The corrosion performance of AISI-309 exposed 5 days to molten salts 50 mol% V2O5-50 mol% Na2SO4at 700°C is reported in this paper. Such evaluation was made using three electrochemical techniques: potentiodynamic polarization curve (PC), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (Rp). FromPC, the Tafel slopes,Icorr, andEcorrwere obtained. From Nyquist and Bode plots, it was possible to determine two different stages; the first one showed just one loop, which indicated the initial formation of Cr2O3layer over the metallic surface; after that, the dissolution of Cr2O3formed a porous layer, which became part of the corrosion products; at the same time a NiO layer combined with sulfur was forming, which was suggested as the second stage, represented by two capacitive loops. EIS plots were in agreement with the physical characterization made from SEM and EDS analyses. Fitting of EIS experimental data allowed us to propose two electrical circuits, being in concordance with the corrosion stages. Parameters obtained from the simulation of EIS data are also reported. From the results, it was stated that AISI-309 suffered intergranular corrosion due to the presence of sulfur, which diffused to the metallic surface through a porous Cr2O3layer.

In order to obtain the structural and electronic properties of pristine copper clusters and Cu 13 –SF 6 , Cu 43 –SF 6 , Cu 55 –SF 6 , Cu 13 –2SF 6 , Cu 43 –2SF 6 , and Cu 55 –2SF 6 systems, DFT calculations were carried out. For Cu 13 – m SF 6 , its surface suffers a drastic deformation, and Cu 43 – m SF 6 at its outer surface reveals strong interaction for the first chemical molecule; when the second molecule is interacting, these outer surfaces are not severely affected. These two cases degraded fully the first SF 6 molecule; however the second molecule is bonded to the latter systems and for Cu 55 – m SF 6 ( m = 1 and 2) a structural transformation from SF 6 →SF 4 appears as well as inner and outer shells that display slight deformations. The electronic gaps do not exhibit drastic changes after adsorption of m SF 6 molecules, and the magnetic moment remains without alterations. The whole system shows thermal and vibrational stability. In addition, for Cu 13 – m SF 6 the values of the optical gap and intensity of the optical exhibit changes with respect to the pristine case (Cu 13 ), and the rest of the systems do not exhibit major oscillations. These icosahedral copper clusters emerge as a good option to degrade m SF 6 molecules.

TiO2 nanotubular structures were fabricated on Ti polished and unpolished foils exposed to H2O-Glycerol (50-50Vol.%)+0.27 M NH4F at 20V. The obtained TiO2 nanostructures were analyzed by SEM obtaining the morphological characterization, from which the roughness factors were calculated. Crystalline phases of both TiO2 nanotubular films were obtained by XRD after annealing at 450 °C and 600 °C for 2 h. The electrochemical stability of the TiO2 nanotubular films was obtained from the potentiodynamic polarization curves (PC) and the linear polarization resistance (Lpr) techniques, exposing the samples in 1M Na2SO4 + H2SO4 solution (pH = 3.2), such pH is in accordance with the acidic wastewater containing sulfur compounds coming from the industries or acid waters of the aquifers, which have been contaminated from the volcanoes nearby. It was concluded that the electrochemical stability of the crystallized nanotubular films is improved with the increase of the annealing temperature of the amorphous TiO2 arrays, which is associated to the higher composition of anatase and rutile, observing that the major amount of rutile improved the corrosion performance. The photoelectrochemical measurements were carried out in 0.5 M Na2SO4 solution using an 8 W UV lamp at a λ= 365 nm, whose results were recorded at zero bias during 10 min under darkness and illumination intervals of 1 min each. The obtained results were in agreement with the necessary features for being used in photocatalytic water remediation.

The array of the TiO2 nanotubular films, also called one-dimensional nanostructures is carried out by electrochemical anodization tests, for which, titanium sheets were used with a high purity (99.7% and 0.25 mm thickness) in a solution of deionized water and glycerol (50:50 vol.%) + 0.27M NH4F applying a voltage of 20V. Electrochemical tests were performed at an anodization time of 2:30 hours and 3:30 hours. For the tests mirror polished foils and unpolished foils with flat surfaces to achieve better uniform arrays during the anodic growth of nanotubes were used. After anodizing, samples were observed in the scanning electron microscope (SEM) to determine the geometry and morphology of the films. Also, potentiodynamic polarization curves were performed for samples crystallized at 600 °C and 450 °C (polished and unpolished) to determine the electrochemical stability of the films, which were presented at two aqueous solutions: 1M of Na2SO4 (pH= 6.7) and 1M Na2SO4 + H2SO4 (pH= 3.2). Mechanical characterization was also performed by nanoindentation technique through the application of loading/unloaings of: (1, 2.5, 5, 10 mN). Chemical characterization was performed using XRD analysis, with the aim to determine the crystalline phases formed in the films crystallized at 450 °C and 600 °C. The electrochemical characterization showed that the TiO2 nanotubular film obtained by mirror polished and crystallized at 600 °C showed better electrochemical stability. Nanoindentation tests showed deformation curves, and the parameters such as hardness, Vickers hardness, elastic modulus and the maximum penetration depth were determined as mechanical parameters.