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Various paths of equal channel angular pressing (ECAP) and conventional post-deformation via forging and rolling were performed to improve the mechanical properties (particularly, the strength and hardness) of a copper-free silver alloy. The microstructure was investigated with optical and scanning electron microscopy. The primary grain size of approximately 130 μm was significantly refined to ultrafine-grained (UFG) conditions with mean grain sizes of 0.6 μm and 0.5 μm via ECAP and ECAP with forging and rolling, respectively. The remarkable improvement of the mechanical properties was confirmed via hardness measurements and tensile and compression tests. ECAP and subsequent forging and rolling increased the initial hardness and tensile yield strength by +234% and +355%, respectively. Furthermore, ECAP led to a much more homogeneous hardness distribution over the entire cross-sections of the bars. The thermal stability of the UFG material at room temperature, 100 °C, and 150 °C was maintained for at least 27 months, 1000 h and 4 h, respectively. Finally, the UFG state exhibited a better tarnishing resistance than the coarse-grained state. Thus, ECAP can overcome the most significant weaknesses of lean, silver-based alloys (i.e. poor mechanical and tarnishing properties), thereby creating opportunities for their wider use.

The great interest of the electrochemical industry toward materials that exhibit high electrocatalytic activity and long service-life in electrolytic processes has constantly prompted fundamental research, enhancing the understanding of electrode behavior and the improvement of their performance. One of the most important class of industrial devices is represented by the so-called DSAs, which consist of an electrocatalytic oxide film (usually based on RuO2 and/or IrO2) deposited on a suitable metal support (titanium). To increase the stability of the material, other oxides (TiO2 ,S nO2, etc.) are added to the electrocatalytic one, with the double purpose of increasing the corrosion resistance of the coating and of diluting the main oxide (to minimize the production costs). In this work, mixtures of 35 mol% IrO2 ‐6 5 mol% TiO2 deposited on titanium supports have been studied by ex-situ (RBS, XRD, ERDA, AFM) and on-site (CV) techniques. Electrodes prepared by an updated sol-gel method and reactive sputtering, at two different temperatures (350 and 450 ◦ C), were investigated with the aim of correlating structural information with electrochemical performances, in terms of number of active electrocatalytic iridium sites. Based on roughness indexes, morphological properties, and of data obtained by nuclearmethodsforsurfaceanalysisandcyclicvoltammetry,thebehaviorofiridiumsiteshasbeendiscussed,attemptingaqualitative distinction of roles of roughness and intrinsic catalytic activity in a model-electrochemical reaction, like oxygen evolution reaction. Sputtered samples appear, in general, more compact than sol-gel ones, and a low temperature of pyrolysis favours a more extended electroactive surface. The study of OER demonstrates that the kinetics of gas evolution proceeds via the electrochemical oxide formation pathway (Volmer-Heyrovsky mechanism) on all samples.

The corrosion properties of the nickel–aluminium bronze (NAB) in aqueous chloride media were investigated at different pHs by using linear potential sweep voltammetry and scanning electron microscopy. The NAB electrochemical behaviour was dependent on the solution pH, due to the different stabilities of the phases present within its microstructure. In particular, at solution pHs higher than 4.0 the NAB oxidation was driven by the dissolution of the copper-rich ?-phase, whereas at pH values lower than 4.0 its anodic behaviour was controlled by the oxidation of the iron-, nickel- and aluminium-rich ?I-, ?II- and ?IV-phases. Furthermore, a kinetic model for the NAB oxidation, in neutral chloride solutions, was developed on the basis of the observed behaviour, i.e., order of reactions of NAB with respect to protons and chloride. Finally, considering the high affinity of benzotriazole for copper, the corrosion performance of NAB was studied in the presence of the inhibitor in neutral (pH of 6.2) and acidic (pH of 3.5) chloride solutions, where NAB exhibited different anodic behaviours.

This work demonstrates the potential to assess Ni(II) concentration in neutral and acidic chloride environments on a boron-doped diamond electrode, without the introduction into the solution of an external chelating agent or markedly raising the pH. The nickel-ion quantification was achieved in solutions with pH values ranging from 8 to 4 using the electrochemical response associated with the Ni(II)/Ni(III) transition on a bare boron-doped diamond electrode. The associated electrochemical reaction was determined to be sensitive to the pH with a dependence relying on a proton stoichiometric number of 0.5 per mole of electrons. The detection protocol consisted of a reagentless electrodeposition of Ni in neutral or acidic solutions followed by oxidation to Ni(II) using differential pulse anodic voltammetry. This allowed the nickel-ion quantification with a limit of detection of 26.1 μM and a linearity over the concentration interval from 10 to 500 μM in a solution pH of 6.2. The regeneration of the pristine electrode surface was also achieved in the sample solution with an electropolishing treatment by holding the applied potential at +1.3 V vs. Ag/AgCl for 30–240 s, thus allowing a fast and efficient surface recovery.

Corrosion induced structural failures continue to be a costly problem in many industrial situations, and the development of robust corrosion sensing systems for structural health integrity monitoring is still a demanding challenge. The applicability of corrosion monitoring of copper alloys using a boron-doped diamond electrode (BDD) has been performed based on determination of copper ions within localised corrosion microenvironments. The electrochemical behaviour of copper ions on the BDD electrode surface were first reported in details in 0.60 M NaCl aqueous solution, and the results revealed that the electrochemical processes of copper ions on the BDD electrode proceed as two successive single electron transfer steps producing two well-separated pairs of peaks in cyclic voltammograms in the chloride ion containing electrolyte solutions. Compared with perchlorate and sulphate ions, chloride ions were observed with a significant stabilization effect on copper ions via the formation of CuCl2- complex, thus having two well-separated pairs of peaks in the obtained cyclic voltammograms on the BDD electrode in the chloride ion electrolyte solution. The apparent rate constant for the redox couple of Cu2+/Cu+ in chloride ion electrolyte was determined as 0.94 × 10–6 cm s–1 by using quasi-steady polarisation technique, thus indicating a quasi-reversible electron transfer process of Cu2+/Cu+ redox couple. Moreover, differential pulse voltammetric results exhibited the BDD electrode is promising for corrosion monitoring of copper alloys with an excellent relationship between peak current and concentration of copper ions without significant interference from the commonly presented metal ions within the simulated marine corrosion environments.

a b s t r a c t In the present work, the electrolytic process of diluted aqueous chloride solutions was investigated at Ti/RuO2·2SnO2 and Ti/Pt electrodes, at different values of current density, temperature and electroly- sis time. The time evolution of chlorine-related species (i.e., active chlorine (dissolved Cl2, HClO, OCl − ), chlorite, chlorine dioxide, chlorate and perchlorate) was investigated in order to establish whether their formation and consumption was related to either chemical or electrochemical path of reactions. The estimated Faradic efficiencies demonstrated the better catalytic activity of the Ti/RuO2·2SnO2 electrode towards the chlorine evolution reaction with respect to the Ti/Pt anode, and the key-role played by the temperature, which reflects the different activation energies of the two competing electrochemical reac- tions, i.e., chloride and water oxidations. The concentration trends of chlorate and perchlorate indicated that the electrochemical route was responsible for their presence in the bulk solution, instead of a chem- ical path. The low concentration levels assessed for chlorites throughout the tests did not suggest the preponderance of the chemical over the electrochemical depletion process; however, further potentio- dynamic tests suggested their high reactivity towards both anodic and cathodic surfaces, thus suggesting that the electrochemical path of depletion could prevail over the chemical. Conversely, due to a solution pH unfavourable to the stability of chlorine dioxide, its low concentration level was associated with a chemical depletion route.

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)2 electrode prepared by potential cycling of a Ni electrode in 1 M NaClO4. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH3 rather than NH4+ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)2 is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule. Keywords: Electrochemical ammonia removal, Nickel electrode, Nickel hydroxide, Nitrate formation, Urine treatment

The electrochemical oxidation of ammonia (NH4+/NH3) in sodium perchlorate was investigated on IrO2 electrodes prepared by two techniques: the thermal decomposition of H2IrCl6 precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(111) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.