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Microstructure and properties of Cu–Nb and Cu–Ag nanofiber composites

Rdzawski Z., Głuchowski W., Stobrawa J., Kempiński W., Andrzejewski B.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 3

689--697

EN

There is a growing demand for new high strength and high electrical conductivity materials for the advanced electric applications. The promising materials for generators used to produce strong and variable magnetic fields are Cu–Ag and Cu–Nb wires. Two classical copper alloys were selected for this investigation. The third material used in the studies was produced by bundle drawing of niobium wire in a copper tube. Microstructure, mechanical and electrical properties were examined in relation to processing technology. Microstructure of Cu–Ag wires consisted of silver-rich bands distributed in a copper-rich matrix, whereas that of the Cu–Nb alloy wire was not homogeneous. Despite significant plastic deformation, globular particles of niobium, which do not contribute to the increase of mechanical properties, were also observed in addition to narrow bands of niobium-rich phase. Multiple drawing of Nb wire bundle in a copper jacket is a promising method for the production of Cu–Nb microcomposites. The number of wires increases in geometric progression during subsequent bundling, which results in the reduction of Nb band cross-section. Under this work, a wire having more than 820,000 niobium filaments of a diameter between 100 and 200 nm evenly distributed in a pure copper matrix was produced.

2

New superconducting phases in Mo2Re3Bx-Mo3Re2Bx eutectic

Andrzejewski B., Guilmeau E., Kowalczyk A., Szlaferek A.

Materials Science Poland

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2007

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Vol. 25, No. 4

1259--1266

EN

We report on the discovery and on some basic properties of the eutectic alloy composed of two new superconducting phases; Mo2Re3Bx with Tc = 8.7 K and of Mo3Re2Bx with Tc = 6.6 K (where x ??1). The two phases in the eutectic form complex globular structure and areas of locally ordered lamellar patterns. The lamellae are separated by thin interface of excess boron and behave like a regular network of Josephson junctions. Distinct two-step superconducting transition indicates that this eutectic belongs to inhomogeneous systems with no evidence for the proximity effect. The parameters of the dominating Mo3Re2Bx phase are as follows: the lower and the upper critical fields are equal to .mu.0Hc1 = 13 mT and to .mu.0Hc2 = 6.5 T, respectively.This corresponds to the penetration depth .lambda.?= 2040 A, to the coherence length .xi.?= 70 A and to Ginzburg-Landau parameter .kappa.= 29. Linear temperature dependence of Hc2(T) may be due to unconventional mechanism of superconductivity in dominating Mo3Re2Bx phase.

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Magnetic and transport properties of Fe/Si multilayers with various iron thicknesses

Wandziuk P., Luciński T., Andrzejewski B.

Materials Science Poland

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2007

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Vol. 25, No. 2

599--602

EN

Resistivity, temperature coefficient of resistance and magnetization as functions of iron thickness have been studied in a series of magnetron sputtered Fe/Si multilayers with constant Si layer thickness. At the Fe/Si interfaces, a significant amount of deposited iron is transformed into nonmagnetic (0.5 nm) and ferromagnetic (up to 2 nm) nonuniform Fe-Si mixture with a gradient of Fe concentration. Finally, for iron thicknesses above 2.5 nm a bcc-Fe phase appears.

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Cobalt nanoparticles processed by thermal decomposition of metal containing monomer

Sówka E., Leonowicz M., Andrzejewski B., Pomogailo A.D., Dzhardimalieva G.I.

Materials Science Poland

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2006

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Vol. 24, No. 2/1

311--317

EN

Polymer matrix ferromagnetic nanocomposites, containing Co nanocrystallites, were processed by an innovative fabrication method using frontal polymerisation of cobalt acrylamid (AAm) complex, followed by subsequent thermolysis at temperatures 873 and 1073 K. The thermolysis products were in the form of irregular powder particles having broad range of size distribution, from 10 up to 300 žm. The powder particles contained nanocrystallites of Co having mean size in the range 12-15 nm, depending on the thermolysis temperature. The hysteresis loops recorded for materials processed at 873 and 1073 K, respectively proved that the coercivity depends on the processing temperature and very slightly on the measurement temperature. The thermolysis product, processed at 873 K, showed soft magnetic properties. The particles were randomly distributed and their size and agglomeration can be controlled by the processing variables.

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Otrzymywanie i własności nanokompozytów typu polimer-cząsteczka magnetyczna

Sówka E., Leonowicz M., Andrzejewski B.

Kompozyty

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2005

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R. 5, nr 4

3-7

PL

Nanokompozyty wykazują unikalne własności dzięki nanometrycznym rozmiarom elementów struktury. Otrzymano materiały zawierające nanocząstki o własnościach ferromagnetycznych w osnowie polimerowej. Nanoeząstki magnetyczne wygenerowano w trakcie polimeryzacji akryloamidu w stałej fazie, metodą samorozprzestrzeniającego się frontu polimeryzacji czołowej. Otrzymane polimery poddawano pirolizie w dwóch różnych temperaturach: 600 i 800°C. Następował wówczas drugi etap, w którym polimer ulegał rozkładowi z wydzieleniem krystalitów metalicznego kobaltu. Badano również wpływ czasu wygrzewania na własności kompozytów. W celu scharakteryzowania i porównania struktury spreparowanych materiałów przeprowadzono rentgenowskie, mikroskopowe i magnetyczne badania wybranych układów. Stwierdzono obecność krystalitów kobaltu o wielkości od kilku do kilkudziesięciu nanometrów w zależności od temperatury pirolizy. Badania z zastosowaniem wysokorozdzielczego mikroskopu elektronowego potwierdziły i rozszerzyły posiadane informacje o mikrostrukturze materiałów. Ziarna proszku próbek pirolizowanych w temperaturach: 600 i 800°C miały rozmiary rzędu 50:250 mikrometrów, nieregularny kształt oraz pory o średnicach około 15 mikrometrów. Badania magnetyczne potwierdziły, że są to układy o własnościach ferromagnetycznych. Koercja na poziomie 0,01 T klasyfikowała kompozyty jako materiały magnetycznie miękkie.

EN

Nanocomposites show unique properties because of their nanosized structural elements (Figs 3-5). Ferromagnetic materials containing nanoparticles were prepared in polimeric matrix (Table 1). Magnetic nanoparticles were generated during acrylamide polymeryzation in solid phase. Obtained polymers were pyrolized at two different temperatures: 600 and 800°C. It was followed by second stage, when the polymer was decomposed yelding metallic cobalt crystallites. The influence of heating time on composites properties was tested. The structures of obtained materials were characterized by X-ray (Figs 1-3), microscopic (Figs 4-7) and magnetic method (Figs 8-10). The presence of cobalt crystallites of size a few to tenths nanometers depending of pyrolize temperature was detected. The studies with use of HRTEM confirmed the information about materials microstructures. The size of patricles after pyrolisys in temperatures 600 and 800°C was of 50+250 micrometers, irregural shape and pores diameter ca 15 micrometers. The ferromagnetic properties of the systems were confirmed by magnetic measurements. The coersive force on the level 0.01 T, clasified the composites as magnetic soft materials.