Wyniki 1-4 spośród 4 dla zapytania: authorDesc:"Marcin Dośpiał"

Structure and magnetic properties of high coercivity, nanocrystalline alloy based on Nd-Fe-B compound with overstoichiometric Nd content

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The powders for production of modern, hard magnetic materials obtained on the basis of intermetallic compounds, rare earths and transition metals are mainly produced by rapid cooling methods (the mechanical alloying and hydrogenation, disproportionation, desorption, recombination methods are also used) [1÷5]. One of the most popular method is the so-called melt-spinning, which allows to receive the alloy in the form of thin ribbons which are quenched in the next step of production process [6]. In this method, depending on the selection of manufacturing parameters such as pressure inside the vacuum chamber, the linear velocity of a copper wheel or push pressure of the liquid alloy from a quartz tube, allow to obtain the amorphous, partially crystallized or nanocrystalline material [7]. Manufactured nanocrystalline materials, while maintaining appropriate selection of production parameters does not require heat treatment in order to obtain good functional properties (in this case magnetic) [8], in contrast to partially crystallized or amorphous materials. Proper selection of annealing parameters such as temperature, time and cooling method allows to obtain the optimal microstructure, for which alloy will have the best magnetic properties [9]. Next to proper selection of manufacturing parameters, modifications in the alloy atomic composition allow to adjust functional properties of the alloy [10]. In the Figure 1 three types of structure found for the Re-Fe-B type alloys are presented, respectively, with excessive amount of rare earth in relation to the stoichiometric composition Re2Fe14B phase, with stoichiometric composition and with an excessive amount of iron. Oversteichiometric capacity of rare earth leads to the formation of structure, consisted of large nanograins (above 40 nm) isolated with a thin amorphous matrix (Fig. 1a). This allows to obtain the alloy with high resistance to external demagnetization fields, i.e. coer[...]

Modelling the formation parameters in thin-film HTSC

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Superconductivity means a state of matter when superconducting material, below critical temperature TK conducts electricity at zero resistance. Resistivity at room temperature (20°C) amounts to, respectively, for metals Ag 1,62·10-8 Ωm, for semiconductors e.g. ntype silicon 8,7·10-4 Ωm, for insolators e.g. glass 1010÷1014 Ωm [1]. For some materials, transition into superconducting state is possible at higher pressures. Superconductors include a variety of chemical elements, chemical compounds, metal alloys, ceramics or organic compounds. The scientists worldwide have investigated a variety of different materials, searching for superconductors with even better functional parameters such as: critical current JC, critical field HC or critical temperature TC. A record critical temperature of 254 K was observed for superconductor (TlBa)Ba2Ca2Cu7O13. The most recognized superconducting materials include superconductors based on Bi - Bi2Sr2CaCu2O9 (BSCCO) with TC of ca. 110 K, and YBa2Cu3O7 (YBCO) with TC of ca. 90 K [2]. High-temperature ceramic superconducting tapes today are characterized by very good current parameters [2÷8]. Typical current parameters of this group of superconductors are considerably deteriorated during their moulding, i.e. giving them a shape required by the particular application. All superconducting tapes are delivered with technical specification of a manufacturer, which contains information about e.g. minimal radius in moulding curve and maximal moulding force. However, it does not provide information about the effect of deformation on current parameters in superconductors and relationship between moulding radius and moulding force. It can be assumed that, with moulding radius higher than minimal, it is possible to use moulding force higher than maximal. This issue is particularly interesting in terms of its application since transformer efficiency is determined by, among other thing[...]

The impact of manufacturing inaccuracies on the filtration properties of Thue-Morse aperiodic superlattice systems

  Multilayers constructed with advanced composite materials are used in solid state physics, optoelectronics, optics and modern photonics [1÷8]. This refers mainly to the ongoing work on photonic crystals [9÷15], optical fiber photonics [16], quasicrystals [17÷24] and multilayer structures [5, 25÷30]. By superlattice we mean alternating layers constructed with differing properties of suitable topological configuration of the constituent components. Prediction by Veselago [31] in 1968 materials, which characterized by a negative refractive index, and the first experimental confirmation of their existence in the year 2000 [32] led to increased research on interesting properties of these structures [33÷39]. Thanks to high technology of multilayer systems production with specified configuration, the types of materials and layer thicknesses [40÷44] and the presence of the photonic band gap has become possible to design an applicationspecific materials. Consequently, it has become reasonable to carry out possible most detailed simulation of specific properties for multilayer structures, escpecialy the transmission properties which are the subject of research in this paper. In order to investigate the transmission properties of the superlattice, two most commonly used methods which are complementary to each other are used. The first one known as finite difference time domain method (FDTD) [39] is based on the study of the behaviour of electromagnetic waves described by differential Maxwell equations using an iterative algorithm. Fast Fourier Transform (FFT) [39] made simultaneously with the simulation, allows to determine the frequency characteristics of wave leaving test structure. The use of the matrix method allows to obtain of more information on the electromagnetic wave transmission by multilayer medium, which is made of layers of dielectric materials or modern composite materials with a negative refractive index otherwise known[...]

Improvement of mechanical properties of Fe-based alloys by application of rapid solidification method and Ti doping

  Nowadays, the industry is looking for the modern functional materials with unique functional properties [1, 2]. Very interesting group of alloys for special applications are those made on the basis of iron modified with titanium. These alloys, due to their increased strength and relatively low density (ρTi = 4.507 g/cm³), can be used in many industries. Ti admixture in this type of alloys results in a partial or complete oxidation of the surface, as the Ti has high affinity for oxygen [3]. Titanium is known to be an element well tolerated by the human body, and therefore it is successfully used in implantology [3, 4]. It is applied to produce cores, both for large hip implants, as well for mini dental implants. However, without proper chemical or mechanical treatment, titanium does not overgrown tissue and is only a foreign body. Recently, blasting method has been a very popular technique for refinement of the top layer of alloys containing titanium, regarding dental implants. The technique is very simple and cheap, but it is not without drawbacks as stratification because of grit used in mechanical polishing. Its small parts are sticking into the surface of the implant. What in turn leads to tearing down the structure of the surface. So, it can be stated that a lot depends on the grit used in the discussed process, which usually are small aluminum granules. The problem of aluminum contamination of dental implants has been eliminated by the chemical digestion process. Materials containing titanium are characterized by low weight and relatively high strength, they are used to build most of metal components used in the aerospace and military industry [5, 6]. Titanium alloys are also adopted in jewelry and become a good alternative to a few percent of the population showing an allergic reaction to silver, gold or platinum. They were also widely used in optics as part of eyeglass frames (flex-titanium, β-titanium). T[...]

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