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► The electrochemical behaviour of three ZrTi alloys in saline and in Ringer's solutions has been characterized. ► ZrTi alloys attain a passive regime when immersed in Ringer's ...solution, and this happens spontaneously at the open circuit potential. ► Titanium addition to zirconium results in greater corrosion resistance and thicker passive films, less susceptible to localized corrosion. ► Localized differences in electrochemical reactivity of the materials could be established by SECM measurements. ► Polarization of the alloys at anodic polarizations that can be achieved in the human body leads to an increase in surface reactivity.
The electrochemical behaviour of three ZrTi alloys (Zr5Ti, Zr25Ti and Zr45Ti) in Ringer's solution has been investigated. Their resistance against localized corrosion has been determined from cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy (EIS) measurements, whereas scanning electrochemical microscopy (SECM) was applied to investigate the local reactivity of the passive films developed on the materials, and scanning electron microscopy (SEM) was employed to characterize the surface morphology of the alloys subjected to anodic polarization. An increased reactivity could be detected with SECM when the metal samples were polarized at +0.50VSHE, though the extent of this feature greatly depended on the nature of the metallic material. In addition, At 37°C, the Zr5Ti alloy was susceptible to localized corrosion. Though Zr25Ti alloy presented rather low pitting potential, the spontaneous corrosion potential of the material was sufficiently negative to require overpotentials around 600mV for breakdown to occur. Finally, the Zr45Ti alloy exhibited a larger passive range in the polarization curve, and it was resistant to localized corrosion.
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•Horse-chestnut extract (HCE) applied on bronze for corrosion protection.•HCE addition decreased corrosion current and enhanced the surface film resistance.•The best protection was ...achieved after 14 h in a solution containing 0.5 g L−1 HCE.•HCE-bronze interaction arises from physisorption described by Langmuir isotherm.•Novel analytical methodology for SECM kinetic study on inhibitor adsorption.
Horse-chestnut ethanolic extract was tested as potential corrosion inhibitor of bronze in simulated acid rain. The extract was analysed by FTIR, GC–MS and HPLC-PDA, and its anti-corrosion behaviour studied using a multiscale electrochemical approach by polarization curves, EIS and scanning electrochemical microscopy, along with SEM-EDS. 94 % inhibition efficiency was attained by developing a surface physisorbed film. A novel methodology for kinetic evaluation of dynamic adsorption of inhibitive species on metal surface is proposed using SECM, achieving good agreement with results from conventional electrochemical techniques. Excellent adsorption-desorption kinetic constants (ka = 0.102 s−1 mol−1 L; kd = 3.33 × 10-5 s−1) were determined.
•Copper protection in 3.5 wt.%NaCl by 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT).•High inhibitive efficacy of PyODT on Cu corrosion was reached at long exposure.•A uniform and compact inhibitor ...film was formed on copper surface.•Interaction between Cu and PyODT proceeded through thiol and oxadiazole groups.•Machine learning algorithms and Raman data were firstly applied in corrosion study.
An oxadiazole derivative with functional groups favouring its adsorption on copper surface, namely 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol, has been explored as potential inhibitor of copper corrosion in 3.5 wt.% NaCl. Electrochemical evaluation by electrochemical impedance spectroscopy, potentiodynamic polarization and SVET reveals high inhibition efficiencies. Surface microscopy inspection and spectroscopic analysis by Raman, SEM-EDX and XPS highlight the formation of a compact barrier film responsible for long-lasting protection, that is mainly composed of the organic molecules. Machine learning algorithms used in combination with Raman spectroscopy data were applied successfully for the first time in corrosion studies to allow discrimination between corroded and inhibitor-protected metal surfaces. Quantum Chemistry calculations in aqueous solution and Molecular Dynamic studies predict a strong interaction between copper and the thiol group and an extensive coverage of the metal surface, responsible for the excellent protection against corrosion.
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Pterodon emarginatus Vogel is a Brazilian species that belongs to the family Fabaceae, popularly known as sucupira. Its oil has several biological activities, including potent larvicidal property ...against Aedes aegypti. This insect is the vector of dengue, a tropical disease that has been considered a critical health problem in developing countries, such as Brazil. Most of dengue control methods involve larvicidal agents suspended or diluted in water and making active lipophilic natural products available is therefore considered a technological challenge. In this context, nanoemulsions appear as viable alternatives to solve this major problem. The present study describes the development of a novel nanoemulsion with larvicidal activity against A. aegypti along with the required Hydrophile Lipophile Balance determination of this oil. It was suggested that the mechanism of action might involve reversible inhibition of acetylcholinesterase and our results also suggest that the P. emarginatus nanoemulsion is not toxic for mammals. Thus, it contributes significantly to alternative integrative practices of dengue control, as well as to develop sucupira based nanoproducts for application in aqueous media.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Endophytic fungi are microorganisms capable of colonizing the interior of plant tissues without causing damage to them. The study of the secondary metabolites produced by their vast biodiversity ...fungal is relevant for the discovery of new products for biotechnological and agrochemical applications. In addition, extract of the endophytic fungus
Aspergillus
sp., isolated from the almonds of
Bertholletia excelsa
Humn & Bonlp collected in the Brazilian Amazon, oviposition deterrent, and larvicidal activity of against
Aedes aegypti
. In the oviposition deterrence test was observed that females able to lay eggs preferred the control oviposition sites (46.6%). Furthermore, the extract showed larvicidal activity with LC50 26.86 µg/mL at 24 h and 18.75 µg/mL at 48 h. Molecular docking studies showed the compound Aspergillol B a potent larvicide by to inhibit the acetylcholinesterase enzyme (− 7.74 kcal/mol). These results indicate that compounds from secondary metabolites of
Aspergillus
sp., isolated from almonds of
B. excelsa
, are useful biological potential against vectors
A. aegypti.
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•The detrimental effect of cathodic polarization on the passive state of titanium was determined using SECM.•Cathodic polarization produces electrical conductivity changes in the ...surface film facilitating the occurrence of electron transfer reactions.•The modification of the passive state was quantitatively described in terms of electron transfer rates at the titanium surface.•Occurrence of hydrogen intercalation into the titanium dioxide film was proved operating SECM in the redox-competition mode.
The effect of cathodic polarization on the electrochemical behavior of the thin titanium dioxide film formed by anodic pretreatment over pure commercial titanium metal for biomaterial application was investigated in situ using scanning electrochemical microscopy (SECM). Quantitative information on the electron transfer rates (keff) at the titanium surface was obtained using the feedback operation of SECM with ferrocene-methanol (FcMeOH) as electrochemical mediator. An increase of keff values with the increase of the negative polarization was detected, a feature that correlates well with the decrease of titanium oxide resistance with increasing cathodic polarization observed using electrochemical impedance spectroscopy (EIS). In addition, SECM operation in the redox competition mode proved that hydrogen was absorbed in the surface oxide film leading to changes in conductivity and electrochemical reactivity.
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•Heterogeneous surface characteristics develop on nitinol after application of anodic polarization even for a limited time.•The development of anodic and cathodic sites owing to the ...onset of localized corrosion processes were detected by SECM.•Hydrogen gas evolution from localized sites was monitored using SECM in substrate generation/tip collection mode (SG/TC).•SECM operated in potentiometric mode evidenced local acidification around anodic sites related to Ni2+ discharge.
Scanning electrochemical microscopy (SECM) in a combined amperometric/potentiometric operation was used to characterize the electrochemical activity of nitinol, before and after anodic treatment, in 0.1 M NaCl solution. The SECM operation in the feedback mode showed that the nitinol surface was homogeneously passive after surface finishing and storage under ambient conditions, while heterogeneous surface characteristics occurred after application of anodic polarization, even for a limited time. That is, the development of anodic and cathodic sites has been detected due to the onset of localized corrosion processes on the metal surface. The evolution of hydrogen gas from localized sites was monitored using SECM in the substrate generation/tip collection mode (SG/TC), while SECM operated in potentiometric mode was used to map the pH distribution in the electrolyte volume adjacent to the nitinol surface. Local acidification was observed around anodic spots associated with the Ni2+ discharge, as well as alkalinization above the cathodic zones.
Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). ...Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-alloy.
•Oxidation in air of ZrTi alloys produces materials with very high corrosion resistance in Ringer's solution at 37°C.•The electrochemical behaviour corresponds to materials covered by passive oxide ...layers with barrier characteristics.•The current densities related to passivity are 2–3 orders of magnitude smaller than those determined for the untreated alloys.•Electrochemical impedance spectra exhibited two relaxation constants consistent with a two-layer structure.•The oxide layer is a mixture of ZrO2 and TiO2.
Oxidation in air of ZrTi alloys at 500°C for 2h produces oxide-covered materials with a very high corrosion resistance in Ringer's solution at 37°C. The oxide layers present a two-layer structure, comprised by a thin and very compact inner layer of ca. 5nm thickness, and a less compact, more porous and thicker outer layer. The thickness of the outer layer greatly varies with the composition of the base ZrTi alloy, but has very little influence in the overall electrochemical behaviour of the material. The nature of the oxide layer is a mixture of ZrO2 and TiO2, and no evidence of higher oxidation states of the metal could be found using XRD data. Anodic dissolution through the passive layers formed on the oxidized alloys is greatly diminished compared to those measured from the untreated materials, allowing all the alloying ratios between Zr and Ti to be potentially considered for implant application. The combination of alloying with titanium and oxidation in air at 500°C resulted in materials that do not exhibit the characteristic susceptibility of zirconium towards the initiation of localized corrosion processes in aqueous chloride-containing electrolytes even for anodic polarizations up to +1.00V vs. SCE, a value well above the highest polarization experienced in the human body. Though all the oxidized alloys exhibited remarkable corrosion resistances, the best behaviour was found for oxidized Zr45Ti.
Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of ...operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn
and OH
ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described.
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