Navegando por Palavras-chave "Electrical Conductivity"

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    Efeito da deformação plástica severa por ECAP na dureza e na condutividade elétrica da liga Cu-0,81Cr-0,07Zr
    (Universidade Federal de São Paulo (UNIFESP), 2019-12-06) Dalan, Filipe Caldatto [UNIFESP]; Cardoso, Kátia Regina [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The combination of severe plastic deformation methods (SPD) and heat treatments of Cu-Cr-Zr system alloys provides an ultrafine grains (UFG) structure with nanometric second phase particles dispersed homogeneously in the copper matrix, conferring an excellent combination of mechanical strength and electrical conductivity, arousing interest in applications ranging from electric to nuclear industry. The Equal-Channel Angular Pressing (ECAP) is a promising method to be used as an additional treatment to the traditional thermomechanical processes to increase the mechanical resistance. In age-hardened alloys, in addition to an UFG structure, ECAP processing results in changes in the precipitation kinetics due to the interaction of second phase particles with the defects generated during deformation. The aim of this work was to study the effect of ECAP deformation on hardness and electrical conductivity of the commercial Cu-0,81Cr-0,07Zr alloy. The alloy in the as received condition (drawing and aged) was deformed by ECAP at room temperature and at 300°C. A second study plan was based on the combination of deformation by ECAP and heat treatments, in which samples were solution treated, submitted to ECAP and aged. The structural characterization was performed by X ray diffraction (XRD) and phase precipitation temperatures were analyzed by differential scanning calorimetry (DSC). The microstructural evolution was analyzed mainly by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Vickers hardness (HV) and electrical conductivity were measured at each stage of thermomechanical treatment. It was observed in the studies of the alloys in as received condition that the average number of insoluble second phase particles in the copper matrix decreased more than 50% with the increase of the deformation. The exothermic reactions in DSC graphics only in the samples deformed by ECAP and the reduction of the lattice parameter of the copper matrix, indicates the deformation-induced dissolution of particles. These results were supported by the reduction of electrical conductivity, since the electron scattering is severely affected by distortions on the crystalline lattice caused by solute atoms in the matrix. In the samples deformed by ECAP with previous solid solution treatment, occured the increase in the precipitation kinetics during the aging stage, when compared to the only solution treated samples, the values of hardness peak were reached at lower temperatures of aging. In the samples with better hardness and electrical conductivity combinations, the hardness values were between 191 HV and 201 HV with a loss of the electrical conductivity between zero and 13% IACS. The mechanical strength was attributed to the combination of grain refinement, the increase in the density of dislocations and by the precipitation of nanometric second phase particles in the copper matrix. Finally, the influence of deformation by ECAP on the precipitation kinetics was verified, besides to provide hardness and electrical conductivity values higher than commercial Cu-Cr-Zr alloys.
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    Structural and Conductivity Relationship of Binary and Ternary Composites of Polypyrrole, Montmorillonite and Silver
    (Amer Scientific Publishers, 2017) Franca, Debora; Rebessi, Ana Claudia; Lacerda Rubinger, Carla Patricia; Ribeiro, Geraldo Mathias; Camilo, Fernanda Ferraz [UNIFESP]; Faez, Roselena
    This work focuses on the synthesis of binary composites of polypyrrole and silver and of ternary composites of polypyrrole, silver and organomontmorillonite performed in the presence of mixtures of two surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), in aqueous media. Polypyrrole-silver composites were obtained easily by the direct oxidation of pyrrole by silver nitrate using surfactant mixture. These samples exhibited polypyrrole doped with dodecylsulfate and nitrate and silver contents varied between 60 and 90 wt.%. The electrical conductivity is highly dependent on SDS/CTAB presence and proportions. NO3- acts as the main dopant in the absence of surfactants and the resistivity reaches the highest for PPy-OMt composites compared to silver-content ones. Besides the dopant effect, the surfactants mixtures have noticeable influence on silver particle size and morphology. In ternary composites the silver nanoparticles were spherically (around 100-200 nm) and well dispersed in the polymeric matrix. Activation energy, density of states and hopping characteristic length were calculated and it was found to be influenced by intercalating doped polypyrrole into the layers of montmorillonite in the presence of the Ag and surfactant. One-dimensional Mott's variable range hopping process was observed and interpreted in terms of straightening and linearization of the polymer chains.