Papers by Keyword: Magnetic Effect

Abstract: 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.

Abstract: Metallic conductors have different degrees of their electrical conductivity. The aim of this research is to measure the electrical conductivity degree for some metallic conductors by measuring the induced voltage in a coil probe, which moves inside the metallic conductor sample tube. When a low frequency of alternating current flows through the LC circuit, it will pass through the solenoid and will generate a magnetic field, which will be reduced due to the presence of the metallic sample tube. The magnetic flux strength generated inside the solenoid determine the electrical conductivity (σ ) of this metallic tube by measuring the EM force induced on the solenoid in the presence the sample tube and without it. Measurements are conducted on two sample models (zinc and aluminum). Test results shows deviation of 10 % compared with the reference values ​​.

Abstract: Impact of a constant magnetic field on decomposition of supersaturated solid solution is investigated for the system Cu-Be-Ni. A technical bronze Cu-1.9Be-0.3Ni (in wt.%) was water-quenched after holding at 800°C (0.5 h) and subsequently heat treated at 325°C, 350°C and 400°C for 1 hour without and with application of a constant magnetic field of 0.7 T. The annealing in magnetic field is found to influence significantly the precipitation characteristics in diamagnetic Cu-based alloy, especially at 325°C. The nucleation barriers for discontinuous precipitation at grain boundaries are decreased, while the growth rates seem to be decreased, too, in magnetic field. A possible mechanism of the magnetic effect on discontinuous precipitation in the Cu-based is discussed.

Abstract: Unidirectional solidification of Al-In, Cu-Pb and Cu-Pb-Al monotectic alloys was performed under static magnetic fields up to 10T for formation of the regularly aligned-rod structure. mThe imposition of static magnetic fields exceeding 4T suppressed movement of the In liquid droplets at the Al solidifying front and enhanced the engulfment of the In droplets into the front. As a result, the eutectic-like structure was obtained in the Al-10 and 15at%In hypermonotectic alloys. The micro X-ray tomography indicated that the continuous In rods with diameters of 10-20 µm were aligned parallel to each other. In the case of the Cu-Pb and the Cu-Pb-Al alloys, the imposition of static magnetic fields also enhanced the formation of the aligned Pb rods. The electrochemical etching by using a 10% HNO3 solution successfully removed the minor phase, and the porous aluminum and copper with deep pores were fabricated.