Wyniki 1-10 spośród 18 dla zapytania: authorDesc:"MARCIN LEONOWICZ"

Synthesis and properties of magnetorheological fluids

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Magnetorheological fluids (MRFs) belong to a group of smart materials, which have the ability of “intelligent" response to external stimuli. In the case of MRFs external factor is magnetic field. MRFs contain micrometric size magnetic particles, randomly distributed in non-magnetic liquid, which usually is synthetic or natural oil, water etc. The change of rheological parameters under magnetic field is called magnetorheological effect. MRFs were discovered by Jacob Rainbow in 1948 y. However, more extended interest in MRFs occurred at the end of XX century, when advantages of their potential application were noticed. The considerable interested in MRFs arise from their unique ability of rapid and reversible changes of rheological properties. Applications of MRFs include actuators, shock absorbers, dampers, brakes and clutches [3÷6]. MRFs are composite materials that basically consist of three components: -- filler material - magnetically polarizable particles, which provide the magnetorheological effect, -- carrier fluid, having a function of dispersing medium, -- stabilizer - protecting the particles from agglomeration. Factors that influence properties of MRFs can be classified into two groups: 1. Extrinsic factors: -- strength of magnetic field, -- shear rate, -- temperature. 2. Intrinsic factors: -- type of magnetic particles, their saturation magnetization and coercive force, -- size of magnetic particles and particle size distribution, -- volume (mass) fraction of components, -- carrier liquid type, its viscosity and thermal stability, -- stabilizer type. In order to increase the yield stress capability it is necessary to have a higher percentage of metal powder to support the chain structure in a magnetic field [1]. The saturation magnetization of the particles should be high enough to achieve strong magnetorheological effect. Moreover, low coercivity of the magnetic particles is required to ensure reversi[...]

Texture Analysis in Die-Upset Forged Nd-Fe-B Magnets

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Die-upset forging of Nd-Fe-B magnets results in the production of anisotropic crystallographic structure. The degree of anisotropy depends on the parameters of the deformation process. The investigation of the crystallographic orientation has been carried out using transmission electron microscopy. It has been found that directional crystal growth is the dominant mechanism during the early s[...]

Phase constitution and magnetic properties of nanocrystalline barium ferrite powders produced by mechanical alloying

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The effect of the chemical composition of the mixture of the starting Fe2O3 and BaCO3 powders on the phase constitution and magnetic properties of the materials produced by mechanical alloying was examined. This method consists of the two operations: high-energy milling and annealing (ferritization). The best magnetic properties (Br=0.26T, Hc=375kA/m) were achieved for the mixture where the [...]

Effect of annealing on the structure and properties of Ni46.4Mn28.5Ga25.1 single crystal

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Ferromagnetic Heusler alloys are based on the X2YZ phase. The first notice on such alloys comes from Friedrich Heusler et al. who characterized the Cu2MnAl alloy in 1903 [1]. That alloy showed ferromagnetic properties although none of the components was ferromagnetic. In 1934 Bradley and Rodgers reported on the effect of heat treatment of Cu2MnAl alloy [2]. Main conclusion coming from this work is that the ferromagnetism of the Heusler-based alloys depends not only on the chemical composition but also on the positions of neighbouring atoms. The Ni2MnGa-type alloys due to their magnetic field induced strain (MFIS), up to 10%, attract attention of the scientists and engineers. Over ten years of studies, since the first report, the magnetic shape memory effect (MSME) [3] has brought many publications on the structure and properties of the Ni2MnGa alloys. Especially structure of the martensite, its type and forming conditions is an object of great interest of many researchers. Various heat treatment procedures were proposed. For example Gaitzsch et al. have found that annealing at 803 K for 24 h leads in the Ni50Mn30Ga20 alloy to formation of the 7M martensite [4]. In our previous work we studied the effect of annealing temperature and the cooling rate on the structure of the polycrystalline Ni50Mn29Ga21 alloy [5]. It was found that the final structure strongly depends on the conditions of heat treatment and the 7M martensite can be produced by annealing [...]

Magnetic and rheological properties of materials used in magnetorheological devices

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Results of laboratory tests for the evaluation of the magnetic properties of three different types of magnetorheological fluids and of the coil’s core materials used in dampers, are presented. The characteristic magnetic properties of these fluids and of the structural elements play an important role in the working efficiency of the MR dampers. The analysis of these results allows for the [...]

Hard magnetic properties of bulk Nd-Fe-Al glasses

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Rapidly cooled Nd-Fe-Al alloys of, containing about 60at.% of Nd and about 10at.% of Al, are hard magnetic materials. They can be produced in the form of massive large-size samples. When examined by the X-ray methods they seem to be amorphous, but in fact, their phase structure contains both amorphous and ordered regions. The present study is concerned with the effect of the Nd content (from [...]

Struktura i właściwości spiekanych magnesów Alnico 8

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Magnesy z grupy Alni i Alnico zostały opracowane na początku lat 30. ubiegłego wieku przez Mishimę. Pierwotny stop, o składzie odpowiadającym w przybliżeniu formule Fe2NiAl, stał się podstawą wszystkich stopów tej grupy magnesów. Materiały te charakteryzują się wysoką remanencją, koercją niższą niż magnesy z ziem rzadkich i ferryty, w zakresie 119÷143 kA/m, stosunkowo niską energią magnetyczną oraz wysoką stabilnością temperaturową. Temperatura Curie, zależnie od gatunku wynosi 810÷860°C, a temperatura pracy 450÷550°C [1, 2]. Od czasu pierwszych wytopów magnesy Alni były modyfikowane dodatkami stopowymi (Co, Ti, Cu, S, Nb) oraz udoskonalano techniki ich wytwarzania (obróbka w polu magnetycznym, wytworzenie struktury kolumnowej). Te zabiegi spowodowały wzrost energii magnetycznej stopu z ziarnami kolumnowymi obrabianego cieplnie w polu magnetycznym do poziomu ponad 72 kJ/m3. Obecnie magnesy Alni oraz Alnico zawierają 0÷40% mas. Co, 12÷30% mas. Ni, 7÷14% Al, 0÷8% mas. Ti, 0÷6% mas. Cu, reszta Fe [2]. Magnesy Alnico, zawierające powyżej 24% mas. Co, są jedyną grupą materiałów magnetycznie twardych, których obróbka cieplna przebiega z udziałem zewnętrznego pola magnetycznego. Dzięki wysokiej zawartości kobaltu, który znacznie podnosi temperaturę przemiany magnetycznej do zakresu, w którym jest możliwe wywołanie procesu utwardzania magnetycznego. Proces ten ma charakter dyfuzyjny i polega na wydzielaniu się fazy silnie magnetycznej (Fe-Co) w postaci mikrowydzieleń wydłużonych w kierunku działania pola magnetycznego w osnowie fazy słabo magnetycznej (Al-Ni). Pierwotnie materiały te produkowano jako odlewane. Otrzymane w ten sposób magnesy są twarde (ok. 50÷55 HRC) i przez swą gruboziarnistość podatne na kruche pękanie. Własności te sprawiają szereg trudności podczas wytwarzania. Obróbka cieplna i mechaniczna powoduje powstawanie w tym materiale pęknięć, wykruszeń, a podczas szlifowania - wyrywanie całych ziaren z obrabianej powie[...]

Synthesis of magnetic nanocrystallites in carbon matrix

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Nanoscopic magnetic systems attract substantial scientific attention due to the unusual properties which differ them from their bulk counterparts. In the consequence of reduced dimensions increases overall magnetic anisotropy of the particles, which is accompanied by decrease of the magnetic moment and Curie temperature. Magnetic nanostructures exhibit several new phenomena, which do not occur in bulk magnetics, such as superparamagnetism, magnetic quantum tunneling, giant magnetoresistance, exchange bias, spin torque, spin Hall effect and other. Magnetic nanoparticles can exist as individual nanocrystallites [1] or be dispersed within beads [2÷7]. Their properties depend on the size and nature of magnetic interactions. Single domain particles, below certain critical size, usually 5÷15 nm, may exhibit superparamagnetic properties, in which remanence and coercivity goes to zero and saturation magnetization is the same as in the ferromagnetic ordering. Such nanoparticles do not “stick" together in the absence of the magnetic field, however, they still agglomerate tending to reduce the surface energy. Thus, synthesis of magnetic nanoparticles within larger beads, where they are separated within a matrix, seems to be a proper solution. The characteristic magnetic properties of nanostructures predispose them for various new applications, mostly in electronics and medicine. Biomedical applications are rapidly growing areas of applications for nanosystems and comprise magnetic resonance imaging [8, 9], hyperthermia [10], targeted drug delivery [11÷15], tagging of biological nanomaterials [16, 17], biological sensors and several other. Wide application of magnetic nanosystems is possible due to the rapid development of fabrication and characterization techniques. Among the former one can mention vapour deposition, solution chemistry, elektrophoretic deposition, arc discharge and other. In this study magnetic nanocrystallites we[...]

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