•New potentiometric Al3+ion-selective microelectrode for corrosion monitoring on aluminum-based materials.•SECM imaging of local ion concentration distributions over 2098-T351 al-cu-li alloy welded ...by FSW.•Spatial resolution of Al3+ local concentrations arising from the base material and from distinct weld zones.•High active domains for Al3+ associated to microgalvanic coupling were resolved and characterized.•Electrochemical data correlate well with high-resolution XPS spectra of the tested surfaces.
A novel potentiometric Al3+−ion selective microelectrode (ISME), with internal solid contact, based on the use of a neutral carrier morin as ionophore is reported. The ability of the ISME to image local ion concentration distributions was tested on aluminum alloy surfaces freely corroding in an aqueous solution containing chloride ions. The microelectrode was then used as the sensing tip for scanning electrochemical microscopy (SECM) in potentiometric operation to monitor the reactive sites associated with the dissolution of aluminum that developed in the 2098−T351 Al−Cu−Li alloy as a result of welding by the Friction Stir Welding (FSW) process. The ISME detected differences in the local concentrations of Al3+ species arising from the 2098−T351 Al−Cu−Li alloy (base material) and from the coupled weld joint/heat affected zones (WJ/HAZ) of the alloy produced by the FSW process. More active domains for Al3+ dissolution were found in the HAZ regions coupled to WJ, more specially in the HAZ of the advancing side (AS). These results demonstrate that the Al3+−ISME presented in this work can be used to monitor corrosion sites on aluminum alloys surfaces with combined chemical and spatial resolution.
Display omitted
In this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities on polished and as‐received surfaces of the 2098‐T351 aluminum alloy ...(AA2098‐T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X‐ray photoelectron spectroscopy (XPS). The surface generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H2) evolution and oxygen reduction reactions, respectively. H2 evolution and oxygen reduction were more pronounced on the polished surfaces. The feedback mode of SECM was adopted to characterize the electrochemical activity of the polished surface that was previously corroded by immersion in a chloride‐containing solution, in order to investigate the influence of the products formed on the active/passive domains. The precorroded surface and as‐received surfaces revealed lower electrochemical activities compared with the polished surface showing that either the NSDL or corrosion products largely decreased the local electrochemical activities at the AA2098‐T351 surfaces.
•Microelectrochemical characterization of the electrochemical activity on welded zones in FSW 2098-T351 Al-Cu-Li alloy.•Imaging of galvanic coupling effects and local electrochemical activity on ...welded zones using amperometric and potentiometric probes.•Galvanic interactions within and between the coupled welded zones were visualized by SVET and SECM analyses.•Pt and Sb/Sb2O3 probes used to map reactive sites developed on the coupled welding joint/heat affected zones (WJ/HAZ).•Spatially-resolved images of anodic and cathodic sites associated with oxygen consumption and local pH changes were monitored and studied.
Localized electrochemical methods supported by surface analytical characterizations were employed to investigate galvanic coupling effects and local electrochemical activity developed along the welded zones in Friction Stir Welded 2098-T351 Al-Cu-Li alloy. The investigation was carried out in the coupled weld joint/heat affected zones (WJ/HAZ) for both, the retreating (RS) and the advancing (AS) sides. The correlation between the surface chemistry, the microstructural characteristics and the electrochemical activity of these welded areas was studied. The results showed the development of galvanic interactions within and between the WJ and HAZ regions, which were imaged using the scanning vibrating electrode technique (SVET), and scanning electrochemical microscopy (SECM). SVET analyses showed that HAZ was more susceptible to the development of anodic sites than WJ. SECM in amperometric operation mode showed that WJ coupled to HAZ exhibited higher oxygen consumption and higher cathodic activity compared to HAZ. Furthermore, SECM in potentiometric operation showed alkalinization around WJ and increased acidity in HAZ, mainly at sites of severe localized corrosion (SLC). Based on the SVET and SECM results in combination with the surface analyses, it is proposed that the microgalvanic cells formed within these welded zones are due to the presence of secondary phases in the 2098-T351 alloy and their interactions with the adjacent matrix.
Display omitted
INVESTIGATION OF THE ELECTROCHEMICAL ACTIVITY OF AN Al-Cu-Li ALLOY AFTER FRICTION STIR WELDING PROCESS. In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding ...(FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).
Ciprofloxacin (CIP) is a substance that, although it shows benefits to human beings due to its antibiotic activity, is also an organic pollutant of difficult removal from the environment via ...conventional methods. As an alternative, photocatalytic methods may promote the degradation of this molecule to non-toxic compounds. Beyond that, photocatalysts with different morphologies may present diverse performances in the reaction process. In this study, the photoactivity of CeO
2
nanostructured materials (CeNTs and CeO
2
) was evaluated in the photodegradation of CIP, and a possible photodegradation mechanism was proposed. The CeNTs and CeO
2
were obtained from alkaline hydrothermal synthesis and calcination of Ce(NO
3
)
3
.6H
2
O, respectively. Based on the TG, XRD, SEM, and UV–Vis diffuse reflectance characterizations, it was verified that the materials are partially hydrated, constituted by CeO
2
with crystalline cubic fluorite structure and
Fm-3 m
space group, and with morphologies formed by an aggregate of particles (CeO
2
) and a fibrillar morphology (CeNTs). XPS revealed changes in the surface states and Ce
4+
to Ce
3+
ratio, indicating a greater amount of oxygen vacancies in the fibrillar nanostructures. Both showed optical activity in the presence of UV light and a reduction of band gap energies, going from 2.95 for CeO
2
to 2.80 for CeNTs. The CIP removal by photodegradation was 61% and 89% for the CeO
2
and CeNTs, respectively. The higher photocatalytic activity of the CeNTs was attributed to better superficial and optical properties, resulting in an increase in the velocity of photoactivation with the final degradation of CIP being approximately 28% higher than the CeO
2
. Therefore, it was confirmed that the fibrillar morphology can change properties of CeO
2
and increase your applications as photocatalyst.
Graphical abstract
•Microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys.•The friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the ...electrochemical behavior of the different regions investigated.•Galvanic interactions between the coupled welded zones were visualized by SVET and SIET analyses.•Spatially-resolved images of anodic and cathodic sites associated to corrosive attack, evolution of hydrogen and local pH changes were obtained and studied.
In this work, the effects of friction stir welding (FSW) on the microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys have been investigated. Local electrochemical tests supported by surface analytical characterization were used to study the local electrochemical activities developed along the weld zones of the dissimilar alloys. The investigation was carried out on the cross-section of the welded Al alloys. The results showed that the friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the electrochemical behavior of the different regions (HAZ, TMAZ, SZ) formed by the welding process. Scanning vibrating electrode technique (SVET) and micropotentiometry by using an ion-selective microelectrode showed that TMAZ was the zone with the highest electrochemical activity. This zone corresponded to the transition region between the two welded alloys. The high electrochemical activity observed in this region was associated with the effect of welding on the microstructure and, also, with the galvanic coupling between the two alloys, where the alloy AA7050 acted as an anode and the AA2050 as a cathode. Preferential corrosion attack on the AA7050 alloy was also evident.
Display omitted
•Characterization of the near-surface deformed layer (NSDL) in FSWelded 2098-T351.•Spatially resolved electrochemical activity in NSDL obtained by potentiometric SECM.•Mg-enriched bands affect the ...electrochemical behavior of welded areas.•The NSDL has an anodic electrochemical behavior with respect to the bulk material.•Highest activity for Mg2+ dissolution observed in the HAZ of the retreating side.
The development of heterogeneous electrochemical activity in the welded zones of aluminum alloy 2098-T351 by friction stir welding (FSW) associated with the formation of a near-surface deformed layer (NSDL) upon exposure to an aqueous chloride-containing solution was characterized using scanning electrochemical microscopy (SECM) in potentiometric operation. A solid-contact Mg2+ ion-selective microelectrode allowed in situ monitoring of the corrosion reactions sites for magnesium dissolution from different zones of the FSW weld upon exposure to a chloride-containing aqueous environment. In this way, localized corrosion reactions developing in the galvanically coupled joint/heat affected zones (WJ/HAZ) of the weld were detected and imaged with spatial resolution. The most active domains for local Mg2+ concentrations were associated with the HAZ of the retreating side (RS), and these corresponded to Mg oxidation from the Mg-enriched oxide bands in NSDL.
Display omitted
The effects of surface finishing on the corrosion behavior and electrochemical activity of AA2098-T351 (Al–Cu–Li alloy) were investigated on the basis of the correlation between surface chemistry, ...microstructure and electrochemical activity. The alloy was evaluated in the as-received and polished conditions. The morphology of the two types of surfaces was investigated using confocal laser scanning microscopy (CLSM), optical microscopy and optical 3D profilometry. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning microelectrochemical techniques (namely, localized electrochemical impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) in potentiometric mode) were used to examine the electrochemical activity of the surfaces. The results showed that on the as-received surface, the near surface deformed layer (NSDL), which is composed of Mg-rich bands, influenced the corrosion activity of the alloy. Higher electrochemical activity and greater susceptibility to severe localized corrosion were related to the polished surface condition compared to the as-received one.
Display omitted
•Surface finishing effects on chemical activity of 2098-T351 Al–Cu–Li alloy studied using scanning microelectrochemical techniques.•The effect of the near-surface deformed layer (NSDL) on 2098-T351 Al–Cu–Li was investigated for different surface finishes.•A solid contact magnesium ion-selective microelectrode (Mg2+ ISME) employed to monitor Mg2+ distributions over the surfaces.•SVET, LEIS, and SECM in potentiometric operation produced high spatial resolution images of reactive sites on the surfaces.•The surface chemistry, microstructure and electrochemical activity of the alloy with and without NSDL were correlated.
In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005 mol L
−1
NaCl solution. The severe type ...of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Aim
To evaluate the effects of low‐volume resistance training on the physical and functional capacity of older patients with Parkinson's disease.
Methods
A total of 54 patients (aged ≥60 years) were ...randomly divided into two groups: (i) a control group comprising 13 men and 14 women; and (ii) a resistance training group with 14 men and 13 women. The resistance training group, in addition to maintaining their pharmacological treatments, carried out 6 months of resistance training twice a week, whereas the control group maintained their pharmacological treatments. Handgrip strength, flexibility, aerobic endurance, gait speed and balance were assessed in both groups.
Results
After 6 months, patient functionality in the control group was reduced, whereas patients who carried out low training volumes showed significantly improved flexibility (Pre × Post: P = 0.008), aerobic resistance (Pre × Post: P = 0.006), gait speed (Pre × Post: P = 0.006) and balance (Pre × Post: P = 0.043). Significant improvement (P = 0.042) was also observed in right handgrip strength in the resistance training group.
Conclusions
The results of the present study showed that low‐volume resistance training improves the physical capacity of older people with Parkinson's disease. Therefore, we suggest that resistance training be a central component in exercise programs for patients with Parkinson's disease. Geriatr Gerontol Int 2019; 19: 635–640.
PDF
