Abstract Aluminum alloys have been widely used in multiple applications, such as in civil construction and engine pistons. They are subjected to loads that may impair their mechanical properties. Thereby, this research aims to study the influence of anodization on the mechanical properties of alloy samples and evaluate the behavior of oxide films when subjected to tensile testing. The mechanical properties of specimens have been evaluated based on tensile and Knoop hardness tests, and strain, tensile strength, and modulus of elasticity of specimens have been determined based on the stress-strain curve. The morphology of oxide films was analyzed by scanning electron microscopy (SEM) and optical microscopy (OM). Results of anodized Al-Si alloys in both modes, i.e. pulsed and direct currents, were compared, and it was found that pulsed current was more efficient than direct current with respect to uniformity of the formed film, and that the anodization process can affect a few mechanical properties of samples. The tension testing results also revealed that the oxide film has been fractured perpendicularly towards traction. However, the oxide film hardness was not affected by the anodization mode (pulsed or direct currents). In addition, a heat treatment was efficient at improving the uniformity of anodic films.

The objective of this work was to investigate the effects of anodization parameters on the anatase phase formation of titanium oxide films, which have been grown on both electropolished and non-electropolished titanium surfaces by direct current anodization in 0.25 and 2.5 mol L-1 H3PO4 solutions, respectively, at three anodization times (3, 6 and 12 hours). SEM, Raman spectroscopy and X-ray diffraction techniques revealed the characteristics of anodic films. Films were characterized according to presence of crystalline nuclei of anatase phase on an amorphous matrix. It was found that differences in size, shape and distribution of crystalline grains on anodized surfaces are affected by the type of polishing given to substrates. The particles on electropolished surfaces were grown in well-defined layers following cone-shaped grains. On the other hand, the crystallization phenomenon on non-electropolished substrates has led to the appearance of smaller particle sizes and a larger number of particles distributed along the surface as well.

This study addresses an inherent problem to the oil and natural gas exploration and production industry, the corrosion of pipes and tanks by H2S. H2S with water emulsified in the oil or H2S with the water vapor mixed in the gas, they make the acid environment leading to corrosion. This is commonly manifested by the formation of insoluble sulfides on the surface of the carbon steels destined for this purpose. The evolution of the corrosion process depends on the composition and physicochemical characteristics of sulfide film. In this context, we intend to interpret the conditions of formation and precipitation of iron sulfides as a function of pH, using concepts of chemical equilibrium, electrode potential and electrochemical cell that are part of the subjects of chemistry.

In this paper, a simple and rapid method of evaluating galvanized steel sheet corrosion in a CuSO4 solution, as an experimentation proposal for corrosion teaching. Galvanized steel corrosion is present in tanks and tubing by leading of natural or industrial waters which contain soluble copper compounds. This was the rationale for choosing the Cu2+ ions solution as an oxidizing agent. The method principle is based on visual colorimetry because the used oxidant has an intense blue color. Thus, a change in its concentration as a result of the corrosive process can be followed by a color intensity change in the solution thereby allowing evaluation of the corrosion rate.

In this paper it is proposed an indirect method to evaluate the corrosion rate of an aluminum and zinc alloy in alkaline solution by using a well-known device for collecting gases over water. The hydrogen gas formation, a corrosion product, is monitored at different time intervals and associated with the alloy mass loss. It has been suggested that the students should work in groups, which may make feasible the social interaction among them and that results discussion may be done collectively under a professor orientation. This proposal may propitiate the learning of terminology and involved concepts as well as contribute to a better understanding of corrosion phenomena that occur in their everyday life.

In this work one proposes a didactic experience to simulate atmospheric corrosion of copper and nickel, due to sulfur dioxide presence. This is an opportunity to understand some basic aspects of atmospheric corrosion, by using fundamental concepts in chemistry, reactions of extraction and characterization of pollutants, as well as their participation in corrosion process. This subject opens a space for discussion about necessity of pollutant gases emissions control for preservation of materials and the environment.

Ligas Ni-Cr-Mo são amplamente utilizadas como próteses dentárias fixas, sendo utilizados diferentes procedimentos de refundição que podem alterar as propriedades mecânicas e resistência à corrosão. O objetivo desse trabalho foi analisar o comportamento eletroquímico, as microestruturas e a dureza de duas ligas refundidas pelo processo de refundição em chama aberta (maçarico oxi-GLP) e por indução em forno de alta frequência. A análise metalográfica revelou estruturas dendríticas com grãos largos e precipitados nos seus contornos. As ligas refundidas por indução apresentam menor resistência à corrosão em soro fisiológico, a 37 ºC e maiores valores de dureza.

Ni-Cr-Mo alloys are widely used as fixed dental prostheses, and different procedures for remelting are used which can change the mechanical properties and corrosion resistance. The main aim of this study was to analyze the electrochemical behavior, microstructures and hardness of two remelted alloys by the open flame process (oxy-GLP torch) and by induction in high frequency furnace. Metallography analysis showed dendritic structures with large grains and precipitates in their contours. Alloys recast by induction displayed a lower corrosion resistance in physiologic serum, at 37 °C and higher hardness values.