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The paper considers the influence of low-frequency pulsed force of an electromagnetic field on the formation of a solidifying metal structure, investigated experimentally. Pulses in the range from 0.1 to 10 Hz were applied to the melt, during the ingots growth in the cylindrical volume, to create the conditions of the forced convection. The final metal structure and deformation of the samples free surface, solidified in different conditions was analyzed. The reduction of porosity in metal ingots was stated for the cases of forced convection under the pulsed frequencies from 0.1 to 1 Hz, in comparison to the structure, formed by permanent electromagnetic stirring. The specimens, grown under the pulsed forcing with equal time of the pulses and the pauses have concave free surface, as well as in the cases of natural convection and permanent stirring. A flatter form of the free surface was obtained during the solidification process under the short pulses of electromagnetic force. Intorduction

The article presents the results of the numerical and physical experiments, aimed to recognize the influence of pulsed force of electromagnetic field on the melt motion and the fluid velocities. The experiment was performed on the eutectic alloy galinstan in the cylindrical volume, where Ultrasonic Doppler Velocimeter was employed for velocity measurements under conditions of pulsed and steady EM field application. A numerical simulation of the melt flow, forced by the steady forcing, involved a 2D axisymmetric model. The k-epsilon turbulence model was used to obtain the information about the melt velocities. The verification of the numerical model was carried out for the steady case. The effects of pulsed and steadily applied Lorentz force were compared using the physical experiment. An intensity of the velocity pulsations in galinstan for the pulsed frequencies in the range from 0.05 to 1 Hz considerably exceeded the values, measured in the permanently stirred melt. For higher values of pulsed frequencies (from 1 to 10 Hz) the effect decreases and only slightly differs from the influence of the permanently applied Lorentz force.

Nickel nanoparticles were synthesized at room temperature by a one-step method of chemical reduction of Ni ions from NiCl 2 ∙6H 2 O using NaBH 4 . The microstructure of the nanoparticles was studied by x-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopy. An analysis of x-ray diffraction and Raman spectroscopy data showed that the obtained nanoparticles had the cubic metallic Ni structure with a crystallite size (coherent scattering region) of 3–6 nm. Studies of the morphology indicated that the Ni nanoparticles were spherical in shape and in contact with each other to form large agglomerates of nanograins.