Concentrations Of Magnetite Nanoparticles Research Articles

Dielectric properties of transformer paper impregnated by mineral oil based magnetic fluid

The influence of combined magnetic and electric field on permittivity of transformer paper used in power transformers was observed. Transformer paper was impregnated by pure transformer oil ITO 100 and magnetic fluids based on transformer oil ITO 100 with different concentrations of magnetite nanoparticles. The measurements were carried out with help of high precision capacitance bridge. The electric intensity between circular planar electrodes was in the region of weak electric field (E > 106 V/m). The increase of electric permittivity of transformer paper impregnated by magnetic fluid opposite pure transformer paper was observed. The experiments showed that permittivity of insulator system consisting of pure transformer paper and impregnated transformer paper naturally depends on number of paper layers. The magnetodielectric effect was found to be dependent on magnetite nanoparticles concentration in magnetic fluids.

Effect of Particle Size of Magnetite Nanoparticles on Heat Generating Ability under Alternating Magnetic Field

In this study, magnetite nanoparticles (MNPs) with series of size varying from 8 nm to 103 nm were synthesized by a chemical co-precipitation and an oxidationprecipitation method to aim for finding the optimum particle size which has high heating efficiency in the applied magnetic field (9.6–23.9 kA·m–1, 100 kHz). Their in vitro heating efficiencies in agar phantom, at a MNPs concentration of 58 mg Fe·ml–1, were measured in the applied field. The temperature increase (ΔT) of the agar phantom at 30 s was 9.3 °C for MNPs of 8 nm, exhibiting a high heating efficiency in a field intensity of 9.6 kA·m–1. The ΔT of agar was 55 °C for MNPs of 24 nm and 25 °C for MNPs of 8 nm in a field intensity of 23.9 kA·m–1. The excellent heating efficiency for MNPs of 24 nm might be a combined effect of relaxation loss and hysteresis loss of the magnetic particles.

Effect of magnetic nanoparticles on the thermal properties of some hydrogels

Magnetic hydrogels (ferrogels) based on poly(vinyl alcohol) (PVA) and poly(hydroxyethyl methacrylate) (PHEMA) with magnetite (Fe 3O 4) nanoparticles were prepared. PVA ferrogels were synthesised by submitting the aqueous solution of polymer and Fe 3O 4 to freezing–thawing (F–T) cycles yielding a physical gel. Different samples were prepared by varying (i) the concentration of PVA, (ii) the concentration of magnetite and (iii) the number of F–T cycles applied. PHEMA ferrogels were prepared by a crosslinking polymerization reaction in the presence of magnetite yielding chemical gels. Different samples were prepared by varying (i) the concentration of HEMA, (ii) the concentration of EGDMA and (iii) the concentration of magnetite nanoparticles. All ferrogel samples were first dried before been analysed in a thermogravimetric analyzer. The resulting thermograms showed that the concentration of magnetite nanoparticles does affect the thermal stability of either ferrogels system, a general improvement in comparison with PVA and PHEMA hydrogels, respectively, being observed. The apparent activation energy ( E a) of the thermal degradation for PVA ferrogels was evaluated and calculated applying the Flynn–Wall and the Kissinger methods. Values of apparent E a increased with the content of Fe 3O 4 in the ferrogel sample.

A study of magnetic liquids with the help of a paramagnetic sensor

The paramagnetic sensor method was used to study local magnetic fields in a magnetite aqueous suspension. The sensor was 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, a stable nitroxide radical. The lines in the EPR spectrum of the sensor were demonstrated to be broadened due to the dipole-dipole interaction with magnetite nanoparticles. It was established that no spin exchange occurred between sensor molecules and magnetite nanoparticles. The g-factor was found to decrease with the concentration of magnetite nanoparticles in the suspension. The mean strengths of the local magnetic fields calculated from changes in the EPR spectrum of the sensor proved to be substantially lower than the values determined from magnetic measurements. This difference was accounted for by the formation of linear aggregates of magnetite nanoparticles under the action of a magnetic field.

Magnetorheology for suspensions of solid particles dispersed in ferrofluids

In this work, the magnetorheological properties of suspensions of micron-sized iron particlesdispersed in magnetite ferrofluids were studied. With this aim, the flow properties ofthe suspensions in the steady-state regime were investigated using a commercialmagnetorheometer with a parallel-plate measuring cell. The effect of both magnetite andiron concentration on the magnitude of the yield stress was studied for a broad range ofmagnetic fields. In addition, the experimental values of the yield stress were compared withthe predictions from the chain model. With this purpose the values of the yield stresswere obtained by means of finite element calculations. Interestingly, it was foundthat the experimental yield stress increases with the concentration of magnetitenanoparticles in the ferrofluid. Unfortunately, this behaviour is not obtained fromcalculations based on the chain model, which predict just the opposite trend.