1,721,009 research outputs found
Hydrogen sorption kinetics of magnesium hydride enhanced by the addition of Zr8Ni21 alloy
No full textHydrogen absorption and desorption kinetics, and thermodynamics of MgH 2 ball milled with addition of the Zr 8Ni 21 alloy have been studied. Different additive amounts were used from 3 to 12.5 wt%. The highest reversible capacity of 6.5 wt% of hydrogen was found for the samples with 3 and 5 wt% of additive. The best reaction kinetics was found with 10 wt% of additive: 5.9 wt% H 2 was desorbed in 4 min at 300 °C and 0.1 bar of hydrogen pressure. Regardless of the different storage capacities, all the samples were almost fully hydrided in 1 min using a hydrogen pressure of 10 bar at 250 and 300 °C. The enthalpy of formation of magnesium hydride was not affected by the presence of the additive.Fil: Pighin, Santiago Alberto. Università di Padova; Italia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Capurso, Giovanni. Universita Di Padova. Dept.di Ingeniería Meccanica; ItaliaFil: Lo Russo, Sergio. Università di Padova; ItaliaFil: Peretti Hollemaert, Hernán Américo. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentin
Innovative Materials and Systems for Solid State Hydrogen Storage
Full text linkThe research presented in this doctoral thesis concerns with the development of novel
materials and systems for solid state hydrogen storage.
The first group of works presented is on alkaline and alkaline-earth borohydrides. The
possibility to enhance their properties with the help of nanosupports has been widely
explored. An attempt to improve the dehydrogenation kinetics of lithium borohydride has
been made dispersing this material on the surface of modified nanotubes and graphite.
The resulting nanoconfined material displayed a decreased decomposition temperature in
comparison with pure material and further decreasing was observed when the surface area
of the supports was increased. An analogous experiment was performed to investigate this
effect in combination with the assets of a reactive hydride composite, where two materials
are mixed to obtain a compound with a lower decomposition enthalpy. The effect of the
mixture was beneficial in presence of the support, due to lower temperature melting. For
calcium borohydride an ordered mesoporous carbon was used after chemical activation.
The increased properties of this support resulted in lower decomposition temperature and
improved reversibility for a number of cycles at different pressure values.
The second research line is focused on magnesium hydride. To improve its kinetic properties
a zirconium-nickel alloy was investigated to evaluate its influence on the reaction
rate, both in absorption and desorption. The degradation observed in experimental reactors,
of different magnesium hydride powders catalyzed with a transition metal oxide,
motivated the fabrication of pellets with the addition of a binding agent, to obtain mechanical
resistance, still allowing hydrogen diffusion. Each pellet was supposed to behave
as an independent system, so they were also tested in a small reactor. Several hydrogen
absorption/desorption cycles were performed to compare the behaviour of the small reactor
with the laboratory data obtained on smaller quantity of powdered and pelletized
specimens.
Finally, the feasibility of a vehicular hydrogen tank system was investigated using an
interstitial metal hydride as storage material. Apart from material basic characterization,
two different kinds of experiment were performed. Static tests (measurements with automatic
flow control and constant settings) were used to evaluate wether the requirements
for desorption are met by the tank set-up. Then, dynamic tests were designed and applied
on the tank, where the hydrogen flow was fluctuating following a hypothetical on-road
trial. It was possible to underline the heat management issues of high-demanding performances
and to analyze some solutions for that. Different cycles were carried out on the
tank to find the ideal setting for high average and peak flows in a realistic experiment
Ball-milling and AlB2 addition effects on the hydrogen sorption properties of the CaH2+MgB2 system
No full textAmong the borohydrides proposed for solid state hydrogen storage, Ca(BH4)2 is particularly interesting because of its favourable thermodynamics and relatively cheap price. Composite systems, where other species are present in addition to the borohydride, show some advantages in hydrogen sorption properties with respect to the borohydrides alone, despite a reduction of the theoretical storage capacity. We have investigated the milling time influence on the sorption properties of the CaH2 + MgB2 system from which Ca(BH4)2 and MgH2 can be synthesized by hydrogen absorption process. Manometric and calorimetric measurements showed better kinetics for long time milled samples. We found that the total substitution of MgB2 with aluminum boride in the starting material can improve the sorption properties significantly, while the co-existence of both magnesium and aluminum borides in the starting mixture did not cause any improvement. Rietveld refinements of the X-ray powder diffraction spectra were used to confirm the hypothesized reactions
The structural change of graphene oxide in a methanol dispersion
No full textGraphene oxide is a derivative of graphene which contains oxygen domains. Its debatable structure depends on the specific functional groups bonded to the graphene basal plane which have an impact on its reactivity. Here, we report the influence of methanol which affects the functionalization of pristine graphene differently to water
Nanoconfinement in activated mesoporous carbon of calcium borohydride for improved reversible hydrogen storage
No full textMesoporous carbon frameworks were synthesized using the soft-template method. Ca.BH4/2 was incorporated into activated mesoporous carbon by the incipient wetness method. The activation of mesoporous carbon was necessary to optimize the surface area and pore size.
Thermal programmed absorption measurements showed that the confinement of this borohydride into carbon nanoscaffolds improved its reversible capacity (relative to the reactive portion) and performance of hydrogen storage compared to unsupported borohydride.
Hydrogen release from the supported hydride started at a temperature as low as 100 C and the dehydrogenation rate was fast compared to the bulk borohydride. In addition, the hydrogen pressure necessary to regenerate the borohydride from the dehydrogenation products was reduced
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Study of the failure mechanism of a HDPE liner in a Type IV high-pressure storage tank [Dataset related to publication]
No full textData type: SEM micrographs; ATR-FTIR spectra; XRD patterns, DSC profiles and analyses.
Data format: *.tif; *.dat; *.asc; *.opj.
Origin of the data: laboratory equipment from University of Udine (SEM, ATR-FTIR, XRD, DSC)
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