148 research outputs found
Ultrasonic melt treatment in a DC casting launder: The role of melt processing temperature
No full textEPSRC (UK) Ultramelt2 project (EP/R011001/1, EP/R011044/1, and EP/R011095/1)
Effect of ultrasonic melt treatment on the sump profile and microstructure of a direct-chill cast AA6008 Aluminum Alloy
No full textThis work focuses on the effects of ultrasonic melt treatment (UST) during direct-chill (DC) casting on the temperature distribution across the billet, sump profile, and the resulting microstructure. Two AA6008 billets were cast; one was treated with UST in the hot top while the other was not. To determine the temperature distribution along the billet, multi-point temperature measurements were made across the radii of both billets. The sump profile was also analyzed through macrostructure analysis, after Zn was poured into the sump, while structure refinement was quantified through grain-size measurements. A numerical model of ultrasound-assisted DC casting is validated using the temperature measurements. As an outcome, this study provides information on the extent to which UST affects the sump profile and the corresponding changes in the microstructure. The knowledge gained from this study paves the way towards optimization of UST parameters in DC casting
Effects of pendent phenol functional groups on secondary coordination spheres of heme like Fe-salen complexes
No full textSince the beginning of industrial revolution, burning of fossil fuels has mainly led to increase in atmospheric concentration of CO2 , a Green House Gas (GHG), from 250 ppm to 400 ppm between 1800 and 2012. One way to reduce the burning of fossil fuels and CO2 emission rate is to explore alternative carbon free fuels to meet the energy demand.This project aims at the synthesis and study of metal complexes inspired by biological models that will help better design catalysts to perform water oxidation more effectively.This poster won the Dean, Faculty of Science award (2020). Advisor: Dr. Linus Chiang, Departmen of Chemistry
21st-century scholarship and Wikipedia
No full textWikipedia, the world’s fifth most-used Web site, is a good illustration of the growing credibility of online resources. In his article in Ariadne earlier this year, “Wikipedia: Reflections on Use and Academic Acceptance”, Brian Whalley described the debates around accuracy and review, in the context of geology. He concluded that ‘If Wikipedia is the first port of call, as it already seems to be, for information requirement traffic, then there is a commitment to build on Open Educational Resources (OERs) of various kinds and improve their quality.’ In a similar approach to the Geological Society event that Whalley describes, Sarah Fahmy of JISC worked with Wikimedia and the British Library on a World War One (WWI) Editathon. There is a rich discourse about the way that academics relate to Wikipedia
Evolution of nano- and microstructure during the calcination of Bayer gibbsite to produce alumina
No full textThe microstructure of Metallurgical Grade Alumina (MGA) has extensive consequences on how it performs as a raw material for aluminium production. MGA is produced primarily in the Bayer process in which both the precipitation and the calcination steps play important roles for the development of alumina microstructure. Calciner technology is progressively moving from rotary kilns to more energy efficient gas suspension or circulating fluidised bed processes, which influences the intricate interplay of calcination parameters and therefore effects the development of structure and properties in the alumina. The evolution of structural features during the calcination of Bayer gibbsite is a complex process that involves both a dehydroxylation reaction and a rearrangement of the crystal lattice. Due to the highly agglomerated starting material, the pseudomorphic nature of the reactions and the incomplete transformation to the thermodynamically stable alpha alumina, a mixed phase meso- to macro porous material results. As a consequence of the wide range of particle sizes, rapid heating rates, short residence times and other inhomogenities in the modern calcination process a diversity and mixture of aluminium oxide products are formed. Deviations from the average transition alumina structures are also observed. In this thesis an integrated approach to evaluate alumina micro- and nanostructure is presented. Using a suite of modern analytical techniques, in conjunction with more traditional approaches, the structures that make up the MGAs are probed and insights into the development of structural features and the transformation reactions during the calcination process are obtained. It is shown that the alumina phase composition is influenced by the calcination conditions, which for the MGAs are dictated by the calciner technology, and that compositional variations are observed even within individual alumina grains. The results indicate that these compositional variations arise both due to the distribution of sodium and other impurities which catalyse the transition to alpha alumina, and as a result of the rapid heating rates. It is proposed that the rapid heating rates in modern calcination processes result in the formation of a boehmite-like structure within the particles. The internal boehmite formation may be promoted by desorption resistance of the product water, from surfaces and pore openings, due to the rapid decomposition rates. Electron microscopy investigations reveal that a lamellar and sponge-like network of interconnected pores and channels is formed with relatively large alpha alumina crystallites growing in the transition alumina matrix. Furthermore, it is shown that alpha alumina may be directly observed in cross sectioned alumina grains through Charge Contrast Imaging using an Environmental SEM. It is also demonstrated that multiple field Solid-state Magic Angle Spinning NMR can be used to quantitatively assess the phase composition of MGAs. The availability of high magnetic fields significantly aids this quantification. The NMR results indicate that the MGAs are relatively ordered on the short range, and that only small amounts of pentahedral aluminium are present. Furthermore, using X-ray Absorption Near-edge Structure (XANES) spectroscopy it was observed that the short range order is influenced by the precursor material and the calcination conditions. This offers a possible explanation for some of the discrepancy in the literature regarding the structural relationship between the gibbsite and boehmite derived transition aluminas. The results also indicate that changes in the intermediate range ordering occur with increasing calcination temperature. Even in the complex mixed phase MGAs some long range order is observed, which seems to be closely tied to the formation of alpha alumina in the samples. XANES is very sensitive to these long range structures. However quantitative or structural analysis is difficult due to the complex and overlapping resonances arising from multiple scattering interactions in the samples. The complex mixture of phases and the high level of disorder in the MGAs present significant challenges in understanding their structure, particularly with relation to the performance as a raw material for aluminium metal production. The structures that make up the MGAs transcend short-range ordering, on the nano-scale, and into longer range domains. Therefore, to examine MGA microstructure and better understand its impact in smelter operations, it is essential to evaluate structural ordering on several different scales. This requires advanced and often multiple analytical techniques
The nature and impacts of fines in smelter-grade alumina
No full textFines in smelter-grade aluminas art recognized (is a significant process problem in aluminum smelting. However understanding the nature of this fine material and how it impacts the reduction process arc, less clearly understood The combination of new analytical methods such as variable pressure scanning electron microscopy and very; high field solid state nuclear magnetic resonance provide new insights into the phases present and their spatial distribution within aluminas, and suggest how such fine materials are generated, particularly during calcination in the alumina refinery
How Many Answers Are Enough? Optimal Number of Answers for Q&A Sites
No full textWith the proliferation of the social web, questions about information quality and optimization attract the attention of IS scholars. Question-answering (QA) sites, such as Yahoo!Answers, have the potential to produce good answers, but at the same time not all answers are good and not all QA sites are alike. When organizations design and plan for the integration of question answering services on their sites, identification of good answers and process optimization become critical. Arguing that ‘given enough answers all questions are answered successfully,’ this paper identifies the optimal number of posts that generate high quality answers. Based on content analysis of Yahoo! Answers’ informational questions (n=174) and their answers (n=1,023), the study found that seven answers per question are ‘enough’ to provide a good answer
Power Relations and Social Classes in Pengakuan Pariyem by Linus Suryadi AG: Reflection of Masculine Ideology
No full textThe study aims to explore power relations and social classes as the reflections of the masculine ideology of the author in the novel Pengakuan Pariyem by Linus Suryadi AG. The theories implemented in the study are van Dijk’s power relations and social classes theory and Connell’s masculinity theory. The study is qualitative descriptive and applies the Critical Discourse Analysis (CDA) method, used to dismantle the ideology that is produced and reproduced through the language within the novel. The research data are lingual units that indicate power relations and social classes which simultaneously reflect the notion of masculinity. The results of the study are as follows. First, Pariyem as the central character in the novel lives within a hierarchical and dualistic Javanese society. Her submission as the babu (housemaid) of a priyayi (noble) family does not only lead Pariyem to be dominated symbolically, but also legitimizes the priyayi (aristocrats) power over wong cilik (commoners). It is reinforced by the representations of the priyayis’ world views in terms of culture, aristocracy, bureaucracy, and education orientation. It shows that priyayis are culturally dominant. Secondly, since Pariyem is a character created by a male author, her behaviors and actions reflect the ideology of masculinity. Rather than voicing women, the power relations that Pariyem experiences through the events constructed in the novel show that she embodies the masculine ideology, or masculinity.
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