RESUMO
Lead-acid batteries need to evolve to keep up with the electrification of vehicles and not lose ground to other technologies. The grid designed using a lead alloy thus plays a very important role in the performance of the battery, as, in the course of the various cycles, this component undergoes a natural corrosion process at positive potential, while immersed in a sulfuric acid solution. The aim of this study is therefore to examine the effect of the addition of calcium and bismuth on the microstructure, mechanical behavior and corrosion resistance of the Pb1.5%Sn alloy, with a view to using this in the positive grid of lead-acid batteries. The alloys developed during this study were evaluated using optical microscopy and scanning electron microscopy. Mechanical properties were investigated using universal tensile and hardness tests. Electrochemical tests of cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were carried out in a 5M sulfuric acid solution at 25 °C to simulate the behavior of the alloy when in operation. The composition of the corrosion products formed were subsequently characterized by morphological analysis using scanning electron microscopy and the composition was determined using energy dispersive X-ray spectroscopy and X-ray diffraction analysis. The results indicate that the Pb1.5Sn0.12Bi alloy presented better corrosion resistance characteristics than the Pb1.5Sn0.05Ca alloy, making it suitable for inclusion in the composition of the positive electrode of a lead-acid battery. Further investment is however required to compensate for the shortcomings in relation to the mechanical properties of the material.
RESUMO
A evolução de técnicas conservadoras contribui para uma melhora estética e a microabrasão do esmalte vem sendo pesquisada e indicada como tratamento para remoção de manchas superficiais do esmalte dentário. O objetivo deste estudo in vitro foi comparar através da análise por perfilometria digital 3D, a rugosidade superficial (Sa) do esmalte bovino microabrasionado com ácido fosfórico a 37% e pedra pomes (A) associado a três tipos de pontas aplicadoras: taça de borracha (T), ponta cônica (C) e opal cups (O). Para a análise de superfície foram selecionados 9 espécimes, previamente planificados e divididos em 3 grupos (AT; AC; AO) contendo 3 amostras cada. No presente experimento, optou-se por fazer 6 aplicações de 10 segundos, utilizando método de aplicação mecânico, com rotação do micromotor de 12.000rpm, sendo a carga atuante sobre os espécimes de 30g. Observou-se que para as três pontas houve diferença estatística significante entre a rugosidade superficial inicial (SaI AT = 0,023µm; AO = 0,026µm e AC = 0,026µm) e rugosidade superficial final (SaF AT = 0,384µm; AO = 0,442µm; AC = 0,305µm; Wilcoxon, p<0,05). Os menores valores de rugosidade superficial foram promovidos pela ponta cônica, seguidos por taça de borracha e Opal Cups.
The evolution of conservative techniques contributes to improve aesthetics. Enamel microabrasion has been researched and performed as a treatment to remove stains on enamel surface. The aim of this in vitro study was to compare surface roughness (Sa) of microabrasioned enamel with 37% phosphoric acid and pumice (A) associated with three types of applicator tips: cup rubber (T), conical tip (C) and opal cups (O). For surface analysis 9 specimens were selected, they were previously flattened and divided into 3 groups (AT, AC, AO) with 3 samples each. In this experiment, 6 applications of 10 seconds were performed using mechanical rotation of 12.000 rpm under 30g acting load on the samples. Statistically significant difference between the initial surface roughness was observed for the three tips: (SaI AT = 0.023 µm; AO = 0.026 µm and AC = 0.026 µm) and final surface roughness (SaF AT = 0.384 µm; AO = 0.442 µm; AC = 0.305 µm; Wilcoxon, p <.05). The lower surface roughness values were promoted by tapered tip, followed by rubber and Opal Cups.