This study investigated the feasibility of H2 production by acid corrosion, employing a by-product from the fertilizer industry (Hexafluorsilic acid - H2SiF6) and waste iron sources. Different masses of metal from three different sources: iron powder (waste from metal workshops), steel wool and rebar (construction waste), were reacted with various proportions of H2SiF6 with HCl. The influence of the variables was evaluated by factorial design, verifying greater production of H2 for materials with higher contact areas. The lowest production was observed for construction industry waste (rebar) probably due to the presence of protective films and lower contact area. The gas produced was analyzed by gas chromatography and was found to consist only of H2 (up to 99%) and air. The results indicate a promising application of H2SiF6, which is generated in large quantities during phosphate fertilizer production and has few commercial applications. The method proposed is promising, it does not emit toxic or polluting gases, contributing to the sustainable generation of H2.

ABSTRACT This work aims to evaluate the influence of welding parameters, current intensity and deposition speed, on the bead geometry, dilution, morphology and properties of a nickel-based alloy coating. For this, single beads of Inconel 625 alloy were deposited on the substrate of ASTM A36 Steel, by PTA-P process. The samples were sandblasted and polished. The samples were chemically etched by a solution of 92 mL HCl, 3 mL HNO3 and 5 mL H2SO4 for 5 minutes. The geometry of the beads (reinforcement height, bead width, penetration and contact angle) was measured through the digital stereoscope microscope. The microstructures of the cross sections were evaluated by optical microscopy and scanning electron microscopy (SEM), to identify the possible presence of precipitated phases in the ferrite matrix. The chemical composition of these present phases, as well as the diffused iron content from the substrate for the coating, were measured by EDX. The type of the phases precipitated by x-ray diffraction in the top samples of the coating were also evaluated, in 1.5 mm height of reinforcement. For mechanical property analysis, the microhardness of the coatings was measured by Vickers microhardness test to evaluate their relationship with the iron present in the coatings, which diffused from the substrate. The results confirmed the influence of welding parameters on coating dilution - Current is the parameter of greatest response. The morphologies of the coatings were presented as a γ matrix with second phase precipitation composed of Ni, Nb, Cr and Mo. The concentration of these precipitations decreased with increasing dilution. This occurred because of the increased migration of Fe present in the substrate of the coating through the diffusion phenomena, with increasing dilution. The Fe reduced the solubility of Nb and Mo of the γ matrix, causing the decrease of its hardness.

RESUMO O presente trabalho teve como objetivo desenvolver e caracterizar revestimentos nanocompósitos de Ni e Ni-Grafeno aplicados em superfície de aço API 5L X80, utilizando o processo de eletrodeposição, para obter melhores propriedades anticorrosivas. Corpos de prova de dimensões de 20x20x3 mm foram submetidos à limpeza e preparação metalográfica, para posterior deposição dos revestimentos. Para o processo de eletrodeposição foi utilizado um banho à base de níquel contendo dodecil sulfato de sódio (SDS) como surfactante. Para obtenção dos revestimentos Ni-Grafeno, foram adicionadas partículas de grafeno (0,2g/L) ao banho eletrolítico. Os eletrodepósitos obtidos foram caracterizados por Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV). A resistência à corrosão dos revestimentos foi avaliada por meio de ensaios de Polarização Linear (PL) e Espectroscopia de Impedância Eletroquímica (EIE). A inserção de grafeno ao revestimento promoveu a formação de depósitos com grãos mais refinados, e com a direção de crescimento de cristais bem definida. Foram observados depósitos com estruturas lamelares sobrepostas, associadas ao grafeno incorporado à matriz de Ni. A deposição de grafeno influenciou na orientação preferencial dos grãos durante o processo de eletrodeposição, sendo o plano (200) idenfiticado como a orientação preferencial para o nanocompósito Ni-Grafeno. O revestimento Ni-Grafeno obteve melhor desempenho anticorrosivo em comparação ao revestimento de Ni puro e ao metal base, apresentando valor de potencial de corrosão (Ecorr) mais elevado, menor valor de densidade de corrente de corrosão (icorr) e módulo de impedância (|Z|) superior.

ABSTRACT The aim of the present work was to develop and characterize nanocomposite coatings of Ni and Ni-Graphene applied on API 5L X80 steel surface, using the electrodeposition process, to obtain better anticorrosive properties. Test specimens of dimensions of 20x20x3 mm were submitted to metallographic cleaning and preparation, for later deposition of the coatings. For the electrodeposition process, a nickel-based bath containing sodium dodecyl sulfate (SDS) was used as the surfactant. To obtain the Ni-Graphene coatings, graphene particles (0.2 g/L) were added to the electrolytic bath. The electrodeposits obtained were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The insertion of graphene to the coating promoted the formation of deposits with more refined grains, and with a well-defined crystal growth direction. Deposits with overlapping lamellar structures were observed and associated to the graphene incorporated into the Ni matrix. The deposition of graphene influenced the preferential orientation of the grains during the electrodeposition process, with the plane (200) being identified as the preferred orientation for the Ni-Graphene nanocomposite. The Ni-Graphene coating obtained better corrosion performance in comparing to the coating of pure Ni and the base metal, presenting a higher corrosion potential value (Ecorr), lower corrosion current density (icorr) value and higher impedance modulus (|Z|).

Silver, a malleable metal, ductile, bright, known since prehistoric times is widely used in photographic industry, of jewelry and decorative objects. Due to its remarkable physical and chemical properties, new applications have emerged. Considering the importance of this element, this article describes their history, properties and applications.

Plata, un metal maleable, dúctil, brillante, conocido desde tiempos prehistóricos y muy utilizado em la industria fotográfica, de joyería y objetos de decoración. Debido a sus notables propiedades físico-químicas, han surgido nuevas aplicaciones. Considerando la importancia de este elemento, este artículo describe su historia, propiedades y aplicaciones.

Tetracyclines exhibits activity to a broad range of Gram-negative and Gram-positive bacteria and this fact allied to the low toxicity, low cost, and the advantage of administration by oral route led to their indiscriminate use, which caused the appearance of bacterial resistance to these agents, wich has restricted its clinical utility, though new applications have emerged. On the other hand, the glycylcyclines, semi-synthetic products are similar to tetracyclines, which are active against many bacteria resistant to tetracycline and other classes of antibiotics. The purpose of this paper is to give an overview of this important class of antibiotics focusing on its coordination chemistry and possible applications.