Connectivity Doping And Anisotropy In Highly Dense Magnesium Diboride Mgb2
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Connectivity Doping And Anisotropy In Highly Dense Magnesium Diboride Mgb2
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Author : Guangze Li
language : en
Publisher:
Release Date : 2015
Connectivity Doping And Anisotropy In Highly Dense Magnesium Diboride Mgb2 written by Guangze Li and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
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.
Influences Of Crystalline Anisotropy Doping Porosity And Connectivity On The Critical Current Densities Of Superconducting Magnesium Diboride Bulks Wires And Thin Films
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Author : Michael Adam Susner
language : en
Publisher:
Release Date : 2012
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 has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
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.
Chemical Addition And Superconducting Phase Formation In Magnesium Diboride
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Author : Fang Wan (Ph. D. in materials science)
language : en
Publisher:
Release Date : 2020
Chemical Addition And Superconducting Phase Formation In Magnesium Diboride written by Fang Wan (Ph. D. in materials science) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Magnesium diboride categories.
The low-cost, ease-of-fabrication, and intermediate critical temperature (Tc) of 39 K are key factors enabling magnesium diboride (MgB2) conductors be promising for application. However, the most important parameter for evaluating the electrical performance of MgB2 conductors is the critical current density (Jc). For MgB2 strands, the Jc can be discussed in terms of layer Jc, non-barrier Jc, and engineering Je. The aim of this dissertation is to explore effective routes to enhance the Jcs and Jes of MgB2 conductors, which requires a solid understanding of how superconducting properties are related with microstructure, band scattering, and phase formation in MgB2. Previous studies have shown that the Jcs of MgB2 bulks and layer Jcs of MgB2 strands, which are determined by intrinsic properties of MgB2, can be improved through increases of Bc2/Birr and the density (grain connectivity) of the MgB2 phase. On the other hand, the Jes of MgB2 strands can be further improved by increasing the area fraction of MgB2 relative to the whole strand because Je = layer Jc × A(MgB2)/A(strand) , where A(MgB2) and A(strand) are the transverse cross-sectional area of MgB2 and the transverse cross-sectional area of whole strand, respectively. While the non-barrier Jcs and layer Jcs are identical for powder-in-tube (PIT) in-situ MgB2 strands, the non-barrier Jcs of advanced-internal-magnesium-infiltration (AIMI) MgB2 strands can also be improved by increasing layer Jcs and the MgB2 area fractions within chemical barrier because non-barrier Jc=layer Jc × A(MgB2)/Anb, where Anb is the area within chemical barrier. Chapter 2 summarizes the sample preparation and experimental testing utilized in this dissertation were summarized. Chapter 3 focuses on chemical addition methods including both pure C doping as well as C/Dy2O3 co-addition to improve the non-barrier Jcs (layer Jcs) of PIT in-situ MgB2 strands via increased Bc2/Birr and decreased Bc2 anisotropy. Here C doping was accomplished using pre-C-doped B powders. The doping effects of two types of B powders, SMI B and PVZ B, were compared in terms of the 4.2 K non-barrier Jcs of multifilamentary PIT in-situ strands. By adding 0 ~ 6 wt% Dy2O3 into the 2 mol% C-doped MgB2 strand, non-barrier Jcs with acceptable values were achieved over a wide temperature range of 4.2 to 25 K. The relationship between Bc2 enhancement and band scatterings was investigated. In Chapter 4, a vapor-solid reaction route was established with the aim of increases the area fraction of MgB2 layer in AIMI strands. Moreover, the vapor-solid reaction was also demonstrated to generate MgB2 layers with high levels of uniformity in 18-filamentary AIMI strands. Consequently, high Jes and n-values were achieved by the vapor-solid reacted strands. In Chapter 5, the micron-sized B powders were used to synthesize large-size MgB2 tubes for passive shielding applications The Jcm of 108 A/cm2 was achieved by the best tube at 4.2 K, 1 T. The DC/AC external fields of 0.67 T/1.75 T were completely shielded by the tube at 4.2 K. Long-distance Mg infiltration into B compact and well-connected MgB2 phases were simultaneously obtained using a heat-treatment of 900 oC/36 h.
Mgb2 Superconducting Wires Basics And Applications
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Author : Rene Flukiger
language : en
Publisher: World Scientific
Release Date : 2016-08-10
Mgb2 Superconducting Wires Basics And Applications written by Rene Flukiger and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-08-10 with Technology & Engineering categories.
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.
High Energy Milled Ex Situ Mgb2 For Tapes And Wires
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Author : Anna Kario
language : en
Publisher: Cuvillier Verlag
Release Date : 2011-05-02
High Energy Milled Ex Situ Mgb2 For Tapes And Wires written by Anna Kario and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-05-02 with Technology & Engineering categories.
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
Comprehensive Energy Systems
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Author : Ibrahim Dincer
language : en
Publisher: Elsevier
Release Date : 2018-02-07
Comprehensive Energy Systems written by Ibrahim Dincer and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-02-07 with Science categories.
Comprehensive Energy Systems, Seven Volume Set provides a unified source of information covering the entire spectrum of energy, one of the most significant issues humanity has to face. This comprehensive book describes traditional and novel energy systems, from single generation to multi-generation, also covering theory and applications. In addition, it also presents high-level coverage on energy policies, strategies, environmental impacts and sustainable development. No other published work covers such breadth of topics in similar depth. High-level sections include Energy Fundamentals, Energy Materials, Energy Production, Energy Conversion, and Energy Management. Offers the most comprehensive resource available on the topic of energy systems Presents an authoritative resource authored and edited by leading experts in the field Consolidates information currently scattered in publications from different research fields (engineering as well as physics, chemistry, environmental sciences and economics), thus ensuring a common standard and language
Advanced Materials Design And Mechanics
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Author : Jing Guo
language : en
Publisher: Trans Tech Publications Ltd
Release Date : 2012-09-28
Advanced Materials Design And Mechanics written by Jing Guo and has been published by Trans Tech Publications Ltd this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-09-28 with Technology & Engineering categories.
These are the proceedings of the 2012 International Conference on Advanced Materials Design and Mechanics (ICAMDM 2012) held on June 5-7th 2012 in Xiamen, China. The 167 peer-reviewed papers are grouped into 5 chapters: Advanced Materials Design; Materials Engineering; Manufacturing, Technology and Processing; Mechanical Engineering; Applied Computer Technologies and Control. Volume is indexed by Thomson Reuters CPCI-S (WoS).
Jjap Letters
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Author :
language : en
Publisher:
Release Date : 2006
Jjap Letters written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Physics categories.
Unconventional Superconductors
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Author : Iman Askerzade
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-01-13
Unconventional Superconductors written by Iman Askerzade and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-01-13 with Science categories.
This book presents the anisotropy and multiband effects in newly discovered unconventional superconductors: cuprate superconductors, borocarbides, magnezium-diboride and oxypnictides. The physical properties of these unconventional superconductors and the application of the two-band Ginzburg-Landau theory to these superconducting compounds are explained. Temperature dependencies of fundamental superconducting parameters are calculated using the GL theory taking into account multiband-and anisotropy effects. A comparision of theoretical results and experimental data is conducted. Additionally, the analytical solution of the microscopical Eliashberg theory and of the BCS theory is developed for two-band and anisotropic superconductors. Fluctuation effects in newly discovered superconductors are also discussed.
Studies Of High Temperature Superconductors Superconducting Magnesium Diboride
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Author : A. V. Narlikar
language : en
Publisher:
Release Date : 2002
Studies Of High Temperature Superconductors Superconducting Magnesium Diboride written by A. V. Narlikar and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with High temperature superconductors categories.