Synthesis of a Cr-Cu surface alloy using a low-energy high-current electron beam

A Cr-Cu surface alloy is synthesized using successive operations of Cr film deposition followed by mixing in a melted phase with the Cu substrate by a low-energy, high-current electron beam (LEHCEB). The parameters of LEHCEB are as follows: electron energy 20–30 keV and pulse duration 2–4 μs. Depending on the LEHCEB energy density, the concentration of Cr in the alloy is in the range from 60 to 20 at.%. The alloy microstructure has been analyzed, and its morphology is shown to represent nanosized chromium particles measuring 10–30 nm uniformly distributed in the copper matrix. The synthesized Cr-Cu surface alloys demonstrate a more than a factor of 3 a decrease in wear coefficient, which is nearly as low as the wear coefficient of Cr coatings. Some defects such as networks of cracks and pores, are observed in the lengthy regions of chromium. They are attributed to the tensile thermal stresses taking place during solidified melt cooling due to a large difference between the thermal expansion coefficients of copper and chromium. Keywords: Surface alloy, Cr-Cu alloy, Pulsed electron beam, Wear resistance, Nanostructurin

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

Contribution to the study of uniform corrosion by means of the maximum entropy production rate principle

The content of the article is about the principle of maximum entropy production rate applied to the description of uniform corrosion. The corroding metal surface is described as an ensemble of microcells randomly moving on the surface. The theory allows to calculate the ratio of the anodic to cathodic areas, as well as the corrosion current, under the hypothesis that the concentration overvoltages and the ohmic drops are both negligible

Optimization of heterogeneous photoelectrocatalysis on nanotubular TiO2 electrodes: Reactor configuration and kinetic modelling

Photoelectrocatalytic degradation of target molecules on nanotubular titanium dioxide (TiO2) immobilized on meshed conductive substrate was assessed by measuring the photoelectrochemical response (i.e., generated photocurrent) as indicator of TiO2performance. Furthermore, a simple and reliable methodology for degradation modelling and laboratory reactor optimization has been proposed and validated. Nanotubular TiO2was grown by anodic oxidation of Ti wire meshes and characterized by ESEM and XRD. Immobilized TiO2on Ti wire mesh was used as photo-anode under UV irradiation (254 nm) and subjected to electrical polarization. The photocurrent was monitored in a three-electrode cell, by varying polarization voltage, TiO2electrode relative positioning to the UV source (distance), and concentration of a model azo dye compound (Reactive Red 243, RR243). Photoelectrochemical response was modelled as a function of operating parameters and guidelines for photoreactor configuration were identified. Optimized batch photoreactor configuration (1.8 L) was used for degrading a 25 mg Lâ1RR243 aqueous solution, achieving 90% decolorization in 45 min and 60% mineralization in 100 min. Decolorization kinetics were effectively described by means of a modified Langmuir-Hinshelwood model based on experimentally measured photocurrents, accounting for the dynamic behaviour of the process due to the change in solution transmittance over time determined by the degradation of target compounds

Processi di ossidazione avanzata (AOP) per il trattamento di acque reflue: tecnologie consolidate e recenti sviluppi

L’esigenza di trattamenti di depurazione delle acque in grado di rimuovere composti organici caratterizzati da elevata stabilità chimica e bassa biodegradabilità ha suscitato notevole interesse nei confronti dei processi di ossidazione avanzata (AOP). Tali trattamenti si basano sull’ossidazione chimica degli inquinanti per mezzo di specie radicaliche a elevata reattività e permettono di degradare un’ampia gamma di composti organici in intermedi di peso molecolare inferiore, potenzialmente fino alla loro completa mineralizzazione. Nel seguente articolo sono descritti i meccanismi di reazione dei processi di ossidazione avanzata e sono classificate le principali tecnologie in funzione delle modalità di generazione delle specie ossidanti. Successivamente, si riportano alcuni casi studio di processi di ossidazione avanzata finalizzati al trattamento di acque reflu

Growth of carbon nanotubes on aluminium foil for supercapacitors electrodes

A new approach for the preparation of carbon nanotubes (CNTs) electrode is proposed in the present work. Multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapour deposition on aluminium strips pre-plated with a nickel thin film as the catalyst. The CNTs were characterized by scanning and transmission electron microscopy, Brunauer–Emmett–Teller surface area measurement and thermogravimetric analysis. The nickel-plated aluminium foil with a layer of CNTs was further characterized for an assessment of its electrochemical behaviour as electrode for supercapacitors. The specific capacitances of the electrode, as derived from cyclic voltammetry measurement at 0.1 V s-1 scan rate, was found to be 54 and 79 F g-1 in aqueous and organic electrolytes, respectively, in line with the highest reported values for either activated carbon or MWCNTs electrodes. Further evidence in support of the viability of the present approach for the preparation of a CNTs electrode was obtained from electrochemical impedance spectroscop

Composite Supercapacitor Electrodes by Electrodeposition of MnO2 on MWCNT Felt Directly Grown on Aluminum

Manganese oxide \ carbon nanotube (CNT) thin film electrodes were fabricated by direct growth of a carbon nanotube layer on aluminum substrate (i.e. a commercially viable material for use as current collector) by chemical vapor deposition, in the presence of an electrochemically deposited thin film nickel catalyst, followed by anodic electrodeposition of MnO2. A proof of concept of this approach is demonstrated showing that the fabrication process, even in its simplest and unsophisticated implementation –notably without any deliberate effort to control the CNT growth arrangement and consequently the composite microstructure– allows the preparation of MnO2/CNT/Al prototype electrodes having almost a three-fold increase in capacitance compared to MnO2/Ni electrodes and, more significantly, comparing favorably with composite electrodes of similar design and fabrication. MnO2/CNT/Al electrodes ensured also improved cyclic stability compared to the reference case of MnO2/Ni electrodes. The proposed scheme is an effective procedure for the fabrication of thin film composite MnO2/CNT/Al electrodes, which may be amenable to significant improvements by tailoring thickness and microstructure of the CNT scaffold and manganese oxide film. Furthermore, a similar process scheme, may be proposed for the fabrication of active electrodes of different scopes with a proper choice of the substrate