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Desenvolvimento de multicamadas metálicas do tipo Pt/Ir/Pt eletrodepositadas em titânio para eletrocatálise
(Universidade Federal de São Carlos, 2012-04-19) Zulke, Alana Aragon; Souza, Ernesto Chaves Pereira de; https://lattes.cnpq.br/1505400360366643; https://lattes.cnpq.br/3148428465823048
Regarding to the search for new energy sources, of renewable character, fuel cells fall into one of the most studied proposals on Electrochemistry. More specifically, the direct fuel cells (DAFCs) using short-chain alcohols as fuel, have attracted the attention of researchers over the past two decades. Problems related to the energy efficiency of Pt-based catalysts for use in fuel cells, drive several studies in the literature concerning to the modification of these catalytic systems. Thus, have been proposed in the literature, other materials than pure Pt, such as alloys in binary and ternary composition, and more recently, metallic multilayered structures(MM), the latter being the study object of this work. Platinized titanium electrodes were prepared by potentiostatic electrodeposition technique (0.05 V vs RHE), and times of 1000 sec were necessary to obtain an identical polycrystalline platinum voltammetric profile, with guaranteed reproducibility. On these substrates, Ir/Pt bilayered systems were electrodeposited controlling films thickness through the deposition charge. Calculations revealed mass loading of platinum between13.4 and 26.3 μg and maximum film thickness of 43.2 nm. AFM images confirmed the homogeneity of the coatings as well as the total covering of the substrate. A screening of variables with the aid of a 22 factorial design with central point showed better intrinsic catalytic activity (current density normalized by the electroactive area) for the Ti/Pt25mC/Ir6mC/Pt system, which answers were around 270% higher than those obtained for Ti/Pt systems. In addition to the methanol oxidation voltammetry, chronoamperometric tests of methanol oxidation and CO stripping voltammetry suggest the MM-like systems are less susceptible to the catalyst poisoning phenomenon compared to the Ti/Pt systems. Assuming that there are no area effects due the current normalization through the electroactive area, nor the possibility of a bifunctional mechanism occurring,considering that are just Pt catalytic centers exposed, an explanation for the purposes of promoting catalytic activity may be based on electronic effects due to the possible compressive stress generated by the bilayer Ir/Pt causing an energy enlargement of the d band, lowering the adsorbates energy of adsorption. EIS data indicated a lower resistance to charge transfer in the reactions performed on MM systems, which strengthens the argument regarding the positive electronic effects associated with MM-like structures.
Ensino de química para alunos cegos : desafios no ensino médio
(Universidade Federal de São Carlos, 2012-04-19) Aragão, Amanda Silva; Caiado, Kátia Regina Moreno; https://lattes.cnpq.br/0803778280883949; https://lattes.cnpq.br/7257235226412428
The using of models on Chemistry Teaching is tying the understanding of various subjects, namely, molecular representation, chemical functions, stoichiometry, and others, to visual signification. These skills are important for a critical and conscious formation of the student, regarding the using of chemical substances on his daily life. Therefore, it is essential to comprehend how blind students can apprehend Chemistry notions, since that they are connected to social questions in which the individuals are involved. To understand the context of participation of these students at school in Chemistry classes, were interviewed visually impaired students of two classes of the first year of High School, of a state school in a city in São Paulo state, their Chemistry teachers and the teacher of the resources room. Beyond that, to understand the dynamics of school Chemistry classes, was performed the participant observation in these classes. Through this monitoring, was possible a better contact with the visually impaired students, what became essential for the understanding of their school routine. Regarding the difficulties on Chemistry learning is possible to say that, considering the contact with the students, they are connect to the subjects that demand visual perception and spatial interpretation, like graphics. Beyond the observation, were made pedagogical evaluations about the subject Substances and Mixtures and Atomic Models, with the aim to understand how the students apprehended the concepts involved in these subjects. Based on these data, was developed a lesson plan regarding the subject of atomistic, considering the presuppositions of historical-critical pedagogy. The classes about atomic theory resulted on the preparation of a pedagogical-didactic material in order to provide means for the apprehension of Chemistry concepts by the students. The material was used in Chemistry classes, and the elaboration of concepts, from such material, was accompanied during the process of students development and learning process.