Bernd Weidenfeller

Magnetic properties of polymer bonded soft magnetic particles for various filler fractions

Samples of polypropylene filled with iron powder from 20to85vol% filler content were produced and examined. The permeabilities of the materials versus the magnetic field strength (up to 50kA∕m) were recorded as well as the low field and maximum permeability and the coercivity versus filler fractions were measured and compared with existing mathematical models. Investigations of the permeability as well as of the coercivity of two materials containing 85vol% filler material varying in mean particle size versus frequency (1Hz⩽f⩽2000Hz) and magnetic field strength have been carried out. Results show permeabilities μlow>100 for highest filled materials with low coercivities. Measurement data were compared with theoretical models.

Theoretical and experimental approach to characteristic magnetic measurement data of polymer bonded soft magnetic composites

Soft magnetic composites consisting of an organic binder and FeCoV particles have been produced and examined afterward regarding the dependence of magnetic field H at polarization J on filler content C. In general, the applied magnetic field to achieve a certain value of polarization is proportional to the inverse filler content, following H∼1∕C, and the polarization is directly proportional to the filler content, following J∼C. With use of the evaluated material data and the inner demagnetization factor Ni a model for calculating the permeability of soft magnetic composites has been derived. As input values the permeability of the soft magnetic particles μ, the filler content C, and the geometric demagnetization factor of the particles Np are used. The elaborated approach shows an excellent agreement with experimental permeability data of the FeCoV composites.

Electrodeposition of iron and iron–aluminium alloys in an ionic liquid and their magnetic properties

In this work we show that nanocrystalline iron and iron-aluminium alloys can be electrodeposited from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C. The study comprises CV, SEM, XRD, and magnetic measurements. Two different sources of iron(ii) species, Fe(TfO)2 and FeCl2, were used for the electrodeposition of iron in [Py1,4]TfO. Cyclic voltammetry was employed to evaluate the electrochemical behavior of FeCl2, Fe(TfO)2, and (FeCl2 + AlCl3) in the employed ionic liquid. Thick iron deposits were obtained from FeCl2/[Py1,4]TfO at 100 °C. Electrodeposition of iron-aluminium alloys was successful in the same ionic liquid at 100 °C. The morphology and crystallinity of the obtained deposits were investigated using SEM and XRD, respectively. XRD measurements reveal the formation of iron-aluminium alloys. First magnetic measurements of some deposits gave relatively high coercive forces and power losses in comparison to commercial iron-silicon samples due to the small grain size in the nanometer regime. The present study shows the feasibility of preparing magnetic alloys from ionic liquids.

Frequency dependence of loss-improvement of grain oriented silicon steels by laser scribing

Abstract Dynamical hysteresis loops of unscribed and laser scribed grain oriented silicon steels were measured in the frequency range from 0.05 to 500 Hz for polarizations from 1.4 to 1.7 T to determine frequency dependent loss improvement. For low frequencies the plot of fractional loss change show increased power losses due to laser scribing. However by increasing the frequency the fractional loss change is decreased until an optimum in relative loss reduction is reached, dependent on laser treatment. The loss change due to laser scribing depending on frequency can be explained by the assumption that the number of movable domains is increased by the same amount for all frequencies.

Domain refinement and domain wall activation of surface treated FeSi sheets

Abstract The loss reduction of grain oriented iron silicon steels by laser scribing or related techniques is usually explained by a domain refinement. Changes in power losses can also be due to a change of the activation behaviour of domain walls. It was found that the activation behaviour and not the increase of domains due to surface treatment is decisive for the improvement of dynamic losses.

Polyurethane–magnetite composite shape-memory polymer Thermal properties

Shape-memory polymer–magnetite (Fe3O4) composite samples were prepared by extrusion compounding and injection molding. Thermal diffusivity, conductivity and specific heat capacity were measured from 290 K to 340 K. Increasing filler fraction decreases specific heat capacity and increases thermal diffusivity. Experimental results show a good agreement with Agari–Uno and Hashin–Shtrikman models but not with Bruggeman model. The interconnectivity of the particles is very poor. Agari–Uno model leads to a high influence of polymer on thermal properties. Below 350 K mainly the polymer and above 350 K mainly the Fe3O4 influences specific heat capacity that shows drastic changes around 310 K (recovery temperature) and 357 K.

Thermal diffusivity and mechanical properties of polymer matrix composites

Polypropylene–iron-silicon (FeSi) composites with spherical particles and filler content from 0 vol. % to 70 vol. % are prepared by kneading and injection molding. Modulus, crystallinity, and thermal diffusivity of samples are characterized with dynamic mechanical analyzer, differential scanning calorimeter, and laser flash method. Modulus as well as thermal diffusivity of the composites increase with filler fraction while crystallinity is not significantly affected. Measurement values of thermal diffusivity are close to the lower bound of the theoretical Hashin-Shtrikman model. A model interconnectivity shows a poor conductive network of particles. From measurement values of thermal diffusivity, the mean free path length of phonons in the amorphous and crystalline structure of the polymer and in the FeSi particles is estimated to be 0.155 nm, 0.450 nm, and 0.120 nm, respectively. Additionally, the free mean path length of the temperature conduction connected with the electrons in the FeSi particles toget...

Permeability of Soft Magnetic FeCoV-Composites for Varying Filler Fractions

The dependence of permeability on the magnetic field in the initial magnetization curve for different Fe49 Co49V2-polymer composites is investigated. For a measurement frequency of f = 1 Hz and a low filler fraction of x = 0.1 the permeability is nearly constant with increasing magnetic field with a small maximum at H = 26100 A/m. Increasing filler fraction causes an increase of initial permeability and also the maximum permeability becomes more and more distinctive. Additionally the position of the maximum shifts to a lower magnetic field of H = 3027 A/m for filler fraction x = 0.8. At this filler fraction the maximum permeability is ¿max = 57 and the initial permeability is ¿i = 36. At the magnetic field where the maximum permeability was found also the frequency dependence from 1 Hz to 2000 Hz of the permeability was estimated. While the permeability is nearly constant in the whole examined frequency range for a filler fraction x ¿ 0.2, a higher filler fraction causes a reduction of permeability at higher frequencies. For the composite with 80-vol. % Fe49Co49V2 content the permeability is decreased for frequencies f > 100 Hz.

Metallurgical Phenomena during Processing of Cold Rolled TRIP Steel

Metallurgical phenomena taking place during processing of TRIP Steel are investigated and described with the aim of achieving better understanding of the microstructure development throughout the entire integrated processing routes. Different TRIP steel structure sizes were created by controlling the hot rolling process prior to cold rolling. After that the specimens were intercritically annealed under different conditions to obtain prescribed austenite fractions, and subsequently quenched in salt bath at the bainite transformation temperature. The microstructures had been investigated using light optical microscopy (LOM) and the amount of retained austenite was determined by magnetometry.

Electrodeposition and magnetic characterization of iron and iron-silicon alloys from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate.

The electrodeposition of soft magnetic iron and iron-silicon alloys for magnetic measurements is presented. The preparation of these materials in 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C with FeCl2 and FeCl2 +SiCl4 was studied by using cyclic voltammetry. Constant-potential electrolysis was carried out to deposit either Fe or FeSi, and deposits of approximately 10 μm thicknesses were obtained. By using scanning electron microscopy and X-ray diffraction, the microstructure and crystallinity of the deposits were investigated. Grain sizes in the nanometer regime (50-80 nm) were found and the presence of iron-silicon alloys was verified. Frequency-dependent magnetic polarizations, coercive forces, and power losses of some deposits were determined by using a digital hysteresis recorder. Corresponding to the small grain sizes, the coercive forces are around 950-1150 A m(-1) and the power losses were at 6000 J m(-3), which is much higher than in commercial Fe(3.2 wt %)Si electrical steel. Below a polarization of 1.8 T, the power losses are mainly caused by domain wall movements and, above 1.8 T, by rotation of magnetic moments as well as domain wall annihilation and recreation.