Effect of oxygen contamination on densification of Fe(Se,Te)

Abstract The optimization of sintering behaviour of iron chalcogenides superconducting materials is mandatory to enhance their critical current density, in order to pursuit their application in the production of superconducting wires. In this context it has been investigated here the effect of oxygen contamination on the material densification, considering the issues related to industrial oxygen-free isolated production lines. Our results show that the densification process is negatively affected by oxygen contamination. However, despite the difference in density, all sintered samples are characterized by similar structural and morphological features, and show comparable electrical and magnetic properties, with low critical current densities (Jc<103 A/cm2). These results suggest that densification is not the key limiting factor in these conditions, and that grain boundary or misorientation factors may play a greater role in limiting the performance of sintered iron chalcogenides superconductors

Neuropilin-1/GIPC1 Signaling Regulates α5β1 Integrin Traffic and Function in Endothelial Cells

Neuropilin 1 (Nrp1) is a coreceptor for vascular endothelial growth factor A165 (VEGF-A165, VEGF-A164 in mice) and semaphorin 3A (SEMA3A). Nevertheless, Nrp1 null embryos display vascular defects that differ from those of mice lacking either VEGF-A164 or Sema3A proteins. Furthermore, it has been recently reported that Nrp1 is required for endothelial cell (EC) response to both VEGF-A165 and VEGF-A121 isoforms, the latter being incapable of binding Nrp1 on the EC surface. Taken together, these data suggest that the vascular phenotype caused by the loss of Nrp1 could be due to a VEGF-A164/SEMA3A-independent function of Nrp1 in ECs, such as adhesion to the extracellular matrix. By using RNA interference and rescue with wild-type and mutant constructs, we show here that Nrp1 through its cytoplasmic SEA motif and independently of VEGF-A165 and SEMA3A specifically promotes α5β1-integrin-mediated EC adhesion to fibronectin that is crucial for vascular development. We provide evidence that Nrp1, while not directly mediating cell spreading on fibronectin, interacts with α5β1 at adhesion sites. Binding of the homomultimeric endocytic adaptor GAIP interacting protein C terminus, member 1 (GIPC1), to the SEA motif of Nrp1 selectively stimulates the internalization of active α5β1 in Rab5-positive early endosomes. Accordingly, GIPC1, which also interacts with α5β1, and the associated motor myosin VI (Myo6) support active α5β1 endocytosis and EC adhesion to fibronectin. In conclusion, we propose that Nrp1, in addition to and independently of its role as coreceptor for VEGF-A165 and SEMA3A, stimulates through its cytoplasmic domain the spreading of ECs on fibronectin by increasing the Rab5/GIPC1/Myo6-dependent internalization of active α5β1. Nrp1 modulation of α5β1 integrin function can play a causal role in the generation of angiogenesis defects observed in Nrp1 null mice

Electrochromic cerium-vanadium mixed oxides

Dottorato di ricerca in scienza dei materiali. 12. ciclo. A.a. 1998-99. Relatore Franco Decker. Relatore esterno Enrico MasettiConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Preparation of albumin-ferrite superparamagnetic nanoparticles using reverse micelles

Micellar systems are widely applied as reactors to encapsulate inorganic nanoparticles in polymeric materials. However, only low inorganic contents and microscale dimensions are often achieved. The adsorption of albumin protein on ferrite nanoparticles permits to increase the stability of inorganic dispersions in water by inhibiting particle flocculation. Subsequent glutaraldehyde addition induces protein crosslinking and ferrite entrapment. Polymer–ferrite composite nanoparticles were obtained in this way. The magnetic albumin nanoparticles (25 nm mean diameter) obtained contain about 40wt% of ferrite and show superparamagnetic behaviour. The composite powder was successfully functionalized with amodel drug and the biological activity was evaluated

Magnetic Vortex Phase Diagram for a Non-Optimized CaKFe4As4 Superconductor Presenting a Wide Vortex Liquid Region and an Ultra-High Upper Critical Field

To draw a complete vortex phase diagram for a CaKFe4As4 polycrystalline iron-based superconductor, different kinds of magnetic measurements have been performed focusing on the critical parameters of the sample. Firstly, magnetic moment versus field measurements m(H) were performed at low fields in order to evaluate the lower critical field Hc1. After that, by performing relaxation measurements m(t), a field crossover Hcross was detected in the framework of a strong pinning regime. The irreversibility field Hirr as a function of the temperature curve was then drawn by plotting the critical current densities Jc versus the field for temperatures near Tc. Jc(H) has demonstrated a second magnetization peak effect phenomenon, and the second peak field Hsp has been identified and plotted as a function of temperature, providing information about an elastic to plastic transition in the vortex lattice. Finally, the upper critical field Hc2 as a function of the temperature has been obtained. Hc1, Hcross, Hsp, Hirr, Hc2 have been fitted and used for drawing the complete vortex phase diagram of the sample. It can be helpful for the understanding of the applicative ranges in the field and temperature of the materials with not-optimized fabrication characteristics, as usually is found in superconducting wires and cables for power applications

Magnetic Vortex Phase Diagram for a Non-Optimized CaKFe₄As₄ Superconductor Presenting a Wide Vortex Liquid Region and an Ultra-High Upper Critical Field

To draw a complete vortex phase diagram for a CaKFe4As4 polycrystalline iron-based superconductor, different kinds of magnetic measurements have been performed focusing on the critical parameters of the sample. Firstly, magnetic moment versus field measurements m(H) were performed at low fields in order to evaluate the lower critical field Hc1. After that, by performing relaxation measurements m(t), a field crossover Hcross was detected in the framework of a strong pinning regime. The irreversibility field Hirr as a function of the temperature curve was then drawn by plotting the critical current densities Jc versus the field for temperatures near Tc. Jc(H) has demonstrated a second magnetization peak effect phenomenon, and the second peak field Hsp has been identified and plotted as a function of temperature, providing information about an elastic to plastic transition in the vortex lattice. Finally, the upper critical field Hc2 as a function of the temperature has been obtained. Hc1, Hcross, Hsp, Hirr, Hc2 have been fitted and used for drawing the complete vortex phase diagram of the sample. It can be helpful for the understanding of the applicative ranges in the field and temperature of the materials with not-optimized fabrication characteristics, as usually is found in superconducting wires and cables for power applications

Critical Current and Pinning Features of a CaKFe4As4 Polycrystalline Sample

We analyze the magnetic behavior of a CaKFe4As4 polycrystalline sample fabricated by a mechanochemically assisted synthesis route. By means of DC magnetization (M) measurements as a function of the temperature (T) and DC magnetic field (H) we study its critical parameters and pinning features. The critical temperature Tc has been evaluated by M(T) curves performed in Zero Field Cooling-Field Cooling conditions. These curves show the presence of a little magnetic background for temperatures above Tc, as also confirmed by the hysteresis loops M(H). Starting from the M(H) curves, the critical current density Jc of the sample has been calculated as a function of the field at different temperatures in the framework of the Bean critical state model. The Jc(H) values are in line with the ones reported in the literature for this typology of samples. By analyzing the temperature dependence of the critical current density Jc(T) at different magnetic fields, it has been found that the sample is characterized by a strong type pinning regime. This sample peculiarity can open perspectives for future improvement in the fabrication of this material

Hydrogen production by water splitting on manganese ferrite-sodium carbonate mixture. Feasibility tests in a packed bed solar reactor-receiver

The sodium manganese mixed ferrite thermochemical cycle Na(Mn1/3Fe2/3)O2/(MnFe2O4 + Na2CO3) for sustainable hydrogen production has been implemented in a solar reactor-receiver, packed with indirectly heated MnFe2O4/Na2CO3 mixture pellets, with the aim of verifying its feasibility and of determining the critical aspects of the process. The reactor operates at nearly constant temperature in the range 750–800 °C; the shift between the hydrogen-producing and regeneration steps is obtained by switching the reactive gas from water to carbon dioxide. Hydrogen produced during 1-h operation of the reactor is in the range of 130–460 μmol/g of mixture, depending on experimental conditions. Compared to other existing prototypes, the implemented process obtains comparable production efficiencies while operating at lower temperature both in the hydrogen production and regeneration phases

Studio dell'effetto del ball milling sulla reattività electtrochimica del NaAlH4

Gli idruri metallici complessi sono composti ampiamente studiati come materiali per l'accumulo d'idrogeno. Tra questi, il sodio alluminio idruro (NaAlH4) è tra i più studiati [1] grazie alle favorevoli proprietà termodinamiche e all'elevata densità volumetrica di idrogeno (7.5 wt % H2 and 94 gH2/L). Recentemente, è stato dimostrato che il suo uso può essere esteso all'accumulo di energia elettrica. Nello specifico, il sodio alluminio idruro si è dimostrato un promettente candidato da utilizzare come materiale anodico in batterie litio-ione [2, 3]. Studi elettrochimici in celle al litio hanno messo in luce la sua elevata reattività. Il sodio alanato è in grado di scambiare più di 3.5 equivalenti di litio durante il primo ciclo di scarica, corrispondente a una capacità specifica quasi pari a quella teorica (1985 mAh/g). Il processo redox, che avviene attraverso reazione di conversione [4], consiste di step multipli e prevede l'iniziale formazione di LiNa2AlH6 e Na3AlH6 intermedi e, poi, la loro successiva decomposizione in Na e Al metallico e LiH [2]. Purtroppo, tale tipo di materiale è caratterizzato da un'elevata irreversibilità: alla fine della prima ricarica, viene scambiato solo 1 dei quasi 4 equivalenti di litio scambiati durante la scarica. E' noto che i materiali elettrodici che agiscono mediante un meccanismo a conversione siano caratterizzati da una grande isteresi di potenziale tra scarica e carica. La causa di tale fenomeno è l'elevata espansione volumetrica in seguito alla consistente riorganizzazione strutturale a cui il materiale è sottoposto durante il processo di conversione. In questo modo, il volume aumenta durante l'incorporazione del litio e diminuisce in seguito all'estrazione di esso. La conseguenza è la disgregazione delle particelle, il disfacimento dell'elettrodo e la conseguente perdita del contatto elettrico. Nel caso di NaAlH4, se si considera la completa riduzione secondo la reazione: NaAlH4 + 4Li+ + 4e- → 4LiH+ Al +Na, si può stimare una variazione del volume di circa il 72 %. Importanti miglioramenti sulla reversibilità del processo elettrodico e, quindi, sull'efficienza di cella sono stati ottenuti sottoponendo il materiale di partenza a macinazione, mediante High Energy Ball Milling. Soprattutto, la macinazione in mulino del NaAlH4 con un carbone conduttivo, ha portato ad un significativo miglioramento dell'efficienza di cella, passando da un 30 % per il materiale tal quale al 70 % per il materiale sottoposto a trattamento meccanochimico [2]. Infatti, la riduzione delle dimensioni delle particelle di materiale attivo e, soprattutto, la macinazione con un opportuno carbone conduttivo (e.g., il SuperP) migliora l'efficienza del processo di conversione [2, 5], in quanto il carbone distribuendosi sulla superficie dell'idruro, porta alla formazione di un vero e proprio composito che, oltre a migliorarne la conducibilità, previene l'agglomerazione delle particelle di idruro durante i processi redox e attenua le variazioni volumetriche. Considerati i notevoli miglioramenti ottenuti sulle performance del sodio alluminio idruro in celle al litio, sono state analizzate le principali differenze tra il campione di NaAlH4 sottoposto a macinazione in mulino e il materiale tal quale. Nello specifico, le caratteristiche strutturali e morfologiche sono state valutate mediante misure statiche di NMR allo stato solido e microscopia elettronica a trasmissione. Il contenuto d'idrogeno è stato calcolato mediante esperimenti di desorbimento termico in TPD. Infine, la reversibilità del processo elettrochimico è stata confermata mediante misure di MAS NMR allo stato solido. [1] T. K. Nielsen, M. Polanski, D. Zasada, P. Javadian, F. Besenbacher, J. Bystrzycki, J. Skibsted, and T. R. Jensen, “Improved Hydrogen Storage Kinetics of Nanoconfined NaAlH4 Catalyzed with TiCl3 Nanoparticles,” ACS Nano, vol. 5, no. 5, pp. 4056–4064, Maggio 2011. [2] L. Silvestri, L. Farina, D. Meggiolaro, S. Panero, F. Padella, S. Brutti, P. Reale. "The Reactivity of Sodium Alanates in Lithium Batteries". J. Phys. Chem. C, 119 (52), pp 28766–28775, Novembre 2015. [3] J. A. Teprovich, J. Zhang, H. Colón-Mercado, F. Cuevas, B. Peters, S. Greenway, R. Zidan, and M. Latroche, “Li-Driven Electrochemical Conversion Reaction of AlH3, LiAlH4, and NaAlH4,” J. Phys. Chem. C, Febbraio 2015. [4] Y. Oumellal, A. Rougier, G. A. Nazri, J.-M. Tarascon, and L. Aymard, “Metal hydrides for lithium-ion batteries,” Nat. Mater., vol. 7, no. 11, pp. 916–921, Nov. 2008. [5] Brutti S., Mulas G., Piciollo E., Panero S., Reale P. "Magnesium hydride as a high capacity negative electrode for lithium ion batteries". Journal of Materials Chemistry, Vol. 22, p. 14531-14537, Maggio 2012