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The Effect of Metal Oxides Additives on the Absorption/Desorption of MgH2 for Hydrogen Storage Applications
No full textMagnesium is considered as one of the more promising candidates for hydrogen
storage, primarily because of its abundance and the high hydrogen capacity of MgH2,
magnesium dihydride (7.6 wt%). Unfortunately, practical applications of MgH2 are
limited by poor hydrogen sorption kinetics and high thermodynamic stability, resulting
in slow charging and the need for high temperatures to release the hydrogen. Methods to
improve the sorption kinetics of MgH2, through ball-milling, alloying and introducing
small amounts of additives are currently under investigation. The aim of this work was
to investigate the effect of different transition metal oxides, as well as other catalysts, on
the hydrogen sorption kinetics, hydrogen release temperature and cycling stability of
MgH2.
The rate of MgH2 absorption is determined by the physisorption and dissociation of
molecular hydrogen, diffusion through the hydride layer and then nucleation of the
hydride. Whereas desorption is determined by nucleation of metal phase, diffusion of
atomic hydrogen through the metal and hydride, and recombination to form molecular
hydrogen at the surface before dissociation of the molecule form the surface.
The addition of small amounts of additives (< 10 mol%) to MgH2 during milling have
been shown to have a significant effect on the kinetics of absorption and desorption of
hydrogen. In addition, the effect of oxygen as a component of these additives has been
extensively studied. Although a surface layer of MgO is known to slow the diffusion of
hydrogen into metal, niobium oxide, Nb2O5, is one of the best additives for kinetic
improvement of MgH2. It has been suggested that higher valance oxides have a greater
effect on the kinetics; also recent studies have indicated that the formation of
magnesium-niobium ternary oxide compound may be responsible for the enhancement,
however the exact mechanism by which Nb2O5 enhances the kinetics is still unclear.
Various transition metal oxides have proved to be effective additives for hydrogen
absorption/desorption of Mg-based hydrides e.g., Nb2O5 and TiO2. In this work organometallic
additives based on transition metal oxides (Ti and V) and halides have been
chosen, some of which are liquid at room temperature. These additives were chosen to
extend the oxide valency to higher values, provide a comparison between liquid and
solid oxide additives, and compare a non-oxide transition metal additive (Ti-based
chloride). Nb2O5 was used as the benchmark for comparisons.
A range of different amounts of transition metal (Ti and V) oxides and other additives,
both liquid and solid, were ball milled with pre-milled MgH2 under different gas
environments and the hydrogen sorption behaviour of the ball milled composite samples
was investigated using a TPD/TDS Sieverts apparatus. A key difference from previous
work in this area was the use of organo-metallic compounds, some of which were liquid
at room temperature. Samples were characterized using X-Ray Diffraction, and, where
feasible, Scanning Electron Microscopy and Raman Spectroscopy before and after
recording the hydrogen sorption behaviour.
A Sievert apparatus was improved, then modified to include TPD and TDS capability to
determine the hydrogen uptake and release and to perform all these measurements in
one consistent environment.
With the aim of understanding what effect the ball milling gas environment might have
on the MgH2 sorption kinetics, two different gases, Ar and H2, were used. MgH2, with
and without additives (C60, TTIP (Titanium TetraIsoPropoxide) and Nb2O5) were milled
under the two different gases. In most cases the milling gas had little to no effect on
desorption kinetics, but a noticeable effect in the absorption uptake was observed - by
up to 2 wt% - depending on the gas used.
To understand the role of an organo-metallic oxide liquid additive on MgH2 sorption
kinetics, a systematic survey was performed by milling up to 2 mol% of TTIP with
MgH2 and the results compared to composite samples with Nb2O5 as the additive. TTIP
was found to be equally as effective as Nb2O5 with superior hydrogen capacity, and, just
as for Nb2O5, only a small amount of additive, 0.5 mol% of TTIP was found to be
sufficient for kinetics enhancement. Interestingly, 0.5 mol% TTIP hand-mixed with the
pre-milled MgH2 was also found to be effective for desorption, but not for the
absorption kinetics.
To further investigate the effect of organo-metallic liquid oxides, particularly transition
metal oxides, on the enhancement of the sorption kinetics of MgH2, a range of liquid
oxides (Ti-based and V-based oxides) were milled with MgH2 and compared to powder
oxides. Ti-based oxides were found to have superior desorption enhancement, with the
liquids performing better than the powders. The V-based oxides (all liquids) showed
faster absorption and higher uptake when compared to Ti-based oxides. The Ti-chloride
based organo-metallic additive was investigated to compare a non-oxide transition metal
additive to the oxide additives. It was found that a small amount of 1 mol% of additive milled for short time (1 h) had the best desorption of all the additives investigated in this
work - but with quite poor absorption.
Overall, this project established that the use of transition metal oxides as additives has a
great impact on improving the sorption kinetics of MgH2. The TTIP additive produced
results at least as good as the benchmark additive Nb2O5, but with the significant
advantage of being able to be mixed with MgH2 without ball-milling. The Ti and V
based oxides additives were also shown to be effective, Ti-based achieving better
desorption enhancement, whereas V-based oxide samples had faster absorption and
higher uptake. It was also determined the ball milling gas environment can have a
significant effect on the sorption kinetics, but the effect depended on the additive. The
difference in the effect of additives on desorption and absorption cycles confirms the
need to study combinations of additives for optimal overall benefit.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)School of Environment and ScScience, Environment, Engineering and TechnologyFull Tex
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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