reflection loss (RL), which implies electromagnetic (EM) wave absorption properties, were analyzed based on the complex permeability, permittivity spectra. In the RL map plotted as functions of sample thickness (<i>d</i>) and frequency (<i>f</i>), the intensive EM absorbing area (RL < -30 dB) shifted to a high frequency region with increasing Co substitution. This can be attributed to a permeability spectra shift, due to the increase in ferromagnetic resonance frequency produced by the Co substitution. The samples with <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0.2 and <i>y</i> = 0 also exhibited a very broad-ranged EM wave absorbing performance with a <i>d</i> < 3 mm, indicated by RL < -10 dB being satisfied in the frequency range 7~14 GHz.

Electrophysical properties of the multiferroic PFN–ferrite composites obtained by spark plasma sintering and classical technology

The multiferroic (ferroelectric–ferromagnetic) composites (PFN–ferrite) based on ferroelectromagnetic PbFe1/2Nb1/2O3 powder and ferrite powder (zinc–nickel ferrite, NiZnFeO4) were obtained in the presented study. The ceramic PFN–ferrite composites consisted of 90% powder PFN material and 10% powder NiZnFeO4 ferrite. The ceramic powders were synthesized by the classical technological method using powder calcination, while densification of the composite powders (sintering) was carried by two different methods: (1) free sintering method (FS) and (2) spark plasma sintering (SPS). The composite PFN–ferrite samples were thermally tested, including DC electrical conductivity and dielectric properties. Besides, XRD, SEM, EDS (energy-dispersive spectrometry) and ferroelectric properties (hysteresis loop) of the composite samples were tested at room temperature. At the work, a comparison was made for the results measured for PFN–ferrite composite samples obtained by two methods. The X-ray examination of multiferroic ceramic composites confirmed the occurrence of the strong diffraction peaks derived from ferroelectric (PFN) matrix of composite as well as weak peaks induced by the ferrite component. At the same time, the studies showed the absence of other undesired phases. The results presented in this work revealed that the ceramic composite obtained by two different technological sintering methods (free sintering method and spark plasma sintering technique) can be the promising materials for functional applications, for example, in sensors for magnetic and electric fields.