Optimization of High Entropy Borides for Advanced Applications

In the last decades, a steep increase in the demand of materials that can withstand extreme environments has been registered. The most representative field where these are encountered is the aerospace. For instance, wing lead edges, nosetips and propulsion systems are subjected to a combination of harsh conditions (high temperatures, oxidising environment, mechanical stresses). To this aim, a significant attention was focused by the scientific and industrial communities on the Ultra High Temperature Ceramic (UHTC) materials, based on transition metal borides and carbides, which are characterised by several advantageous physico-chemical properties, such as elevated melting temperatures, chemical inertness, good thermal and electrical conductivities, etc. In addition, UHTCs are also known to exhibit an intrinsic spectral selectivity and low thermal emittance, which makes them suitable for solar absorbers for applications in concentrating solar plants. In this context, the recently discovered High Entropy Borides (HEBs), where five or more metal cations are combined in near-equimolar percentages to generate a single phase crystalline solid solution, i.e. (Hf0.2Mo0.2Ti0.2Ta0.2Zr0.2)B2, were found to display peculiar properties that could provide a possible further advancement in this field. In particular, preliminary investigations evidenced that members of the HEB class showed better performances in terms of mechanical properties and oxidation resistance, when compared to the corresponding individual boride constituents. The first aim of the present thesis is to optimize the conditions for the fabrication of different HEB ceramics, namely (Hf0.2Mo0.2Ti0.2Nb0.2Ta0.2)B2, (Hf0.2Mo0.2Ti0.2Ta0.2Zr0.2)B2 and (Hf0.2Mo0.2Ti0.2Nb0.2Zr0.2)B2, in highly dense form. This will be conducted by taking advantage of the combination of two efficient synthesis and sintering techniques, i.e. Self-propagating High-temperature Synthesis (SHS) and Spark Plasma Sintering (SPS), respectively. The effect of the most important processing parameters, and additive introduction, in product characteristics will be systematically investigated to achieve nearly full dense andmonophasic ceramics

High-entropy transition metal diborides by reactive and non-reactive spark plasma sintering: A comparative investigation

The direct synthesis and consolidation by SPS (1950 °C, 20 min, 20 MPa) of high-entropy (Hf0.2Mo0.2Zr0.2Nb0.2Ti0.2)B2 from elemental powders resulted in a multiphase product. An increase of the heating rate determined a change of the mechanism governing the synthesis reaction from gradual solid-state diffusion to rapid combustion regime, while the final conversion degree was 67 wt.%. The sintered product displayed a non-uniform microstructure with the presence of 10–15 μm sized pores, due to volatilization phenomena occurring during the combustion synthesis reaction. In contrast, when the SPS process was preceded by powder synthesis via SHS, a homogeneous single-phase ceramic was obtained. Clear benefits are derived by the use of SHS, able to provide very shortly powders with elemental species very well intermixed, so that the obtainment of (Hf0.2Mo0.2Zr0.2Nb0.2Ti0.2)B2 during the subsequent SPS stage is strongly promoted. The resulting 92.5% dense product shows superior oxidation resistance with respect to individual borides prepared with the same method.ARCHIMEDES project sponsored by Regione Autonoma della Sardegna (Italy) - Fondo di Sviluppo e Coesione (FSC) 2014-2020 (Cod. RAS: RASSR88309, Cod. CUP: F76C18000980002). One of the authors (G.T.) performed her activity in the framework of the International PhD in Innovation Sciences and Technologies at the University of Cagliari, Italy. One of us (G.C.) acknowledges the results obtained in this manuscript as quite important for the “Ithermal” and “Generazione E” projects, sponsored by Sardegna Ricerche, Italy (Cod. CUP: F21I18000130006) and by the Italian Ministry of Education, University and Research, Italy (Cod. CUP: B96G18000560005), respectivel

Clinical randomized comparison of Medetomidine and Xylazine for isoflurane balanced anesthesia in horses

Introduction: To assess drug plasma levels, preanesthetic sedation, cardiopulmonary effects during anesthesia and recovery in horses anesthetized with isoflurane combined with medetomidine or xylazine.Study design: Prospective blinded randomized clinical study.Animals: Sixty horses undergoing elective surgery.Methods: Thirty minutes after administration of antibiotics, flunixine meglumine or phenylbutazone and acepromazine horses received medetomidine 7 μg kg$^{−1}$ (group MED) or xylazine 1.1 mg kg$^{−1}$ (group XYL) slowly intravenously (IV) and sedation was assessed 3 min later. Anesthesia was induced with ketamine/diazepam and maintained with isoflurane in oxygen/air and medetomidine 3.5 μg kg$^{−1}$ h$^{−1}$ or xylazine 0.69 mg kg$^{−1}$ h$^{−1}$. Ringer's acetate 10 mL kg$^{−1}$ h$^{−1}$ and dobutamine were administered to maintain normotension. All horses were mechanically ventilated to maintain end-tidal carbon dioxide pressures at 45 ± 5 mmHg (5.3–6.7 kPa). Heart rate (HR), invasive arterial blood pressures, inspired and expired gas compositions, pH, arterial blood gases, electrolytes, lactate and glucose were measured. For recovery all horses received intramuscular morphine 0.1 mg kg$^{−1}$ and medetomidine 2 μg kg$^{−1}$ or xylazine 0.3 mg kg$^{−1}$ IV. Recovery was timed and scored using three different scoring systems. Plasma samples to measure medetomidine and xylazine concentrations were collected at predetermined timepoints. Repeatedly measured parameters were analyzed using a two-way repeated-measures analysis of variance for differences between groups and over time; p < 0.05 was considered statistically significant.Results: Mean arterial blood pressures (MAP) stayed within normal ranges but were higher (p = 0.011) in group XYL despite significant lower dobutamine doses (p = 0.0003). Other measured parameters were within clinically acceptable ranges. Plasma levels were at steady state during anesthesia (MED 2.194 ± 0.073; XYL 708 ± 18.791 ng mL$^{−1}$). During recovery lateral recumbency (MED 42.7 ± 2.51; XYL 34.3 ± 2.63 min; p = 0.027) and time to standing (MED 62.0 ± 2.86; XYL 48.8 ± 3.01 min; p = 0.002) were significantly shorter in group XYL compared to group MED. Recovery scores did not differ significantly between groups.Conclusion and Clinical Relevance: In horses anesthetized with isoflurane and medetomidine or xylazine, xylazine maintained higher MAP, reduced the dobutamine consumption and recovery time, whilst overall recovery quality was unaffected

Ultra high temperature high-entropy borides: effect of graphite addition on oxides removal and densification behaviour

The introduction of 0.5–1.0 wt.% graphite to the powders prepared by Self-propagating High-temperature Synthesis (SHS) is found to be highly beneficial for the removal of oxide impurities (from 2.7-8.8 wt.% to 0.2–0.5 wt.%) during spark plasma sintering (1950°C/20 min, 20 MPa) of (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 and (Hf0.2Mo0.2Ta0.2Zr0.2Ti0.2)B2 ceramics. Concurrently, the consolidation level achieved is enhanced from about 92.5% and 88%, respectively, to values exceeding 97%. While a further increase of graphite slightly improves samples densification, final products become progressively richer of the unreacted carbon. It is assumed that graphite plays a double role during SPS, e.g. not only as a reactant during the carbothermal reduction of oxides contaminant, but also as lubricating agent for the powder particles. The latter phenomenon is likely the main responsible for the densification improvement when 3 wt.% or larger amounts of additive are used. Another positive effect is the crystallite size refinement of the high-entropy phases with the progressive abatement of oxides, to confirm that their presence promotes grain coarsening during the sintering process.ARCHIMEDES project sponsored by Regione Autonoma della Sardegna (Italy) - Fondo di Sviluppo e Coesione (FSC) 2014–2020 (Cod. RAS: RASSR88309, Cod. CUP: F76C18000980002). One of the authors (S.B.) performed his activity in the framework of the International PhD in Innovation Sciences and Technologies at the University of Cagliari, Italy. One of us (G.C.) acknowledges the results obtained in this manuscript as quite important for the “Ithermal” and “Generazione E” projects, sponsored by Sardegna Ricerche, Italy (Cod. CUP: F21I18000130006) and by the Italian Ministry of Education, University and Research, Italy (Cod. CUP: B96G18000560005

Optical Properties of Bulk High-Entropy Diborides for Solar Energy Applications

So far, the studies regarding the innovative High-Entropy Borides (HEBs), which belong to the more general class of Ultra-high temperature ceramics (UHTCs), have been entirely confined to their fabrication or characterization from the microstructural, mechanical and oxidation resistance viewpoints. In this work, the optical properties of two members of HEBs, i.e. (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, are evaluated for the first time to assess their possible utilization in the thermal solar energy field. The bulk samples (96.5 and 97.4% dense, respectively) are obtained as single-phase products by Spark Plasma Sintering (1950 °C/20 min/20 MPa) starting from powders previously synthesized by Self-propagating High-temperature Synthesis (SHS). The optical characterization, whose results are discussed by comparing HEBs to the individual borides, shows that they are characterized by intrinsic spectral selectivity and low thermal emittance, resulting therefore interesting for high-temperature solar absorbers applications

Come to light: Detailed analysis of thermally treated Phenyl modified Carbon Nitride Polymorphs for bright phosphors in lighting applications

International audienceCarbon Nitride and its polymorphs have recently gained large interests for their huge properties and applications in different fields, from lighting to photocatalysis. Further, several attempts were recently devoted to tune and control its optical and electrical properties. In this report we analyze phenyl modified Carbon Nitride structures obtained by simple thermal polymerization at different temperatures (250-400°C) of the starting precursor: 2,4-diamino-6-phenyl-1,3,5-triazine. A multi-technique experimental data (XRD patterns, Raman, TGA and DTG, steady-time and time resolved Luminescence, Photoluminescence Excitation spectra, Reflectivity spectra) was applied to analyze the relationship between structural and optical properties and to give more insight on the effect of synthesis procedure on the final polymer. The optical properties evidenced an interesting shift towards the visible region of the absorption spectrum of the phenyl modified g-C 3 N 4 polymer that, associated with the high optical quantum yield (about 60%) and to a broad emission in the green-red spectral region, makes the samples very suitable for lighting applications. Indeed, we report a first prototype of white LED emission by assembly of a commercial blue LED and the Phenyl modified g-C 3 N 4 powders as phosphor, verifying the structural and optical stability over about 10,000 working hours

Processing and optical behavior of dense (Hf,Zr)B2 solid solutions for solar energy receivers

While individual borides and, more recently, quinary High Entropy Transition Metal Borides have been investigated, the fabrication and characterization of bulk binary to quaternary solid solutions are barely explored. In this work, dense (Hf0.5Zr0.5)B2 is produced by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature (SHS). SHS produced a multiphase product, whose secondary phases are fully converted into the desired diborides during the subsequent SPS step. Optical properties of (Hf0.5Zr0.5)B2 are evaluated for the first time with focus on the possible use as novel high-temperature solar thermal absorber, by hemispherical reflectance measurements and calculation of solar absorptance, temperature-dependent spectral selectivity and absorber opto-thermal efficiency at various solar concentration ratios. To optimize the material, a chemically etched surface texture was realized to modify the optical properties. The etched sample showed a higher solar absorptance (0.71) and a lower spectral selectivity than the unetched one, with consequent higher opto-thermal efficiency at all temperatures for solar concentration ratios 1000 ÷ 3000, while at lower concentration ratios and temperatures >1400 ÷ 1600 K, the unetched sample shows the highest efficiency. These results show the promising properties of binary diborides for solar thermal applications

Mercati & Competitività. The Journal of the Italian Marketing Association

Nata per merito della Società Italiana di Marketing questa Rivista vuole innanzitutto costituire una sede privilegiata della sua politica culturale e scientifica. Ciò tramite l’attivazione di tutte quelle sinergie e collaborazioni che possano garantirci di farne una rivista espressione del meglio di ciò che in Italia, e non solo, si produce in fatto di conoscenza e applicazioni del marketing. È ambizione della Rivista acquisire oltre che contributi delle migliori Scuole di marketing italiane anche un crescente numero di lavori di ricerca sviluppatisi in campo internazionale grazie a collaborazioni scientifiche ed editoriali con alcuni dei centri di eccellenza esistenti in Europa, negli Stati Uniti ed in prospettiva nel mondo asiatico. Il confronto tra diverse Scuole di marketing è assai opportuno in una fase in cui i paradigmi tradizionali e più consolidati del marketing management di origine anglosassone sono messi in discussione da nuovi modelli e prospettive di analisi e di gestione del mercato. Da tempo in Italia si sono sviluppate correnti di pensiero che si discostano dagli approcci più ortodossi e numerosi sono i contributi che, seppure ancora con una certa frammentazione, cercano di proporre e di sviluppare prospettive se non alternative almeno integrative e complementari a quelle più consolidate (il marketing relazionale, il marketing digitale, il co-operative marketing). In considerazione di tali aspetti la Rivista vuole essere un momento di aggregazione e di confronto sia tra studiosi sia tra questi e figure del mondo professionale e manageriale. Pur nascendo dall’interno di un’associazione scientifico-culturale la Rivista non è destinata a rimanere un campo di interessi e di contributi riservato. L’impegno è piuttosto quello di offrire per il suo tramite una visione aggiornata e scientificamente fondata dei campi e degli strumenti della scienza e delle tecniche del marketing, a beneficio di un più vasto e composito pubblico di autori e lettori. La "domanda di marketing" sta crescendo ovunque, nelle scuole e nelle università, nelle imprese e nel terzo settore del non profit, nella consulenza e nelle istituzioni pubbliche nazionali e locali. Non sempre a questa maggiore domanda corrisponde un’adeguata crescita dell’offerta di competenze e skills professionali, creando così disallineamenti e divari tra domanda e offerta. Non solo, ma spesso appare diffuso un "concetto di marketing" distorto e parziale nel quale vengono fatte convergere unicamente attività di comunicazione e di vendita, trascurandosi, per non dire ignorandosi, l’essenza e l’eterogeneità della cultura e delle attività di marketing management che investono una pluralità di processi di comprensione, generazione e trasmissione di ciò che è valore per il cliente. Anche in considerazione di ciò la Rivista vuole rispondere offrendo contributi preziosi per l’elevazione e l’aggiornamento culturale e scientifico di coloro che intendono occuparsi di marketing in modo specialistico e professionale, nella scuola e nell’università così come nel mondo produttivo e istituzionale

Mercati e competitività

Il comitato editoriale lavora alla pianificazione delle linee strategiche di sviluppo della rivista, partecipando attivamente anche ai processi di referaggio blind e all'organizzazione delle special issue