<p> </p><p>In order to optimise the ladle treatment mass transfer modelling of aluminium addition and homogenisation time was carried out. It was stressed that incorporating slag-metal reactions into the mass transfer modelling strongly would enhance the reliability and amount of information to be analyzed from the CFD calculations.</p><p> </p><p>In the present work, a thermodynamic model taking all the involved slag metal reactions into consideration was incorporated into a 2-D fluid flow model of an argon stirred ladle. Both thermodynamic constraints and mass balance were considered. The activities of the oxide components in the slag phase were described using the thermodynamic model by Björkvall and the liquid metal using the dilute solution model. Desulphurization was simulated using the sulphide capacity model developed by KTH group. A 2-D fluid flow model considering the slag, steel and argon phases was adopted.</p><p> </p><p>The model predictions were compared with industrial data and the agreement was found quite satisfactory. The promising model calculation would encourage new CFD simulation of 3-D along this direction.</p><p> </p>

Subsurface contamination is common at nuclear sites and it is likely that radioactive wastes will be managed in the long-term via burial in a deep Geological Disposal Facility (GDF). The migration of radionuclides in the geosphere from such sites is a major societal concern. In particular, long-lived, redox-active radionuclides (in the case of this thesis: 99Tc and Np) can migrate over large distances due to their high solubility under oxic conditions. Bioremediation has been proposed as a mechanism to limit the migration of 99Tc and Np in the environment. Here, an electron donor is supplied to the subsurface and soluble Tc(VII) and Np(V) are reduced to poorly soluble Tc(IV) and Np(IV), respectively. Reduction occurs via direct microbial action (termed bioreduction) or through radionuclide reaction with the by-products of microbial metabolism (primarily Fe(II)). Given the ubiquity of microorganisms and Fe in the geosphere, similar reactions can be expected in the deep subsurface surrounding a GDF. Once reduced, the long-term stability of the Tc(IV) and Np(IV) phases will significantly impact migration rates. Oxidative dissolution of Tc(IV)- and Np(IV)-bearing solids has been demonstrated in the literature and can be pervasive, thus questioning the efficacy of bioreduction. However, these studies have been conducted over short time-scales and during a single period of oxidation. Given the long half-life of 99Tc and Np and the ephemeral nature of redox conditions in the subsurface, there is a need to better understand 99Tc and Np biogeochemistry during longer time-scales and across multiple redox cycles. In this thesis, microcosm experiments have been used to address this knowledge gap. Sediment and groundwater used in the microcosms were representative of the Sellafield Ltd. nuclear site. For Tc, three successive redox cycles (reduction followed by oxidation with O2) over 2 years, gradually reduced the extent of Tc remobilisation during oxidation, and molecular scale characterisation of solids revealed that sediment associated Tc was always present as Tc(IV). Further, over time sequential extractions and EXAFS revealed an increased significance of Tc-Fe bonding in the sediment at the expense of TcO2. Despite this, a small but significant fraction of Tc(IV) was also found to be stable in solution during the experiments and XAS and TEM analysis suggested this was Tc(IV) associated with magnetite colloids. In other experiments completed with higher concentrations of bioavailable Fe (added as ferrihydrite to sediments, and in pure culture experiments with Geobacter sulfurreducens), the significance of Tc-Fe bonding was again highlighted, and potential Tc(IV) incorporation into biogenic magnetite was also documented. In experiments with Np, virtually all of the Np(V) added to oxic groundwater was removed to the sediment commensurate with microbially mediated Fe(III) reduction. Further, in systems with elevated bioavailable Fe, Np removal from solution was more extensive. Taken together, the data for Tc and Np reveals critical links between redox-active radionuclides and Fe cycling in sediments over periods of years and across multiple redox cycles. Furthermore, these processes help to predict the long-term fate of radioactive contamination at the Sellafield Ltd. nuclear site and have implications for contaminated land worldwide.

Reoxidation is a phenomenon that occurs in steel products during the initial stage of the formation of liquid steel, mainly during casting. This leads to the formation of inclusions which is a common problem that affects the properties, such as strength and ductility of the steel, and thus decreases its quality. To investigate these inclusions an electrolytic extraction and a scanning electron microscope(SEM) were performed on four carbon steel samples taken before and throughout continuous casting. To get a better understanding of the inclusions, the chemical composition, morphology, and sizes were analyzed, these were measured with the software ImageJ. As a result, five types of inclusions were identified, these include reoxidation, deoxidation, desulphurization, and complex compositions. Each type was represented by specific compounds and elements, such as FeO for reoxidation inclusions and Al2O3 for deoxidation inclusions. Additionally, inclusion morphology and size were significant classification factors, with film inclusions presenting larger sizes compared to other types, while spherical inclusions were observed perfectly, spherical ones were often associated with pure FeO content. Despite successful electrolytic extraction and SEM analysis, the number of inclusions obtained was lower than expected due to the presence of an additional layer of carbides. Future research may benefit from additional heating treatments to facilitate deeper analysis of inclusions. / Reoxidation är ett fenomen som uppstår i stålprodukter under gjutning. Detta leder till bildning av inneslutningar vilket är ett vanligt problem som påverkar egenskaperna, såsom hållfasthet och formbarhet hos stålet, och därmed minskar dess kvalitet. För att undersöka dessa inneslutningar utfördes en elektrolytisk extraktion och en SEM på fyra kolstålprover tagna före och under stränggjutning. För att få en bättre förståelse av inneslutningarna analyserades den kemiska sammansättningen, morfologin och storlekarna, dessa mättes med programvaran ImageJ. Som ett resultat identifierades fem typer av inneslutningar, dessa inkluderar reoxidation, deoxidation, avsvavling och komplexa kompositioner. Varje typ representerades av specifika föreningar och element, såsom FeO för reoxidationsinneslutningar och Al2O3 för deoxidationsinneslutningar. Dessutom var inklusionsmorfologi och storlek signifikanta klassificeringsfaktorer, med filminneslutningar som presenterade större storlekar jämfört medandra typer, medan sfäriska inneslutningar, observerades perfekt sfäriska sådana var ofta associerade med rent FeO-innehåll. Trots framgångsrik elektrolytisk extraktion och SEM-analys var antalet erhållna inneslutningar lägre än förväntat på grund av närvaron av ytterligare ett lager karbider. Framtida forskning kan dra nytta av ytterligare värmebehandlingar för att underlätta djupare analys av inneslutningar.

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The aim of this thesis was to analyze the formation of defects in a given casting of ductile cast iron EN - GJS - 600-3 cast in sand molds bentonite, which is formed jolting with coining and then find a solution to remedy these defects. To resolve this issue, the influence of the composition of the sand mixture, the effect of metal flow in a cavity forms and the influence of deoxidation of metal in the presence of defects. Obtained results showed the importance of the influence Reoxidation metal cavity mold. Specifically, in this case succeeded in reducing the incidence of PINHOLES. Removal of PINHOLES to achieve deoxidation aluminum melt. This has reduced the production of nonconforming castings under 3% from the original 6.5%.

QC 20101203

In order to optimise the ladle treatment mass transfer modelling of aluminium addition and homogenisation time was carried out. It was stressed that incorporating slag-metal reactions into the mass transfer modelling strongly would enhance the reliability and amount of information to be analyzed from the CFD calculations.   In the present work, a thermodynamic model taking all the involved slag metal reactions into consideration was incorporated into a 2-D fluid flow model of an argon stirred ladle. Both thermodynamic constraints and mass balance were considered. The activities of the oxide components in the slag phase were described using the thermodynamic model by Björkvall and the liquid metal using the dilute solution model. Desulphurization was simulated using the sulphide capacity model developed by KTH group. A 2-D fluid flow model considering the slag, steel and argon phases was adopted.   The model predictions were compared with industrial data and the agreement was found quite satisfactory. The promising model calculation would encourage new CFD simulation of 3-D along this direction. / QC 20110414

No description available.

This work is about development and methodology verification of data collection which will be used in the research of the reoxidation in steel castings. To examine reoxidation rate will be measured oxygen activity in the furnace, in the ladle and in the mould. Next it will be evaluated the chemical structure of mould slag, the chemical changes of steel and measured the volume and the area of the casting defects. Each technique is briefly described by the principle of measurement and each method has the results which are analysed. In the conclusion the experiment is summarized and there are mentioned the observations from this experiment.