Portugaliae
Electrochimica Acta

Titanium dioxide electrodes were prepared in three stages: (i) electrodeposition of Pt layer on a Ti substrate that was (ii) covered by a TiO2 thin film deposited by DC Magnetron Sputtering technique, at constant pressure of 0.8 Pa and oxygen partial pressure of 0.08 Pa, and (iii) annealed at 400 ºC. The structural (XRD) characterization of the films was performed, showing a predominant anatase-TiO2 phase, where some peaks corresponding to the Ti/Pt substrate were also observed. The average crystallite size for the films was 44 nm, showing the nanocrystalline nature of these anatase-TiO2 films. The surface morphology of the films was studied by scanning electron microscopy and revealed agglomerates of nanosized grains or particulates, distributed over the substrate surface with a ‘blooming flower-like’ appearance. The nanosized grains result in an increase in active surface area and also promote the formation of porous TiO2 films. The performance of Ti/Pt/TiO2 as anode was evaluated in the electrodegradation of an azo dye, the acid orange 7 (AO7). Assays were run at 0.1, 0.25 and 1 mA cm-2, using AO7 concentration of 50 mg L-1, and after 12 h assays colour (484 nm) and chemical oxygen demand removals up to 97 and 70% were obtained, respectively. The energetic yield decreased with the increase in current density, which is typical from a process controlled by diffusion. The platinization of the substrate improves the adhesion of the TiO2 film, increasing its lifetime, and increases the conductivity of the films, decreasing the energetic costs of the process.

The corrosion inhibition of mild steel in a 1.0 M hydrochloric acid solution by 2-(4,5-diphenyl-4,5-dihydro-1h-imidazol-2-yl)-5-methoxyphenol (P1) has been studied in relation to the concentration of the inhibitor, as well as to the temperature, using chemical (weight loss) and electrochemical techniques. All the employed methods were in reasonable agreement. The protection efficiency increased with an increased inhibitor’s concentration. The obtained thermodynamic adsorption parameters (∆G*ads, ∆H*ads, ∆S*ads) indicated that this polymer retarded both cathodic and anodic processes through physical adsorption, and blocked the active corrosion sites. It was also found that this compound obeyed the Langmuir’s adsorption isotherm.

People are implanted with orthodontic wires made of different materials, to regulate their teeth. The various toothpastes that they use during the course of the treatment may have a corrosive effect on these materials. Hence, the main objective of this study was to evaluate the corrosion behaviour of an SS 316L alloy in artificial saliva in the presence of a sparkle fresh toothpaste. An electrochemical study has been used to investigate the corrosion behaviour of this alloy. Scanning electron microscopy (SEM) imaging gave the morphological data for the sample; however, by using X-ray spectroscopy in conjunction with SEM (EDAX), the elemental composition was determined. Further, the analysis of the protective film formed on the metal surface was done using UV-visible absorption and fluorescence spectra. The corrosion resistance of the SS 316L system in various solutions decreases in the following order: AS+ toothpaste> toothpaste>AS. For AS+ toothpaste system, LPR= 1813475 Ohm cm2; Icorr = 2.464 x10-8A/cm2; Rct =14961 Ohm cm2; Cdl= 3.4088 x10-10 F/cm2 and impedance = 4.397 log z/Ohm. The high corrosion resistance offered by the toothpaste is due to the formation of a protective film. It confirmed that the active principles of the toothpaste ingredients have co-ordinated with the SS 316L metal ions through their polar atoms to form a complex.

In this study, lignin, a polyhydroxy compound, was extracted from black liquor of pulp and paper industry, and characterized. In view of the potential of such polyhydroxy compounds to adsorb onto metal surfaces, the corrosion inhibition efficiency of lignin on the corrosion of mild steel by 0.5 M H2SO4 has been studied using weight loss method, electrochemical polarization and impedance methods. The morphological changes of the surface during corrosion, in the presence and absence of the inhibitor, were studied by scanning electron microscopy. Results of these studies show that lignin does inhibit the corrosion of mild steel by sulfuric acid, and that the inhibition efficiency increased with lignin’s concentration.

The incorporation of composite and eco-friendly particles or fluids to develop new engineering materials has recently changed the coating world. In this study, a Zn-TiO2-TiB2 ternary alloy was produced from a sulphate bath on a mild steel substrate. Solanum tuberosum (ST) was later introduced to the bath to evaluate the effect of the organic additive on the ternary alloy. The study was conducted under constant plating time and current density. The fabricated matrix was systematically investigated using scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) for structural properties. The micro hardness and anti-corrosion properties of the deposits were studied using, respectively, a diamond base micro hardness tester and potentiodynamic polarization method. The anti-wear properties and thermal stability of the electrodeposited alloy were studied using a MTR-300 abrasive tester and an isothermal furnace at 250 ºC. From the observed result, the coatings presented good stability, especially for Zn-TiO2-TiB2-ST, as compared to the Zn-TiO2-TiB2 coating. The addition of ST improved the hardness properties of the matrix from 182.4 to197.2 HV, and the corrosion rate from 0.9805 to 0.7711 mm/yr. This work established that co-deposition of mild steel with TiO2/TiB2/ST is promising in anti-wear and corrosion resistance properties.