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The corrosion behavior of three types of steels, pre-oxidized and without pre-oxidation, coated with sodium sulfate was evaluated in the present work by using electrochemical techniques, including polarization resistance, Tafel curves, electrochemical impedance, and gravimetric techniques like weight gain, at 600 and 650 °C. It was determined that the steel exhibiting the lowest corrosion rate was 304H, being the most resistant coated specimen with solid Na2SO4 in air atmosphere because its oxide layer formed initially was maintained even at high temperatures. For ferritic steels, a slight increase in corrosion rate was noted, presenting a small diffusion of sulfur and sulfide formation at the alloy /oxide interface, given that it fractured due to the difference in the thermal expansion coefficients. In general, a solid Na2SO4 deposit over the steels used in systems working at high temperatures is not a risk factor that influences material degradation. [ABSTRACT FROM AUTHOR]

The development and characterization of bioactive surfaces based on chitosan-polyethylene glycol coatings modified with hydroxyapatite on Ti6Al4V alloy were conducted to enhance bioactivity. Characterization techniques such as scanning electron microscopy, X-ray diffraction, infrared spectroscopy, atomic absorption spectroscopy, and electrochemical impedance spectroscopy were used to evaluate coating properties, apatite formation after immersion in simulated body fluid, and electrochemical stability. Results demonstrated apatite deposition due to the bioactivity of the polymer-ceramic composite, with calcium accumulation observed on the substrate surface after 5 days of immersion. Electrochemical impedance spectroscopy revealed a highly capacitive layer in the 50:50 chitosanpolyethylene glycol coating with 0.05% w/v hydroxyapatite, indicating increased interaction with the biological medium while preserving the protective resistive properties of the Ti6Al4V alloy. These findings suggest that this coating composition is a promising material for bone tissue regeneration applications. [ABSTRACT FROM AUTHOR]