Hybrid ceramic self-healing coatings for corrosion protection of Al alloys in 3% NaCl solution

This work focuses on the development of sol–gel self-healing coatings for corrosion protection of Al alloys. The use of this method will help to reduce the costs associated with the coating as well as their environmental impact. Coatings were made of a titania matrix loaded with microparticles of poly(vinyl-alcohol) (PVA) containing cerium nitrate as an inhibitor. The PVA particles dissolve in water, so that the cerium nitrate deposits on the Al surface subjected to corrosion. The PVA microspheres were made via the emulsion method, and then loaded with cerium nitrate. The amount of cerium nitrate loaded in the microspheres was evaluated using UV–Vis. As a second step, the titania coating with embedded PVA microspheres loaded with cerium nitrate was deposited on an AA6082 substrate via a sol–gel route. The corrosion resistance of the coated samples was tested in NaCl solution. The coating microstructure, before and after the corrosion tests, was analysed with the use of an SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy), while the corrosion resistance was investigated by EIS (electrochemical impedance spectroscopy). The results showed that the coatings were uniform and compact. They also showed the ability of the hybrid TiO2-based coating to provide protection for the AA6082 from corrosion. The coatings with an induced defect (scratch) were also analysed, and the EIS analysis of the coatings over time showed an increase in resistance, confirming the ability of the coating to heal itself

Extra-low dosage graphene oxide cementitious nanocomposites: a nano- to macroscale approach

The impact of extra-low dosage (0.01% by weight of cement) Graphene Oxide (GO) on the properties of fresh and hardened nanocomposites was assessed. The use of a minimum amount of 2-D nanofiller would minimize costs and sustainability issues, therefore encouraging the market uptake of nanoengineered cement-based materials. GO was characterized by X-ray Photoelectron Spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), and Raman spectroscopy. GO consisted of stacked sheets up to 600 nm × 800 nm wide and 2 nm thick, oxygen content 31 at%. The impact of GO on the fresh admixtures was evaluated by rheology, flowability, and workability measurements. GO-modified samples were characterized by density measurements, Scanning Electron Microscopy (SEM) analysis, and compression and bending tests. Permeability was investigated using the boiling-water saturation technique, salt ponding test, and Initial Surface Absorption Test (ISAT). At 28 days, GO-nanocomposite exhibited increased density (+14%), improved compressive and flexural strength (+29% and +13%, respectively), and decreased permeability compared to the control sample. The strengthening effect dominated over the adverse effects associated with the worsening of the fresh properties; reduced permeability was mainly attributed to the refining of the pore network induced by the presence of GO

Joint Observation of the Galactic Center with MAGIC and CTA-LST-1

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations

Sintesi e caratterizzazione di garnet Y3-xGdxFe5O12 per dispositivi a microonde

Le ferriti per applicazioni a microonde sono utilizzate in un’estesa banda di frequenza (1-100 GHz), nell’industria automobilistica, della comunicazione e nei sistemi di rilevazione radar. I garnet Y3Fe5O12 (YIG) e Y3-xRxFe5-yMyO12 (R= Gd, Sm, Dy, Ho, Er, Yb ; M=Al, Ga, Sc) rientrano in questa famiglia e vengono principalmente utilizzati in dispositivi a microonde come isolatori, circolatori e sfasatori. I requisiti principali per l’utilizzo di questi materiali sono: magnetizzazione di saturazione (4pMs) controllata (0,2<g4pMs/w<0,6, con g rapporto giromagnetico e w frequenza di lavoro) e stabile nell’intervallo di temperature d’esercizio, larghezza di linea di risonanza ferromagnetica (DH) minore di 100 Oe. Le prestazioni dipendono principalmente dalla composizione chimica e dalla microstruttura. I materiali a singola fase, ad elevata densità e caratterizzati da una microstruttura in cui la distribuzione delle dimensioni dei grani sia compresa tra 1 e 30 mm, mostrano eccellenti proprietà. Da un’estesa ricerca bibliografica risulta che nella letteratura internazionale sono presenti diversi lavori riguardanti la preparazione di YIG e R3Fe5O12 mediante la tecnica di coprecipitazione. Tuttavia non è stato pubblicato nessun articolo relativo alla preparazione di garnet in cui l’ittrio è parzialmente sostituito da cationi delle terre rare (R). Quindi, in questo progetto di dottorato, polveri di garnet Y3-xGdxFe5O12 (x = 0, 0,4, 0,5, 0,9) sono state ottenute con la tecnica inversa di coprecipitazione, utilizzando soluzioni dei nitrati metallici stechiometriche [Fe/(Y+Gd)=1,67] e con diversi rapporti Fe/(Y+Gd), allo scopo di individuare i parametri di processo per la produzione di ferriti con caratteristiche ottimali per la realizzazione di sfasatori. La composizione reale dei campioni è stata determinata tramite ICP, ed è stato trovato che i rapporti atomici variano nell’intervallo 1,20< Fe/(Y+Gd)< 1,89. Sulla base dei risultati dell’analisi termica, i prodotti co-precipitati sono stati calcinati tra 600°C e 1200°C e successivamente analizzati attraverso XRD. Misure condotte ad alta temperatura (HT-XRD) hanno mostrato che, per tutti i campioni, la cristallizzazione della fase cubica del garnet avviene intorno a 700°C insieme a quella dell’ortoferrite di ittrio (YFeO3) e a-Fe2O3. Nei campioni ricchi in ferro ed in quelli stechiometrici queste fasi indesiderate, presenti in piccola quantità, scompaiono se calcinati a 1200°C. Se il rapporto Fe/(Y+Gd) è minore del valore stechiometrico, le polveri cotte a 1200°C sono invece costituite dal garnet cubico e dall’ortoferrite di ittrio, in accordo con il diagramma di fase binario Y2O3-Fe2O3. La sinterizzabilità delle polveri calcinate a 1200°C è stata studiata attraverso misure dilatometriche. Sulla base di questi risultati le polveri, formate per pressatura uniassiale a 90 MPa, sono state sinterizzate in aria a 1450°C-1470°C. Le densità ottenute variano tra 88-99% del valore teorico, in funzione principalmente della temperatura di sinterizzazione. La microstruttura dei campioni è stata osservata al SEM. Risulta che tutti i sinterizzati hanno una microstruttura uniforme, omogenea nonostante le deviazioni delle composizioni dal valore stechiometrico e costituita da grani poligonali, le cui dimensioni variano tra 1 e 30 mm. La dimensione media dei grani varia tra 3,0-13,5 mm, in funzione della temperatura di sinterizzazione, del rapporto Fe/(Y+Gd) e della concentrazione della soluzione dei nitrati metallici. I materiali preparati sono stati infine caratterizzati attraverso misure di DH. I valori variano tra 50,7 e 74,2 Oe e sono più elevati nei campioni con maggior contenuto di gadolinio.Microwave ferrites are applied on a broad band (1-100 GHz) in automotive, communication industry and in radar systems. Y3Fe5O12 (YIG) and Y3-xRxFe5-yMyO12 (R= Gd, Sm, Dy, Ho, Er, Yb ; M=Al, Ga, Sc) garnets are microwave materials used in microwave devices such as isolators, circulators and phase shifters. Suitable materials for microwave components are those which have controlled saturation magnetization (4pMs) (0,2<g4pMs/w<0,6, where g is the gyromagnetic ratio and w is the frequency of operation), temperature stability of 4pMs and low ferromagnetic resonance line width (DH<100 Oe). Microstructural features and the chemical composition, controlled by powder production process, of these ferrimagnetic ceramics strictly affect their performances. Excellent characteristics are obtained for single phase and high density materials in which grain size ranging from 1 to 30 mm. To our knowledge, in the international literature, excluding patents, only few papers concerning Gd-substituted YIG ceramics obtained via chemical routes have been published, none of them dealing with coprecipitation technique. In this work, pure and Gd-substituted yttrium iron garnet powders were obtained by coprecipitation reverse strike technique using either stoichiometric [Fe/(Y+Gd)=1,67] and non stoichiometric metal nitrates solutions. The actual composition of all samples was determined by Induced Coupled Plasma spectroscopy (ICP). Dried coprecipitates were calcined between 600°C and 1200°C, on the basis of thermal analysis results and then analysed by XRD. The crystallisation of the cubic garnet phase occurred for all samples around 700°C along with yttrium orthoferrite (YFeO3) and a-Fe2O3, as shown by high temperature XRD measurements (HT-XRD). The extra phase/s disappeared when stoichiometric samples and samples richer in iron, either pure and Gd-substituted, were heated at 1200°C. On the other hand, in iron deficient samples, calcined at 1200°C or above, the yttrium orthoferrite phase persists, according to the Y2O3-Fe2O3 binary phase diagram. Powders calcined at 1200°C were uniaxially formed at 90 MPa and, according to thermal dilatometry, sintered in air at 1450-1470°C for 8 h. The density ranged from 88 to 99% of the theoretical one, depending mainly on sintering temperature. For all specimens the resulting microstructure is uniform and made up of fine polygonal grains whose average size ranges from 3,0-13,5 mm, changing with sintering temperature, Fe/(Y+Gd) ratio and concentration of starting solution. Measurements of ferromagnetic resonance line width (DH) were performed. The values ranging from 50,7 to 74,2 Oe, are higher for samples with a major Gd content

Sustainable phase change materials (PCMs): waste fat from cooking pork meat confined in polypropylene fibrous mat from waste surgical mask and porous bio-silica

In this article, waste fat deriving from the cooking process of pork sausages has been studied as a sustainable phase change material (PCM). The waste fat is composed of saturated and unsaturated fatty acids and presents melting point and melting enthalpy values of 32 &amp; DEG;C and 20 J/g respectively. The BioPCM was confined in two different hosts, namely (i) biosilica (diatomite) and (ii) polypropylene nonwoven mat coming from surgical mask filter waste. Both hosts are effective in entrapping high quantity of BioPCM (i.e. 65-75%) maintaining its physical and thermal properties. A simplified analytical model has been developed to analyze the use of the BioPCM in building passive cooling application simulating the thermal behavior of a building wall containing the BioPCM confined in the hosts. A transmitted thermal power per unit area of 10.2 W/m2 was obtained. This value is 37% less of transmitted thermal power calculated for the wall without the BioPCM (16.2 W/m2), confirming that waste cooking fat can be an effective eco-sustainable solution in a good practice of circular economy

Residual stress measurements on CrN/Cr/CrN multilayer PVD coatings

Hard physical vapour deposition (PVD) based coatings for wear and corrosion protection are successfully being applied in many engineering applications. Nitrides of transition metals, such as CrN, TiN, NbN, have been widely studied, however, because most vapour deposited coatings are relatively thin, they usually offer less resistance to the bulk surface deflection. One approach to overcome this aspect is to adopt multilayer coatings with hard/soft (or high/low elastic modulus) layers. Nevertheless, the residual stress induced during the fabrication process is an important factor that needs to be address, which can limit the coating performance. The present paper is concerned with the residual stress present in multilayer CrN/Cr/CrN coatings produced by cathodic arc evaporation. Three different steel substrates were employed (i.e. AISI H13, AISI 1040 and K340). These substrates were subsequently coated in the sequence CrN (1.6μm)/Cr/CrN (1.6 μm), using three different intermediate Cr layer thickness (i.e. 0.5, 1.0, and 1.6 μm). X-ray diffractometry (XRD) was used to evaluate the strain in the direction perpendicular to the coating surface so as to determine the mean residual stress in the coating. © ASM International

An Insight into Durability, Electrical Properties and Thermal Behavior of Cementitious Materials Engineered with Graphene Oxide: Does the Oxidation Degree Matter?

Due to global environmental concerns related to climate change, the need to improve the service life of structures and infrastructures is imminently urgent. Structural elements typically suffer service life reductions, leading to poor environmental sustainability and high maintenance costs. Graphene oxide nanosheets (GONSs) effectively dispersed in a cement matrix can promote hydration, refine the microstructure and improve interfacial bonding, leading to enhanced building materials’ performance, including mechanical strength and transport properties. Cement-based nanocomposites engineered with GONSs were obtained using two commercial nanofillers, a GO water suspension and a free-flowing GO nanopowder, characterized by fully comparable morphology, size and aspect ratio and different oxidation degrees (i.e., oxygen-to-carbon molar ratio), 0.55 and 0.45, respectively. The dosage of the 2D-nanofiller ranged between 0.01% and 0.2% by weight of cement. The electrical and thermal properties were assessed through electrochemical impedance spectroscopy (EIS) and a heat flow meter, respectively. The results were discussed and linked to micrometric porosity investigated by micro-computed tomography (μ-CT) and transport properties as determined by initial surface absorption test (ISAT), boil-water saturation method (BWS) and chloride ion penetration test. Extra-low dosage mortars, especially those loaded with a lower oxidation degree (i.e., 0.45GO), showed decreased permeability and improved barrier to chloride ion transport combined with enhanced thermal and electrical conductivity with respect to that of the control samples

Culture labelling.

<p>For each condition three replicates were set up.</p

Photoluminescence analysis of frustules by SA-CLSM.

<p>a) 2D reconstruction of frustule signal after argon laser (488) excitation, selected ROIs are also shown. b) Emission spectra recorded through laser excitation at 405, 488, 543, 635 nm for aqueous frustule suspension and for composites frustule of 10 (c) and 20% (d) AA matrices.</p

Power dependency of the PL maximum intensity.

<p>PL peak intensity as a function of the excitation power for the a) unfilled and b) filled sample. Black lines are linear fits of the data. c) Power dependency of the FWHM for the unfilled (brown circles) and filled (green circles) samples.</p