Hybrid magnetorheological elastomer: Influence of magnetic field and compression pressure on its electrical conductivity

Graphene nanoparticles are used to produce a hybrid electro-conductive magnetorheological elastomer (MRE-hybrid). We fabricate a magnetoresistive sensor based on the obtained MRE-hybrid. We measure the electrical resistance of the MRE-hybrid in a transverse magnetic field of intensity 0 ≤ H (kA/m) ≤ 65, and separately, the electrical resistance under the influence of a compression pressure p ≤ 14.4 kPa. From the obtained results we determine the variation of electrical conductivity with H, and respectively with p. We develop a theoretical model which explains the effects of H and p on electrical conductivity of MRE-hybrid. The obtained results are presented and discussed.     

Some mechanisms concerning the electrical conductivity of magnetorheological suspensions in magnetic field

Iron carbonyl is decomposed, at the temperature of 473 K ± 10%, into a liquid matrix formed of silicone oil and stearic acid. For 3.703% and 1.886% stearic acid, magnetorheological suspensions (MRSs) are obtained. The iron particles in MRSs have the mean diameter of 0.356 μm. Magnetoresistors are achieved from MRSs with the dimensions of diameter and length equal to 5 mm. In longitudinal magnetic field, the resistance of the magnetoresistors is measured. Assimilating the resistance of the magnetoresistors with that of a linear resistor, the conductivity σ of MRS is determined. The duration t_c of onset of σ is determined. It is observed that t_c is considerably influenced by the intensity of the magnetic field applied and by the composition of MRSs. Experimental data are discussed, too.     

Influence of the magnetic field on the alignment degree of the anisotropic strontium ferrites for elastomer bonded magnets

In this work, the influence of the magnetic field on the alignment degree of the magnetic particles and on the magnetic energy flux of elastomer bonded magnets are investigated. For the investigations, a strontium ferrite filled nitrile butadiene rubber is used. The change of magnetic flux density in the injection molding tool cavity was realized by changing the current at the rectifier. The alignment degree of the magnetic particles increases with increasing magnetic field in the injection molding tool cavity. Above a certain current strength, a saturation behavior of the alignment degree of the magnetic particles and the magnetic energy flux is reached. The change of the cavity magnetic field leads to an improvement of the pole angle error up to a current of 10 A. An increase of the current above 10 A leads to hardly any improvement of the pole angle error, since a saturation in the alignment of the magnetic particles has already been reached.     

Effects of transitional phenomena on the electric field induced strain–electrostrictive response of a segmented polyurethane elastomer

The electromechanical properties of a segmented polyurethane elastomer were investigated as functions of temperature and frequency. Two transitional phenomena were observed in the temperature range from -50 to 85°C. In these transition regions, the electric field induced strain coefficient exhibits large increases, which indicate that the effect of the transition processes is significant. The experimental analysis suggests that the transitional processes in the polyurethane are related to the chain-segment motions. From the elastic compliance and the dielectric constant data, the contribution of the uniform Maxwell stress was determined. It was found that the contribution of the Maxwell stress effect to the measured strain coefficient increased from about 10% below the glass transition temperature (T_g) (∼ -25°C) to about 50 and 35% for the frequencies of 10 and 100 Hz, respectively, at ∼ 40°C, which is above T_g. The large difference between the measured strain response and the calculated Maxwell stress effect indicates a significant contribution to the field-induced strain from other mechanisms, such as electrostriction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1363–1370, 1997     

Influence of a magnetic field on the electrodeposition of nickel-iron alloys

The electrodeposition of nickel-iron alloys is studied under the influence of a superimposed external static magnetic field. It is shown that the direction of the magnetic field with regard to the electric field affects the electrodeposition process (current efficiency, composition and morphology of the layers). Furthermore, the influence of the simultaneous action of natural and magnetically driven convection is discussed in function of the orientation of the working electrode. The electrochemical quartz crystal microbalance (EQCM) technique is used to determine the partial current due to the hydrogen evolution reaction (HER). It is observed that the magnetic field applied perpendicular to the electric field lines increases the rate of the HER, while no significant variation is observed in a magnetic field parallel to the electric field.     

Influence of electric field strength on structure,microstructure, and electrical properties of flash sintered 8% mol Yttria-stabilized zirconia as a solid oxide fuel cell electrolyte

To study the effect of electric field on the characteristics of flash sintered materials, 8% mol. Yttria-stabilized zirconia (8YSZ) was isothermally flash sintered under various electric field strengths as a solid oxide fuel cell (SOFC) electrolyte. Structural, microstructural, and electrical characteristics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Electrochemical impedance spectroscopy (EIS), respectively. Results show that the electric field did not affect the relative density of flash sintered 8YSZ. Electric fields stronger than 300 V cm^?1, however, transformed the cubic structure to tetragonal. Microstructural studies show that the average grain size of samples is independent of the applied electric field strength. Electrochemical impedance spectroscopy showed changes in the grain boundary characteristics upon using the electric field for flash sintering. Oxygen vacancy concentration in the grain boundary of flash sintered samples was more than ten times higher than conventionally sintered ones, which improved the conductivity in flash sintered samples.     

A study on the role of polypropylene fibers and silica nanoparticles on the compression properties of silicone rubber composites as a material of finger joint implant

In this study, different contents of SiO₂ nanoparticles and polypropylene fibers were added to silicone rubber matrix as a material of finger joint implants and mechanical properties of these composites were investigated before and after being soaked in simulated body fluid. Results of compression test revealed that compression stress of silicone rubber by addition of the 2 wt% silica and 2 wt% PP fibers increased from 0.98 to 1.9 and 2.37 MPa, respectively. These stresses decreased after being soaked in SBF and water absorption results proved this. Increasing silica contents caused an increase in water absorption while increasing PP fibers showed contrary behavior.