Papers by Keyword: Magnetic Materials

Abstract: Calcium substituted strontium M-Type hexaferrites are synthesized at different calcium concentrations by co-precipitation method. During synthesis process, PH value of 11 is achieved and solution is heated at 70 °C for 3 hours to form gel followed by drying process at 80 °C for 5 hours. Synthesized samples are then sintered at 650 °C for 4 hours at ramp rate of 10 °C/min. XRD analysis reveals that strontium M-Type hexaferrites at all calcium concentrations exhibit single phase hexagonal crystal structure. Change in density is observed for samples sintered at 800 °C as compared to samples sintered at 650 °C due to increase in temperature. SEM shows that the average particle size of strontium M-Type hexaferrites is greater at lower calcium concentration and smaller at higher concentrations. The average particle size varies from 530 nm to 345 nm for different calcium concentrations and fine particle sizes are achieved at all calcium concentrations. EDX results indicate that stoichiometric ratio is properly maintained according to samples composition and no extra peak of impurity or other element is detected in EDX spectrum. According to LCR measurement, pure strontium M-Type hexaferrites exhibit high dielectric constant at lower frequencies as compared to calcium substituted M-Type hexaferrites at different concentrations. Pure strontium M-Type hexaferrites have higher conductivity which might be due to presence of extra Fe³⁺ ions at crystal lattice sites. At lower frequencies pure strontium M-Type hexaferrites have higher conductivity and higher tangent loss at lower frequencies as compared to calcium substituted M-Type hexaferrites. While in the frequency range of 200 Hz to 300 Hz calcium substituted M-Type hexaferrites exhibit higher tangent loss.

Abstract: Magnetron sputtering with a chromium-containing Fe-19at.%Cr alloy is used to improve the corrosion resistance of Fe-20at.%Ga alloy. The structure of the 2 μm coated layer and distribution of the elements (Fe, Cr, and Ga) are investigated. The bcc phase (A2 structure) is observed in the sputtered sample by XRD analysis. The corrosion resistance in 3.5%NaCl solution increases 14 times in the sample with 2 μm Fe-Cr coated layer. At the same time, the magnetron sputtering leads to a 10% decrease in magnetostriction and a 20% decrease in damping. This difference is explained by schemes of loading during magnetostriction and damping tests.

Abstract: Manganese bismuth alloy has gained importance due to its rare earth free elements, positive temperature coefficient and unique magnetic properties. Low temperature phase (LTP) MnBi was successfully prepared by arc melting with subsequent heat treatments and melt spinning technique followed by heat treatment for different durations. LTP MnBi formation was confirmed using XRD analysis and microstructural characterization of the samples was done using field emission scanning electron microscope. MnBi with greater LTP amount was formed by melt spinning route when compared with its counter arc melted one. Magnetic energy density of LTP MnBi formed by melt spinning technique with different heat treatment time was studied.

Abstract: The paper presents the results of experimental studies of strontium hexa-ferrite average particle size and structural characteristics changes during milling process. Coarse strontium hexaferrite was milled in beater mill, without and with electromagnetic effect. Electromagnetic effect was produced by constant and alternating gradient magnetic fields with mutually perpendicular induction lines. Particle sizes were measured by microscopic methods, and structural characteristics were calculated by processing of X-ray diffractograms. Diffraction studies showed that during milling process, both with and without electromagnetic effect, the most intensive changes of coherent scattering region (CSR) sizes, dislocation densities and relative deformation of particulate material occur at earlier stage of milling. At this stage the speed of average particle size decrease is maximal. At later stage both average particle size and structural characteristic changes correlate and have asymptotic character.

Abstract: Magnetostatic shields, based on Ni-Fe alloys, were obtained via electrochemistry method with different thickness of partial magnetic layers. The experimental researches of the magnetic properties and magnetostatic shielding effectiveness of the single-layer and malty-layer cylindrical sample of the shields, based on the electrodeposited Ni₈₀Fe₂₀ and Ni₅₀Fe₅₀ alloy, are carried out. It has been shown that the shields of gradient type (200 μm Ni₅₀Fe₅₀+200 μm Ni₈₀Fe₂₀ and 100 μm Ni₅₀Fe₅₀+300 μm Ni₈₀Fe₂₀), containing layers with different values of saturation induction (B_s), have a higher shielding efficiency than shields of symmetric type (400 μm Ni₅₀Fe₅₀ and 400 μm Ni₈₀Fe₂₀). Maximum efficiency of magnetostatic shielding has been noted for 200 μm Ni₅₀Fe₅₀+ 200 μm Ni₈₀Fe₂₀ sample. It opens wide prospects for practical application for protection of the microelectronics devices against permanent magnetic fields.

Abstract: Magnetostatic shields based on Ni-Fe alloys were obtained via electrochemistry method with different thickness of partial magnetic layers. The experimental researches of the magnetic properties and magnetostatic shielding effectiveness of the single-layer and malty-layer cylindrical sample of the shields based on the electrodeposited Ni₈₀Fe₂₀ and Ni₅₀Fe₅₀ alloy are carried out. It has been shown that shields of gradient type (200 μm Ni₅₀Fe₅₀+200 μm Ni₈₀Fe₂₀ and 100 μm Ni₅₀Fe₅₀+300 μm Ni₈₀Fe₂₀) containing layers with different values of saturation induction (B_s) have a higher shielding efficiency than shield of a symmetric type (400 μm Ni₅₀Fe₅₀ and 400 μm Ni₈₀Fe₂₀). Maximum efficiency of magnetostatic shielding has been noted for 200 μm Ni₅₀Fe₅₀+ 200 μm Ni₈₀Fe₂₀ sample. It opens wide prospects for practical application for protection of the microelectronics devices against permanent magnetic fields.

Abstract: Oxide coatings formed on aluminum alloy in electrolyte with colloidal particles of iron hydroxides show ferromagnetic properties. Iron distribution have been studied using electron scanning microscopy and magnetic force microscopy. It is found that the iron localized in the areas exposed to spark and microarc electric discharges makes the main contribution to the ferromagnetic properties of coatings.

Abstract: Magnetic magnetite, Fe₃O₄ nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe₃O₄ ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe₃O₄ nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe₃O₄ suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C.

Abstract: The experiment focused on the bioleaching and desulfurization of pyrite roasting residues by the bacteria for the recovery of Cu, Zn and the magnetic materials. First of all, the study systematically performed XRD, which provided scientific and technique basis for extraction of valuable metals. Subsequently, the effect of the pH, the temperature and the bacterial inoculum volume ratio on the bioleaching was investigated. The data revealed that the condition under the pH of 1.2, the temperature of 45°C and bacterial inoculum volume ratio of 10% had the most significant effect on the bioleaching and the recovery rates of Cu, Zn and SO₄^2- reached up to 80%, 99% and 80%, respectively. Finally, multi-elements analysis before and after the bioleaching experiments was performed to further explore the ability of the NB bacteria to oxidize the Deerni pyrite roasting residues. The study demonstrated that the total Fe and sulfur contents of the bioleaching residues accounted for 68.47% and 0.28%, respectively. The content of Cu and Zn in the leaching residue were only 0.09% and 0.01%. The desulfurization effects are evident and bioleaching residues meet the requirements as magnetic materials in steel making industry.

Abstract: Compression moulded NdFeB bonded magnets can advantageously replace the sintered version in applications that require specific shape and size. The maximum densities that can be obtained for ready-to-press commercial raw materials are close to 6.0 g/cm³. For large pieces, uniaxially pressed, densities should be limited to values as 5.0 g/cm³ due to the friction during compression. This paper investigate the effects of final density (ranging from 5.0 to 6.0 g/cm³) on the magnetic of compression moulded magnets. A ready-to-press Magnequench MQPB+ was used as raw material. Small cylindrical samples were produced by press and cure. Results are presented and discussed considering aspects related to relative densities. The magnetic properties are dependent of density, and coercivity decreases with deformation during compaction.