Synthesis and Characterization of Ti-Nb Alloy Films Obtained by Magnetron Sputtering and Low-Energy High-Current Electron Beam Treatment.

The aim of the present work is to investigate the synthesis of Ti-Nb alloy films obtained by the physical vapor deposition (PVD) magnetron sputtering of Nb films on Ti substrates, followed by low-energy high-current electron beam (LEHCEB) alloying treatment. Ti-Nb alloys were synthetized under two different regimes, one by varying the deposited amount of Nb (from 25 to 150 nm) and treating samples with low applied voltages and a number of pulses (three pulses at either 20 or 25 kV), the second by setting the amount of Nb (100 nm) and alloying it at a higher applied voltage with a different number of pulses (from 10 to 50 at 25 and 30 kV). The synthetized Ti-Nb alloys were characterized by XRD and GDOES for phase identification and chemical composition; SEM and optical microscopy were employed for morphology evaluation; compositional investigation was done by EDS analysis and mechanical properties were evaluated by microindentation tests. LEHCEB treatment led to the formation of metastable phases (α', α″ and ß) which, together with the grain refinement effect, was responsible for improved mechanical properties.

Improving the Corrosion Resistance of Wrought ZM21 Magnesium Alloys by Plasma Electrolytic Oxidation and Powder Coating.

Plasma Electrolytic Oxidation (PEO) was applied to extruded ZM21 Mg alloys to improve their corrosion resistance in a chloride-containing environment. PEO was carried out in DC mode and voltage control in a fluoride-free electrolyte. Potentiodynamic polarization tests in 3.5 wt.% NaCl aqueous solution and neutral salt spray (NSS) tests were carried out. Microstructural and profilometric characterization, as well as NSS tests were performed in different conditions: (i) bare ZM21, (ii) PEO-treated ZM21, (iii) powder-coated ZM21 (without PEO interlayer), and (iv) PEO-treated ZM21 with powder coating top layer (carboxyl-functionalized polyester resin). The PEO + powder coating double layer was identified as the best-performing corrosion protection.

Photoelectrocatalysis on TiO2 meshes: different applications in the integrated urban water management.

Recently, among AOPs, photoelectrocatalysis (PEC) on TiO2 is gaining interest. In this study, five different real waters sampled in four different points of the integrated urban water management (IUWM) system were tested with PEC and UV alone, for comparison. This work aims to verify the effect of the PEC suggesting the optimal position in IUWM system where the PEC should be located to obtain the best performance. In groundwaters (GWs), PEC effectively removed atrazine-based compounds (> 99%), trichloroethylene, and perchloroethylene (96%), after 15 min of reaction time. However, given the low concentrations of emerging compounds, the synergistic effect of UV radiation with the catalyst and with the polarization of the mesh was not visible, with very few differences compared with the results obtained with UV alone. Pharmaceutical industrial wastewater (IWW) showed a significant increase in biodegradability after 2 h, both if subjected to PEC or UV (200%), despite the absence of COD removal. The PEC applied on IWW from a sewage sludge treatment plant allowed to effectively remove the COD (39.6%) and increase the biodegradability (300%). Good results in terms of COD removal (33.9%) and biodegradability increase (+900%) were also achieved testing PEC on wastewater treatment plant effluent. Except for GWs, PEC allowed significant EEO savings respect to UV alone (76.2-99.1%).

Decolorization and biodegradability of a real pharmaceutical wastewater treated by H2O2-assisted photoelectrocatalysis on TiO2 meshes.

In recent years, photoelectrocatalysis (PEC) for the treatment of industrial wastewaters (IWWs) has been repeatedly proposed. However, despite the number of tests reported in literature, only a few of them were conducted on real IWWs. In this study, real pharmaceutical IWWs showing an intense recalcitrant color were treated by PEC and H2O2-assisted PEC (UV/TiO2/Bias and UV/H2O2/TiO2/Bias, respectively) on TiO2 meshes having sub-micrometric features obtained by Plasma Electrolytic Oxidation. Photolysis (UV), chemical oxidation (H2O2) and H2O2-assisted photolysis (UV/H2O2) were tested in the same reactor for comparison. The configuration UV/H2O2/TiO2/bias showed the best results in term of decolorization efficiency and rate, where decolorization was 55 % (single-step H2O2 dosing) and 44 % (three-step H2O2 dosing), after 2 h of contact time. In the same contact time, UV and UV/TiO2/Bias processes did not give decolorization. A more effective COD removal was measured for the PEC processes, UV/H2O2/TiO2/Bias (-24 %) and UV/TiO2/Bias (-20 %), while COD removal by UV was almost 0 %. Correspondingly, the SOUR values showed that PEC combined with a single-step H2O2 dosage was the most effective configuration, leading to the highest biodegradability of the treated IWW with respect to the other processes. The energy consumption analysis demonstrated that PEC+H2O2 (single-step dosage) optimized energy costs.

Sustainable Hypersaline Microbial Fuel Cells: Inexpensive Recyclable Polymer Supports for Carbon Nanotube Conductive Paint Anodes.

Microbial fuel cells are an emerging technology for wastewater treatment, but to be commercially viable and sustainable, the electrode materials must be inexpensive, recyclable, and reliable. In this study, recyclable polymeric supports were explored for the development of anode electrodes to be applied in single-chamber microbial fuel cells operated in field under hypersaline conditions. The support was covered with a carbon nanotube (CNT) based conductive paint, and biofilms were able to colonize the electrodes. The single-chamber microbial fuel cells with Pt-free cathodes delivered a reproducible power output after 15 days of operation to achieve 12±1 mW m-2 at a current density of 69±7 mA m-2 . The decrease of the performance in long-term experiments was mostly related to inorganic precipitates on the cathode electrode and did not affect the performance of the anode, as shown by experiments in which the cathode was replaced and the fuel cell performance was regenerated. The results of these studies show the feasibility of polymeric supports coated with CNT-based paint for microbial fuel cell applications.

Influence of ECAP process on mechanical and corrosion properties of pure Mg and ZK60 magnesium alloy for biodegradable stent applications.

Equal channel angular pressing (ECAP) was performed on ZK60 alloy and pure Mg in the temperature range 150-250 °C. A significant grain refinement was detected after ECAP, leading to an ultrafine grain size (UFG) and enhanced formability during extrusion process. Comparing to conventional coarse grained samples, fracture elongation of pure Mg and ZK60 alloy were significantly improved by 130% and 100%, respectively, while the tensile strength remained at high level. Extrusion was performed on ECAP processed billets to produce small tubes (with outer/inner diameter of 4/2.5 mm) as precursors for biodegradable stents. Studies on extruded tubes revealed that even after extrusion the microstructure and microhardness of the UFG ZK60 alloy were almost stable. Furthermore, pure Mg tubes showed an additional improvement in terms of grain refining and mechanical properties after extrusion. Electrochemical analyses and microstructural assessments after corrosion tests demonstrated two major influential factors in corrosion behavior of the investigated materials. The presence of Zn and Zr as alloying elements simultaneously increases the nobility by formation of a protective film and increase the local corrosion damage by amplifying the pitting development. ECAP treatment decreases the size of the second phase particles thus improving microstructure homogeneity, thereby decreasing the localized corrosion effects.

Microstructure, texture evolution, mechanical properties and corrosion behavior of ECAP processed ZK60 magnesium alloy for biodegradable applications.

Ultra-fine grained ZK60 Mg alloy was obtained by multi-pass equal-channel angular pressing at different temperatures of 250°C, 200°C and 150°C. Microstructural observations showed a significant grain refinement after ECAP, leading to an equiaxed and ultrafine grain (UFG) structure with average size of 600nm. The original extrusion fiber texture with planes oriented parallel to extrusion direction was gradually undermined during ECAP process and eventually it was substituted by a newly stronger texture component with considerably higher intensity, coinciding with ECAP shear plane. A combination of texture modification and grain refinement in UFG samples led to a marked reduction in mechanical asymmetric behavior compared to the as-received alloy, as well as adequate mechanical properties with about 100% improvement in elongation to failure while keeping relatively high tensile strength. Open circuit potential, potentiodynamic and weight loss measurements in a phosphate buffer solution electrolyte revealed an improved corrosion resistance of UFG alloy compared to the extruded one, stemming from a shift of corrosion regime from localized pitting in the as-received sample to a more uniform corrosion mode with reduced localized attack in ECAP processed alloy. Compression tests on immersed samples showed that the rate of loss of mechanical integrity in the UFG sample was lower than that in the as-received sample.

Engineered fabrication of ordered arrays of Au-NiO-Au nanowires.

In the present paper, a novel method to fabricate ordered arrays of Au/NiO/Au nanowires is described, with the aim of filling the gap between the fundamental study of the electrical properties of scattered single nanowires and the engineered fabrication of nanowire arrays. This approach mainly consists of the following steps: (a) electrodeposition of Au/Ni/Au nanowires into an ordered porous anodic aluminum oxide template; (b) mechanical polishing of the sample to expose the gold tips of Au/Ni/Au nanowires to the template surface; (c) in situ annealing of the Au/Ni/Au nanowires without removing the template. The resulting structure consists in an ordered array of Au/NiO/Au nanowires slightly protruding out of a flat aluminum oxide template. Unlike current approaches, with the described method it is not necessary to remove the template in order to oxidize the middle metal, thus allowing the availability of an entire set of metal/oxide/metal nanowires ordered in a two-dimensional matrix and where single heterojunctions can be accessed individually.