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Venarusso L.B.,Federal University of Mato Grosso do Sul | Bettini J.,Brazilian Nanotechnology National Laboratory LNNano | Maia G.,Federal University of Mato Grosso do Sul
Journal of Solid State Electrochemistry

Nanocrystals (NCs) of a Pt or Pd or Pt–Pd alloy shell supported on a Au core were synthesized and dripped onto a glassy carbon (GC) surface to generate thin films. Their electrocatalytic activity towards the oxygen reduction reaction (ORR) was studied employing hydrodynamic cyclic voltammetry. Of the Pt or Pt–Pd alloy electrocatalysts synthesized over a Au core (including Au cores produced from redox-transmetalation of Ni cores), Pt–Pd@Au, Pt@Au, and Pt@Au′ NCs—which contained heterogeneous NCs with spherical, triangular, squared, pentagonal, hexagonal, heptagonal, and rod-like shapes, with large (about 80 nm in several cases), well-defined crystalline structures, and evidenced a nanodendritic Pt or Pt–Pd alloy covering pattern at the NC surface—exhibited high electrocatalytic activity towards ORR and high stability (without dissolution of inner metallic nanoparticles such as Au) after 10,000 potential scans—features that suggest their utility for use in acid fuel cells. [Figure not available: see fulltext.] © 2016 Springer-Verlag Berlin Heidelberg Source

Witkowskanery E.,University of Campinas | Witkowskanery E.,Polish Academy of Sciences | Santhiago M.,University of Campinas | Santhiago M.,Brazilian Nanotechnology National Laboratory LNNano | Kubota L.T.,University of Campinas

Although paper-based analysis is known for centuries, only during the last decade this simple substrate became an object of detailed microfluidic studies. In order to obtain optimum performance and separation of the analytes in a microfluidic channel, devices should be optimized, both in terms of architecture and paper properties. Enzyme immobilization methods can not only increase the storage stability but also have an impact on the flow in paper matrix, providing additional charges, and changing the porous structure of paper. Therefore it should be guaranteed that the method of choice will not obstruct the flux in the final device. Paper-based device proposed in this study was composed of a bioactive channel, Pt working electrode, pencil drawn pseudo-reference electrode, a buffer filled sponge providing the wicking solution and a stack of wicking pads to guarantee continuous flow. Based on our previous research we chose 4 methods of enzyme immobilization relying on different phenomena (adsorption, covalent linkage, layer-by-layer, capsules). Different channel architectures were also evaluated in order to achieve optimum time of the enzymatic reaction, separation of peaks and the time of measurement. Experimental results were compared with computer simulations. Final device could quantify glucose (2.0-10.0mmolL-1) and uric acid (0.1-1.2mmolL-1) in their clinical range with good repeatability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Maya-Johnson S.,Brazilian Nanotechnology National Laboratory LNNano | Maya-Johnson S.,University of Campinas | Maya-Johnson S.,National University of Colombia | Ramirez A.J.,Ohio State University | Toro A.,National University of Colombia
Engineering Fracture Mechanics

A study of fatigue crack growth rate was conducted in two pearlitic rail steels, namely R260 and R370CrHT. Two crack plane orientations with respect to the rolling direction were tested and separate experiments were performed to cover a wide variation in fatigue crack growth, from the fatigue threshold (circa 10-9m/cycle) to rapid fracture conditions. The fracture surfaces were examined and some correlations between microstructural features such as interlamellar spacing and mechanical properties were made. © 2015 Elsevier Ltd. Source

Grimm D.,Leibniz Institute for Solid State and Materials Research | Grimm D.,TU Chemnitz | Bof Bufon C.C.,Leibniz Institute for Solid State and Materials Research | Bof Bufon C.C.,Brazilian Nanotechnology National Laboratory LNNano | And 10 more authors.
Nano Letters

We fabricate inorganic thin film transistors with bending radii of less than 5 μm maintaining their high electronic performance with on-off ratios of more than 105 and subthreshold swings of 160 mV/dec. The fabrication technology relies on the roll-up of highly strained semiconducting nanomembranes, which compacts planar transistors into three-dimensional tubular architectures opening intriguing potential for microfluidic applications. Our technique probes the ultimate limit for the bending radius of high performance thin film transistors. © 2012 American Chemical Society. Source

Escobar J.D.,National University of Colombia | Velasquez E.,National University of Colombia | Santos T.F.A.,Brazilian Nanotechnology National Laboratory LNNano | Santos T.F.A.,University of Campinas | And 3 more authors.

The cavitation erosion (CE) resistance of an UNS S32205 duplex stainless steel (DSS) was improved through microstructural modification using friction stir processing (FSP). As-received material was processed using 200. rpm and 100. mm/min spindle and travel speeds, respectively. The cavitation erosion tests were performed in a vibratory apparatus according to ASTM G32 standard. The incubation period, the maximum erosion rate and the variation of surface roughness during the tests are reported and the results are compared with those obtained for the base metal samples (BMS). The worn surfaces were characterized using roughness measurements and scanning electron microscopy (SEM). After a CE testing time of 10. h, FSP samples showed a 70% diminution of the mass loss when compared to the BMS. Moreover, a 200% enhancement of incubation time and 100% reduction in the erosion rate were achieved after FPS. The improvement of CE performance is related to the recrystallized and refined microstructure, as well as to the modification of the elongated α/γ interfaces. © 2012 Elsevier B.V. Source

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