POtenzialità della tecnica EIS per il rilievo del degrado delle barriere termiche sottoposte a prove di ossidazione ciclica

reserved3Questo lavoro è dedicato allo studio dell’evoluzione dei rivestimenti tipici delle parti calde delle turbine a gas, costituiti da uno strato metallico e da uno ceramico di zirconia parzialmente stabilizzata con ittria, con funzione di barriera termica. Vengono dapprima mostrati i risultati di una campagna sperimentale svolta su campioni invecchiati in prove di ossidazione ciclica a due diverse temperature e sottoposti ad analisi metallografiche per individuare i meccanismi di degrado indotti dall’esposizione alle elevate temperature e dall’azione di ripetuti cicli termici. Viene poi presa in esame la possibilità di applicare una tecnica di controllo non distruttivo (la spettroscopia d’impedenza elettrochimica) per rilevare il grado crescente di danneggiamento. La variazione degli spettri d’impedenza ottenuti ha confermato la sensibilità della tecnica allo spessore dello strato ceramico, alle sue caratteristiche (porosità e microcriccatura) e alla formazione dello strato di ossido all’interfaccia metallo/ceramico. I risultati ottenuti vengono discussi alla luce delle analisi metallografiche quantitative e delle informazioni reperibili in letteratura. Si suggeriscono infine alcune linee di ulteriore sviluppo.A. Lapina; M. Bestetti; C. RinaldiA., Lapina; Bestetti, Massimiliano; C., Rinald

Test Conditions for Pipeline Materials Selection with High Pressure Sour Gas

Acid gases, such as CO2, H2S, and/or sulfur in oil industry's production fluids, can be responsible for both general and localized corrosion, acting with different mechanisms, which depend on chemical and physical properties of the produced fluids. Materials selection for handling such fluids is performed by combining experience with suggestions from standards and regulations. A good deal of knowledge is available to predict corrosion rates for CO2-containing hydrocarbons, but the effect of high H2S pressure is less understood, mainly due to the difficulty of performing laboratory tests in such challenging conditions. For instance, the so-called NACE solution to assess SSC (Sulfide Stress Cracking) susceptibility of steels is a water-based solution simulating production fluids in equilibrium with one bar bubbling H2S gas. This solution does not represent environments where high gas pressure is present. Moreover, it does not take into account the corrosive properties of sulfur and its compounds that may deposit in such conditions. Besides, properties of high pressure gases are intermediate between those of a gas and those of a liquid: high pressure gases have superior wetting properties and better penetration in small pores, with respect to liquids. These features could enhance and accelerate damage, and nowadays such conditions are likely to be present in many production fields. This paper is aimed to point out a few challenges in dealing with high pressure gases and to suggest that, for materials selection in sour service, a better correspondence of test conditions with the actual field conditions shall be pursued

Electrobioremediation of oil spills

Annually, thousands of oil spills occur across the globe. As a result, petroleum substances and petrochemical compounds are widespread contaminants causing concern due to their toxicity and recalcitrance. Many remediation strategies have been developed using both physicochemical and biological approaches. Biological strategies are most benign, aiming to enhance microbial metabolic activities by supplying limiting inorganic nutrients, electron acceptors or donors, thus stimulating oxidation or reduction of contaminants. A key issue is controlling the supply of electron donors/acceptors. Bioelectrochemical systems (BES) have emerged, in which an electrical current serves as either electron donor or acceptor for oil spill bioremediation. BES are highly controllable and can possibly also serve as biosensors for real time monitoring of the degradation process. Despite being promising, multiple aspects need to be considered to make BES suitable for field applications including system design, electrode materials, operational parameters, mode of action and radius of influence. The microbiological processes, involved in bioelectrochemical contaminant degradation, are currently not fully understood, particularly in relation to electron transfer mechanisms. Especially in sulfate rich environments, the sulfur cycle appears pivotal during hydrocarbon oxidation. This review provides a comprehensive analysis of the research on bioelectrochemical remediation of oil spills and of the key parameters involved in the process

Impact of Polarization Reversal during Photoelectrocatalytic Treatment of WWTP Effluents

Photoelectrocatalysis (PEC) has been already proposed as a polishing treatment for wastewater treatment plants (WWTPs) effluents. In this work, the impact of polarization reversal during PEC process has been studied and evaluated on the basis of the removal of organic substance and color, biodegradability of the matrix, and inactivation of the catalyst. Effluents were sampled from a full-scale WWTP and alternatively treated by electrochemical oxidation (EC), photolysis (PL), photocatalysis (PC), photoelectrocatalysis, and photoelectrocatalysis with reverse polarization (PECr). The efficiency and the kinetics of the process, in terms of removal of organic substance and color, were not affected by reverse polarization and very similar results were obtained by PEC and PECr. The biodegradability of the effluents strongly increased both by PECr (RSBR: 0.84 ± 0.07), and by PEC and PL (0.89 ± 0.11, and 0.78 ± 0.02, respectively). In the selected polarization reversal mode (100 s at −0.1 V every 500 s at 4 V, cell voltage), a similar photocurrent loss after PEC and PECr was observed, suggesting no effect on the activity of the TiO2 mesh. This study can serve as a base for future research on polarization reversal to optimize operation parameters and exploit the procedure to preventing fouling and inactivation of the catalyst

Formazione e caratterizzazione di leghe superficiali Zr-Ti ottenute per deposizione magnetron sputtering di strati sottili di Zr su Ti e successivo trattamento a fascio elettronico

La tecnica di bombardamento con fascio pulsato di elettroni a bassa energia ed alta corrente (LEHCPEB LowEnergy High Current Pulsed Electron Beam) permette di modificare lo strato superficiale di superfici metalliche,per esempio migliorando le caratteristiche meccaniche e corrosionistiche dei materiali metallici attraversomodificazioni microstrutturali. La tecnica LEHCPEB unita a quella di deposizione fisica da fase vapore permettedi realizzare leghe superficiali. Scopo del presente lavoro è la caratterizzazione di leghe Ti-Zr ottenute perdeposizione di zirconio con tecnica PVD magnetron sputtering, seguita da trattamento LEHCPEB. Le leghe Ti-Zrsono state studiate mediante diffrazione di raggi X e spettroscopia ottica a scarica a bagliore. Le modifichemorfologiche e di composizione sono state osservate mediante microscopia elettronica a scansione e lecaratteristiche meccaniche sono state valutate con prove di microdurezza strumentata

POTENZIALITÀ DELLA TECNICA EIS PER IL RILIEVO DEL DEGRADO DELLE BARRIERE TERMICHE SOTTOPOSTE A PROVE DI OSSIDAZIONE CICLICA

Questo lavoro è dedicato allo studio dell’evoluzione dei rivestimenti tipici delle parti calde delle turbine a gas, costituiti da uno strato metallico e da uno ceramico di zirconia parzialmente stabilizzata con ittria, con funzione di barriera termica. Vengono dapprima mostrati i risultati di una campagna sperimentale svolta su campioni invecchiati in prove di ossidazione ciclica a due diverse temperature e sottoposti ad analisi metallografiche per individuare i meccanismi di degrado indotti dall’esposizione alle elevate temperature e dall’azione di ripetuti cicli termici. Viene poi presa in esame la possibilità di applicare una tecnica di controllo non distruttivo (la spettroscopia d’impedenza elettrochimica) per rilevare il grado crescente di danneggiamento. La variazione degli spettri d’impedenza ottenuti ha confermato la sensibilità della tecnica allo spessore dello strato ceramico, alle sue caratteristiche (porosità e microcriccatura) e alla formazione dello strato di ossido all’interfaccia metallo/ ceramico. I risultati ottenuti vengono discussi alla luce delle analisi metallografiche quantitative e delle informazioni reperibili in letteratura. Si suggeriscono infine alcune linee di ulteriore svilupp

Biodegradable magnesium coronary stents: Material, design and fabrication

Biodegradable cardiovascular stents in magnesium (Mg) alloys constitute a promising option for a less intrusive treatment, due to their high compatibility with the body tissue and intrinsic dissolution in body fluids. The design and fabrication aspects of this medical device require an integrated approach considering different aspects such as mechanical properties, corrosion behaviour and biocompatibility. This work gathers and summarises a multidisciplinary work carried out by three different research teams for the design and fabrication of Mg stents. In particular, the paper discusses the design of the novel stent mesh, the deformability study of the Mg alloys for tubular raw material and laser microcutting for the realisation of the stent mesh. Although, the results are not fully validated as the device has not been fully tested, they show the feasibility of the used approaches, as the first prototype stents in Mg alloy were produced successfully. © 2013 Copyright Taylor and Francis Group, LLC

Using WiMAX technology to improve volcano monitoring: the WEIRD System

IEEE 802.16 standards (IEEE, 2004; IEEE, 2005), commonly known as WiMAX (Worldwide Interoperability for Microwave Access Forum), is one of the most promising broadband wireless access technology for next generation all-IP networks. This access technology allows reaching high bit rate and covering large areas with a single Base Station (BS). Thanks to these features, IEEE 802.16 opens the way for the use and the introduction of wireless technologies in particular emergency scenarios, like volcano monitoring. Active volcano surveillance is based prevalently on the analysis of geophysical and geochemical parameters gathered by monitoring networks. Of all, seismology is one of the most useful methods for volcano monitoring. In fact, several types of seismic signals, e.g. volcano-tectonic earthquakes (VT), long-period events (LP), volcanic tremor, can occur before and during an eruption. The analysis and interpretation of these seismic signals are a very important task for the volcanic eruption forecasting (Scarpa and Tilling, 1996). WiMAX technology can be applied to provide broadband wireless access in volcano monitoring scenarios, in order to solve all the problems that today limit the possibility to realize a real-time and accurate monitoring of volcanoes activities in emergency situations. In particular, this paper focus on a novel solution, designed within the IST FP6 EU WEIRD (WiMAX Extension to Isolated Research Data networks) Integrated Project, to perform volcano monitoring using the features offered by IEEE 802.16 networks in order to improve transmission of data acquired by temporary seismic stations deployed during emergencies. Tests performed on field demonstrate the advantages offered by the use of WiMAX compared with other commonly used technologies

Using wireless point-to-point connections to improve volcano monitoring: a feasibility study of the WiMAX technology applied to the Campi Flegrei volcanic area (Southern Italy)

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Innovative photoelectrocatalytic water remediation system for ammonia abatement

Ammonia, produced by human and animal activities, contributes to water and soil pollution because it is toxic for aquatic flora and fauna, and responsible for eutrophication. In this work, the photoelectrocatalytic (PEC) oxidation of ammonia is investigated employing a stainless-steel PEC reactor, consisting of a central UV Hg-vapor lamp surrounded by a metallic Ti mesh coated with a photoactive TiO2 film, directly grown by Plasma Electrolytic Oxidation (PEO). The so prepared TiO2 film is characterized by XRD, SEM, UV–vis DRS and IPCE. The PEC reactor operates at 4 V potential drop between the TiO2 coated mesh (photoanode) and the body of the reactor (cathode). The effect of the operating parameters (recirculation flowrate and air bubbling) and type of electrolyte solution (KCl or K2SO4) on the PEC performance are investigated in terms of ammonia conversion and selectivity to nitrite, nitrate and molecular nitrogen. Full ammonia conversion (XNH3) with a selectivity to molecular nitrogen up to 67 % are attained after 12 h in 5 mM KCl electrolyte solution. Nitrite is produced within the first 6 h irradiation and then fully converted into nitrate. By contrast, only a slight XNH3 (ca. 10 %) is observed in K2SO4 electrolyte solution. These results suggest that chlorine has a crucial role in the ammonia PEC oxidation process: photo-generated holes on the photoanode surface can oxidize Cl− to Cl• (electro-induced process), which is a reactive radical able to oxidase ammonia