Made available in DSpace on 2017-07-21T19:25:46Z (GMT). No. of bitstreams: 1 Joao Luiz Gomes Junior.pdf: 5004861 bytes, checksum: 0e45ece35c737cce76186e1babb5e257 (MD5) Previous issue date: 2015-03-26 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / In this work, the correlation between the structural morphology with thermal, optical and mechanical properties of (1 – x – y)TeO2-xLi2O-yMoO3 glasses was studied. The analysis was divided into three sets of samples, varying according to the composition for technique. The results reveal different behaviors for each set vitreous stabilities. The Raman spectroscopy and FTIR results showed a similar structural change between each set with decrease NBOs and new peaks position. The Raman and FTIR spectra results showed that with increasing content x and y, concomitantly, occur the conversion of TeO4 to TeO3+1 units, then, in addition to TeO3 units. Furthermore occurs change coordination in the structural units Mo atoms 4 to 6 and these structural changes. Li addition causes these structural changes. This fact confirmed by the Band Gap energy values, which increase with the increase of x and y, it decreases the optical basicity and refractive index values. By optical absorption measurements determined the Band Gap energy values of all samples. It was concluded that occur direct transitions allowed in all sets. The behavior of increasing Band Gap values and decreasing Optical basicity confirmed the decreasing in the NBO content leading to an indication of a more polymerized network for a variation of x mol%. Finally the behaviors elastic modulus and hardness, which shows decreased stiffness of the material with the incorporation of Li2O and MoO3 concomitantly, is presented. x / Este trabalho apresenta as correlações entre a morfologia estrutural e as propriedades térmicas, ópticas e mecânicas nos vidros (1 – x – y)TeO2 – xLi2O – yMoO3. Dividiram-se as análises em três conjuntos de amostras, de acordo com variação da composição, para cada técnica utilizada. Os resultados revelam diferentes comportamentos de estabilidades vítreas para cada conjunto. As medidas por espectroscopia de Raman e FTIR mostram mudanças estruturais similares entre cada conjunto com diminuição dos NBOs e novas posições de picos. Os resultados de Raman e FTIR mostram que com o aumento em conteúdo x e y ocorre a transformação de unidades TeO4 para TeO3 + 1 e, em seguida, para TeO3 além disso ocorre a mudança de coordenação do átomo de Mo de 4 para 6 e estas alterações estruturais têm sido relacionados com a adição de átomos de Li. Este fato é confirmado pelos valores de energia de Band Gap, que aumentam com o incremento de x e y, e diminuição dos valores de basicidade óptica e índice de refração. As energias de Band Gap, para todas as amostras, foram determinadas por medidas de absorção óptica na região do Ultravioleta. Foi concluído que ocorrem transições diretas permitidas em todos os conjuntos. E por fim apresenta-se os comportamentos de dureza e Módulo elástico, o que revela diminuição da rigidez do material com a incorporação de Li2O e MoO3 concomitantemente.

La tesi que porta per títol "Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions" ofereix informació complementària a la comunitat científica relacionada amb la química de coordinació amb metalls de transició en general, i particularment a experts en òxids metàl·lics d'elevada nuclearitat, o polioxometal·lats (POMs). Els POMs poden encapsular selectivament espècies iòniques i catalitzar força reaccions orgàniques, també són agents blanquejadors de la polpa de fusta respectuosos amb el medi ambient, funcionen com a membranes, sensors, etc. En el futur, podrien ser aplicats amb èxit en medecina ja que estan sent testats com a agents antivirals. La llista de possibles aplicacions és interminable. Sigui com sigui, molts grups estan treballant per explotar les propietats d'aquests òxids metàl·lics. Per tant, un coneixement acurat de les propietats fonamentals dels POMs és necessari si els experimentalistes volen desenvolupar noves tecnologies.La pràctica totalitat dels resultats presentats en la memòria han estat obtinguts amb mètodes de càlcul mecano-quàntics d'alt nivell. La tècnica més àmpliament utilitzada ha estat el mètode relacionat amb la teoria del funcional de la densitat. Aquesta eina, d'ús rutinari des de fa uns pocs anys, s'ha convertit en la preferida per al càlcul de sistemes de gran mida com els POMs. Els principals temes abordats en aquest treball estan relacionats amb l'estructura electrònica d'alguns heteropolianions (HPAs). Aquests es caracteritzen per posseir dos tipus estructurals d'àtoms a part dels lligands oxo: el(s) central(s) i els perifèrics. Dintre d'aquest subgrup dels POMs, s'han investigat les propietats de les dues estructures més comuns: l'anió de Keggin (XM12O40n) i el de WellsDawson (X2M18O62m), així com alguns derivats. Han estat estudiades sèries amb diferents metalls perifèrics (anomenats addenda), metalls centrals (heteroàtoms), isòmers i estructures, de manera que s'han traçat conclusions valuoses i extrapolables a altres sistemes no estudiats. Aquesta classe de POMs presenta una seqüència d'orbitals moleculars peculiar. Els seus orbitals frontera han estat analitzats detalladament per un grup ampli de compostos. S'ha posat especial èmfasi en conèixer la relació entre els orbitals metàl·lics (normalment buits) i les propietats redox dels HPAs. Un dels èxits del treball ha estat explicar de forma inequívoca i general les tendències en els potencials de reducció segons la composició química d'una espècie, així com el comportament dels electrons metàl·lics―(des)localització. Val a dir que, en la gran majoria dels casos, s'ha trobat una concordància molt bona amb les dades experimentals.El segon gran tema abordat en la tesi és la basicitat dels HPAs. En un compost tipus XxMmOyn existeixen diverses posicions oxo, les quals no sempre són equivalents químicament. La seva basicitat pot ésser, doncs, diferent. Un estudi realitzat sobre una sèrie de compostos amb metalls mesclats ha donat escales relatives de basicitat, estimades a partir de la funció potencial electrostàtic, així com a partir d'energies de protonació. S'ha mostrat que els lligands oxo bicoordinats a metalls solen ser els més bàsics, mentre que els oxígens terminals són, generalment, els menys bàsics. Els processos de dimerització en anions de Keggin solen tenir lloc en medi àcid. Aquests passen per una protonació dels monòmers i s´han abordat en dos casos. L'objectiu era mostrar possibles mecanismes de reacció del procés.El tractament teòric dels POMs és encara en la seva etapa inicial, probablement per les dificultats intrínseques associades al càlcul d'aquestes espècies. Aquestes són, des del punt de vista computacional, molècules grans. A més, degut a que són òxids de metalls de transició, acostumen a ser anions altament carregats amb, de vegades, estats electrònics de capa oberta. Els resultats recopilats en la tesi són una prova de que el DFT ha estat hàbilment aplicat a l'estudi dels POMs. / The thesis titled "Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions" offers complementary information to the scientific community concerned to coordination chemistry with transition metals in general, and particularly to experts in high-nuclearity metal oxide compounds. They are the so-called polyoxometalates (POMs). POM species can encapsulate selectively some ionic species as well as catalyse many organic reactions. They are also environmentally-friendly wood pulp bleaching agents, they work as membranes, sensors, etc. In the close future, they could be successfully applied to medicine since they were tested as antiviral agents. The full list of possible applications is endless. Be that as it may, many groups are working with the aim of exploiting the properties of these metal oxides. Thus, an accurate knowledge of their fundamental properties is necessary if experimentalists are to develop new POM-related technologies.The great majority of the results presented in the thesis were obtained by means of high-performance quantum-mechanics computational methods. The most amply utilised tool in this study was the method derived from the density function theory. This tool, only recently utilised routinely, has arisen as the preferred one for computing molecular systems of large size as POMs are. The main topics studied in this work are related to the electronic structure of some heteropolyanions (HPAs). They are characterised by possessing two structural types of atoms, a part from oxo ligands: the central and the peripheral atoms. Within this subset of POMs, the two most common structures were studied: the Keggin (XM12O40n) and the WellsDawson (X2M18O62m) anions, and some of their derivatives, as well. Large series of compounds with varying peripheral atoms (also known as addenda), central metals (heteroatoms), isomers and frameworks, so that we traced valuable conclusions, extrapolable to other systems not studied here. This class of POMs features a particular molecular orbitals sequence. Their frontier orbitals were carefully analysed for a wide set of compounds. We especially stressed the connection between the metal orbitals (normally empty) and the redox properties of HPAs. One of the successes of the work was to explain unequivocally and in a general way the trends in the reduction potentials depending on the chemical composition of a given species, as well as the behaviour of metal electrons―(de)localisation. It is worth noting that, in virtually all cases, we found a fair accordance of our results with experimental data.The second great topic studied in the thesis is the basicity of HPAs. In a compound like XxMmOyn there exist different oxo positions which are not always chemically equivalent. Their basicity might be, then, different. The study carried out for a series of mixed-addenda molecules gives relative basicity scales, estimated from the electrostatic potential function and from protonation energies. It has been showed that the oxo ligands coordinated to two metals are more basic than terminal position, which in general are the least basic. The dimerisation processes in Keggin anions take place, normally, in acidic media. They occur after protonation of the monomers and were investigated for two cases. The goal was to show possible reaction mechanisms for the process.The theoretical treatment of POMs is still in its initial steps, probably due to the intrinsic difficulties associated to the calculation of such species. They are, from a computational point of view, large molecules. In addition, because they are transition-metal oxides, they are highly charged anions that, sometimes, display open-shell electronic states. The compilation of results of the thesis is a proof that the DFT have been skilfully applpied to the study of POMs.

A good slag practice is essential for production of a high-quality stainless steel. In addition, the electrical and material efficiency of the electric arc furnace (EAF) can considerably be improved by a good slag practice. The metallurgical properties of the slag are strongly influenced by its high-temperature microstructure. Thus, characterization of the phases within the EAF slag as well as the determination of the amount of these phases is of high importance.In addition, the knowledge about the chemical composition of the liquid slag and solid phases at the process temperatures is instrumental in developing a good slag practice.In order to study the slag in EAF high-chromium stainless steelmaking, slag samples were collected from 14 heats of AISI 304L steel (two samples per heat) and 7 heats of duplex steel (three samples per heat).The selected slag samples were petrographically studied both using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) and light optical microscopy (LOM). In some cases, X-ray diffraction (XRD) analyses were also performed. Moreover, computational thermodynamics was used to determine the equilibrium phases in the EAF steelmaking slags at the process temperatures. In addition, parameter studies were performed on the factors influencing the equilibria.More specifically, a petrographical and thermodynamic characterization was performed on the EAF austenitic steelmaking slags. Thereafter, the microstructural evolution of the slag during the EAF duplex steelmaking process was investigated. Moreover, an investigation with focus on the total amount of precipitates within the high-chromium stainless steelmaking slags was done. Finally, the foamability of these slags was quantified and evaluated.The petrographic investigations showed that, during the refining stage, in both austenitic and duplex cases, the main constituent of the EAF slag is a melt consisting of liquid oxides. In addition, the slag samples contain solid spinel particles. However, before ferrosilicon-addition (FeSi), the slag may also contain solid stoichiometric calcium chromite. Moreover, depending on the slag basicity, the slag may contain solid dicalcium silicate at the process temperatures.The evolution of the slag during the refining stage of the EAF was graphically illustrated in the calculated isothermal phase diagrams for the slag system Al2O3-Cr2O3-CaO-MgO-SiO2-TiO2.It was found that the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium-oxide content. More specifically, it was shown that the amount of the spinel particles in the slag increases with an increased chromium-oxide content of the slag. It wasvialso shown that a higher basicity and a lower temperature of the slag contribute to the dicalcium silicate precipitation.In order to evaluate and quantify the foamability of the slags, the slag’s physical properties influencing its foaming index were determined. Computational thermodynamics was used as a tool to calculate the weight fractions of the solid phases within the slag at different EAF process stages. The computational thermophysics was used to estimate the viscosity of the liquid part of the slag samples at the process temperatures. The apparent viscosity of the samples was calculated by combining the above results. By estimating the density, surface tension and the foaming-gas bubble size, the foaming index of the slag samples were quantified. It could be shown that the foaming index of the EAF high-chromium stainless steelmaking slag may be on its minimum as the slag’s basicity takes a value in the range of 1.2 – 1.5. A basicity value of around 1.50 – 1.60 can be suitable for enhancing the foaming index of the slag, during the refining period in EAF high-chromium stainless steelmaking.

O presente trabalho investiga alguns sulfóxidos β-tia-substituidos quanto à sua basicidade relativa e quanto à sua reatividade em relação aos compostos de Grignard aromáticos. O conjunto de compostos investigados foi o seguinte: metil n-propil sulfóxido, metil metiltiometil sulfóxido, etil butil sulfóxido, etil etiltiometil sulfóxido, etil feniltiometil sulfóxido, fenil feniltiometil sulfóxido e 1,3-ditiolano-1-óxido. É apresentada, inicialmente, uma revisão bibliográfica sôbre dois itens: 1. basicidade de sulfóxidos, e 2. reações de sulfóxidos com compostos de Grignard. São apresentados os valores de constantes de associação para dois sulfóxidos β-tia-substituídos e dois não substituídos correspondentes. Estes valores foram calculados a partir de medidas dos deslocamentos químicos dos prótons do fenol em sistemas ternários sulfóxido -fenol-tetracloreto de carbono, pelo dos métodos de Carper e de Mathur. São apresentadas as reações de quatro sulfóxidos com alguns compostos de Grignard aromáticos, tais como os brometos de fenil-, p-anisil-, p-tolilmagnésio, e descritos os métodos de análise dos compostos formados. São descritas as preparações de cincos sulfóxidos e de alguns produtos autênticos. São fornecidos os resultados de algumas experiências de reações de um sulfóxido β-tia-substituído com brometo de fenilmagnésio em presença de base. É apresentada uma discussão na qual se procura interpretar tanto os resultados da literatura como os nossos. Os resultados obtidos demonstram que: a) Há diminuição de basicidade nos sulfóxidos β-tia-substituidos, em comparação com os não substituidos correspondentes. b) A reação dos sulfóxidos β-tia-substituidos com compostos de Grignard aromáticos fornece os mercaptais dos aldeidos aromáticos correspondentes. c) A reação dos sulfóxidos β-tia-substituidos com reagentes de Grignard e impedida por bases fortes. Os rendimentos dos mercaptais são muito mais baixos do que na ausência de base. d) A fixação do organomagnesiano ocorre inicialmente no grupo sulfinila. Um mecanismo envolvendo um estado de transição cíclico é sugerido para explicar a migração preferencial do anel aromático proveniente do composto de Grignard. / This thesis investigates some β-thia-substituted sulphoxides concerning their relative basicity and reactivity toward aromatic Grignard reagents. The following compounds were investigated: methyl n-propyl sulphoxide, methyl methylthiomethyl sulphoxide, ethyl n-butyl sulphoxide, ethyl ethylthiomethyl sulphoxide, ethyl phenylthiomethyl sulphoxide, phenyl phenylthtomethyl sulphoxide and 1,3-dithiolane-l-oxide. A literature review, containing two topics, is presented: 1) basicity of sulphoxides, 2) reactions of sulphoxides with Grignard reagents. The data of the association constants for two β-thiasubstituted and two corresponding unsubstituted sulphoxides are presented. These values were calculated from the chemical shifts of the phenol protons, measured in the ternary systems sulphoxide -phenol-carbon tetrachloride, by methods of Mathur and Carper. The reactivity of four sulphoxides with some Grignard reagents, such as phenyl-, p-anisyl-, and p-tolylmagnesium bromides including the analyses of the resulting products is presented. The preparation of five sulphoxides and of some authentic products are described. Some experiments, in which the Grignard reaction is performed in basic conditions, are reported. The obtained results are discussed in the light of the literature data. It is shown that: a) There is a decrease in basicity going from the unsubstituted sulphoxides to the corresponding β-thia-substituted ones. b) The reaction of β-thia-substituted sulphoxides lead to the corresponding aromatic aldehydes mercaptals. c) The reaction of the β-thia-substituted sulphoxides is inhibited by the presence of a base. The yields of mercaptals are much lower than in the absence of base. d) The attachment of the Grignard reagent occurs, initially, at sulphinyl group. A mechanism, envolving a cyclic transition state, is suggested, in order to explain the preferential migration of the aromatic ring, which belonged originally to the Grignard reagent.

A presente tese tem por objetivo investigar a existência no estado fundamental da interação entre o grupo carbonila e o átomo de enxofre em α, em alguns compostos de fórmula geral (I): (ver arquivo). O método empregado para esta finalidade foi o de medidas relativas de basicidade por ressonância magnética nuclear. Dois apanhados bibliográficos bem distintos são apresentados. O primeiro descreve os principais estudos sobre a transferência de carga intramolecular no espaço, no estado fundamental, em compostos carbonílicos e carboxílicos contendo heteroátomos, dando-se maior ênfase aos átomos de nitrogênio e enxofre. Este apanhado demonstra que as posições relativas do grupo carbonila e do heteroátomo tem grande importância na interação eletrônica. Além disso, indica a existência de dois tipos de interação: a transanular e uma outra que ocorre nos compostos carbonílicos α-alquiltio-substituídos. O segundo apanhado bibliográfico relata os trabalhos que versam sôbre a determinação de basicidade de compostos carbonílicos e carboxílicos por ressonância magnética nuclear. Para maior clareza de exposição são descritos inicialmente alguns princípios gerais relacionados com este método. São apresentadas as medidas de deslocamento de ponte de hidrogênio para dois doadores de proton, fenilacetileno e fenol, em associação com os compostos carbonílicos e carboxílicos α-etiltio-substituídos (I), em comparação com os compostos correspondentes não substituídos e com os seus homólogos. Os resultados obtidos com ambos os doadores de proton, representados graficamente, indicam que: (1) Há uma correlação linear entre estes resultados e os de medidas de basicidade pelo método de i.v. (2) Nas duas séries de compostos, substituídos ou não por um grupo etiltio, existe a seguinte sequência de basicidade. Amidas > Cetonas > Ésteres > Tioésteres (3) A diminuição de basicidade dentro de cada série de compostos é acompanhada por um aumento da frequência de estiramento do grupo carbonila. (4) Os compostos α-etiltio-substituídos são menos básicos do que os correspondentes não substituídos. (5) A diminuição de basicidade em compostos α-etiltiosubstituídos é acompanhada por uma diminuição da frequência de estiramento do grupo carbonila. É apresentada a discussão e são sugeridas as hipóteses para explicar estes resultados. / Abstract not available.

The high temperature microstructure of the solid phases within the electric arc furnace (EAF) slag has a large effect on the process features such as foamability of the slag, chromium recovery, consumption of the ferroalloys and the wear rate of the refractory. The knowledge of the microstructural and compositional evolution of the slag phases during the EAF process stages is necessary for a good slag praxis. In supplement 1, an investigation of the typical characteristics of EAF slags in the production of the AISI 304L stainless steel was carried out. In addition, compositional and microstructural evolution of the slag during the different EAF process stages was also investigated. Computational thermodynamics was also used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. Furthermore, the influence of different parameters (MgO wt%, Cr2O3 wt%, temperature and the top slag basicity) on the amount of the spinel phase in the slag was studied. In supplement 2, a novel study to characterize the electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation was focused on determining the microstructural and compositional evolution of the EAF slag during and at the end of the refining period. Slag samples were collected from 14 heats of AISI 304L steel (2 slag samples per heat) and 7 heats of duplex steel (3 slags sample per heat). Simultaneously with each slag sampling, the temperature of the slag was measured. The selected slag samples were studied both using SEM-EDS and LOM. In some cases (supplement 2), X-ray diffraction (XRD) analyses were also performed on fine-powdered samples to confirm the existence of the observed phases. It was observed that at the process temperature and at all process stages, the stainless steel EAF slag consists mainly of liquid oxides, magnesiochromite spinel particles and metallic droplets. Under normal operation and at the final stages of the EAF, 304L steelmaking slag contains 2-6 wt% magnesiochromite spinel crystals. It was also found that, within the compositional range of the slag samples, the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. Petrographical investigation of the EAF duplex stainless steelmaking showed that, before FeSi-addition, the slag samples contain large amounts of undissolved particles and the apparent viscosity of the slag is higher, relative to the subsequent stages. In this stage, the slag also includes solid stoichiometric calcium chromite. It was also found that, after FeSi-injection into the EAF and during the refining period, the composition and the basicity of the slag in the EAF duplex steelmaking and EAF stainless steelmaking are fairly similar. This indicates that, during the refining period, the basic condition for the utilization of an EAF foaming-slag praxis, in both austenitic and duplex stainless steel cases, is the same. Depending on the slag basicity, the slag may contain perovskite and/or dicalcium silicate too. More specifically, the duplex stainless steel slag samples with a higher basicity than 1.55 found to contain perovskite crystals. / QC 20110413

In the copper smelting processes, the viscosity of the matte and the slag is an important factor for establishing efficiency. Impurities in the concentrates affect the viscosity not only by changing the melt structure but also by promoting precipitation of solid phase which sharply rises it. In this master thesis, a comprehensive methodology was established to study the MgO effects on the properties of a copper smelting slag. Thus, glassy samples were obtained and after confirmation of the composition and the glassy structure with EDS, SEM, and XRD analysis, they were examined through Ramanspectroscopy to study their glassy structure. Moreover, Mössbauer spectroscopy was used to determine the amount of Fe3+ in the samples. Models from the literature were compared to the experimental data. Coherence with the literature was found with the effect of MgO as a network modifier of the oxide melt structure and a promoter of high coordinated structures. Estimations through models were performed to study the iron redox equilibria of the melt and were compared with experimental data, but it was not possible to find the limit of Fe3+ at which precipitation of solid phase initiates. / I kopparsmältningsprocesserna är mattans och slaggens viskositet en viktig faktor för att uppnå effektivitet. Föroreningar i koncentraten påverkar viskositeten inte bara genom att ändra smältstrukturen utan också genom att främja utfällning av fast fas som kraftigt höjer den. I denna magisteruppsats fastställdes en omfattande metod för att studera MgO-effekterna på egenskaperna hos en kopparsmältningsslagg. Således erhölls glasiga prover och efter bekräftelse av kompositionen och den glasiga strukturen med EDS-, SEM- och XRD-analys undersöktes de genom Ramanspektroskopi för att studera deras glasstruktur. Dessutom användes Mössbauerspektroskopi för att bestämma mängden Fe3+ i proverna. Modeller från litteraturen jämfördes med experimentella data. Överensstämmelse med litteraturen hittades med effekten av MgO som ett nätverksmodifierare av oxidsmältstrukturen och en promotor för högkoordinerade strukturer. Uppskattningar genom modeller utfördes för att studera smältans järnredoxjämvikter och dessa jämfördes med experimentella data, men det var inte möjligt att hitta gränsen för Fe3+ vid vilken utfällning av fast fas initierades.

Recognizing the dual ability of the nitride ligand to react as a nucleophile or an electrophile – depending on the metal and other supporting ligands – is a key to their broad-range reactivity; thus, three DFT studies were initiated to investigate these two factors effects (the metal and supporting ligands) for tuning nitride ligand reactivity for C-H and N-H bond activation/functionalization. We focused on studying these factors effects from both a kinetic and thermodynamic perspective in order to delineate new principles that explain the outcomes of TMN reactions. Chapter 2 reports a kinetic study of C–H amination of toluene to produce a new Csp3–N (benzylamine) or Csp2–N (para-toluidine) bond activated by diruthenium nitride intermediate. Studying three different mechanisms highlighted the excellent ability of diruthenium nitride to transform a C-H bond to a new C-N bond. These results also revealed that nitride basicity played an important role in determining C–H bond activating ability. Chapter 3 thus reports a thermodynamic study to map basicity trends of more than a one hundred TMN complexes of the 3d and 4d metals. TMN pKb(N) values were calculated in acetonitrile. Basicity trends decreased from left to right across the 3d and 4d rows and increases from 3d metals to their 4d congeners. Metal and supporting ligands effects were evaluated to determine their impacts on TMNs basicity. In Chapter 4 we sought correlations among basicity, nucleophilicity and enhanced reactivity for N–H bond activation. Three different mechanisms for ammonia decomposition reaction (ADR) were tested: 1,2-addition, nitridyl insertion and hydrogen atom transfer (HAT). Evaluating nitride reactivity for the aforementioned mechanisms revealed factors related to the metal and its attached ligands on TMNs for tuning nitride basicity and ammonia N–H activation barriers.

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness. / <p>QC 20131114</p> / Steel Eco-Cycle

Ce travail porte sur la synthèse et la caractérisation de fluorures à base d’alcalins, d’alcalinoterreuxet de terres rares et sur la réactivité de ces composés vis-à-vis de ReF6 pour lapurification de UF6. L’étude traite dans un premier temps de la synthèse de fluorures tels queKMgF3, MgF2 et CaF2 en couplant une voie solvothermale assistée par micro-ondes et uneétape de fluoration à partir de fluor élémentaire (F2). Les techniques de caractérisationutilisées mettent notamment en avant le caractère basique au sens de Lewis de ces composéset la possibilité de contrôler leur surface spécifique et leur taux d’oxygène, à l’origine dessites basiques, via la température de fluoration (F2) en phase gaz. Dans un second temps, lasolution solide Ce1-xZrxF4 à base de Ce4+ et Zr4+ a été obtenue par fluoration directe d’oxydesmixtes à partir de fluor élémentaire dilué. L’étude par DRX et RMN du 19F montre laprésence d’une solution solide pour des compositions voisines de x=0,5. Enfin, la réactivité deReF6 et UF6 sur KMgF3, MgF2 et CaF2 montre que KMgF3 est un très bon candidat pour lapurification de UF6 vis-à-vis de ReF6, qui dépend à la fois de paramètres intrinsèques auxfluorures divisés (surface spécifique, taux d’oxygène, basicité, cations mis en jeu…) maisaussi du procédé de purification (température, temps de contact). / This work deals with the synthesis and characterization of alkali, alkali-earth and rare earthbased fluorides and the reactivity of the latter with ReF6 for UF6 purification. In a first part,we focused our attention on the synthesis of KMgF3, MgF2 and CaF2 high surface area metalfluorides coupling both microwave assisted solvothermal process and a fluorination step withelemental fluorine (F2). The higher the surface area, the higher the oxygen rate. Thesenanofluorides exhibit Lewis basic character. In a second part, several compositions of theCe1-xZrxF4 solid solution were synthesized by direct fluorination of mixed oxides usingelemental fluorine (F2). XRD an 19F NMR characterizations show the occurence of a newsolid solution for compositions close to x=0.5. Finally, the reactivity between ReF6/UF6 andKMgF3, MgF2 and CaF2 leads to conclude that KMgF3 is the best candidate for thepurification of UF6. This study indicates that the purification depends on several parameters :intrinsic parameters of the divided fluorides (surface area, oxygen rate, basicity, cations…)and parameters directly related to the process (temperature, contact time).