M. Anhalt

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.

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.

Magnetic memory effect in magnetite charged polypropylene composite

Abstract The behaviour of damping and dynamic shear modulus in polypropylene charged with either different volume fraction or size of magnetite (Fe3O4) particles, as a function of the applied magnetic field at 318, 353 and 403 K; has been studied. An increase of the alternating magnetic field oscillating with 50 Hz, leads to an increase of the damping. In addition, during the subsequently decreasing alternating magnetic field, the damping decreases, but a hysteretic behaviour appeared. The behaviour of the damping and the elastic modulus under the application of an alternating magnetic field was explained by the development of a magnetic fatigue damage occurring around the particle interface due to oscillation of magnetite particles. In contrast, during the increase of a direct magnetic field, the damping decreases and the elastic modulus increases. Measurements performed at 353 and 403 K allowed observing the interaction process among the particles of magnetite in the polymer matrix. After the decrease in the direct magnetic field, from the maximum reached value, damping and modulus remain smaller and higher, respectively; giving rise to a memory effect. In addition, a mesoscopic description of magnetite filled polymer composite materials has been performed in the continuous media by considering the interaction between magnetic and mechanical forces. Theoretical predictions of here developed model were qualitatively applied with good success for explaining the memory effect in magnetite filled polypropylene under the application of a direct magnetic field.

Electro-rheological description of solids dielectrics exhibiting electrostriction

An electro-rheological model based in Voigt units which takes into consideration the variation in volume promoted by electrostriction is developed. The model was based on a mean field approximation as an averaging of the mechanical and electrical properties. The electro-rheological coupling which describes the effects of the electrical excitation on the mechanical response and the effects of the mechanical excitation on the electrical response of the dielectric is studied. In the case of an alternating electrical excitation the model reveals the appearance of harmonics in the current through the dielectric promoted by the electrostriction phenomenon. In contrast, for the case of an oscillating mechanical excitation, a current which overtakes the driving mechanical oscillation was resolved to appear. The correlation of the new model with experimental results, obtained from dynamic mechanical analysis tests conducted under high electric field, in polyamide, was found out.

Theoretical consideration of experimental data of thermal and magnetic properties of polymer-bonded soft magnetic composites

Spherical iron silicon (FeSi) particles and irregular shaped magnetite (Fe3O4) particles with particle sizes ≤146 μm and varying volume filler fractions up to x = 0.7 (70 vol%) were mixed with polypropylene (PP) matrix. The samples were prepared by kneading and injection moulding and show particle–particle interaction at elevated filler fraction of x ≥ 0.5. Thermal and magnetic properties of the composites were characterized and show a significant increase at filler fractions of x ≥ 0.3. The thermal conductivity of PP (0.176 W/(m K)) was increased up to seven times to 1.239 W/(m K) at x = 0.7. FeSi-filled composites show slightly higher values of thermal conductivity than Fe3O4-filled composites. The magnetic permeability of the composites rise from 1 for PP to a maximum value of 23.1 for PP/FeSi composites at x = 0.7. The nonlinear increase in the thermal conductivity corresponds with the lower boundary of the Hashin–Shtrikman model. The Bruggeman model can be applied to describe the nonlinear increase in the magnetic permeability. Magnetic permeability increases with mean particle diameter as well as magnetic coercivity and loss dissipation increases with inverse mean particle diameter.

Magnetic Field Dependent Damping of Magnetic Particle Filled Polypropylene

The behavior of internal friction Q-1 and dynamic shear modulus has been studied in polypropylene charged with either different volume fraction or size of magnetite (Fe3O4) particles, as a function of the applied magnetic field at 318 K. An increase of the alternating (AC) magnetic field oscillating with 50 Hz, leads to an increase of the internal friction. In addition, during the subsequently decreasing alternating magnetic field, the internal friction decreases, but a hysteretic behavior appeared. In fact, the internal friction of the decreasing part of magnetic field amplitude is found to be smaller than during the previously increasing amplitude part of the treatment with the alternating magnetic field. Subsequent magnetic treatment cycles, lead to successively decreasing internal friction. In contrast, during the increase of a direct (DC) magnetic field, the internal friction decreases and the elastic modulus increases. The behavior of the internal friction and the elastic modulus during the application of an oscillating magnetic field (AC) is discussed on the basis of the development of both, a new zone with different rheological characteristics than the matrix but of the same material (self-inclusion), and/or a deteriorated or damaged zone (chain’s cuts) of the polymer matrix in the neighborhood of the magnetite inclusion. These effects are promoted by the movement or small relative rotation of the magnetite particles related to the surrounding matrix controlled by the oscillating field. The behavior of the internal friction and elastic modulus during the application of a direct (DC) magnetic field is discussed on the basis of the increase of the internal stresses into the polymer matrix due to the promotion of the magnetomechanical stresses.

Thermal Properties of Polyurethane Shape Memory Polymer Filled With Magnetite Particles

Temperature dependent thermal diffusivity (295K ≤ T ≤ 375K), specific heat capacity (290K ≤ T ≤ 380K) and thermal conductivity (300K ≤ T ≤ 340K) were measured on extrusion compounded and injection molded polyurethane shape memory polymers filled with different volume fractions (0%, 10%, 20%, 30%, 40%) of magnetite particles (10μm, 50μm and 150μm). With increasing particle content thermal diffusivity arises from α(PU + 0% Fe3 O4 ) ≈ 0.13mm2 /s to α(PU + 40% Fe3 O4 ) ≈ 0.31mm2 /s whereas d = 10μm particle sizes lead to higher values than larger particle sizes. Values measured for 150μm large particles are lying between values of composites with 10μm and 50μm particle sizes in the whole investigated temperature range. For higher filler contents differences in thermal diffusivity between composites of different particle sizes disappear. Thermal diffusivity decreases with increasing temperature, while thermal conductivity is increasing from λ(PU+0% Fe3 O4 ) ≈ 0.2W/mK to λ(PU+40% Fe3 O4 ) ≈ 0.6W/mK. Corresponding to glass transition temperatures of the polymer, the specific heat capacity shows a rise between 300K and 320K and a decrease between 350K and 370K.Copyright