Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/277597
Type: TESE
Title: Estudo da composição de fases nos contornos de grãos supercondutores A-15 e sua influência nas propriedades de transporte
Author: Rodrigues Junior, Durval
Advisor: Pinatti, Daltro Garcia, 1940-
Abstract: Resumo: O presente trabalho faz a caracterização completa das propriedades de transporte e microestruturais de fios supercondutores multifilamentares de Nb3Sn, (Nb,Ta)3Sn e (Nb,Ti)3Sn produzidos comercialmente e em laboratório através de diversas técnicas de fabricação. É conseguido o entendimento dos mecanismos de aprisionamento de fluxo que agem nestes materiais e, consequentemente, quais as metodologias que devem ser seguidas para suas otimizações de corrente elétrica. A intensidade de aprisionamento atuando sobre as linhas de fluxo magnético nestes materiais é determinada pela densidade volumétrica de grãos e pela variação da composição de fases proximas de seus contornos. As distribuições de tamanhos de grãos são obtidas por MET enquanto que os perfis composicionais perto dos contornos são obtidos em STEM, com resolução de 2 nm. São determinados os perfis de Nb, Sn, Cu, Ta e Ti dependendo do material supercondutor analisado. As concentrações de Sn e Cu perto dos contornos aumentam rapidamente em relação aos seus valores dentro dos grãos enquanto que o Nb apresenta comportamento oposto. O Ta substitui o Nb na fase supercondutora mesmo próximo dos contornos sendo que as concentrações de ambos elementos diminui nesta região. A concnetração de Ti aumenta nos contornos, substituindo o Nb, provavelmente devido à afinidade do Ti com o Cu. Não foi encontrado Cu no interior dos grãos além de distâncias de 10 nm dos contornos

Abstract: This work completely characterizes the transport properties and microstructures of commercial and laboratory Nb3Sn, (Nb, Ta)3Sn and (Nb, Ti)3Sn multifilamentary superconductor wires made through several fabrication methods. It is understood the flux pinning mechanisms acting in these materials and the best metallurgical routes to improve their critical currents. The pinning strength acting on the flux line lattice in these materia1s is determined by the volumetric grain density and by the composition variation of phases near the grain boundaries. The distribution of grain sizes was determined by TEM and the composition profiles near the boundaries were obtained by STEM, with a 2 nm resolution. It was determined the profiles of Nb, Sn, Cu, Ta and Ti, depending on the conductor type. The concentrations of Sn and Cu near the boundaries increased rapidly in comparison to their values inside the grains, while the Nb showed the opposite behavior . Ta substitutes Nb even near the grain boundaries, where their concentrations decrease. The Ti concentration increases near the boundaries probably due to the affinity to Cu. There is no Cu inside the grains after a distance of 10 nm from the boundaries. The ana1ysis of the superconducting phase formed in the wire filaments were made with SEM and microprobe. The complete characterization of the conductors transport properties included measurements of critical currents versus applied magnetic field, upper critical magnetic field versus temperature, critical temperature and residual resistivity ratio. The models used to understand the flux pinning in the samples led to the conclusion that two mechanisms can act in this type of material: the vortex core interaction with the normal phases at the grain boundaries and the flux line lattice shearing on these boundaries. The pinning forces due to this second mechanism are always lower than those of the first mechanism and the shearing behavior is the only one found experimentally. These models reproduced the experimental data very well giving calculated grain size values very close to those found in the conductor microstructures. Due to the fact that it must exist a direct relation between the flux line lattice spacing and the grain sizes that act in the flux pinning, this work defines the effective grain size, Deffective, which changes with the applied magnetic field. The understanding of the flux pinning behavior in Nb3Sn led to the design of a conductor capable of transporting high critical currents with high stability . This conductor was produced using the solid-liquid diffusion method and reached transport currents as high as 380 A at 10 T (0,81 mm conductor diameter). This gives a current density jc non-Cu of 2200 A/mm2 at 10 T
Subject: Supercondutores
Microscopia eletrônica
Language: Português
Editor: [s.n.]
Date Issue: 1997
Appears in Collections:IFGW - Dissertação e Tese

Files in This Item:
File SizeFormat 
RodriguesJunior_Durval_D.pdf2.25 MBAdobe PDFView/Open


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.