Marcio Antonio Sens

Bio: Marcio Antonio Sens is an academic researcher. The author has contributed to research in topics: Fault current limiter & Crystallization. The author has an hindex of 2, co-authored 3 publications receiving 9 citations.

Development of Bulk Bi2+xSr3-yCa yCu 2O8+delta Superconductors by Partial-Melting Route for Fault Current Limiters Application

Abstract: The production of bulk Bi2+xSr3-yCayCu 2O8+D (Bi-2212) superconductors for fault current limiter application was developed via a partial-melting route. Aiming high Ic (critical current), which is the essential superconducting characteristic for application of this material in the construction of Fault Current Limiters (FCL), the produced blocks have predominance of Bi-2212 phase (83 wt%), which characterizes with high values of zero and onset transport critical temperature of 92K and 97.5K, respectively. A relatively low transition width, DT, from the superconducting to the normal state of 5.5K, revealed a good intergrain connectivity. Consequently, current measurements on the blocks of Bi-2212 show promising Ic values of 230A and 850A for direct and alternate current, respectively. It is expected that further increases in the Ic values will depend on the elimination of an observed amorphous phase and further reduction of amount and grain sizes of secondary phases, still present in the blocks obtained by the proposed partial-melting route. This may be achieved by a further optimization of the partial-melting processing parameters.

The influence of precursor powder on the microstructure and properties of Bi-2212 blocks

Abstract: The present work reports our investigations on the partial melt processing of bulk Bi-2212. Commercial and homemade precursor powders with different nominal compositions were melt-processed into silver molds. Samples were analyzed by XRD, SEM/EDS and DC critical current measurements. The main secondary phases forming upon Bi-2212 peritectic decomposition were 14:24 and 91150, besides 2201, which crystallizes from the liquid. The superconducting properties depended mainly on the precursor and on the maximum processing temperature. The commercial precursors provided the best results. Bi-2212 blocks with Ic = 90–135 A and Jc = 900–1350 A/cm2, at 77 K, have been obtained. However, reducing the amount of coarse secondary phases and optimizing the 2212 oxygen content may enhance the performance of bulk Bi-2212.

High critical current density Bi2Sr2CaCu2Ox/Ag wire containing oxide precursor synthesized from nano-oxides

Abstract: Bi2Sr2CaCu2O x (Bi2212)/Ag-alloy wires are manufactured via the oxide-powder-in-tube route by filling Ag/Ag-alloy tubes with Bi2212 oxide precursor, deforming into wire, restacking and heat treating using partial-melt processing (PMP). Recent studies propose several requirements on precursor properties, including stoichiometry, chemical homogeneity, carbon content and phase purity. Here, nanosize oxides produced by nGimat's proprietary NanoSpray CombustionTM process are used as starting materials to synthesize Bi2212 oxide precursors via solid-state calcination. Oxide powders for wire fill (precursor powder) with precisely controlled stoichiometry and chemical homogeneity containing over 99 vol% of single Bi2212-phase are synthesized. Alkaline-earth cuprate are found to be the only impurity phase in the precursor powders. Phase transformation, carbon release and grain growth during calcination are studied through a series of quench studies. Effects of particle size, surface area, stoichiometry, chemical homogeneity and microstructures of the starting materials on Bi2212 formation and wire transport properties are discussed. Small particle size, high surface area and short diffusion length of the starting materials result in a rapid and homogeneous phase transformation to Bi2212, along with an early and rapid carbon release. The residual carbon in the precursor powder is between 50 and 90 ppm. The strong dependence of transport J c on precursor stoichiometry indicates that compositional variations within precursor powders should be less than 1.5 mol%. Two Bi-rich and Ca-deficient stoichiometries give higher wire transport critical current density, with the highest being 2520 A mm−2 (4.2 K, 5 T) after 1 bar PMP and 4560 A mm−2 (4.2 K, 5 T) after 100 bar overpressure (OP) processing. The low residual carbon content results in smaller and fewer voids within an OP-processed wire filament. Bi-rich and Ca-deficient stoichiometries and small compositional variations within precursor powders may be a method for engineering uniformly-distributed and high-density Bi2201 intergrowths within Bi2212 grains after PMP.

Recent Advances on Bismuth-based 2223 and 2212 Superconductors: Synthesis, Chemical Properties, and Principal Applications

Abstract: This article is focused on principal Bi-containing superconductors. Recent results obtained on Bi-2212, Bi-2223, and related composite materials are discussed. Special attention is paid to various advanced methods of synthesis. Optimization of the superconducting properties by the chemical modifications is considered in terms of most important practical applications.

Phase relations study on the melting and crystallization regions of the Bi-2223 high temperature superconductor

Abstract: The melting and solidification behavior of Bi2Sr2Ca2Cu3 O10 (Bi-2223) precursors has been studied. Nominal compositions corresponding to excess of liquid, Ca2CuO3 and CuO have been investigated. Each sample was made by packing a precursor powder into a silver crucible, in order to approximately simulate the situation found in 2223 silver-sheathed tapes. The samples were partially melted and then slow-cooled, being quenched from different temperatures and analyzed through X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS). The precursors decomposed peritectically during melting, forming liquid and solid phases. Very long plates with compositions falling in the vicinity of the 2223 primary phase field formed upon slow-cooling. The 2223 phase may have been formed and the results suggest that long grains of this phase might be obtained by melting and crystallization if the exact peritectic region and the optimum processing conditions are found.

Proximity Effect in Bulk LaBa_2Cu_3O_{7-y} Samples with Ag Additions

Abstract: Bulk LaBa_2Cu_3O_(7-y) samples with different Ag additions were investigated. It was shown that Ag does not enter the crystallographic structure of the superconductor and segregates on the grain boundary region. Current path in these samples occurs through the proximity connected grains and this was confirmed from the temperature dependence of the critical current density and mutual inductance. By using the theory developed for the thin film structures we conclude that growing of the Ag content increased the effective cross section and the normal metal thickness. The first one prevails at low concentration increasing the current. The second dominates at higher concentration leading to saturation or even lowering of the critical current.

Développement de réseaux d’antennes supraconductrices pour l’imagerie par résonance magnétique haute résolution à champ intermédiaire à champ intermédiaire

Abstract: En microscopie IRM, la sensibilite de detection est critique pour obtenir des images avec un rapport signal sur bruit suffisant car l’intensite du signal RMN devient extremement faible. Une strategie alternative a l’utilisation de champs statiques eleves consiste a ameliorer les performances des antennes radiofrequences qui detectent le signal d’IRM. Plus particulierement, la strategie dans laquelle s’inscrit ce travail de these vise a exploiter la haute sensibilite des antennes miniatures supraconductrices basees sur le principe des resonateurs monolithiques a ligne de transmission avec comme objectif a terme la mise en reseau de ce type d’antennes. Le developpement d’un tel reseau represente un enjeu instrumental majeur car cela permet de profiter de la haute sensibilite intrinseque des antennes miniatures supraconductrices tout en autorisant l’observation de zones etendues ou en profondeur. Cependant, les caracteristiques geometriques de ces antennes et la nature des materiaux utilises posent des difficultes importantes pour realiser les operations d’accord, d’adaptation, ou decouplage mutuel lors de leur utilisation en IRM. Dans le cadre de cette these, nous avons conduit des travaux abordant ces differentes problematiques et permettant la mise œuvre d’un reseau supraconducteur pour l’imagerie haute resolution a champ clinique.Nous avons developpe en premier lieu un systeme permettant de realiser automatiquement et sans contact l’accord et l’adaptation des antennes miniatures monolithiques. Ce systeme utilise des techniques, basees sur le couplage electrique et magnetique, que nous avons prealablement etudiees en utilisant differentes methodes. Les performances de ce systeme ont ete etudiees et la faisabilite de sa mise en œuvre dans une experience d’IRM a ete etablie.Nous avons aborde en second lieu le probleme de decouplage mutuel des elements constituant un reseau. Pour cela, des techniques de decouplage potentiellement compatibles avec les antennes miniatures supraconductrices ont ete etudiees. En particulier, la technique de decouplage par anneau de blindage a ete investie en profondeur, par simulation numerique et experimentalement, et nous avons developpe un modele analytique d’optimisation du niveau de decouplage accessible par cette technique. Nous avons mis en œuvre et valide cette technique avec des reseaux en cuivre de quatre antennes et des premiers essais ont ete conduits avec un reseau constitue de deux antennes miniatures supraconductrices.