Examinando por Autor "de Prado, Javier"

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Exploring Cu-Ge alloys as filler materials for high vacuum brazing application of W and CuCrZr
(Elsevier, 2022-12) de Prado, Javier; Sánchez, María; Izaguirre, Ignacio; Swan, David; Ureña, Alejandro
Cu-Ge system was evaluated for its application as a filler material in W-CuCrZr joints proposed as heat sink components of the future fusion power plants. The selected compositions were rich in Cu, with the aim of retaining the ductility that characterizes copper metal. Three compositions (Cu-13.5Ge, Cu-19.5Ge and Cu-33.2Ge) and two manufacturing routes (flexible and rigid tapes) were evaluated and characterized thermally, microstructurally and mechanically. The brazing temperature decreased as the Ge content increased, giving rise to less base material thermal affectation. The microstructure was dominated by several peritectic reactions that hinder the solid state diffusion control, and three main phases (Cu solid solution, ε and ζ) were detected both in the solidified filler drop and in the joint braze. In addition, the rigid filler manufacturing route seemed to produce more continuous joints due to its more homogeneous composition. The mechanical properties indicated that both lower and richer Ge compositions gave rise to joints with higher strength.
S/TEM examination and nanomechanical response of W-Eurofer joints brazed with Cu interlayers
(Elsevier, 2022-06) Izaguirre, Ignacio; Roldán, Marcelo; de Prado, Javier; Bonache, Victoria; Sánchez, María; Ureña, Alejandro
En este artículo se realiza un estudio preliminar a microescala de una unión soldada de dos materiales que conformarán los futuros reactores de fusión. El tungsteno actuará como material de revestimiento del plasma unido a una estructura hecha de algún acero ferrítico-martensítico de activación reducida (acero tipo Eurofer). El proceso de soldadura propuesto introduce cobre como material de relleno y desarrolla el proceso térmico en una atmósfera de alto vacío a 1135 ◦C durante 10 min. La microestructura resultante se caracteriza por formar una capa de difusión en contacto con el material base de tungsteno constituido por W, Fe y Cr. Además, se forma una fase rica en hierro entre la capa de difusión y la región de soldadura de Cu. Esta banda de acero presentó dos estructuras diferentes: una estructura típica de listones de martensita y otra sin ella. En el centro de la banda de acero, los listones son reemplazados por una matriz más homogénea donde el cobre precipita nucleado debido a su enriquecimiento en este elemento durante el proceso de soldadura. Cabe destacar la presencia de dislocaciones y tensiones residuales en todas las diferentes fases que aparecen asociadas al proceso de soldadura fuerte. Esta presencia de tensiones de dislocación muestra como el análisis nanomecánico incrementa los valores de módulo y dureza de la banda de acero respecto al material base Eurofer. La capa de difusión presenta los valores más elevados en la caracterización mecánica debido a su morfología y a los componentes que la constituyen.
Surface Modifications of Carbon Fiber Electrodes for Structural Supercapacitors
(Springer, 2022) Artigas-Arnaudas, Joaquín; Muñoz, Bianca K.; Sánchez, María; de Prado, Javier; Utrilla, M. Victoria; Ureña, Alejandro
Structural electrodes for supercapacitors based on woven carbon fiber were made from different surface modification approaches, such as spray coating with carbon nanoparticles (graphene nanoplatelets and multiwall carbon nanotubes, GNP and MWCNT, respectively) and direct synthesis of carbon aerogel (CAG) on the surface of the carbon fabric. Suitability of the different modification techniques was stablished based on the results from cyclic voltammetry and single fiber tensile test. Highest capacitance was achieved by the synthesis of CAG although mechanical properties were negatively affected. These treatments produced a good combination of mechanical and electrochemical properties, which suggests these electrodes are suitable for multifunctional applications. In particular, capacitance was improved by increasing the surface area of commercial carbon fiber fabric while keeping its mechanical properties. The best combination of properties was achieved by deposition of GNP by spray coating. Mechanical properties kept unaffected and capacitance was increased by an order of magnitude compared with the pristine carbon fiber.