Chromate coatings used as corrosion protection technologies for aluminum alloys are environmentally harmful and extremely toxic. This paper presents an investigation on the deposition of environmentally friendly cerium oxide-based anticorrosive coatings on aluminum alloy 2024 substrates by the sol - gel method. The influence of the calcination temperature on both the microstructural characteristics and the electrochemical corrosion performance was tested using scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), before and after, periods of immersion in saline corrosive solutions. The ceramic coatings synthesized at 200, 300 and 400 °C showed very resistive behaviors leading to both an efficient passivation of the alloy surfaces and good corrosion protection. This passivation was maintained for 30 days of immersion in saline solutions, as well as, when aggressive electrochemical polarization experiments (until 2.0 V versus saturated calomel electrode) were used. Very high resistances for the charge transfer (0.14-0.28 GΩ) and very low current density values (5 × 10- 14 -5 × 10- 11 A cm- 2) were estimated by EIS and potentiodynamic polarization, respectively, for coatings prepared at 200-400 °C. Thus, the coatings prepared in this study by the sol - gel method appear as an efficient treatment for the corrosion protection of aluminum alloys.
The literature on the challenges of teacher education in undergraduate chemistry teaching is limited. In the present study, the application of didactic proposals elaborated by two authors of this paper, graduate students and teaching assistants of the teaching improvement program at University of São Paulo, was investigated in terms of their contribution to the teaching assistants' education and undergraduate students' receptivity toward them. Such proposals were based on the jigsaw cooperative learning strategy and applied in two undergraduate courses. The results indicate students' good receptivity and suggest their importance to teaching assistants' education.
This paper presents the study of the oxidation of three textile dyes (Remazol black B, Remazol Brilliant Orange 3R and Remazol Golden Yellow RNL) using electrochemical and photoelectrochemical methods. In both methods, electrolysis experiments were performed at a current density of 50 mA cm-2 in an aqueous solution of each dye (30 mg L-1), using a photoelectrochemical flow-cell. For all the dyes studied, the photoelectrochemical method was demonstrated to be more efficient than the electrochemical one. Photoelectrochemical oxidation resulted in complete decoloration after 90 min of electrolysis and total organic carbon (TOC) removal reached up to 36%. It was observed that the dyes presenting chromophores at higher wavelengths are removed the quickest, which indicates that photosensitised (photoassisted) oxidation occurs. The level of color was reduced to levels below the standards presented in the literature, which indicates the viability of the photoelectrochemical process as part of the treatment of textile effluents.