Dielectric Properties of Magnetic Liquids in High Electric Fields

In this work, dielectric properties of magnetic fluids composed of magnetite particles dispersed in transformer oil and subjected to a uniform magnetic field were investigated at the high alternating electric field intensities in the range of 0.5-2.5 MV/m. Dielectric stability of the magnetic fluid with the particle volume concentrationΦ= 0.0019 was observed. The magnetic fluid with the concentrationΦ= 0.019 showed the significant changes of permittivity and dielectric losses, too

Dielectric Properties of Magnetic Liquids in High Electric Fields

In this work, dielectric properties of magnetic fluids composed of magnetite particles dispersed in transformer oil and subjected to a uniform magnetic field were investigated at the high alternating electric field intensities in the range of 0.5-2.5 MV/m. Dielectric stability of the magnetic fluid with the particle volume concentration Φ = 0.0019 was observed. The magnetic fluid with the concentration Φ = 0.019 showed the significant changes of permittivity and dielectric losses, too

Inter‐correlations between emitted lights and corresponding currents associated to different energy level spark discharges in mineral oil submitted to high‐voltage direct current stresses

International audienceThe present work is devoted to the analysis of currents and emitted lights associated to electrical spark discharges in mineral oil in a point-plane electrode system under high-voltage direct current stress. A systematic survey has been led on currents and emitted lights that characterise both positive and negative events through large applied field levels. On the other hand, interrelationships have been established between the currents and their corresponding emitted lights for all types of discharges. A particular attention will be accorded to the inter-correlation function between the recorded currents and light emissions and between their corresponding fast Fourier transforms. In spite of the similar shapes, major differences have been found between the spectral behaviours between currents corresponding to low-energy level discharges and those corresponding to high-energy level ones. On the other hand, photonic signals are found to be more accurate and expressive than the recorded current ones to investigate the physicochemical processes involved in the degradation of the insulating properties of the oil. The total energies of all types of discharges are of comparable magnitudes for both polarities. Their derivatives, i.e. powers, dissipated along the propagation are more expressive of the nature of discharge

Structuring from nanoparticles in oil-based ferrofluids

The effect of magnetic field on the structure formation in an oil-based magnetic fluid with various concentrations of magnetite particles was studied. The evaluation of the experimental data obtained from small-angle X-ray scattering and ultrasonic attenuation indicates the formation of chain-like aggregates composed of magnetite particles. The experimental data obtained from ultrasonic spectroscopy fit well with the recent theoretical model by Shliomis, Mond and Morozov but only for a diluted magnetic fluid. In this model it is assumed that a dimer is the main building block of a B-field-induced chain-like structure, thus the estimation of the nematic order parameter does not depend on the actual length of the structure. The scattering method used reveals information about the aggregated structure size and relative changes in the degree of anisotropy in qualitative terms. The coupling constant lambda, concentrations phi, average particle size d and its polydispersity sigma were initially obtained using the vibrating sample magnetometry and these results were further confirmed by rheometry and scattering methods. Both the particles' orientational distribution and the nematic order parameter S were inferred from the ultrasonic measurements. The investigation of SAXS patterns reveals the orientation and sizes of aggregated structures under application of different magnetic-field strengths. In addition, the magnetic-field-dependent yield stress was measured, and a relationship between the yield stress and magnetic-field strength up to 0.5T was established.<p> </p><p>© The Author(s) 2011. This article is published with open access at Springerlink.com</p