This study involves the experimental and modelling work of high temperature reactions pertaining to steelmaking. / Certain non-metallic inclusions are known to cause deleterious effects in steel products and affect the production efficiency of steelmaking if not controlled. Most of these are oxide inclusions formed during deoxidation in refining processes, especially in the ladle metallurgy furnace (LMF), an understanding of which is essential for process control. The composition of these inclusions changes subsequently while interacting with other phases like slag, alloy additions, and refractories. The efficient removal and composition control of inclusions are important variables to consider for any steelmaker. Moreover, desulphurisation of steel is another aspect that needs attention since excess sulphur can precipitate sulfide inclusions while cooling. Hence, tracking the composition evolution of different phases in a ladle furnace is beneficial for the steelmaking industry. Previous researchers in the authors’ laboratory developed a model that could be used to predict the kinetics of steel-slag-inclusion reactions in aluminium (Al) killed steel. The current work focusses on developing a kinetic model that can be used to describe the inclusion evolution during ladle treatment of silicon-manganese (Si-Mn) killed steel. For this, first, the formation of complex oxides in Si-Mn-killed steel was analyzed using a mathematical model of nucleation and growth of particles in melts. The results revealed that spontaneous nucleation of complex oxides occur during alloy additions, resulting in different compositions of oxide nuclei, based on the local supersaturation conditions. Sensitivity analysis with different parameters was carried out to understand the influence of physicochemical variables on the model. Following this, two kinetic models were built: 1) average inclusion composition tracking method; and 2) multi oxide inclusion (MOI) composition tracking method. The latter approach included the thermodynamics and kinetics of each inclusion formation and could further incorporate the total inclusion number density variation in steel. The MOI model can be used to predict the changes in not only the average inclusion composition but also the type of inclusions precipitating in steel. Following this, laboratory deoxidation experiments were carried out using FeSi and FeMn to understand the inclusion behaviour post alloy additions. The MOI model showed good potential in simulating these laboratory deoxidation experiments and was then coupled with a previously developed steel-slag model to simulate actual ladle refining reactions. The calculated results were compared with different industrial data and showed good agreement with what is observed in reality, showing the success of this new approach. Similar to previous investigations, the rate-determining step could be attributed to the availability of solutes in steel (from slag or alloys) along with their transport to the steel-inclusion interface. The overall model was also able to simulate the desulphurization behaviour in steel. The effects of different processing conditions such as [Al], [O] content, reoxidation, and stirring conditions, were also examined and discussed through a parametric analysis. / Dissertation / Candidate in Philosophy

No description available.

&Ccedil / EMTAS Steel Plant produces alloy steels used principally by the automotive industry. Demands of customers for cleaner steel with &ldquo / fewer, smaller and homogenously distributed inclusions&rdquo / are getting tighter with time. The tight demands of the customers are checked by ultrasonic testing and faulty regions are cut off and scrapped which results in production losses in steel plants. Decreasing production losses due to scrapping by producing cleaner steels is therefore a major concern. The objective of this study is to investigate factors affecting the cleanliness of the steels produced by &Ccedil / EMTAS. With this objective, the steelmaking practice used was thoroughly investigated and the possible origins of inclusions in the final product was tried to be found. Based on the findings, process parameters like temperature, time, quantities of additives to steel, intensity of stirring etc. were varied with the objective of determining the optimum production practice.

<p> This thesis is concerned with the determination of the thermodynamics of the Fe-V-O system. </p> <p> In the first part the thermodynamics of liquid Fe-V-O alloys were studied in the temperature range of 1550-1700ºC using H₂O/H₂ equilibrium and/or an oxygen probe. 1st and 2nd order interaction parameters between V and O were determined, and the deoxidation reactions occurring when V is used as a deoxidizer were studied. Deoxidation diagrams are presented for V concentrations up to 12 wt. %. </p> <p> In the second part the thermodynamic equilibria between the lower oxides of vanadium (V - VO₀ٜ₂₋ₓ, VO₀ٜ₂₊ₓ - VO₁₋ᵧ, VO₁₊ᵧ - VO₁ٜ₅) were determined in the range 800-1400ºC using a solid state EMF technique, and the free energy of the formation of the oxides VO₀ٜ₂₊₍₋₎ₓ, VO₁₊₍₋₎ᵧ, VO₁ٜ₅ was estimated. </p> / Thesis / Doctor of Philosophy (PhD)

<P> A study has been made of the transformation of deoxidation products in the Fe-V-0 system in the temperature range 1545 -1640°C, using galvanic cells with solid electrolytes. The cells used were in the form of Zr02 (caO) immersion probes and Th02(Y2o2) crucible assemblies. The fields of study of Fev2o4(spinel) and v2o3 were established with respect to oxygen activity and temperature. </p> / Thesis / Master of Engineering (MEngr)

In this thesis, both the wettability and the agglomeration characteristics of non-metallic inclusions in liquid iron/steel were studied by using both experimental results and thermodynamic considerations. The mechanisms of the wettability of different types of inclusions were discussed. Also, the agglomeration behaviors of the inclusions were analyzed. Firstly, the wettability of different types of inclusions (including Al2O3, MgO, Ti2O3, TiO2 and TiN) in contact with the liquid iron/steel was studied. For the TiNcase, there is no reaction formation at the interface between TiN and pureiron/steel. In the caseo f pure Fe, the oxygen increase is the main factor for a contact angle decrease. As for the steel case, a sharp decrease of the contact angle is due to the effects of both an increased oxygen content in the liquid steel and a formation of a Ti(N,C,O) phase at the interface. For the Al2O3 and MgO cases, the formation of a FeAl2O4 and a MgO-FeO reaction layer at the interface, respectively, lead to a contact angle decrease. In the case of the Ti2O3/pure Fe case, the reaction at the interface cannot be identified. For the Ti2O3/steel case, the formation of an Al2TiO5 reaction layer is the main reason for a steep decrease of the contact angle. In the TiO2 case, the melting region appears at the temperature below the melting point of pure iron. This is due to the strong formation of a solid solution TiOx-FeO. The main source of the oxygen for the solid solution formationis due to a TiO2 substrate decomposition and a low partial pressure of oxygen in the chamber. Regarding to the non-metallic particle additions (TiO2 and TiN) into the molten steel, the steel composition should be controlled to have a small Al content (&lt;0.005mass%) and a high Ti content (&gt;0.035mass%), so as togeta high number of Ti-rich oxide inclusions with a small size. This conclusionis supported from the view point of the van der Waals force, liquid-capillary force and wettability. Regarding the Ti/Al complex deoxidation in the melt, the “mainly occupied clustered inclusions” with spherical shape is due to a TiOx-FeO liquid inclusion precipitation after an addition of Ti as a pre-deoxidizer. The much lower cluster number in the Ti/Al case than that in the Al case is mainly due to a coagulation of single TiOx-FeO liquid inclusions. Also, the cluster formation in a complex Ti/Al deoxidation is started after an Al addition rather than after a Ti addition. Regarding the Al2O3 cluster formation in deoxidation, the cavity bridge forceis larger than the van der Waals force. However, the difference between them is smaller than 7 times. In the reoxidation process, the influence of the cavity bridge force due to the wettability decreased, and became similar to that of the liquid-capillary force. / <p>QC 20160301</p>

La production de métal à partir de son oxyde est basée sur une réduction en plusieurs étapes. Un procédé à une seule étape a été récemment proposé pour la formation de Ti métal par électrolyse en chlorures fondus. Dans le procédé FFC (Fray, Farthing and Chen), le titane métallique est produit à la cathode pendant que les ions oxyde sont oxydés à une anode en graphite en dioxyde de carbone. Dans le domaine du nucléaire, ce procédé est intéressant car le sel peut être ré-utilisé sans retraitement particulier. Ce travail présente les études électrochimiques réalisées dans CaCl2-KCl et CaCl2 permettant de clarifier le mécanisme de réduction de CeO2, utilisé comme simulant des actinides. Des électrolyses sur de faibles quantités de CeO2 sont réalisées afin d'obtenir les conditions opératoires optimales. La réduction de plusieurs centaines de grammes de CeO2 est aussi discutée. / Reactive metals are currently produced from their oxide by multiple steps reduction techniques. A one step route from the oxide to the metal has been suggested for metallic titanium production by electrolysis in high temperature molten chloride salts. In the so-called FFC process, titanium oxide is electrochemically reduced at the cathode, generating O2- ions, which are converted on a graphite anode into carbon oxide or dioxide. After this process, the spent salt can in principle be reused for several batches which is particularly attractive for a nuclear application in terms of waste minimization. In this work, the electrochemical reduction process of cerium oxide (IV) is studied in CaCl2 and CaCl2-KCl melts to understand the oxide reduction mechanism. Cerium is used as a chemical analogue of actinides. Electrolysis on 10 grams of cerium oxide are made to find optimal conditions for the conversion of actinides oxides into metals. The scale-up to hundred grams of oxide is also discussed.

La découpe de wafers génère des quantités importantes de déchets de silicium de grade solaire qui ne sont pas revalorisés actuellement à cause de la contamination lors du procédé de découpe. Les travaux présentés dans ce manuscrit portent sur l’étude de la purification de déchets de silicium solaire à l’aide d’un procédé assisté par une torche à plasma d’arc non transféré. Cette étude a été menée selon une double approche numérique et expérimentale. Les calculs numériques ont été réalisés à l’aide d’un code de calcul de mécanique des fluides. Ils sont utilisés pour dimensionner la configuration expérimentale et pour comprendre l’influence des paramètres opératoires sur l’écoulement gazeux et le traitement des particules. L’étude expérimentale a consisté à ’injecter des déchets pulvérulents de silicium (sciures de silicium, poudre de concassage) dans un jet de plasma sous atmosphère contrôlée puis à les collecter dans un creuset chaud. La désoxydation et la décarburation de déchets de silicium, notamment de la sciure issue de la découpe des wafers, a été mise en évidence à l’aide du procédé développé. Toutefois, l’élimination des impuretés métalliques dans les sciures de silicium n’a pas été démontrée lors de cette étude. Les résultats expérimentaux et numériques ont mis en évidence que la désoxydation est améliorée avec un jet de plasma lent ainsi qu’avec une teneur en air résiduelle limitée dans la zone de traitement. La carboréduction de la silice ainsi que la volatilisation de la silice par oxydation du silicium semblent être les deux mécanismes de purification mis en jeu lors du procédé. / Wafer manufacturing produces large amounts of solar-grade silicon waste that is not currently recovered because of its contamination during the slicing process. This work deals with the purification of silicon waste using a non-transferred arc plasma process. It was carried out by using a double approach combining numerical simulations and experiments. The former were done using a computational fluid dynamics (CFD) code and made it to size the experimental configuration and understand the effect of process parameters on gas flow fields and powder treatment. The experimental study consisted in injecting powdered silicon waste (sawdust silicon, crushed powder) into the plasma jet under controlled atmosphere and collecting the treated material in a hot crucible. Decarburization and deoxidation of silicon waste, including sawdust resulting from wafer slicing, was achieved by the developed method. However, the removal of metal impurities in silicon sawdust was not demonstrated in this study. The experimental and numerical results showed that deoxidation was improved with a low-velocity plasma jet and limited air content in the area of treatment. Silica carboreduction and silica volatilization by silicon oxidation seemed to be the two mechanisms involved in the purification process.

The work deals with the occurrence of cracks and fissures in the massive steel castings produced in the ŽĎAS a.s. foundry which create in castings through the elimination of the extension. The influence on the final deoxidation on the creation of fissures and cracks is researched at the experimental samples. The beginning of the work is about teoretical analysis of these defects. Next it is described the place of the collection of these samples their chemical composition and cracks identification. After that it is evaluated the appearance of various defects in connection with modificatory and deoxidation additive, observation of experimental material with the microscope and the results of mechanical tests. The conclusion of the work belongs to sum up the individual results and proposal of optimal procedure.

The work deals with the determination of the chemical composition and morphology of inclusions in experimental casting foundry in operating conditions as ŽĎAS in compliance with the optimum content appropriate deoxidation depending on the conditions of solidification. The introductory part is devoted to theoretical analysis of possible defects in castings. We also describe the experimental casting, sampling sites and their markings. Subsequently evaluated morphology microanalysis inclusions and the effect of inclusions on the mechanical properties and the formation of defects in the casting. The conclusion summarizes the results and proposal for further direction in the production of heavy steel castings.