EFFETTO DELLA SOLLECITAZIONE MECCANICA A FLESSIONE SUL COMPORTAMENTO A CORROSIONE DI LEGHE DI Al STRUTTURALI

The present work reports on the effect of constant bending load on the electrochemical behavior of structural aluminum alloys AA 2024-T3 (Al-Cu-Mg) and AA 7075-T6 (Al-Zn-Mg-Cu). The single cycle anodic polarization curves in 0.6 M NaCl (pH 6.5) were carried out using four-point bent beam specimens (4PBB). Lower propensity to localized corrosion has been indicated for compressive stresses. The effect of tensile stresses on the electrochemical response is more complex and depends on the alloy nature

Ellagic Acid as Green Corrosion Inhibitor: a Necessary Validation

Corrosion of metals is an unavoidable but controllable process. Among techniques developed to slow down or prevent metal deterioration the addition of small amount of inhibitors directly in the corrosive environment is a quite common strategy. In particular, among organic compounds effectively used as adsorption inhibitors (thanks to N, O and/or S atoms that act as anchoring groups for metal surface) only a few percentage belongs to the so called \u201cgreen inhibitor\u201d class. In this field most of the studies employ plant extracts being rich in phytochemical constituents considered to be potential eco-friendly corrosion inhibitors. However, the often extraordinary complexity of crude extracts makes difficult the rationalization of the inhibition mechanism. So, from a purely academic point of view, the study of pure compounds is often encouraged. Among potential green inhibitors our attention has been focused on ellagic acid (EA) that can be obtained by hydrolysis of ellagitannin contained in peels of pomegranate. Ellagic acid is a polyphenol having four phenolic and two lactone groups that should act like two and one couples of equivalent sites, respectively, due to the C2h molecular symmetry. Up to know the corrosion inhibition properties of EA was only marginally studied in literature, both theoretically and experimentally. However some reported results need to be validated because of discrepancies concerning some fundamental chemical physical features of the target acid, like i) solubility in pure water (9 mg/dm3 versus 1.2 g/dm3) and ii) pKa values for the two acid dissociation processes. For this purposes, using UV-Vis absorption spectroscopy, a mainly-aqueous medium was selected to assure homogeneity of the EA-based solution; after that the corrosion inhibition properties of ellagic acid toward mild steel was studied by weight loss measurements (according to ASTM G1 standard practice) and by electrochemical tests. Preliminary results performed in 1% v/v MeOH/H2O mixture with HCl 0.05 M point to potentially interesting inhibition effect even working with 1.0 1910\u20135 M EA (i.e., 3 mg/dm3)

The temperature coefficient of the potential of zero charge of Ag single crystal face electrodes in aqueous electrolyte solution

The temperature coefficient of the potential of zero charge of Ag single crystal electrodes, dEσ₌₀/dT , was measured by recording capacitance curves at different temperatures. Two experimental approaches were adopted: the “continuity” and the “discontinuity” method, consisting in recording curves at different temperatures without and with extraction of the electrode from the solution, respectively. Appreciable differences have been observed. The origin of the differences and their significance are discussed in terms of keeping the appropriate conditions for the electrode/solution interface during the experiments.На основі даних для ємності при різних температурах отримано температурний коефіцієнт потенціалу нульового заряду срібних моно-кристалічних електродів. Застосовано два типи експериментів: метод “неперервності” і “розривності”, що полягає в записі кривих ємності при різних температурах без і з виділенням вкладу електрода в розчині відповідно. Виявлена суттєва різниця в результатах, походження і важливість якої досліджується при відповідних умовах експериментів для поверхні розділу електрод-розчин

Crack Growth Studies in Railway Axles under Corrosion Fatigue: Full-scale Experiments and Model Validation

Abstract Crack initiation and growth in full scale railway axle in A1T mild steel have been studied, under three points rotating bending loading conditions and artificial rainwater as corrosive environment. A surface plastic replication technique has been used along with optical microscopy and Scanning Electron Microscopy to monitor the environment assisted fatigue at various stages.A modified Murtaza and Akid empirical model has been employed to predict the corrosion fatigue crack growth rates and a reasonable agreement has been found between experimental and calculated lifetime

Green Corrosion Inhibitors from Natural Sources and Biomass Wastes

Over the past decade, green chemistry has been emphasizing the importance of protecting the environment and human health in an economically beneficial manner aiming at avoiding toxins and reducing wastes. The field of metallic materials degradation, generally faced by using toxic compounds, found a fertile research field in green chemistry. In fact, the use of inhibitors is a well-known strategy when metal corrosion needs to be prevented, controlled, or retarded. Green inhibitors are biodegradable, ecologically acceptable and renewable. Their valorization expands possible applications in industrial fields other than \u2018waste to energy\u2019 in the perspective of circular economy. Although lot of experimental work has been done and many research papers have been published, the topic of green inhibitors is still an open issue. The great interest in the field expanded the research, resulting in high numbers of tested molecules. However, the most frequently adopted approaches are conventional and, hence, not suitable to fully characterize the potential efficacy of inhibitors. All the mentioned aspects are the object of the present review and are meant as a constructive criticism to highlight the weak points of the green inhibitors field as to re-evaluate the literature and address the future research in the field that still lacks rationalization

Hydroxyapatite-Based Electrodes for Metal Detection in Wastewater

Hydroxyapatite (HAp) is a biocompatible versatile material of formula Ca10(PO4)6(OH)2, insoluble in water within a wide pH range, chemically stable, relatively cheap and largely available. This mineral calcium phosphate has caught attention of scientists working in different fields of applied science, from medical engineering, to catalysis and pollution remediation. For environmental application, the absorbent nature of HAp is, probably, the most valuable feature. In particular, heavy metal retention ability is attributed to ion-exchange (Ca2+/ metal ion), surface adsorption/complexation, dissolution-precipitation mechanism, with single or combined action depending on the metal nature. Combining intrinsic affinities of HAp for metals with ductility of electrochemistry is a valuable route to develop monitoring systems and/or pollution remediation protocols. In doing so, the main obstacle for the exploitation of HAp as electrode materials is its electrical insulation nature. To overcome this limitation combination with conductive substrate is necessary, preparing either blends or composite materials. In this context, a series of carbon-containing hydroxyapatite composites (C-HAp) have been prepared by co-precipitation synthesis, by varying the conductive carbon source. The prepared materials have been characterized by various physical-chemical techniques (FT-IR spectroscopy, XRPD, TEM-EDX, N2-adsorption/desorption analyses) and the electrical conductivity has been determined as a function of the carbon source. The most promising C-HAp composites have been used as electrode substrates to quantify some of the common heavy metals found in waste water from urban and/or industrial sites (e.g., Pb2+, Cd2+, Cu2+, Zn2+) using cyclic and differential voltammetry techniques. The sensitivity of C-HAp electrodes was compared with that of glassy carbon ones, chosen as reference material. Different electrode geometries have been taken into consideration (C-HAp powder pressed into a cavity electrode, or free-standing C-HAp one). The work is still in progress and among possible alternative routes we are going to prepare directly HAp-based electrodes by in situ electrodeposition of calcium phosphate on low cost electron collectors such as steel. The final aim is to employ the HAp-based electrode as cathode in microbial fuel cells that could act as sensors for the on-line detection of metal traces in the treated wastes

Atomically dispersed Pt-N-4 sites as efficient and selective electrocatalysts for the chlorine evolution reaction

Chlorine evolution reaction (CER) is a critical anode reaction in chlor-alkali electrolysis. Although precious metal-based mixed metal oxides (MMOs) have been widely used as CER catalysts, they suffer from the concomitant generation of oxygen during the CER. Herein, we demonstrate that atomically dispersed Pt-N-4 sites doped on a carbon nanotube (Pt-1/CNT) can catalyse the CER with excellent activity and selectivity. The Pt-1/CNT catalyst shows superior CER activity to a Pt nanoparticle-based catalyst and a commercial Ru/Ir-based MMO catalyst. Notably, Pt-1/CNT exhibits near 100% CER selectivity even in acidic media, with low Cl- concentrations (0.1M), as well as in neutral media, whereas the MMO catalyst shows substantially lower CER selectivity. In situ electrochemical X-ray absorption spectroscopy reveals the direct adsorption of Cl- on Pt-N-4 sites during the CER. Density functional theory calculations suggest the PtN4C12 site as the most plausible active site structure for the CER