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Correlações entre parâmetros microestruturais, parâmetros térmicos e resistência mecânica de ligas Sn- Bi e Sn-Bi-(Cu,Ag)
(Universidade Federal de São Carlos, 2016-10-07) Silva, Bismarck Luiz; Spinelli, José Eduardo; https://lattes.cnpq.br/8882038118634925; https://lattes.cnpq.br/4377238190630005
The present research aims to develop a theoretical/experimental analysis of the combined effects of solidification thermal parameters, Bi content and addition of ternary elements (Cu, Ag) on the final microstructure aspects and on the final mechanical resistances of directionally solidified Sn-Bi, Sn-Bi-Ag and Sn-Bi-Cu solder alloys under transient heat flow conditions. Hence, experimental interrelations between microstructure and thermal parameters and between mechanical properties and microstructure could be established. The microstructures regarding the Sn-34wt.%Bi and Sn-52wt.%Bi alloys show the presence of β-Sn dendrites with Bi precipitates on their own, being enveloped by a lamellar binary Sn-Bi eutectic. The Sn-58wt.%Bi eutectic alloy show a variety of microstructures along the length of the directionally solidified casting, which includes binary eutectic, Bi plates, Bi trifoils and fishbone eutectic. In the case of the ternary Sn-Bi-Ag and Sn-Bi-Cu chemistries, microstructures are constituted by β-Sn dendrites decorated with Bi particles, Bi-Sn eutectic and Cu6Sn5 and Ag3Sn intermetallic particles for the Cu and the Ag bearing alloys, respectively. Experimental growth laws have been derived for both dendritic (λ1, λ2, λ3) and eutectic (λfine, λcoarse) arrangements considering the following alloys: binary Sn-34wt.%Bi, Sn-52wt.%Bi e Sn-58wt.%Bi alloys and ternary Sn- 34wt.%Bi-0.1wt.%Cu, Sn-34wt.%Bi-0.7wt.%Cu e Sn-33wt.%Bi-2wt.%Ag. Considering the binary Sn-Bi, it has been observed that increasing Bi content (34wt.%-->52wt.%-->58wt.%Bi), may cause a decrease on both strength and ductility, except for the sample at P=6mm of the Sn-52wt%Bi alloy. Hall-Petch type functional correlations have been able to represent the evolution of the tensile mechanical properties for the examined Sn-Bi and Sn-Bi-X alloys.
Aspectos ecológicos da avifauna aquática nas fozes dos rios Tijucas e Inferninho, Santa Catarina, Brasil
(Universidade Federal de São Carlos, 2016-10-07) Rubert, Barbara; Branco, Joaquim Olinto; https://lattes.cnpq.br/3241905846920207; https://lattes.cnpq.br/7507009796249447
Estuaries are highly productive environments susceptible to environmental variables, and important to the life cycle of various species, to waterfowl serve as a point of rest, feeding and nesting. These sites also receive migratory birds seeking the accumulation of energy required for the return to the reproductive areas. These species, as well as residents, have their distribution, occurrence, abundance and behavior influenced by environmental variables, seasonality and human presence. Thus this study aimed to characterize the structure of the community of waterfowl, as well as behavioral pattern, relationship with environmental variables and habitat use by them in the mouths of the rivers Tijucas and Inferninho. The Tijucas’ Bay where this study was conducted, presents sediment deposition and formation of extensive muddy plans. To collect the data length of 1.1 km was covered in each mouth, from June 2015 to May 2016, sampling occurred every two hours, from 08 hours to 16 hours. The data collected were species, average number, activity and micro-habitat. five microhabitats were considered, based on different faces found in two locations, and analyzed environmental variables were: wind speed, tide height, precipitation and temperature. The curve of rarefaction and Jackknife 2 were used to determine the sample sufficiency, Shannon index was used to estimate the annual and monthly diversity and similarity among the studied areas was calculated using the Jaccard index. Analysis of Variance (ANOVA) and Kruskal-Wallis test were used to determine the differences between species richness, average number and behavior of the species for hours and months of sampling. The behavior relative frequency was grouped by similarity of Bray-Curtis, the Indicator Species Analysis was used to determine the association of species with micro-habitats, and used Canonical Correlation Analysis (CCA) to determine the correlation between the variables environmental and behavior and between species. Were recorded 44 species of waterfowl in the voices of the two rivers, 10 migratory. The similarity between the two areas was 75%, indicating high similarity of microhabitats between areas. The diversity at the mouth of the river Tijucas was higher than the mouth of the river Inferninho, this difference is related to river discharge of rivers, hence the nutrient input. The difference in species richness, abundance was significant only between the months of observation, and the months with the highest diversity occurred in the late spring, summer and early fall, probably due to the life cycle and arrival of migratory species. The rest was the most frequent activity, followed by foraging, this was negatively related to temperature variation, it suggests that the higher the temperature, the lower the foraging, avoiding waste of energy and water. Foraging was negatively correlated with the height of the tide as the low tide provides a food resource. The indicator species analysis showed that most of the species was associated with only one micro-habitats, this can be explained by the abundance of available resource, since rich environments allow specialization of species.
Obtenção e caracterização de heteroestruturas epitaxiais magnetoelétricas de [KNbO3]0,9-[BaNi1/2Nb1/2O3-𝛿]0,1 e [La0,7Sr0,3MnO3]
(Universidade Federal de São Carlos, 2016-10-07) Lopez, Andrea Naranjo; Venet, Michel Zambrano; http://lattes.cnpq.br/4256279833398263; Cardoso, Claudio Antonio; https://lattes.cnpq.br/0332061570052918; https://lattes.cnpq.br/7691199952523844
Magnetoelectric materials have been extensively studied in the last decade, particularly due to the applicability for sensors, attenuators, transformers and others. Hence as an objective for this work we propose a study on the fabrication and characterization of materials that may be used as extrinsic magnetoelectrics. Our proposal consists in producing by pulsed laser deposition bilayers of ferroelectric thin films [KNbO_3]_(0,9)-[BaNi_(1/2)Nb_(1/2)O_(3−𝛿)]_(0,1) (KBNNO), grown on magnetic thin films [La_(0,7)Sr_(0,3)MnO_3] (LSMO). Focusing our interest on the KBNNO, because it is a relatively new material, and there is not enough information about its possible applications as magnetoelectric, just as there are for photovoltaic application. Initially, we made a detailed study on the dependence of the ceramic target densification of the ferroelectric phase KBNNO with the sintering temperature, with the aim to determine the appropriate parameters in the fabrication of the ceramic target, obtained by solid state reaction method. It was possible to achive ceramics targets with relative densities greater than 94 %. The structural and morphological properties of the ceramic targets and thin films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The X-ray diffraction profile confirmed the phases and crystal structures of the samples. Particularly, the thin films showed an oriented growth (epitaxial) with formation of nanopilares with different diameters and heights depending on the deposition parameters. The electrical properties were determinated by ferroelectric hysteresis and electric impedance spectroscopy. The magnetoelectric and optical properties were determined by magnetoelectric coupling and photoluminescence measurments, respectively. For the ceramic samples the ferroelectric and dielectric behaviors were confirmed, and for the thin films a magnetoelectric coupling between the ferroelectric and magnetostrictive phases was found. Finally, the value of the gap for ceramic KBNNO was found to be aroud 1.248eV, this result is consistent with values reported in the literature for this material.