Download or read book Influence of Chemical Doping on Microstructures and Superconducting Properties of MgB2 Wires and Bulk Samples written by Yuan Yang and published by . This book was released on 2016 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnesium diboride (MgB2) is a material with a superconducting transition temperature of 39 K. Discovered in 2001, the relatively large coherence length (and associated lack of weak links) together with its simple binary composition (making phase pure formation relatively easy) have made it a material of substantial interest. However, its inadequate in-field performance limits the high field applications. Chemical doping is the key to increasing the Bc2 of MgB2. Chemical doping aiming at Mg site or B site substitution is of interest and both routes are explored in this thesis. Structure-property correlations are developed for dopants that either do or do not, incorporate themselves into the MgB2 matrix. First, the effects of C doping in the state of art MgB2 wires were investigated. In order to do so, a series of state of the art C doped MgB2 wires, in both mono-filamentary and multi-filamentary forms, were fabricated by a local company. Their transport and magnetic performance in various magnetic fields, and mechanical induced degradation, were examined. The C doping influence on the critical current density and the n-values were discussed. Secondly, the effects of rare earth oxide (REO) doping in MgB2 were studied. Two sets of samples including both bulk samples and wires were fabricated. Microstructural evidence obtained by SEM and TEM proved that nano-size inclusions formed after REO doping acted as grain growth inhibitors, as evidenced a reduction of MgB2 grain size in REO doped bulk samples. The results of XRD and magnetic measurements on the bulk samples demonstrated that Dy2O3 and Nd2O3 do not alloy with MgB2, no changes being observed in the lattice parameters, Tc and Bc2 of doped MgB2. Enhancements in flux pinning and Jc were obtained in both bulk samples and wires by REO doping, consistent with the microstructural evidence of notable grain refinements and the presence of nano-size inclusions as new pinning sites in MgB2 grains. Lastly, a set of metal diboride and Dy2O3 added MgB2 bulk samples were synthesized at very high temperatures and pressures (up to 1700°C and 10 MPa) to explore solubility limits of dopant species in MgB2 and enhance diffusion during the sample synthesis. The microstructure was studied by XRD, EDS, TEM and STEM, and doping the influence of doping on superconducting properties were investigated by magnetic measurement. The chemical doping induced changes in microstructure and properties of MgB2 bulk samples were discussed.
Download or read book Mgb2 Superconducting Wires Basics And Applications written by Rene Flukiger and published by World Scientific. This book was released on 2016-08-10 with total page 667 pages. Available in PDF, EPUB and Kindle. Book excerpt: The compendium gives a complete overview of the properties of MgB2 (Magnesium Diboride), a superconducting compound with a transition temperature of Tc = 39K, from the fundamental properties to the fabrication of multifilamentary wires and to the presentation of various applications. Written by eminent researchers in the field, this indispensable volume not only discusses superconducting properties of MgB2 compounds, but also describes known preparation methods of thin films and of bulk samples obtained under high pressure methods.A unique selling point of the book is the detailed coverage of various applications based on MgB2, starting with MRI magnets and high current cables, cooled by Helium (He) vapor. High current cables cooled by liquid hydrogen are also highlighted as an interesting alternative due to the shrinking He reserves on earth. Other pertinent subjects comprise permanent magnets, ultrafine wires for space applications and wind generator projects.
Download or read book Investigation on the Link Between Microstructures and Superconducting Properties of MgB2 Bulk Samples written by Zilin Gao and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tuning the Superconducting Properties of Magnesium Diboride written by Rudeger Heinrich Theoderich Wilke and published by . This book was released on 2005 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: The changes in normal state and superconducting properties of MgB2 as a result of various perturbations have been investigated. Carbon doping was achieved using a two step reaction process wherein boron filaments were doped with carbon via a chemical vapor deposition technique. The subsequent filaments were then exposed to magnesium vapor to form the superconducting phase. Studies on the effects of defects introduced by neutron irradiation were performed on both pure and carbon doped MgB2 wires that were exposed to thermal neutron fluences in the range 1018-1019 n/cm2. Different techniques for synthesizing carbon doped MgB2 powders were investigated. Bulk Mg(B[subscript l-x]C[subscript x])2 samples were synthesized in sintered pellet form from mixtures of elemental Mg, B, and the binary compound B4C. Nano-scale carbon doped boron particles, that are ideally suited for powder-in-tube processing of superconducting wire, were synthesized by a gas phase plasma synthesis method. The effects of the various processing conditions on the critical current density are presented. Additionally, Ti was added to Mg(B[subscript l-x]C[subscript x])2 filaments in order to explore the feasibility of creating TiB[subscript x] precipitates in carbon doped MgB2 samples in order to enhance in-field critical current densities.
Download or read book High Energy Milled Ex situ MgB2 for Tapes and Wires written by Anna Kario and published by Cuvillier Verlag. This book was released on 2011-05-02 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1. The optimum solution for the difficulties during conductor deformation was to use the ex situ precursor powder which is not sensitive to heat treatments in the range of temperatures needed for the working stress release of the sheath metal. Two different ex situ powders are studied: homemade ex situ (based on mechanically alloyed in situ powder) and commercial powder with reduced crystallite size achieved by high energy ball milling. 2. As the first approach, ex situ powder is prepared using mechanical alloying. A detailed phase analysis shown secondary phases, such as MgO and MgB4+x. A high critical current density for unsintered tapes and wires was obtained. It is observed that non of the applied final heat treatments of the conductors improve their superconducting properties. It is assumed that, heat treatments influence the crystallite size which is explained by MgO at the grain boundaries blocking grain growth. Additional milling or chemical treatment of the powder to clean the grains is needed to accomplish a smaller particle size. However, if medium Jc values are sufficient, the MA in-ex situ powder is an interesting precursor powder for conductors needed for the react & wind method of superconducting coil preparation, because the final heat treatment of a such a conductor is not needed. 3. As the second approach, commercially available ex situ powder was milled to reduce grain size. The average crystallite size of the powder is reduced by ball milling drastically from 47 nm to 15 nm, however, this powder is highly reactive. Powders after 2 h or longer milling times exposed to air react rapidly with oxygen and create up to 40 wt% of secondary phases, like MgB4+x and MgO. This reaction can be avoided by using exclusively a protective atmosphere for the sample preparation. Ex situ MgB2 stability examination via the decomposition behaviour. 4. The decomposition of MgB2 to Mg and higher borides at high annealing temperatures is observed in bulks and conductors. The temperature of the MgB2 decomposition decreases with increasing milling time. Unfortunately, the decomposition takes place at temperatures which are in the same range as the temperature needed for ex situ sintering. With increasing milling time, the crystallite size decreases and more powder is decomposed. It was found that an increased grain connection due to the milling and a decreased crystallite size play a larger role in increasing Jc than secondary phases. The milling process creates fresh reaction surfaces without a MgO layer for an improved grain connectivity. 5. The high reactivity of the powder caused by the high energy ball milling might be reduced by carbon addition. Carbon is successfully introduced into the lattice, as proved by a change in the lattice parameter, a decrease of Tc, an increase of the upper critical field and a change of the Jc dependence on applied field. The carbon substitution in the lattice is accomplished via high energy ball milling. 6. The best Jc results ( Jc=104 A/cm2 at 12.4 T) are obtained for the tape with the 20 h milled powder with 5 wt% of carbon addition. The precursor powder is well deformable: the 2 m long conductor was prepared using a combination of swaging, drawing and rolling with the help of intermediate heat treatments. Such additional heat treatments do not influence the precursor powder. Furthermore the carbon addition to the tape precursor increases the decomposition temperature of the powder, decreases its reactivity and improves the Jc(H) dependence of the tape in comparison to the tape with undoped precursor. The tapes prepared from that powder do not show a Jc anisotropy in respect to the field direction. The ex situ powder was used as superconducting diffusion barrier for copper sheathed conductors to prevent reaction between filament and sheath. 7. In addition, ex situ powder is used as a chemical barrier in Glidcop® in situ wires, substituting Nb or Ti which are commonly used. It is proved that the wire deformation by drawing with the powder barrier is possible. The effectiveness of the barrier in preventing a reaction between the Glidcop® sheath and the in situ MgB2 in wires heat treated both under ambient pressure and under high gas pressure was studied. It is found that this barrier is effective in preventing diffusion between Mg and Cu in the sheath only in the case of high pressure sintering. This novel technique allows to get relatively high values of the engineering critical current density Je (Je=104 A/cm2 at 5.3 T) because a high superconductor filling factor of 50% can be achieved. This is usually very challenging in powder-in-tube composite conductors with a diffusion barrier. Homepage IFW Dresden
Download or read book The Effect of Pr6O11 Doping on Superconducting Properties of MgB2 written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper we report the effect of Pr6O11 doping on the structural and superconducting properties of MgB2. The bulk samples of Pr6O11-doped MgB2 have been prepared with nominal compositions Mg1-x(Pr6O11)x/6B2 (where x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) via a standard solid-state reaction route by sintering in a reducing atmosphere of Ar/H2. The superconducting transition temperature Tc of MgB2 is found to decrease from 39 to 37 K when x increases from 0 to 0.05. The XRD results show the presence of MgO and PrB6 secondary phases in the doped samples besides the main hexagonal phase of MgB2. Improvement in critical current density (Jc), irreversibility field (Hirr), and upper critical field (Hc2) of doped samples has been observed. The Jc values at 10 and 20 K of the x = 0.03 sample are higher in the entire field region (0-6 T). At 10 K and 2 T field the Jc values of undoped and 0.03 Pr6O11-doped samples are 1.09 × 105 and 2.21 × 105 A/cm2, respectively. Variations of Hc2, Jc, Hirr, and flux-pinning force (Fp) with doping concentrations have been studied in this paper and a correlation between these superconducting properties and structural characteristics of the samples has been found in the present work.
Download or read book Connectivity Doping and Anisotropy in Highly Dense Magnesium Diboride MgB2 written by Guangze Li and published by . This book was released on 2015 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnesium diboride (MgB2) is a superconducting material which can be potentially used in many applications such as magnetic resonance imaging system (MRI), wind turbine generators and high energy physics facilities. The major advantages of MgB2 over other superconductors include its relatively high critical temperature of about 39 K, its low cost of raw materials, its simple crystal structure, and its round multifilament form when in the form of superconducting wires. Over the past fourteen years, much effort has been made to develop MgB2 wires with excellent superconducting properties, particularly the critical current density Jc. However, this research has been limited by technical difficulties such as high porosity and weak connectivity in MgB2, relatively small flux pinning strength, low upper critical field Bc2 and relatively high anisotropy. The goal of this dissertation is to understand the relationship between superconducting properties, microstructure, and reaction mechanisms in MgB2. In particular, the influences of connectivity, Bc2, anisotropy and flux pinning were investigated in terms of the effects of these variables on the Jcs and n-values of MgB2 superconducting wires (n-value is a parameter which indicates the sharpness of resistive V-I transition). The n-values of traditional "Powder in Tube (PIT)" processed MgB2 wires were improved by optimizing precursor species after the identification of microstructural defects such as so-called "sausaging problems". Also, it was found that "high porosity and weak connectivity" was one of the most critical issues which limited the Jc performance in typical MgB2. To overcome this problem, highly dense, well-connected MgB2 conductors were successfully fabricated by adopting an innovative "Advanced Internal Magnesium Infiltration (AIMI)" process. A careful study on the reaction kinetics together with the microstructural evidence demonstrated how the MgB2 layer was formed as the infiltration process proceeded. As a result, it is possible to control the MgB2 layer growth in the AIMI-processed MgB2 wires. The best AIMI wires, with improved density and connectivity, accomplished an outstanding layer Jc, which was 1.0 × 105 A/cm2 at 4.2 K and 10 T, nearly 10 times higher than the Jcs of PIT wires. The engineering Je of AIMI wires, namely the critical current over the whole cross-sectional area in the wire, achieved 1.7 × 104 A/cm2 at 4.2 K, 10 T, 200 % higher than those of PIT wires. Finally, two promising dopants, Dy2O3 and O, were engineered to incorporate with MgB2. Dy2O3 nanopowders, co-doped with C in AIMI wires, enhanced the Jc performance at elevated temperatures such as 20 K. Oxygen, on the other hand, doped into MgB2 thin films through a newly-developed O2 annealing process, improved Bc2 to 14 T at 21 K. Both of the doping studies were helpful to understand the superconducting nature of MgB2.
Download or read book Fabrication of Chemically Doped High Upper Critical Field Magnesium Diboride Superconducting Wires written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Controlled chemical doping of magnesium diboride (MgB2) has been shown to substantially improve its superconducting properties to the levels required for high field magnets, but the doping is difficult to accomplish through the usual route of solid state reaction and diffusion. Further, superconducting cables of MgB2 are difficult to fabricate because of the friable nature of the material. In this Phase I STTR project, doped and undoped boron fibers were made by chemical vapor deposition (CVD). Several>100m long batches of doped and undoped fiber were made by CVD codeposition of boron plus dopants. Bundles of these fibers infiltrated with liquid magnesium and subsequently converted to MgB2 to form Mg-MgB2 metal matrix composites. In a parallel path, doped boron nano-sized powder was produced by a plasma synthesis technique, reacted with magnesium to produce doped MgB2 superconducting ceramic bodies. The doped powder was also fabricated into superconducting wires several meters long. The doped boron fibers and powders made in this program were fabricated into fiber-metal composites and powder-metal composites by a liquid metal infiltration technique. The kinetics of the reaction between boron fiber and magnesium metal was investigated in fiber-metal composites. It was found that the presence of dopants had significantly slowed the reaction between magnesium and boron. The superconducting properties were measured for MgB2 fibers and MgB2 powders made by liquid metal infiltration. Properties of MgB2 products (Jc, Hc2) from Phase I are among the highest reported to date for MgB2 bulk superconductors. Chemically doped MgB2 superconducting magnets can perform at least as well as NbTi and NbSn3 in high magnetic fields and still offer an improvement over the latter two in terms of operating temperature. These characteristics make doped MgB2 an effective material for high magnetic field applications, such as magnetic confined fusion, and medical MRI devices. Developing fusion as an energy source will dramatically reduce energy costs, global warming, and radioactive waste. Cheaper and more efficient medical MRI devices could lower examination costs, find potential health problems earlier, and thus also benefit society as a whole. Other potential commercial applications for this material are devices for the generation and storage of electrical power, thus lowering the cost of delivered electricity.
Download or read book Influences of Crystalline Anisotropy Doping Porosity and Connectivity on the Critical Current Densities of Superconducting Magnesium Diboride Bulks Wires and Thin Films written by Michael Adam Susner and published by . This book was released on 2012 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Magnesium diboride (MgB2) is a material with a superconducting transition temperature of 39 K. Discovered in 2001, the relatively large coherence length (and associated lack of weak links) together with its simple binary composition (making phase pure formation relatively easy) have made it a material of substantial interest. However, it has been difficult to assess in detail the relative importance of the roles of flux pinning, crystalline anisotropy, porosity, connectivity, doping, and doping homogeneity on the observed transport limitations of this conductor. This work focused on deconvoluting the most dominant of these effects. First, the overall effects of electrical connectivity and crystalline anisotropy of critical current density (Jc) were investigated. In doing so the Jcs of dense, well-connected c-axis oriented films were compared with the relatively degraded Jcs of standard powder-in-tube MgB2 wires. With the aid of a percolation model it was deduced that at 4.2 K, 10 T. about 60% of the degradation was due to MgB2's crystalline anisotropy and the remaining 40% to porosity. Second, chemical substitutions onto both the Mg and B sites were investigated in terms of effects on structure and superconducting properties. The homogeneity of C-substitution onto the B site was quantified in terms of the width of the superconducting specific heat transition. Analysis of the results led to optimization of methods for homogeneous doping of C into the B sublattice. Zr substituted onto the Mg sublattice was investigated using samples prepared by pulsed laser deposition (PLD). Changes in magnetic, resistive, superconductive, chemical, and structural properties were studied over a wide range of Zr composition.
Download or read book MgB2 Superconductors written by Mohit Bhatia and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The basic formation of in-situ MgB2, and how variations in the formation process influence the electrical and magnetic properties of this material was studied. Bulk MgB2 samples were prepared by stoichiometric, elemental powder mixing and compaction while strand samples were prepared by a modified PIT with subsequent reaction. The influence of various reaction schedules on the formation reaction was studied. Two different optimum reaction-temperature windows were identified, namely, low-temperature heat-treatment (650°C) and high-temperature heat-treatment (650°C) for the preparation of MgB2. XRD was used to confirm phase formation and microstructural variations were studied with the help of SEM. Following this, the focus turned to critical field enhancement via doping with various compounds targeting either Mg or B sites. Large increases in irreversibility field, and upper critical field, of bulk and strand superconducting MgB2 were achieved by separately adding SiC, amorphous C, and selected metal diborides (NaB2, ZrB2, TiB2) in bulk samples and different sizes of SiC (~200 nm, 30 nm and 15 nm) in strand samples. Lattice spacing shifts and resistivity measurements were consistent with dopant introduction to the lattice. The increases in the Bc2 were also complimented by an increase in the transport Jcs, especially for the SiC doped samples. Flux pinning analysis performed on SiC doped samples showed that while some small level of particulate-enhanced pinning was present, the majority of the pinning was associated with a grain boundary mechanism, suggesting that transport Jc increases were predominantly Bc2 related. Normal-state resistivities were measured for various binary and doped MgB2 samples as a function of temperature and were modeled based on the Bloch-Gruneissen equations. This allowed extraction of the residual resistivities, Debye temperatures and current carrying volume fractions, well as providing information on the electron-phonon coupling constant. The residual resistivity was found to increase by a factor of three, Debye temperature decreased and the electron-phonon coupling constant increased marginally for the SiC doped samples as compared to the binary sample. This change in [rho]0 and [theta]D confirmed the XRD evidence that the dopants were increasing [mu]oHirr and Bc2 by substituting on the B and Mg sites of the crystalline lattice.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2566 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book MgB2 Superconducting Wires written by Rene Flukiger and published by World Scientific Series in Applications of Superconductivity and Related Phenomena. This book was released on 2016 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt: The compendium gives a complete overview of the properties of MgB2 (Magnesium Diboride), a superconducting compound with a transition temperature of Tc = 39K, from the fundamental properties to the fabrication of multifilamentary wires and to the presentation of various applications. Written by eminent researchers in the field, this indispensable volume not only discusses superconducting properties of MgB2 compounds, but also describes known preparation methods of thin films and of bulk samples obtained under high pressure methods. A unique selling point of the book is the detailed coverage of various applications based on MgB2, starting with MRI magnets and high current cables, cooled by Helium (He) vapor. High current cables cooled by liquid hydrogen are also highlighted as an interesting alternative due to the shrinking He reserves on earth. Other pertinent subjects comprise permanent magnets, ultrafine wires for space applications and wind generator projects.
Download or read book Superconductivity and Its Applications written by Yi-Han Kao and published by American Institute of Physics. This book was released on 1992 with total page 804 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Handbook of Nanofibers written by Ahmed Barhoum and published by Springer. This book was released on 2019-09-10 with total page 1300 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Handbook covers all aspects related to Nanofibers, from the experimental set-up for their fabrication to their potential industrial applications. It describes several kinds of nanostructured fibers such as metal oxides, natural polymers, synthetic polymers and hybrid inorganic-polymers or carbon-based materials. The first part of the Handbook covers the fundamental aspects, experimental setup, synthesis, properties and physico-chemical characterization of nanofibers. Specifically, this part details the history of nanofibers, different techniques to design nanofibers, self-assembly in nanofibers, critical parameters of synthesis, fiber alignment, modeling and simulation, types and classifications of nanofibers, and signature physical and chemical properties (i.e. mechanical, electrical, optical and magnetic), toxicity and regulations, bulk and surface functionalization and other treatments to allow them to a practical use. Characterization methods are also deeply discussed here. The second part of the Handbook deals with global markets and technologies and emerging applications of nanofibers, such as in energy production and storage, aerospace, automotive, sensors, smart textile design, energy conversion, tissue engineering, medical implants, pharmacy and cosmetics. Attention is given to the future of research in these areas in order to improve and spread the applications of nanofibers and their commercialization.
Download or read book 100 Years of Superconductivity written by Horst Rogalla and published by Taylor & Francis. This book was released on 2011-11-11 with total page 866 pages. Available in PDF, EPUB and Kindle. Book excerpt: Even a hundred years after its discovery, superconductivity continues to bring us new surprises, from superconducting magnets used in MRI to quantum detectors in electronics. 100 Years of Superconductivity presents a comprehensive collection of topics on nearly all the subdisciplines of superconductivity. Tracing the historical developments in supe
Download or read book Energy Storage written by Robert Huggins and published by Springer. This book was released on 2015-11-13 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt: Energy Storage explains the underlying scientific and engineering fundamentals of all major energy storage methods. These include the storage of energy as heat, in phase transitions and reversible chemical reactions, and in organic fuels and hydrogen, as well as in mechanical, electrostatic and magnetic systems. Updated coverage of electrochemical storage systems considers exciting developments in materials and methods for applications such as rapid short-term storage in hybrid and intermittent energy generation systems, and battery optimization for increasingly prevalent EV and stop-start automotive technologies. This nuanced coverage of cutting-edge advances is unique in that it does not require prior knowledge of electrochemistry. Traditional and emerging battery systems are explained, including lithium, flow and liquid batteries. Energy Storage provides a comprehensive overview of the concepts, principles and practice of energy storage that is useful to both students and professionals.
Download or read book Electrophoretic Deposition of Nanomaterials written by James H. Dickerson and published by Springer Science & Business Media. This book was released on 2011-09-18 with total page 381 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive overview of contemporary basic research, emerging technology, and commercial and industrial applications associated with the electrophoretic deposition of nanomaterials. This presentation of the subject includes an historical survey, the underlying theory of electrophoresis, dielectrophoresis, and the colloidal deposition of materials. This is followed by an assessment of the experimental equipment and procedures for electrophoretic and dielectrophoretic aggregation, manipulation, and deposition of nanoparticles, nanotubes, and other nanomaterials. Additional chapters explore the specific science and technology of electrophoretic film formation, using widely studied and application-driven nanomaterials, such as carbon nanotubes, luminescent nanocrystals, and nano-ceramics. The concluding chapters explore industrial applications and procedures associated with electrophoretic deposition of nanomaterials.
