1,721,146 research outputs found
Deformation conditions for Ni powders undergoing mechanical processing
No full textNi powders were submitted to mechanical processing by ball milling. The microstructural refinement of the processed powders was followed by X-ray diffraction by evaluating the average crystallite size and the average strain content. The Vickers micro-hardness was also measured. The experimental evidences were rationalized using a phenomenological model, which allowed to estimate the amount of powder processed at individual collisions. The density of dislocations was also estimated and correlated with the experimental Vickers micro-hardness values. The connection between the work- and gain-hardening mechanisms described by the Bailey–Hirsch and Hall–Petch relationships is discussed
Mesostructural refinement in the early stages of mechanical alloying
No full textThis study focuses on the early stages of the mechanical alloying of 22 different binary mixtures. In each case, the number of alloyed particles increases linearly with the number of collisions, and the volume of powder effectively processed during a single collision is ∼9.0 × 10−3 mm3. The alloyed particles exhibit a heterogeneous mesostructure with characteristic lengths decreasing exponentially with the number of collisions. The rate of mesostructural refinement is inversely proportional to the difference between the hardnesses of the individual metals
Kinetics of the mechanochemical synthesis of alkaline-earth metal amides
No full textA phenomenological framework is developed to model the kinetics of the formation of alkaline-earth metal amides by the ball milling induced reaction of their hydrides with gaseous ammonia. It is shown that the exponential character of the kinetic curves is modulated by the increase of the total volume of the powder inside the reactor due to the substantially larger molar volume of the products compared to the reactants. It is claimed that the volume of powder effectively processed during each collision connects the transformation rate to the physical and chemical processes underlying the mechanochemical transformation
Application of IR and UV–VIS spectroscopies and multivariate analysis for the classification of waste vegetable oils
Full text linkDue to the ever-increasing worldwide interest in the exploitation of waste vegetable oils, the development of
analytical tools able to detect their adulteration with edible oils, is considered a priority for the scientific and
industrial community. In this work, edible and waste vegetable oils have been analysed by Fourier Transform-
InfraRed (FT-IR) and Ultraviolet-Visible (UV–VIS) spectroscopies and the corresponding spectral data subjected
to statistical multivariate analysis for classification purposes. In particular, Principal Component Analysis
(PCA) and Partial Least Square Discriminant Analysis (PLS-DA) were performed in order to develop an analytical
tool which is able to distinguish between edible and waste vegetable oil. Qualitative analysis of the spectra
suggested FT-IR and UV–VIS as the more suitable techniques to distinguish between wastes and edible samples.
Also, statistical multivariate analysis revealed that FT-IR-based methodology is more adequate for the target,
even if the elevated sensibility of the method produces an undesired distinction between edible oils of the same
type. Finally, further attempts on UV–VIS data obtained in reflection mode allowed to produce a good dataset
which after statistical treatment gave a clear differentiation between edible and waste oil samples
Composto di ossido ternario a base di Magnesio e Niobio, mesoporoso, altamente ordinato, procedimento per la sua preparazione e suoi usi.
No full textSurface area effects on the early stages of the mechanical alloying of Ag50Cu50 powder mixtures
No full textNovel processing route for the fabrication of bulk high-entropy metal diborides
Full text linkA single high-entropy phase material with hexagonal structure is produced by a two-steps processing method. Elemental reactants are first remarkably converted by Self-propagating High-temperature Synthesis (SHS). The completion of the chemical transformation to the desired (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 phase and its concurrent consolidation up to 92.5% relative density is achieved by processing the SHS powders at 1950 °C via Spark Plasma Sintering. It is clearly evidenced that the use of the SHS technique is extremely beneficial to promote the formation of high-entropy ceramics, as compared to the time consuming ball milling treatment alternatively adopted
Hydrogenation of carbon monoxide over nanostructured systems: a mechanochemical approach
No full textn this study we investigated the mechanochem. hydrogenation of carbon monoxide over nanostructured FeCo- and Mg2Ni-based catalysts. To this aim powd. materials, prepd. by mech. alloying, were subjected to mech. treatment under CO + H2 atmosphere. A methodol. to evaluate the activity of the solid catalysts on an abs. basis was developed. Conversion data were, indeed, expressed as turnover frequency, TOF, and related to the occurrence of ball to powder collision events through the mechanochem. turnover frequency parameter, MTOF. Differences in the catalytic activity and selectivity were obsd. for the two FeCo-based studied systems, the solid soln. Fe50Co50 and its dispersion on TiO2 support. As for the Mg2Ni system, we explored the possibility to est. the specific role of hydrogen pre-activation step. The catalytic properties of the mech. alloyed Mg2Ni system were compared with the conversion data shown by the same system pre-hydrogenated and subsequently milled under CO at
Remarkable hydrogen storage properties of MgH<sub>2</sub>doped with VNbO<sub>5</sub>
Full text linkThe present work concerns the catalytic effect of VNbO5, a ternary oxide preparedviaa solid-state route, on the sorption performance of MgH2.</p
Ultra high temperature high-entropy borides: effect of graphite addition on oxides removal and densification behaviour
Full text linkThe 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
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