Behaviour of alumina powder fed into molten electrolytic bath

The dissolution of alumina (aluminium-oxide) in an electrolyte is an essential process in the production of aluminium, the second most commonly used metal on Earth. In the state-of-the-art aluminium reduction cells, smelter grade alumina powder is added on the surface of the molten cryolitic bath in doses varying between 0.5-2 kg. While dissolving a powder in its solvent might seem trivial, there are several particularities to this process that hinder the rapid dispersion of alumina. The dubious dissolution may undermine the cell control, and the undissolved alumina could form agglomerates that can decrease the efficiency and lifetime of the cell. The objective of this PhD was to analyse the mechanisms that promote the formation of agglomerates, and hinder the fast dispersion of alumina added into cryolitic bath, mostly focusing on: • the raft formation: the spreading of the powder, injected onto the bath surface; • the evolution of alumina rafts, with regard to the flotation of the raft on the bath surface; • the flotation behaviour of agglomerates on the bath-metal interface. The methods used in this work include mathematical modelling, experiments in cryolitic bath, analysis of alumina rafts, and experiments in analog powder-liquid systems. A mathematical model was developed to analyse the conditions of steady-state flotation of axisymmetric objects on a liquid surface. The model was applied to the surface of the electrolytic bath. For the bath-metal interface, the static model was extended, to consider the initial velocity of the agglomerate and dynamics of the interface penetration. The contact angle between alumina and cryolitic bath (an important input parameter for the flotation model) was measured by Wilhelmy method. Experiments were conducted in the cryolitic bath to study and analyse raft formation. Moisture content was identified as an important property of alumina that influences the shape, structure, and microstructure of the alumina raft, forming upon injection. Raft samples were prepared by leaching to remove cryolite, revealing the underlying alumina structure, then the pore structure analysed. Compressed alumina discs as artificial alumina rafts were prepared to obtain rafts with controlled shape and size, while leaving the main processes (bath solidification, infiltration, sintering and dissolution) unchanged. The uniformity of the artificial rafts permitted the easy comparison between samples removed after different stages, and to follow the advancement of the line of infiltration in time. The density of the rafts, along with the video footage of the experiments proved that the surface tension can contribute to the flotation of alumina rafts. Two-dimensional thermal model of alumina rafts was created to predict bath solidification, infiltration and apparent density – therefore possibility of flotation for the raft. Thermal properties of primary smelter grade alumina were measured by monotonic ramp heating device, and due to the complex pore structure of the alumina, a two-level model was applied to be able to estimate its thermal conductivity with different packing densities. The detachment of infiltrated grains or clumps from the main body of the raft decreases its size and also its apparent density. The disintegration of a raft is controlled by the opposing effects and the dynamics of sintering and dissolution. While dissolution is often considered as the main goal of research concerning the behaviour of alumina in the electrolyte, it should rather be considered as an opposing but parallel process to sintering, and should be investigated simultaneously. In the frame of this work, carbon content was identified as a factor that aids disintegration via weakened sintering. Powder injections in low-temperature analog liquid-liquid systems were conducted to gain insight on their interactions. While in many aspects, the analog systems fail to represent faithfully the alumina-bath-aluminium system, certain phenomena may apply for the electrolysis cell. These observations are of special importance for the liquid-liquid interface. La dissolution de l'alumine (oxyde d'aluminium) dans l’électrolyte est un procédé essentiel dans la production d'aluminium, le deuxième métal le plus utilisé sur Terre. Dans les cellules actuelles de réduction d'aluminium, la poudre d'alumine de fonderie est ajoutée à la surface du bain cryolitique fondu à des doses variant entre 0,5 et 2 kg. Bien que la dissolution d'une poudre dans son solvant puisse sembler anodine, ce processus présente plusieurs particularités qui entravent la dispersion rapide de l'alumine. La dissolution douteuse peut saper le contrôle cellulaire, et l'alumine non dissoute peut former des agglomérats qui peuvent diminuer l'efficacité et la durée de vie de la cellule. L'objectif de cette thèse était d'analyser les mécanismes qui favorisent la formation d'agglomérats, et d'entraver ainsi la dispersion rapide de l'alumine ajoutée dans le bain cryolitique, en se concentrant principalement sur: • la formation du radeau: l'étalement de la poudre, injectée sur la surface du bain; • l'évolution des radeaux d'alumine, en ce qui concerne la flottation du radeau à la surface du bain; • le comportement à la flottation des agglomérats à l'interface bain-métal. Les méthodes utilisées dans ce travail comprennent la modélisation mathématique, des expériences en bain cryolitique, l'analyse de radeaux d'alumine et des expériences dans des systèmes analogiques poudre-liquide. Un modèle mathématique a été développé pour analyser les conditions de flottation en régime permanent d'objets axisymétriques sur une surface liquide. Le modèle a été appliqué à la surface du bain électrolytique. Pour l'interface bain-métal, le modèle statique a été étendu pour prendre en compte la vitesse initiale de l'agglomérat et la dynamique de la pénétration de l'interface. L'angle de contact entre l'alumine et le bain cryolitique (un paramètre d'entrée important pour le modèle de flottation) a été mesuré par la méthode Wilhelmy. Des expériences ont été menées dans le bain cryolitique pour étudier et analyser la formation de radeaux. La teneur en humidité a été identifiée comme une propriété importante de l'alumine qui influence la forme, la structure et la microstructure du radeau d'alumine, se formant lors de l'injection. Des échantillons de radeau ont été préparés par lixiviation pour éliminer la cryolite, révélant la structure d'alumine sous-jacente, puis la porosité était analysée. Des disques d'alumine compressés en tant que radeaux d'alumine artificiels ont été préparés pour obtenir des radeaux de forme et de taille contrôlée, tout en laissant les principaux processus inchangés. L'uniformité des radeaux artificiels a permis de comparer facilement les échantillons prélevés après différentes étapes et de suivre l'évolution de la ligne d'infiltration dans le temps. La densité des radeaux, ainsi que les séquences vidéo des expériences ont prouvé que la tension superficielle peut contribuer à la flottation des radeaux d'alumine. Un modèle bidimensionnel de radeaux d'alumine a été créé pour prédire la solidification du bain, l'infiltration et la densité apparente, donc la possibilité de flottation pour le radeau. Les propriétés thermiques de l'alumine primaire de fonderie ont été mesurées par un dispositif de chauffage à rampe monotone, et en raison de la structure complexe de la porosité de l'alumine, un modèle à deux niveaux a été appliqué pour pouvoir estimer sa conductivité thermique avec différentes densités. Le détachement des grains saturés ou des amas du radeau principal diminuerait sa taille ainsi que sa densité apparente. La désintégration d'un radeau est dictée par les effets concurrents et la dynamique du frittage et de la dissolution. Bien que la dissolution soit souvent considérée comme le but ultime de la recherche concernant le comportement de l'alumine dans l'électrolyte, elle devrait plutôt être considérée comme un processus parallèle mais opposé au frittage, et enquêter simultanément sur les deux. Dans le cadre de ce travail, la teneur en carbone a été identifiée comme un facteur favorisant la désintégration en affaiblissant le frittage. Des injections de poudre dans des systèmes liquide-liquide analogiques à basse température ont été effectuées pour mieux comprendre leurs interactions. Alors que dans de nombreux aspects, les systèmes analogiques ne représentent pas fidèlement le système alumine-bain-aluminium, certains phénomènes peuvent s'appliquer à la cellule d'électrolyse. Ces observations sont d'une importance particulière pour l'interface bain-métal

Personalised trails and learner profiling within e-learning environments

This deliverable focuses on personalisation and personalised trails. We begin by introducing and defining the concepts of personalisation and personalised trails. Personalisation requires that a user profile be stored, and so we assess currently available standard profile schemas and discuss the requirements for a profile to support personalised learning. We then review techniques for providing personalisation and some systems that implement these techniques, and discuss some of the issues around evaluating personalisation systems. We look especially at the use of learning and cognitive styles to support personalised learning, and also consider personalisation in the field of mobile learning, which has a slightly different take on the subject, and in commercially available systems, where personalisation support is found to currently be only at quite a low level. We conclude with a summary of the lessons to be learned from our review of personalisation and personalised trails

Seguimiento y determinación de la composición florística en la revegetación realizada en la margen de la quebrada agua caliente, Sector Mina Iza – Boyacá

Las revegetaciones son una estrategia de recuperación de áreas finales de minería ampliamente utilizada en el sector minero, por ello la compañía Holcim (Colombia) S.A desde aproximadamente una década viene realizando actividades de revegetación en un área de 4 hectáreas en la margen de la quebrada Agua Caliente, afluente del río Tota, en el Municipio de Iza, en el Departamento de Boyacá, en la zona de influencia de la mina de puzolana, con el ánimo de conocer el estado actual de las plantaciones realizadas se hace necesario 1) realizar un seguimiento y evaluación de la revegetación , 2) Caracterizar florísticamente zona de estudio , 3) Determinar la diversidad florística y 4) establecer acciones para el manejo de las plantaciones en las áreas de la mina destinadas para rehabilitación ambiental. Mediante la ejecución de un inventario forestal del 100% y una extrapolación en ciertas áreas de difícil acceso se obtuvo la información suficiente para identificar un total de 7853 individuos distribuidos de la siguiente manera: 27 familias, 37 géneros y 41 especies, de los cuales se encuentran 28 especies nativas, 13 especies exóticas. Dentro de las especies nativas identificadas se registró 1 especie categorizada como vulnerable y se registró la presencia de 1 especie invasora. El índice de diversidad en la zona es media. y se plantean acciones de manejo para el control o reemplazo de especies exóticas.Revegetations are a strategy for the recovery of final mining areas widely used in the mining sector, for this reason the company Holcim (Colombia) SA has been carrying out revegetation activities in an area of 4 hectares on the margin of the Agua Caliente creek for about a decade, a tributary of the Tota River, in the Municipality of Iza, in the Department of Boyacá, in the area of influence of the pozzolana mine, with the aim of knowing the current status of the plantations carried out, it is necessary to 1) monitor and evaluation of revegetation, 2) Characterize the study area floristically, 3) Determine the floristic diversity and 4) establish actions for the management of plantations in the areas of the mine destined for environmental rehabilitation. Through the execution of a 100% forest inventory and an extrapolation in certain areas of difficult access, enough information was obtained to identify a total of 7,853 individuals distributed as follows: 27 families, 37 genera and 41 species, of which They found 28 native species , 13 exotic species, 1 species categorized as Vulnerable and the presence of 1 invasive species was recorded. The diversity index in the area is average. and management actions are proposed to control or replace exotic species

Indirect Firm Valuation and Earnings Stability

This paper investigates statistical significance of earnings stability in the within-company indirect valuation method. We empirically establish superiority of a within-company earnings multiple valuation technique for the relatively most stable companies. Favourable empirical results are robust against different means of operationalization of the stability construct and valuation multiples. Results of this paper indicate that the indirect within-company price-to-earnings valuation yields the most precise and the most accurate value estimates

LADA type diabetes, celiac diasease, cerebellar ataxia and stiff person syndrome. A rare association of autoimmune disorders.

Celiac disease--in its typical form--is a chronic immune-mediated enteropathy with typical clinical symptoms that develops against gliadin content of cereal grains, and is often associated with other autoimmune diseases. In cases of atypical manifestation classic symptoms may be absent or mild, and extra-intestinal symptoms or associated syndromes dominate clinical picture. The authors present a longitudinal follow-up of such a case. A 63-years old woman was diagnosed with epilepsy at the age of 19, and with progressive limb ataxia at the age of 36, which was initially thought to be caused by cerebellar atrophy, later probably by stiff person syndrome. At the age 59, her diabetes mellitus manifested with type 2 diabetic phenotype, but based on GAD positivity later was reclassified as type 1 diabetes. Only the last check-up discovered the celiac disease, retrospectively explaining the entire disease course and neurological symptoms. By presenting this case, the authors would like to draw attention to the fact that one should think of the possibility of celiac disease when cerebellar ataxia, progressive neurological symptoms and diabetes are present at the same time. An early diagnosis may help to delay the progression of disease and help better treatment

Human Fetuin-A Rs4918 Polymorphism and its Association with Obesity in Healthy Persons and in Patients with Myocardial Infarction in Two Hungarian Cohorts.

BACKGROUND Human fetuin A (AHSG) has been associated with the development of obesity, insulin resistance, type 2 diabetes mellitus, and atherosclerosis. Observations on the role of AHSG rs4918 single-nucleotide polymorphism are contradictory. We investigated the association between variants of rs4918 and parameters of obesity, lipid status, tumor necrosis factor-alpha (TNFalpha), adipokines (adiponectin, resistin, leptin), and insulin resistance in healthy persons and in patients with previous myocardial infarction. MATERIAL AND METHODS This was a cross-sectional study comprising cohort 1 (81 healthy individuals) and cohort 2 (157 patients with previous myocardial infarction). We used the allele-specific KASP genotyping assay to detect rs4918 polymorphism. RESULTS In cohort 1, G-nucleotide carriers had significantly lower serum TNFalpha, adiponectin, and higher leptin concentrations than in non-G carriers. These differences, however, were not observed in cohort 2. In cohort 2, G-carriers had lower BMI and waist circumferences than in non-G carriers. The G allele was more frequent among lean than obese patients (RR=1.067, 95%CI=1.053-2.651, p=0.015). An association between BMI and rs4918 polymorphism was observed among patients without diabetes (CC/CG/GG genotypes: p=0.003, G vs. non-G allele: p=0.008) but not in diabetics. In addition, a strong linearity between BMI and the CC/CG/GG genotypes (association value: 4.416, p=0.036) and the frequency of the G allele (7.420, p=0.006) could be identified. In cohort 2, non-obese, non-diabetic G-carriers still had lower BMI and waist circumferences than in non-G carriers. CONCLUSIONS The rs4918 minor variant is associated with lower TNFalpha and adiponectin, higher leptin levels in healthy persons, and more favorable anthropomorphic parameters of obesity in cohort 2

Constrained TRPV1 agonists synthesized via silver-mediated intramolecular azo-methine ylide cycloaddition of α-iminoamides

As part of an effort to identify agonists of TRPV1, a peripheral sensory nerve ion channel, high throughput screening of the NIH Small Molecule Repository (SMR) collection identified MLS002174161, a pentacyclic benzodiazepine. A synthesis effort was initiated that ultimately afforded racemic seco analogs 12 of the SMR compound via a silver mediated intramolecular [3+2] cycloaddition of an azo-methine ylide generated from α-iminoamides 11. The cycloaddition set four contiguous stereocenters and, in some cases, also spontaneously afforded imides 13 from 12. The synthesis of compounds 12, the features that facilitated the conversion of 12–13, and their partial agonist activity against TRPV1 are discussed

Liquid chromatography at critical conditions (LCCC): Capabilities and limitations for polymer analysis

This paper investigates liquid chromatography at critical condition (LCCC) for polymer analysis. Based on controversial claims on the separation of cyclic polymers from linear analogues in the literature, the efficiency of LCCC for separation and purity analysis is questioned. Polyisobutylene (PIB) and poly(3,6-dioxa-1,8-octanedithiols) (polyDODT) were used for the study. The structure of low molecular weight cyclic and linear polyDODT was demonstrated by MALDI-ToF. NMR did not show the presence of thiol end groups in higher molecular weight PIB-disulfide and polyDODT samples, so they were considered cyclic polymers. When a low molecular weight polyDODT oligomer with only traces of cycles, as demonstrated by MALDI-ToF, was mixed with an M_n = 27 K g/mol cyclic sample, LCCC did not detect the presence of linear oligomers at 6 wt%. Based on the data presented here, it can be concluded that the LCCC method is not capable of measuring <6 wt% linear contamination so earlier claims for cyclic polystyrene (PS) samples purified by LCCC having <3% linear contaminants are questioned

Liquid chromatography at critical conditions (LCCC): Capabilities and limitations for polymer analysis

This paper investigates liquid chromatography at critical condition (LCCC) for polymer analysis. Based on controversial claims on the separation of cyclic polymers from linear analogues in the literature, the efficiency of LCCC for separation and purity analysis is questioned. Polyisobutylene (PIB) and poly(3,6-dioxa-1,8-octanedithiols) (polyDODT) were used for the study. The structure of low molecular weight cyclic and linear polyDODT was demonstrated by MALDI-ToF. NMR did not show the presence of thiol end groups in higher molecular weight PIB-disulfide and polyDODT samples, so they were considered cyclic polymers. When a low molecular weight polyDODT oligomer with only traces of cycles, as demonstrated by MALDI-ToF, was mixed with an M_n = 27 K g/mol cyclic sample, LCCC did not detect the presence of linear oligomers at 6 wt%. Based on the data presented here, it can be concluded that the LCCC method is not capable of measuring <6 wt% linear contamination so earlier claims for cyclic polystyrene (PS) samples purified by LCCC having <3% linear contaminants are questioned