O presente estudo 3 tem como tema a produção e reprodução da vida de trabalhadores migrantes temporários nordestinos da construção civil que trabalham no Campus central da Universidade Federal de Santa Catarina — UFSC, em Florianópolis/SC. Seu objetivo principal é analisar as condições de vida, trabalho, moradia e escolarização dos trabalhadores diante do crescimento das migrações na atualidade. Na pesquisa empírica foi realizado um trabalho de campo nos canteiros de obras no campus, com o propósito de identificar as empresas que prestam serviço na universidade e também quais as empresas que empregavam maior número de trabalhadores migrantes temporários nordestinos. Na coleta de dados foram realizadas entrevistas semiestruturadas com os trabalhadores migrantes e com as empresas nos canteiros de obras da universidade. A pesquisa de campo envolveu ainda conversas informais com os trabalhadores migrantes, com as empresas e registros fotográficos.

Dissertação de mestrado

N-Doped porous carbon with uniformly dispersed CoZn alloy nanoparticles has been synthesized through the pyrolysis of a bimetallic zeolitic imidazolate framework containing Zn and Co elements. The surface area, pore size distribution and graphitization of the composites can be modulated easily through changing the molar ratio of Zn to Co in the zeolitic imidazolate framework. Upon increasing the Zn content, the level of graphitization drops gradually and the surface area first increases and then decreases. The increased surface area results in the enhancement of dielectric loss and impedance matching. The sample with a Zn to Co molar ratio of 0.2 in its precursor has the most prominent electromagnetic wave absorption properties, due to appropriate surface area and graphitization properties. The minimum reflection loss reaches −59.7 dB and the widest bandwidth is up to 5.3 GHz. The composites can be good candidates for electromagnetic wave absorption and shielding applications, considering their outstanding performance and simple synthesis route. This study not only offers a simple and facile method for improving dielectric loss and impedance matching of carbon materials, but also sheds light on a new strategy for constructing porous structures, especially porous carbon.

Metal organic framework-derived CoZn alloy/N-doped porous carbon nanocomposites: tunable surface area and electromagnetic wave absorption properties

Tweaking the composition of NiMoZn alloy electrocatalyst for enhanced hydrogen evolution reaction performance

Zn–Fe, Zn–Ni and Zn–Ni–Fe coatings were electrodeposited galvanostatically on mild steel from acidic baths (pH 3.5) consisted of ZnCl 2 , NiCl 2 , FeCl 2 , gelatin, sulfanilic ( p -aminobenzenesulfonic) acid and ascorbic acid. Cyclic voltammetry showed that the effect of gelatin was more pronounced than that of sulfanilic acid, and that the deposition of the ternary alloy behaved differently from the deposition of the binary alloys. In all three systems, the Faradaic efficiency was higher than 88%, the rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, and the deposition was of anomalous type. For each applied current density, the concentrations of Ni and Fe in the ternary alloy were higher than the corresponding concentrations in the binary alloys. The hardness of Zn–Ni coatings was the highest, while that of Zn–Fe coatings was the lowest. The Zn–Ni–Fe coatings were the smoothest, had distinguished surface morphology, and contained ZnO in the bulk, not just on the surface. The lowest corrosion rate in each alloy system (214, 325 and 26 μm year −1 for Zn–Ni, Zn–Fe and Zn–Ni–Fe, respectively) was characteristic of coatings deposited at 30, 30 and 40 mA cm − 2 , respectively. The higher corrosion resistance of the ternary alloy was also reflected by a higher corrosion potential, a higher impedance and a higher slope of the Mott-Schottky line. The enhanced corrosion behavior of the ternary alloy was thus attributed to its chemical composition, phase content, roughness and the synergistic effect of Ni and Fe on the n -type semiconductor surface film.

Electrodeposition of Zn–Ni, Zn–Fe and Zn–Ni–Fe alloys

Zn–Ni, Zn–Co and Zn–Ni–Co coatings were electrodeposited on mild steel from an acidic chloride bath containing p-aminobenzenesulphonic acid (SA) and gelatin. These additives changed the phase content in the coatings, most likely as a result of their adsorption at the surface of the cathode. The effect of gelatin was more pronounced than that of SA. The Faradaic efficiency was higher than 90%. As the current density was increased or the bath temperature was decreased, the concentration of the nobler metal in the coating increased. Both concentrations of Ni and Co in the ternary alloy increased as the applied current density was increased. Nickel and cobalt were found to have a synergistic catalytic effect. The thickness of all coatings increased as the applied current density was increased. The hardness increased with current density to a peak value, and then decreased. The rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, while the rates of Ni and Co deposition were not. The anomalous codeposition was explained by the great difference between the exchange current densities of Zn and the iron-group metal. Potentiodynamic polarization scans and electrochemical impedance spectroscopy showed that the corrosion resistance of the ternary Zn–Ni–Co alloy coatings was approximately 10 times higher than that of Zn–Ni and 7 times higher than that of Zn–Co. The improved corrosion resistance of the ternary alloy was attributed to its surface chemistry, phase content, texture, and surface morphology. The ternary Zn–Ni–Co coating may thus replace the conventional Zn–Ni and Zn–Co coatings in a variety of applications.

Electroplating and characterization of Zn–Ni, Zn–Co and Zn–Ni–Co alloys

Ternary Zn–Ni–Mo (1.2 wt.% Ni, 4.5 wt.% Mo) and Zn–Co–Mo (6 wt.% Co, 4 wt.% Mo) as well as reference binary Zn–Ni and Zn–Co alloy coatings were electrodeposited from citrate–sulphate baths. The influence of molybdenum on the surface morphology, structure, phase composition, corrosion and mechanical properties of the deposits was investigated. The XPS results revealed that the coatings with molybdenum contained appreciable amounts of Zn 2+ inclusions, which is probably due to the low hydrogen evolution overpotential on the ternary alloys. The increase in the interfacial pH, promoted by intensive hydrogen evolution, causes the formation of oxidized zinc species which incorporate into the coating. The presence of MoO 4 2− ions in the bath modified the morphology of the deposits — alloys with smoother surface were deposited. Polarization resistance measurements proved the beneficial influence of molybdenum on corrosion properties of examined alloy coatings. The presence of molybdenum improves the microhardness of the zinc-based alloys, but it has negative influence on the adhesion of the ternary coatings.

A. Laszczyńska

Papers

Influence of molybdenum on properties of Zn–Ni and Zn–Co alloy coatings