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Prior, David V. "Hydrogen-bond basicity." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/847920/.
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A general scale of solute hydrogen-bond basicity has been constructed using a vast body of 1:1 hydrogen-bond equilibrium constants taken from literature. The data is assembled as a series (or set) of log K values for bases measured against a given hydrogen-bond acid in dilute tetrachloromethane solution. 34 such sets have been collected and a computational method regresses the log K data into 34 optimized equations of the form; log K[(set1)] = LA[i]. log K[H][B] + De[i] (1) For each set, the constants (LA and De) characterize the particular reference acid and the log K HB values characterize (and thereby scale) the bases over all sets. Certain acid-base combinations must, however, be excluded from equation 1 and this provides evidence that the log K HB scale is not entirely general towards all reference acids. In the regression procedure, use has been made of the novel observation that the lines represented by equation 1 intersect at a point where log K = log K HB = -1. 1. It is further shown that this condition enables the estimation of 1: 1 hydrogen-bond log K values in tetrachloromethane via equation 2; log K = 0.3421. (log K HA + 1. 1)(log HB + 1. 1) - 1.094 (2) where log K HA is a scale of solute hydrogen-bond acidity. The log K HB scale has been analysed in terms of the two principle factors of basicity according to the method devised by Maria and Gal et al. This analysis is shown to be informative in establishing and interpreting the relationships of log K HB with other basicity-dependent properties. For the most part, the experimental studies undertaken are concerned with a critical examination of the existing methods of determining G and H for 1:1 hydrogen-bond formation. The customary assumption of an exclusive 1:1 model of acid-base association in dilute solution has been tested with respect to the interaction of cyclohexanone with 3,5-dichlorophenol in cyclohexane. Using infrared spectroscopy, evidence for higher complex formation is presented and a method has been developed for determining simultaneously the formation constants of both the 1: 1 (AB) and 2: 1 (A2B) complexes (K1 and K2, respectively). 2:1 complex formation is also shown to interfere significantly with the K and H values obtained from a classical calorimetric titration procedure, limiting its application to hydrogen-bonding studies. For this reason, an improved calorimetric method for the independent determination of 1:1 hydrogen-bond enthalpies has been developed. Application of the devised methods to the interaction of 3,5-dichlorophenol with series of aliphatic ketones and aliphatic ethers in cyclohexane has yielded the values of K1 and K2, together with the thermodynamic parameters (G1, H1 and S1) of 1:1 hydrogen-bond formation. Within each series, the small differences in K1 and H1 resulting from the very subtle structural variations in the base component are discussed in terms of electronic and steric effects. The values of K1 and K2 are found to be consistent with a theoretically derived equation predicting a linear relationship between log K1 and log K2, and the values of H1 are used to critically appraise the validity of the Badger-Bauer relationship.
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Lee, Sze Chung. "The acidity and basicity of the atmosphere in Hong Kong /." access abstract and table of contents access full-text, 2006. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-bch-b21471411a.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2006."Submitted to Department of Biology and Chemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.
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López, Fernández Xavier. "Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions." Doctoral thesis, Universitat Rovira i Virgili, 2003. http://hdl.handle.net/10803/9069.
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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 WellsDawson (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 WellsDawson (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.
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Blignaut, Annalie. "Influence of basicity in Fischer-Tropsch synthesis over supported iron-based catalysts." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/7477.
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Includes bibliographical references (leaves 115-124).The Fischer-Tropsch synthesis catalyzed by iron is a well-established process for the production of synthetic fuels, waxes and high-value chemicals, such as α-olefins. A draw-back of the currently used iron-based catalysts is their short lifetime, caused by sintering and particle break-up. These disadvantages might be overcome by utilizing a supported iron-based catalyst. However, supported iron Fischer-Tropsch synthesis, which has been tested up to now, show a high methane selectivity. This might be caused by a lack of alkali near the catalytic site, which can be alleviated by using a basic support. Classical basic supports such as CaO and MgO will react with CO2 (a major by-product in iron-catalyzed Fischer-Tropsch synthesis) yielding carbonates and can therefore not be used, since the formation of carbonates will result in a large particle expansion. An alternative would be to generate a silica-based basic support by attaching basic groups to the silica. In this study iron Fischer-Tropsch catalysts supported on silica were tested for conversion of synthesis gas to hydrocarbon products. Silica was modified with aminopropyltriethoxysilane (APTeS) by impregnation followed by calcination to provide basic surface groups onto the silica surface. The CHN analysis and IR-analysis indicate the presence of amine groups in the APTeS-modified silica. The pore radius distribution of silica is slightly shifted towards higher pore radii in comparison to APTeS-modified silica. It might thus be stated that aminopropyltriethoxysilane covers the pore walls and does not seem to result in pore blockage. Thermal gravimetric analysis indicates that the thermal stability of APTeS-modified silica is low. A major difference between silica and APTeS-modified silica was their zeta-potential. Whereas the surface of silica is mainly negatively charged in the pH-range of interest during impregnation, the surface of APTeS-modified silica is mainly positively charged. This is attributed to the presence of amine groups on the surface. Iron was brought onto the support by impregnation. The surface modification of silica with APTeS seems to be destroyed upon calcination of the impregnated catalysts. The iron phase in the calcined iron catalyst supported on silica catalysts is mainly hematite (Fe203), whereas the iron phase in the calcined iron catalyst supported on APTeS-modified silica catalysts is mainly iron oxide hydroxide FeOOH. The presence of basic amine groups may favour the formation of FeOOH crystallites during the impregnation/calcination on the APTeS-modified silica. The FeOOH-crystallites on the APTeS-modified silica support are typically smaller than the Fe203 crystallites on silica. The maximum catalytic activity is obtained at 0.01 mol K I mol Fe for the iron catalyst supported on silica and at 0.02 mol K I mol Fe for the APTeS-modified catalyst, indicating the optimum potassium loading. The difference in the optimum potassium loading might be linked to the smaller crystallite sizes obtained with the APTeS-modified catalyst. All the potassium promoted catalysts show a lower methane selectivity compared to the 0 K iron catalyst supported on silica and the 0 K iron catalyst supported on APTeS-modified silica. The 1-olefin and n-olefin content in the fraction of linear hydrocarbons increase with increasing potassium loading over all the iron catalyst supported on silica promoted with potassium except for the catalysts 0.005 K and 0.01 K. Increasing potassium content on the catalyst resulted in higher 1-olefin content in the fraction of linear olefins. The trend suggests that potassium promotion suppresses secondary double bond isomerisation of 1-0lefin into internal olefins. The high degree of branching obtained with the 0.005 K catalyst and the 0.01 K catalyst, is characteristic of weak alkali promotion. The iron catalysts supported on APTeS-modified silica indicate an increase in the degree of branching with increasing potassium content.
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An, Feng [Verfasser], and Herbert [Akademischer Betreuer] Mayr. "Reactivity and basicity: insight into organocatalysis by secondary amines / Feng An ; Betreuer: Herbert Mayr." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1203066961/34.
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Chen, Yao-Jung. "Secondary amine catalyzed-oximation of cyclopentanone and basicity and reactivity of 1-azabicyclo[2.2.1]heptane /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487265555441794.
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Green, Anthony James. "Computation of hydrogen bond basicity as a descriptor in bioisosterism : a quantum chemical topology perspective." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/computation-of-hydrogen-bond-basicity-as-a-descriptor-in-bioisosterism-a-quantum-chemical-topology-perspective(068da139-48b0-4881-a131-5c281fd4af8a).html.
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Hydrogen bonding is a regularly occurring non covalent interaction in biological systems. Hydrogen bonding can influence a drug’s interaction with its target. It is therefore important to practically measure the relative strengths of hydrogen bonds. Hydrogen bond basicity is a measure of a hydrogen bond acceptor’s capacity to accept hydrogen bonds. There are many hydrogen bond basicity scales. However, the pKBHX scale is claimed to be the most relevant to medicinal chemists because it gives a thermodynamically deducible values for each site in polyfunctional bases. A computed property, the change in energy of the hydrogen bond donor hydrogen bond atom ΔE(H), derived from the quantum theory of atoms in molecules has been found to correlate strongly with pKBHX values for OH and NH hydrogen bond donors. In particular, R2 values of 0.95 and 0.97 have been found when methanol and methylamine respectively are used as hydrogen bond donors. The property ΔE(H) has also been successfully used to predict the pKBHX values of an external data set and the values of polyfunctional bases. The strength of the correlations are not dramatically affected by using scaled down fragments of bases, or by relaxing the convergence criteria during the geometry optimisation step of calculations. The relationship between ΔE(H) and pKBHX has been found to break down for tertiary amines, and more generally for strong proton acceptors with pKBH+ values greater than 6. The successful pKBHX prediction model was, however, unsuccessful in predicting drug binding data and pKBHX values of bases that accept two separate hydrogen bonds. At this moment in time both the reason why the relationship between pKBHX and ΔE(H) is present and then breaks down for strong proton acceptors is unfortunately unknown.
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Melang, Me Nze Vanessa. "Préparation de nouveaux matériaux pour l'élimination catalytique des composés organiques volatils." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2272/document.
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Cette étude concerne la préparation de nouveaux matériaux pour l'élimination catalytique d'un composé organique volatil (COV) : l'acide acétique. La décomposition de cette molécule gazeuse conduit à la formation de produits nocifs tels que le CO2, l'acétone et le formaldéhyde. En présence d'oxygène, des études antérieures ont mis en évidence le caractère réfractaire de l'acide acétique en milieux aqueux. En phase gaz, la dégradation de la molécule est améliorée en présence de catalyseurs basiques et réductibles tels que les oxydes mixtes MgAl. Ces matériaux ont été synthétisés via les méthodes co-précipitation (cp) et sol-gel (sg). Sur chaque catalyseur, du cérium est déposé en surface afin d'améliorer les propriétés réductrices initiales. Les échantillons MgAlCey_cp et MgAlCey_sg (y : 0,03% ; 0,07% ; 0,14% molaire) ont montré une augmentation de la capacité de stockage de l'oxygène (CSO) et du nombre de sites basiques forts dues à la multiplicité des espèces oxygènes (O22-, O2- et/ou O2-) de surface provenant de la cérine (CeO2). En effet, la basicité et la CSO des matériaux ont augmenté pour les catalyseurs MgAlCey_sg tandis que pour MgAlCey_cp un effet de synergie apparait. La réductibilité des solides semble être indépendante du mode de préparation initial. En revanche, le nombre de sites basiques est supérieur pour les catalyseurs MgAlCey_cp par rapport à MgAlCey_sg. Cette basicité accrue des catalyseurs co-précipités leur confère une activité supérieure mais limitée par la formation supposée de carbonates au cours de la réaction d'oxydation de l'acide acétique. Hormis la cérine, la meilleure activité est obtenue par les matériaux MgAlCe0,14_cp et MgAlCe0,14_sgThis work is devoted to the preparation of the new materials for the catalytic removal of volatile organic compound (VOC) : acetic acid. Decomposition of this gaseous molecule generate dangerous products such as CO2, acetone and formaldehyde. Removing acetic acid in aqueous phase is more difficult than gas phase. In fact, the presence of basic and redox catalysts like mixed oxides MgAl improve the oxidation of acetic acid reaction. This catalysts were prepared by co-precipitation and sol-gel methods. On each catalyst, cerium is deposited on the surface in order to improve their reducibility. MgAlCey_cp and MgAlCey_sg catalysts (y : 0.03% ; 0.07% ; 0.14% molar) have shown the increase of oxygen storage capacity (OSC) and number of strong basic sites because of various oxygen species (O22-, O2- and/or O2-) located on the surface of the materials and provided by ceria (CeO2). In fact, oxygen storage capacity of these catalysts is increased for MgAlCey_sg whereas a synergy effect appears for MgAlCey_cp. The results have shown that the reducibility of the catalysts is not related to the initial preparation method. However, basicity of MgAlCey_cp catalysts is higher than MgAlCey_sg. This basicity gives a high activity to co-precipitated catalysts which is limited by possible formation of carbonates during the oxidation reaction of acetic acid. Except for ceria, the best activity is obtained by MgAlCe0.14_cp and MgAlCe0.14_sg catalysts
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Luo, Zhaohui. "GC/FT-ICR Mass Spectral Analysis of Complex Mixtures: A Multidimensional Approach for Online Gas Phase Basicity Measurements." Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/LuoZX2006.pdf.
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Mayer, Robert Josef [Verfasser], and Armin [Akademischer Betreuer] Ofial. "Reactivity of oxygen and sulfur nucleophiles and basicity scales toward heteroatom Lewis acids / Robert Josef Mayer ; Betreuer: Armin Ofial." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1236846087/34.
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RebouÃas, Vanessa Tomaz. "ReavaliaÃÃo da faixa ideal de pH e da tolerÃncia de juvenis de tilÃpia do nilo, Oreochromis niloticus, Ã acidez elevada da Ãgua de cultivo." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=14504.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoDois estudos consecutivos foram realizados para reavaliar a faixa ideal de pH e a tolerÃncia de juvenis de tilÃpia do Nilo, Oreochromis niloticus, à acidez elevada da Ãgua de cultivo, em condiÃÃes eutrÃficas de cultivo. Os pesos iniciais dos animais eram semelhantes em ambas as fases. No primeiro trabalho, foram adotadas quatro condiÃÃes distintas de pH da Ãgua de cultivo: pH = 5,56  1,21 (pH 5); pH = 6,59  0,77 (pH 6); pH = 8,25  0,39 (pH 8); pH = 9,21  0,37 (pH 9), obtidas pelas aplicaÃÃes de soluÃÃes Ãcidas ou alcalinas à Ãgua. Os animais foram mantidos em tanques externos de 250 L por oito semanas. NÃo houve renovaÃÃo da Ãgua de cultivo ao longo de todo o trabalho. Neste trabalho, foram observadas variÃveis de qualidade de Ãgua, solo, zootÃcnicas e metabÃlicas. As maiores concentraÃÃes de nitrogÃnio amoniacal total da Ãgua foram encontradas nos tanques pH 5 e as menores nos tanques pH 8. A concentraÃÃo de gÃs sulfÃdrico na Ãgua foi maior nos tanques pH 5. O peso corporal final, a taxa de crescimento especÃfico e a produtividade do pescado nos tanques pH 5 foram maiores do que o observado nos tanques pH 9. Observou-se maior consumo de oxigÃnio nos respirÃmetros de pH 9. Concluiu-se que a faixa ideal de pH da Ãgua para o cultivo de juvenis de tilÃpia do Nilo, em Ãguas eutrofizadas, vai de 5 a 8. O delineamento experimental do segundo trabalho foi constituÃdo por quatro tratamentos, a saber: Ãguas de cultivo com diferentes valores de pH (pH 4: 4,12  0,84; pH 5: 5,13  0,74; pH 6: 6,14  0,64 e pH 8: 8,06  0,48), com cinco repetiÃÃes cada. NÃo houve troca da Ãgua de cultivo, apenas reposiÃÃo para manter o nÃvel inicial. Durante oito semanas, foram observadas variÃveis de qualidade de Ãgua, solo, zootÃcnicas, metabÃlicas e qualidade de efluentes. Embora a concentraÃÃo de nitrogÃnio amoniacal total (NAT) na Ãgua tenha sido menor nos tanques pH 8, sua concentraÃÃo de amÃnia nÃo-ionizada (NH3) foi maior que nos demais. Ao final, o menor peso corporal dos peixes foi observado nos tanques pH 8. Houve significativa melhora nos resultados de conversÃo alimentar e na taxa de eficiÃncia proteica com a acidificaÃÃo da Ãgua. As concentraÃÃes de NH3 nos efluentes dos tanques acidificados foram reduzidas. Concluiu-se que a acidificaÃÃo gradual da Ãgua de cultivo de juvenis da tilÃpia do Nilo atà pH 4 à benÃfica ao crescimento corporal dos peixes. A avaliaÃÃo de todos os resultados permite inferir que a faixa de pH da Ãgua para cultivo de O. niloticus seja de 4 a 8.
The first experiment aimed to reassess the Nile tilapiaâs optimum range of water pH for culture in eutrophic conditions. The initial weights of the animals were similar in both phases. There were four different conditions of water pH: pH = 5,56 Â 1,21 (pH 5); pH = 6,59 Â 0,77 (pH 6); pH = 8,25 Â 0,39 (pH 8); pH = 9,21 Â 0,37 (pH 9), that were obtained by acidic or alkaline applications upon the rearing waters. The fishes were maintained in twenty outdoor 250-L tanks for eight weeks. No water exchange was performed over the entire study. Variables of water and soil quality, growth performance and metabolism were monitored in the 1st work. The highest concentration of total ammonia nitrogen was observed in the pH 5 tanks and the lowest ones in the pH 8 ones. The hydrogen sulfide concentrations were higher in the pH 5 tanks. Fish final body weight, specific growth rate and yield were higher in the pH 5 tanks than in the pH 9 ones. There was a higher consumption of dissolved oxygen in the pH 9 respirometers than in the other ones. It was concluded that the optimum water pH range for Nile tilapia culture in eutrophic waters is 5 â 8. The second experiment aimed to determine the tolerance of Nile tilapia juveniles to high acidic culture waters and the effects of the culture water acidification upon the tanksâ effluents quality. The experimental design had four treatments, e.g., waters with different pH values (pH 4: 4,12 Â 0,84; pH 5: 5,13 Â 0,74; pH 6: 6,14 Â 0,64 e pH 8: 8,06 Â 0,48), with five replicates each. No water exchange was carried out over the entire study, just water replenishment to maintain the initial level. Variables of water quality, soil, growth performance, metabolism and effluents were observed over eight weeks. In spite of the lower total ammonia nitrogen (TAN) concentration in the pH 8 tanks, their levels of non-ionized ammonia (NH3) were the highest. At the end, the lowest fish body weight was observed in the pH 8 tanks. There was a significant improvement in the feeding conversion ratio and protein efficiency rate by the water acidification. The concentrations of NH3 were reduced in the acidic tank effluents. It was concluded that the gradual water acidification up to pH 4 is good to Nile tilapia juvenilesâ growth performance. The evaluation of all the results shows that the water pH range for cultivation of O. niloticus is 4-8.
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Mathieu, Romain. "Solubilité du sodium dans les silicates fondus." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL044N/document.
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Les alcalins, généralement lithophiles à basse température, deviennent volatils à haute température et/ou sous des conditions réductrices. Il existe peu de données expérimentales sur les relations activité-composition dans les silicates fondus et aucun modèle thermodynamique ne permet de prédire leur comportement dans les liquides silicatés. Pour acquérir une base de données cohérente sur ces relations, nous avons développé un nouveau système expérimental permettant d'imposer et de contrôler, à haute température, une pression partielle de sodium sous des conditions d'oxydoréduction fixées. Une cellule thermochimique originale, simple de mise en œuvre et efficace a été conçue pour contraindre l’ensemble de ces paramètres thermodynamiques. Les résultats de cette étude montrent que les processus de condensation et de volatilisation du sodium dans les liquides silicatés du système CaO-MgO-Al2O3-SiO2 peuvent être décrits par une équation simple de type : Na(gaz) +1/2 O2(gaz) = Na2O(liq). Les données obtenues à l'équilibre sur des liquides de compositions différentes ont permis de dériver un modèle permettant de prédire la solubilité et les coefficients d’activité (aNa2O et ?Na2O) dans un liquide silicaté du système CaO-MgO-Al2O3-SiO2, à différentes températures et différentes PNa, en fonction de la composition de ce dernier. Ce modèle est basé sur la détermination de la basicité optique du liquide sans sodium, c'est-à-dire suivant l’état de polymérisation du liquide et suivant ses interactions acide-base entre oxydes. Par ailleurs, ces travaux ont permis la détermination d’un nouveau type de diagramme de phase à isoPNa. Enfin cette étude a de nombreuses applications en cosmochimie, sidérurgie et magmatologieAlkalis in molten silicates have a complex behaviour, changing from lithophile to volatile elements depending on temperature and/or reducing conditions. However, due to the lack of experimental data concerning activity/composition relationships, there is no thermodynamic model available to describe alkali solubility in silicate melts, and their partitioning between melts, minerals and gases. In order to tackle this issue, we have developed a new device for the determination of sodium oxide activity in silicate melts by equilibration of melts with gaseous environment of known Na partial pressure at high temperature and fixed oxygen fugacity (PO2) following: Na(gaz) +1/2 O2(gaz) = Na2O(liq). Using equilibrium data we have establish a model able to predict the sodium solubility and activity in silicate melt belonging CaO-MgO-Al2O3-SiO2 system, at differents PNa and temperatures, as a function of optical basicity, i.e. melt composition. These results have allowed us to determine new type of phase diagram at isoPNa. Finally, this study have to many applications in cosmochemistry, steel and magmatic process
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Elahipanah, Zhaleh. "Thermo-Physical Properties of Mould Flux Slags for Continuous Casting of Steel." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101270.
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Due to the high efficiency and productivity of continuous casting process, this method has been the most employed process to produce steel in past decades. The need to improve and optimize the finished product made it essential to gain more knowledge about the process, types of defects that may occur and the reasons for them. Moreover, the solutions for reducing the shortcomings in continuous casting process have been an intriguing subject to study. Many attempts have been done in order to reach this goal. Understanding, determining and optimizing the mould flux slag properties is especially important, since it plays an important and significant role in this process. For this, it is of outmost importance to acquire more knowledge about different properties of mould flux powders. Hence, there has been a world wide effort to measure and model the properties of mould flux properties, such as liquidus and solidus temperatures, heat capacity, enthalpy, thermal expansion, density, viscosity, electrical conductivity, surface tension and thermal conductivity. This thesis presents a brief review on continuous casting process, mould flux powder and its properties and characteristics. Furthermore, it focuses on the thermo-physical properties of mould fluxes. In present work, different industrial mould flux powders have been analyzed to measure their viscosity, break temperature, physical properties such as density, flowablity of powder, slag structure and chemical composition. The experimental data have been compared to some of the most commonly used models such as Riboud model, Urbain model, Iida model and KTH model.
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Kosgei, Cosmas Kipyego. "Investigation of the effect of basicity and Concentration ofproton accepting bases on the potential of Quinones for highpotential quinone based cathode materials." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-288369.
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Batoon, Patrick Henry M. "Thermochemical differences in lysine and lysine-homolog containing oligopeptides: Determination of basicity and gas-phase structure through mass spectrometry, infrared spectroscopy, and computational chemistry." Scholarly Commons, 2016. https://scholarlycommons.pacific.edu/uop_etds/127.
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The data presented in this thesis is a comprehensive study on the nature of peptide structure and how subtle and systematic changes in sequence and sidechain affect the basicity, ion stability, and conformation of a peptide. The peptides characterized were acetylated polyalanine di-, tri-, and tetra- peptides containing a proton-accepting probe: lysine and or the non-proteinogenic lysine-homologs: ornithine, 2,4-diaminobutyric acid, and 2,3-diaminopropionic acid. Peptides were studied in isomeric pairs for which the basic amino acid was placed closest to the N-terminus or the C-terminus of each peptide family (A n Probe vs. ProbeA n ). Using a variety of mass spectrometry based techniques and infrared multiphoton dissociation ion spectroscopy, the isomeric families of polyalanine peptides were characterized. Quantum chemical techniques were employed in parallel to provide theoretical predictions of three-dimensional structure, physical properties (dipole moment, polarizability, and accessible surface area), thermochemical values, and vibrational IR spectra, to gain further understanding of the peptides studied and to push the limits of current theoretical models. Overall it was found that the AnProbe peptide was more basic than their ProbeAn isomer. For the dipeptide systems, the greater basicity of AProbe peptides was due to efficiently charge-solvated ions which formed more compact structures compared to their ProbeA counterpart. For the tri- and tetra- peptide systems, greater basicity of the A 2,3 Probe peptides was likely due to formation of α or 3 10 helix-like structures in the protonated forms., introducing the macrodipolar effect, which cooperatively encouraged helical formation while stabilizing the charged site. On the other hand, ProbeA 2,3 peptides formed charge-solvated coils which do not exhibit any kind of dipole effect, resulting in lower basicity than their A2,3Probe counterpart.
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Oliveri, Ivan Pietro. "Zinc(II) Schiff Base Complexes and their Aggregation/Deaggregation Properties: Versatile and Multifunctional Materials as Chemosensors and Building Blocks for New Supramolecular Architectures." Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1292.
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In this PhD thesis the synthesis, characterization, and study of the aggregation/deaggregation properties of a series of amphiphilic bis(salicylaldiminato)ZnII Schiff base complexes, involving different bridging diamino groups, and their applications as molecular probes, nonlinear optical (NLO) and vapochromic materials, as well as synthons for the formation of new fibrillar and branched supramolecular nanostructures, are reported.
Through detailed 1H NMR, DOSY NMR and optical spectroscopic studies, it is found that these species always form aggregates in solution of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of all complexes occurs because of the axial coordination to the ZnII ion, accompanied by considerable changes of the 1H NMR and optical absorption and fluorescence spectra. Moreover, an easy switch-on of the NLO response upon addition of a Lewis base, such a pyridine, with formation of a 1:1 adduct, or 1,2-bis-(4-pyridyl)ethane, with formation of a 2:1 adduct, is observed. As the amount of the coordinating species for the complete deaggregation of the complexes is dependent of the Lewis character of the ZnII ion, an order of the Lewis acidic character can be established for the aggregate species in non-coordinating solvents. The effect of the alkyl chain length seems to play a minor role in the aggregation properties, since 1H NMR data, optical absorption and fluorescence spectra remain almost unaltered upon changing the chain lengths. The complexes having benzene ring bridge form fibrillar nanostructures whose width is influenced by the degree of interdigitation of side alkyl chains.
The Lewis acid properties of the complexes having 2,3-diaminomaleonitrile bridge, with respect a series of primary, secondary and tertiary aliphatic amines, and several alkaloids, are also investigated. Through the analysis of fluorescence titrations, it is found that the binding interaction, the selectivity and the sensitivity of these complexes are strongly influenced by the steric characteristics of the nitrogen based donors and then by their Lewis basicity, leading to high selectivity, in the micromolar range, and sensitivity for pyridine-based, cinchona alkaloids, primary and alicyclic amines. A distinct selectivity is also observed along the series of secondary or tertiary amines, paralleling the increasing steric hindrance at the nitrogen atom. Moreover, these complexes have been also involved as reference Lewis acids, to build up a reliable Lewis basicity scale in dichloromethane for amines and various common solvents whose trend is influenced by the steric hindrance of both the Lewis bases and the reference Lewis acid. The these complexes have also investigated as vapochromic materials, able to change their colour upon exposure to volatile Lewis bases, allowing their application as chemosensors for volatile Lewis bases in the solid state.
Finally, new branched nanostructures have been achieved for a ZnII Schiff base complex having an alkyl ammonium bromide in the alkyl side chains. Unlike to studies on the aforementioned amphiphilic complexes, in this case the control of the supramolecular architecture is governed by intermolecular Zn---Br interactions.
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Mai, Paolo. "Effect of iron redox state on crystallization behaviour of Fayalite slags." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-286327.
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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.
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Toom, Lauri. "Bispidine Derivatives : Synthesis and Interactions with Lewis Acids." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6735.
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Landau, Shaun Errick. "Pushing the limits of acidity and basicity of transition metal hydride complexes, studies of acidic dicationic dihydrogen complexes of iron (II) and basic anionic hydride complexes of iridium (III)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0004/MQ45928.pdf.
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Dong, Pengli. "Measurements of the thermodynamic activities of chromium and vanadium oxides in CaO-MgO-Al2O3-SiO2 slags." Licentiate thesis, KTH, Materials Science and Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9940.
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In the present work, the thermodynamic activities of chromium and vanadium oxide in CaO-SiO2-MgO-Al2O3 slags were measured using gas-slag equilibration technique. The slag was equilibrated with a gas mixture of CO, CO2 and Ar gases enabling well-defined oxygen partial pressures in the gas mixture (PO2=10-3,10-4,10-5 Pa) at temperatures 1803, 1823K, 1873, 1923 K. The slags were kept in Pt crucibles during the equilibration and the duration of which was 20 h. From a knowledge of the thermodynamic activity of chromium and vanadium in Cr or V in Pt alloy, obtained from literature, and the oxygen partial pressure in the gas stream calculated by Thermo Calc software, the thermodynamic activity of chromium, vanadium oxide in the slags could be observed.An assessment of the experimental studies in earlier works reveal that, the activities of chromium at low chromium contents and vanadium in their respective alloys in platinum exhibits a strong negative deviation from ideality, the logarithms of activity coefficient of these elements were found to increase with increasing mole fractions of these metals in the Pt-alloys.Regarding the slag phase, all the chromium in the slags was assumed to be present in the divalent state in view of the low Cr contents and the low oxygen potentials employed in the present studies. Analogously, vanadium in the slag was assumed to be in the trivalent state in view of the low vanadium contents in the slag and the low oxygen partial pressure in the gas phase. Activity of chromium oxide, CrO decreases with increasing temperature and decreasing content of chromium oxide in slag and oxygen partial pressure in the gas phase. Activity of vanadium oxide, VO1.5 in slag phase shows a negative deviation from ideality. Activity coefficient of vanadium oxide shows a decrease with basicity of slag and the “break point” occurs at about slag basicity of 1 under the oxygen partial pressure of 10-3 Pa and temperature of 1873 K.A relationship for estimating the actual content of chromium, vanadium in slag as a function of activities of chromium or vanadium, temperature, oxygen partial pressure and slag basicity were developed from the present results, the agreement between the estimated and experimental values is satisfactory, especially at lower oxygen partial pressure.
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Rasmussen, Danne Rene, and danne@optusnet com au. "A Theoretical Approach to Molecular Design: Planar-Tetracoordinate Carbon." The Australian National University. Research School of Chemistry, 2000. http://thesis.anu.edu.au./public/adt-ANU20010702.115616.
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A number of novel hydrocarbon cage systems have been designed and characterized using ab initio molecular orbital calculations at the MP2 and B3-LYP levels. In particular,equilibrium structures for five families of molecules, hemialkaplanes, hemispiroalkaplanes, alkaplanes, spiroalkaplanes and dimethanospiroalkaplanes, have been examined in detail with the aim of designing a saturated hydrocarbon with a planar-tetracoordinate carbon atom and with a view to identifying appropriate synthetic targets.
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The hemialkaplanes and hemispiroalkaplanes are constructed from a spiropentane or neopentane subunit, respectively, which is capped by a cyclic hydrocarbon. The hemispiroalkaplanes are predicted to contain a pyramidal-tetracoordinate carbon atom possessing a lone pair of electrons. Protonation at this apical carbon atom is found to be highly favorable, resulting in a remarkably high basicity for a saturated hydrocarbon. The proton affinities of the hemispiroalkaplanes are calculated to be more than 1170 kJ mol[superscript -1] , even greater than those for the diamine "proton sponges".
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The alkaplanes and the spiroalkaplanes, which are constructed by bicapping a neopentane or spiropentane subunit, respectively, with a pair of cyclic hydrocarbons, show unprecedented flattening of a tetracoordinate carbon atom. Linking the spiroalkaplane caps with methano bridges gives the dimethanospiroalkaplanes, two of which, dimethanospirooctaplane and dimethanospirobinonaplane, achieve exact planarity at the central carbon atom. They are the first neutral saturated hydrocarbons predicted to contain an exactly planartetracoordinate carbon atom. This has been achieved through structural constraints alone. The electronic structure at the central carbon atom results in a highest occupied molecular orbital corresponding to a p-type lone pair. Consequently, the adiabatic ionization energies for octaplane, spirooctaplane and dimethanospirooctaplane (approximately 5 eV) are predicted to be similar to those of lithium and sodium - incredibly low for a saturated hydrocarbon.
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Some consideration has been given to likely pathways for unimolecular decomposition for all species. Predicted structures, heats of formation and strain energies for all the novel hydrocarbons are also detailed. Tetramethylhemispirooctaplane and dimethanospirobinonaplane are identified as the preferred synthetic targets.
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Du, Plessis John. "Control of diffusible weld metal hydrogen through arc chemistry modifications." Diss., Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-05152007-131110.
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EL, GHOMARI MOHAMED-JAMAL. "Basicite molle et antithyroidiens." Nantes, 1996. http://www.theses.fr/1996NANT2020.
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La determination d'une nouvelle echelle thermodynamique de basicite molle a partir des energies de gibbs de complexation des bases organiques par le diiode revele que les thiourees sont les bases molles les plus fortes. Or les agents antithyroidiens les plus actifs presentent le pharmacophore thiouree. Nous avons donc etabli un lien entre structure, basicite et activite antithyroidienne pour les deux antithyroidiens les plus prescrits, le methimazole et le carbimazole. Nous proposons que non seulement la basicite molle, par complexation de i+, mais egalement la basicite dure, par complexation de l'heme de la peroxydase thyroidienne, sont a l'origine de l'activite antithyroidienne
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Ben, Salem Roua. "Catalyseurs à base d'oxydes métalliques fluorés : synthèse, caractérisations et applications catalytiques." Electronic Thesis or Diss., Lyon 1, 2023. https://n2t.net/ark:/47881/m6c53kx4.
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Ces travaux de thèse portent sur la synthèse de nouveaux catalyseurs fluorés, utilisant d’acide trifluoroacétique (TFAH) comme précurseur de Fluor, leurs caractérisations physico-chimiques et l’étude de leurs propriétés acido-basiques en phases gazeuse et aqueuse. Une première méthode consiste en l’échange anionique entre des supports oxo/hydroxo de titane, de niobium ou de zirconium, de surfaces spécifiques élevées, et une solution de TFAH. La rétention du fluor, avant et après calcination, est plus importante au contact du support à base de zirconium. La présence de fluor inhibe la basicité de la zircone et génère une acidité de Brønsted expliqué par l’effet électroattracteur de fluor et rend la surface du catalyseur plus hydrophobe. La zircone fluorée convertit sélectivement l’isopropanol en propène en phase gazeuse et la dihydroxyacétone en pyruvaldéhyde dans l’eau. La deuxième synthèse est une nouvelle approche multi-étape couplant la décomposition d’un précurseur de fluor à base d’yttrium Y(TFA)3(H2O)3 en NPs de YF3 et leur incorporation dans un gel de TiO2. Différentes techniques de caractérisations physico-chimique (XPS, DRX, RMN 19F) indiquent que le fluor existe sous la forme YF3 dans la matrice de TiO2, stable après une calcination à 500°C. YF3 dispersé dans TiO2 de surface spécifique élevée catalyse efficacement la conversion de la dihydroxyacetone (DHA) dans l’eauThis thesis work focuses on the synthesis of new fluorinated metal catalysts, using trifluoroacetic acid (TFAH) as fluorine precursor, their physico-chemical characterizations and the study of their acid-base properties in the gas and aqueous phases. The first synthesis is the anionic exchange between oxo/hydroxo supports of titanium, of niobium and of zirconium, with high specific areas, and a solution of TFAH. The fluorine retention, before and after calcination, is greater using the zirconium support. The presence of fluorine inhibits the basicity of the zirconia and generates Brønsted acidity due to the electron-withdrawing effect of fluorine and makes the catalyst’s surface more hydrophobic. Fluorinated zirconia produces selectively propene from isopropanol in gas phase and pyruvaldehyde from dihydroxyacetone in water. The second synthesis is new multi-step approach coupling the decomposition of an yttrium-based fluorine precursor Y(TFA)3(H2O)3 into YF3 NPs and their incorporation into TiO2. Various physico-chemical characterization techniques (XPS, XRD, 19F NMR) indicate that fluorine exists in the form of YF3 in the TiO2 matrix, stable at after calcination at 500°C. YF3 dispersed in TiO2 of high surface area catalyzes efficiently the conversion of dihydroxyacetone (DHA) in water
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Mostafaee, Saman. "A Study of EAF High-Chromium Stainless Steelmaking Slags Characteristics and Foamability." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33754.
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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.
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Clarenc, Romain Pierre. "Synthèse et caractérisation de composés fluorés pour le piégeage de fluorures gazeux." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14094/document.
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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)
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Mostafaee, Saman. "A Study of EAF Austenitic and Duplex Stainless Steelmaking Slags Characteristics." Licentiate thesis, KTH, Materials Science and Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12064.
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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.
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Stoll, Ragnar Samson. "Design of photoswitchable catalyst systems." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/15937.
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Photokontrolle von Eigenschaften einzelner Moleküle und größerer Molekülvereinigungen ist ein faszinierendes Feld aktueller chemischer Forschung. Das schlichte Potential der genauen Adressierbarkeit von chemischer Reaktivität sowie die Möglichkeit durch Ausnutzen des katalytischen Zyklus einen Lichtstimulus in ein verstärktes chemisches Signal zu übersetzen, machen die Photokontrolle über katalytische Aktivität zu einem besonders attraktiven Ziel. Daher wurde im Rahmen dieser Dissertation ein allgemeines Konzept zur Realisierung von photoschaltbaren Katalysatoren entwickelt, das auf der reversiblen sterischen Abschirmung eines katalytisch aktiven Zentrums durch eine photochrome Abschirmungsgruppe beruht. Durch Vorgabe des Schaltzustandes des Photochromes kann die Aktivität des Katalysators bestimmt werden. Das Konzept wurde durch die Entwicklung von konformativ eingeschränkten, photoschaltbaren Piperidinbasen umgesetzt, die synthetisch leicht durch einen in hohem Maße modularen Zugang erhalten werden konnten. Die Piperidinbasen erlaubten die Photokontrolle der Katalysatoraktivität in der Nitroaldol-Reaktion (Henry-Reaktion). Durch die Optimierung der Substituenten konnten bemerkenswerte katalytische AN/AUS-Verhältnisse erreicht werden. Die Reaktivitätsunterschiede konnten mit Änderungen der Basizität in Abhängigkeit vom Schaltzustand korreliert werden. Systematische NMR-spektroskopische und theoretische Untersuchungen der strukturellen Dynamik des Katalysators in Lösung ermöglichten die Formulierung von detaillierten Struktur-Reaktivitäts-Beziehungen. Eine Erweiterung des Konzepts auf intrinsisch reaktivere Katalysatoren sollte zu einer verbesserten Anwendbarkeit beitragen. Daher wurde das Konzept der reversiblen sterischen Abschirmung auf katalytisch aktive N-heterozyklische Carbene übertragen. Eine erfolgreiche Synthese wurde durch ungünstige sterische Wechselwirkungen zwischen den abschirmenden Gruppen an den Stickstoffatomen des Carbens verhindert.Photocontrol over properties of single molecules and assemblies thereof is an appealing area of current chemical research. The mere potential to selectively address chemical reactivity as well as the possibility to transform an incoming light stimulus into an amplified chemical signal by exploiting the associated catalytic cycle renders photocontrol of catalytic activity a particularly attractive goal. In this dissertation, a general concept for the realization of photoswitchable catalysts was developed, based on reversible steric shielding of a catalyst’s active site by a photochromic blocking group. Dictating the photochrome’s switching state enables gated access to the active site, thereby photocontrolling the catalyst’s chemical reactivity. The concept was realized by designing conformationally restricted, photoswitchable piperidine bases, which were easily synthesized exploiting a highly modular approach. Indeed, the developed piperidine bases allowed to photocontrol the catalysts’ activities in the nitroaldol reaction (Henry reaction) and by tuning of the substituents significant catalytic ON/OFF-ratios were achieved. The reactivity differences could be correlated with changes of basicity depending on the photochrome’s switching state. Systematic NMR-spectroscopic and computational studies of the catalysts’ structural dynamics in solution enabled the formulation of detailed structure-reactivity relationships. Strategies for the implementation of the concept of reversible steric shielding into the N-heterocyclic carbene (NHC) motif were devised to exploit the high reactivity of NHCs in numerous catalytic processes, which is expected to greatly enhance the utility of the concept. However, profound steric shielding of the active site to suppress unwanted OFF-state reactivity prevented the synthetic realization of the concept due to unfavorable steric interactions upon formation of the heterocyclic carbene from suitable precursors.
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Gomes, Junior João Luiz. "CORRELAÇÕES MORFOLÓGICAS ESTRUTURAIS: UM ESTUDO DAS PROPRIEDADES DE VIDROS TELURETOS DO SISTEMA TeO2 - Li2O - MoO3 EM FUNÇÃO DA COMPOSIÇÃO." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2015. http://tede2.uepg.br/jspui/handle/prefix/841.
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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.
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Fenyvesi, Jakab. "Etude de l'acido-basicité d'oxydes métalliques simples et supportés." Lyon 1, 1994. http://www.theses.fr/1994LYO10207.
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L'acido-basicite des supports a ete modifiee par l'ajout d'un deuxieme oxyde de nature variable et dans differentes proportions. L'acido-basicite a ete caracterisee par microcalorimetrie d'adsorption des molecules sondes et par test catalytique de conversion du propan-2-ol. Nous avons trouve des correlations entre: a, l'acido-basicite des oxydes dopes et quelques donnes physico-chimiques telles que l'electronegativite, la charge de l'oxygene, la charge et le rayon ionique et effet specifique des ions. B, l'acido-basicite des oxydes supportes ou mixtes et la theorie sur l'acidite selon seiyama. C, les resultats de microcalorimetrie et le test catalytique
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Bailly, Marie-Laurence. "Approche moléculaire de la chimie de coordination et de la réactivité des anions 02- d'oxydes alcalino-terreux : relation avec la basicite." Paris 6, 2003. http://www.theses.fr/2003PA066503.
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Graton, Jerome. "Basicité des Amines et de Nicotines : Liaison Hydrogène et Protonation." Phd thesis, Université de Nantes, 2001. http://tel.archives-ouvertes.fr/tel-00090950.
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La principale propriété des amines est leur basicité. Nous avons donc mesuré un type de basicité des amines non encore réellement étudié à ce jour, leur basicité de liaison H. Nous l'avons fait par la détermination des paramètres thermodynamiques, ∆G, ∆H et ∆S, de la réaction de formation de liaison H entre le 4-fluorophénol, et une centaine d'amines. Nous avons également déterminé l'échelle spectroscopique de basicité de liaison H, ∆ν(OH) et montrons que chacune des échelles ∆G, ∆H et ∆ν(OH) apporte sa contribution à la connaissance de la basicité des amines. L'étude de différents descripteurs empiriques (effets de substituants) et théoriques (potentiel électrostatique, variation d'énergie électronique par complexation) de la basicité de liaison H est réalisée. La lipophilie d'environ 150 bases azotées est modélisée avec succès à partir de seulement deux paramètres structuraux : le volume molaire et l'énergie de Gibbs de liaison H. Nous montrons également que l'échelle de basicité de liaison H est différente des échelles de basicité de Brönsted pKa en solution aqueuse ou GB en phase gazeuse. Dans ce contexte nous avons étudié l'aptitude de la nicotine et la nornicotine à former des liaisons H et à se protoner en phase gazeuse. En effet la nicotine possède une riche activité biologique et son pharmacophore est constitué d'un azote amino protoné et d'un azote pyridinique accepteur de liaison H. Nous montrons que l'azote sp3 est un second site accepteur de liaison H, pour la nicotine et la nornicotine, expliquant la lipophilie de ces bases. Le site de protonation de la nornicotine en phase gazeuse est l'azote sp2, très favorisé par une liaison intramoléculaire CHLN. Par contre les basicités protoniques des deux azotes de la nicotine semblent très peu différentes.
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Maria, Pierre-Charles. "Chimiometrie de la basicite : contribution a l'etude de la solvatation." Nice, 1987. http://www.theses.fr/1987NICE4086.
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Methode microcalorimetrique permettant la mesure des enthalpries de complexation par bf::(3) de molecules organiques en solution, appartenant a des familles modeles (pyridines, composes carbonyles, nitrites) ou communement utilises comme solvants.
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GRATON, JEROME. "Basicite des amines et de nicotines : liaison hydrogene et protonation." Nantes, 2001. http://www.theses.fr/2001NANT2014.
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La principale propriete des amines est leur basicite. Nous avons donc mesure un type de basicite des amines non encore reellement etudie a ce jour, leur basicite de liaison h. Nous l'avons fait par la determination des parametres thermodynamiques, g, h et s, de la reaction de formation de liaison h entre le 4-fluorophenol, et une centaine d'amines. Nous avons egalement determine l'echelle spectroscopique de basicite de liaison h, v(oh) et montrons que chacune des echelles g, h et v(oh) apporte sa contribution a la connaissance de la basicite des amines. L'etude de differents descripteurs empiriques (effets de substituants) et theoriques (potentiel electrostatique, variation d'energie electronique par complexation) de la basicite de liaison h est realisee. La lipophilie d'une centaine de bases azotees est modelisee avec succes a partir de seulement deux parametres structuraux : le volume molaire et l'energie de gibbs de liaison h. Nous montrons egalement que l'echelle de basicite de liaison h est tres differente des echelles de basicite de bronsted pk a en solution aqueuse ou gb en phase gazeuse. Dans ce contexte, nous avons etudie l'aptitude de la nicotine et de la nornicotine a former des liaison h et a se protoner en phase gazeuse avec pour objectif d'analyser les interactions potentielles entre ces molecules et leurs recepteurs. En effet la nicotine possede deux sites basiques concurrentiels : un azote amino et un azote pyridinique. Nous montrons que l'azote amino sp 3 est un site accepteur de liaison h secondaire, pour la nicotine et la nornicotine, ce qui permet d'expliquer la lipophilie de ces bases. Le site de protonation de la nornicotine en phase gazeuse est l'azote pyridinique sp 2, tres favorise par une liaison intramoleculaire ch---n. Par contre les basicites protoniques des deux azotes de la nicotine apparaissent tres voisines.
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ROUSSELOT, ISABELLE. "Etude structurale et mesure de la basicite d'hydroxydes doubles lamellaires." Clermont-Ferrand 2, 2001. http://www.theses.fr/2001CLF22271.
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Le travail presente dans ce memoire concerne l'etude structurale et la mesure de la basicite d'hydroxydes doubles lamellaires (hdl). Tout d'abord, dans le but de mieux comprendre les conditions de stabilisation du type structural hydrocalumite, minoritaire dans la famille des hdl, nous avons entrepris la synthese et la caracterisation structurale de nouveaux composes de type hydrocalumite : ca 2m 3 +(oh) 6cl -,2h 2o avec m 3 + = al 3 +, sc 3 +, fe 3 +, et ga 3 +. A notre connaissance, l'incorporation du gallium et du scandium est tout a fait originale. La cristallinite des poudres, obtenues par coprecipitation a ph constant, a permis une etude structurale par diffraction des rayons x. Comme dans le cas des composes de type hydrotalcite, l'augmentation de la taille du cation trivalent entraine une compression des couches octaedriques. L'existence de la phase ca-sc nous permet de penser que la distorsion du feuillet imposee par la coordinence 6+1 de l'element calcium, plutot que l'ecart entre les rayons des cations divalent et trivalent, serait responsable de la distribution ordonnee des cations. Dans la deuxieme partie de ce memoire, nous examinons la relation entre la composition chimique des hdl et leurs proprietes acido-basiques. Celles-ci sont evaluees a partir d'une reaction test de catalyse basique et par microcalorimetrie d'adsorption de co 2. Il apparait que l'activite catalytique de ces materiaux est determinee a la fois par la densite et la force des sites basiques. L'allure des isothermes, de type langmuir, indique une surface homogene. Le nombre de sites basiques augmente avec l'electronegativite moyenne des cations constitutifs du feuillet. De plus, les enthalpies pseudo-differentielles d'adsorption, refletant la force des sites, varient lineairement avec la charge partielle moyenne des groupements oh.
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BERTRAND, WILLIAM. "Basicite en phase gazeuse de ceto alcools et de ceto ethers." Paris 11, 1999. http://www.theses.fr/1999PA112283.
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Cette these presente une etude realisee sur la basicite de ceto alcools et de ceto ethers 1,2, 1,3 et 1,4 aliphatiques ou cycliques et sur la reactivite des formes protonees correspondantes. Les basicites en phase gazeuse, bg, ont ete mesurees par la methode des equilibres et par la methode cinetique sur un appareil a resonance cyclotronique ionique (rci), un spectrometre de masse a haute pression (hpms) et un spectrometre de masse tandem b-e. Les valeurs d'affinites protoniques, ap, et de variation d'entropie de protonation s\p, ont ete determinees a l'aide d'experiences a temperature variable (hpms). Ces grandeurs ont egalement ete estimees par des calculs d'orbitales moleculaires. L'accord avec l'experience est tout a fait correct, l'ecart n'excede pas quelques kj. Mol - 1 sur les bg et les ap. Nous constatons que les valeurs de bg et d'ap augmentent fortement lorsqu'on passe d'un ceto alcool au ceto ether correspondant et lorsque la chaine separant les deux fonctions s'allonge. Ces deux observations s'expliquent par une augmentation simultanee de la force de la liaison hydrogene intramoleculaire existant dans la forme protonee. La reactivite unimoleculaire des formes protonees de ces composes a ete etudiee a l'aide d'experiences de spectrometrie de masse tandem et de calculs d'orbitales moleculaires. Il s'agit exclusivement de reaction d'elimination d'une molecule d'eau ou d'une molecule de methanol. Nous avons pu ainsi identifier les produits formes et explorer les differents mecanismes reactionnels associes a ces fragmentations.
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STRAIDI, KHADIJA, and CHRISTIAN LAURENCE. "Chimiometrie de la basicite de l'eau et des alcools monomeres et polymeres." Nantes, 1991. http://www.theses.fr/1991NANT2079.
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Une echelle de basicite de liaison hydrogene des alcools et de l'eau monomeres a ete etablie a l'aide des relations lineaires d'enthalpie libre, des deplacements des vibrateurs oh en infra rouge et des grandeurs thermodynamiques de formation de liaison hydrogene. La methode de comparaison solvatochromique a ete appliquee aux alcools. La determination de leur basicite de liaison hydrogene a l'etat liquide pur ainsi obtenue n'est cependant pas totalement satisfaisante compte tenu du caractere amphotere des sondes d'interactions moleculaires utilisees. Cette limitation a ete surmontee grace a la methode de comparaison solvato vibrationnelle que nous avons mise au point. La basicite de liaison hydrogene des alcools polymeres a pu ainsi etre etablie, a l'exception des plus acides et de l'eau
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SAUVAGE, ARNAUD. "Influence de la basicite des zeolithes faujasite sur les proprietes du palladium disperse." Paris 6, 1996. http://www.theses.fr/1996PA066696.
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Ce travail montre l'influence de la basicite des zeolithes de type faujasite sur les ions et les particules de palladium. La basicite des zeolithes a ete modulee en preparant des echantillons de differentes teneurs en aluminium (zeolithe nay ou nax) echanges par differents cations alcalins compensateurs de charge (na#+ ou cs#+), la basicite augmentant avec la teneur en aluminium et le rayon du cation alcalin. Le palladium a ete introduit sous forme de complexe palladium ii tetrammine dans ces echantillons. La decomposition du complexe palladium tetrammine sous differentes atmospheres a ete etudiee sur les echantillons de differentes basicites grace a de nombreuses techniques de caracterisation (tpo-tpr, #2#9si mas rmn, spectroscopie uv-visible-pir, drx, methr). Une forte influence du caractere acido-basique du reseau zeolithique sur les mecanismes de decomposition du complexe ammine a ete mise en evidence. Les ions palladium ii sont d'autant plus facilement et plus rapidement stabilises par les oxygene du reseau zeolithique que ceux-ci sont plus basiques. Differents complexes successifs de palladium partiellement ammines et coordines a des oxygene de la zeolithe ont ete identifies. Les ions palladium obtenus apres complete desammination sont finalement coordines a trois oxygene d'une fenetre hexagonale du reseau zeolithique faujasite. Dans ces complexes, une augmentation avec le basicite de la zeolithe du caractere covalent des liaisons palladium-oxygene a ete demontree. L'etude des proprietes electroniques des particules de palladium supportees a ete effectuee par adsorption d'une molecule sonde sur la surface metallique, le co, et par mesure de l'activite catalytique du palladium dans la reaction d'hydrogenation du benzene. Les resultats obtenus suggerent que l'augmentation de la basicite de la zeolithe entraine un enrichissement de la surface metallique des particules supportees. Par ailleurs, l'etude de la redispersion, en ion palladium ii, des particules de palladium supportees a montre que les reactions mises en jeu dans ce phenomene dependent de la basicite du support.
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Yildirim, Ismail. "Surface Free Energy Characterization of Powders." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/27525.
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Microcalorimetric measurements and contact angle measurements were conducted to study the surface chemistry of powdered minerals. The contact angle measurements were conducted on both flat and powdered talc samples, and the results were used to determine the surface free energy components using Van Oss-Chaudhury-Good (OCG) equation. It was found that the surface hydrophobicity of talc increases with decreasing particle size. At the same time, both the Lifshitz-van der Waals (gSLW) and the Lewis acid-base (gSAB) components (and, hence, the total surface free energy (gS)) decrease with decreasing particle size. The increase in the surface hydrophobicity and the decrease in surface free energy (gS) can be attributed to preferential breakage of the mineral along the basal plane, resulting in the exposure of more basal plane surfaces to the aqueous phase.
Heats of immersion measurements were conducted using a flow microcalorimeter on a number of powdered talc samples. The results were then used to calculate the contact angles using a rigorous thermodynamic relation. The measured heat of immersion values in water and calculated contact angles showed that the surface hydrophobicity of talc samples increase with decreasing particle size, which agrees with the direct contact angle measurements. A relationship between advancing water contact angle qa, and the heat of immersion (-DHi) and surface free energies was established. It was found that the value of -DHi decrease as qa increases.
The microcalorimetric and direct contact angle measurements showed that acid-base interactions play a crucial role in the interaction between talc and liquid. Using the Van Oss-Chaudhury-Goodâ s surface free energy components model, various talc powders were characterized in terms of their acidic and basic properties. It was found that the magnitude of the Lewis electron donor, gS-, and the Lewis electron acceptor, gS+, components of surface free energy is directly related to the particle size. The gS- of talc surface increased with decreasing particle size, while the gS+ slightly decreased. It was also found that the Lewis electron-donor component on talc surface is much higher than the Lewis electron-acceptor component, suggesting that the basal surface of talc is basic.
The heats of adsorption of butanol on various talc samples from n-heptane solution were also determined using a flow microcalorimeter. The heats of adsorption values were used to estimate % hydrophilicity and hydrophobicity and the areal ratios of the various talc samples. In addition, contact angle and heat of butanol adsorption measurements were conducted on a run-of-mine talc sample that has been ground to two different particle size fractions, i.e., d50=12.5 mm and d50=3.0 mm, respectively. The results were used to estimate the surface free energy components at the basal and edge surfaces of talc. It was found that the total surface free energy (gS) at the basal plane surface of talc is much lower than the total surface free energy at the edge surface. The results suggest also that the basal surface of talc is monopolar basic, while the edge surface is monopolar acidic. The results explain why the basicity of talc surface increases with decreasing particle size as shown in the contact angle and microcalorimetric measurements.
Furthermore, the effects of the surface free energies of solids during separation from each other by flotation and selective flocculation were studied. In the present work, a kaolin clay sample from east Georgia was used for the beneficiation tests. First, the crude kaolin was subjected to flotation and selective flocculation experiments to remove discoloring impurities (i.e., anatase (TiO2) and iron oxides) and produce high-brightness clay with GE brightness higher than 90%. The results showed that a clay product with +90% brightness could be obtained with recoveries (or yields) higher than 80% using selective flocculation technique. It was also found that a proper control of surface hydrophobicity of anatase is crucially important for a successful flotation and selective flocculation process. Heats of immersion, heats of adsorption and contact angle measurements were conducted on pure anatase surface to determine the changes in the surface free energies as a function of the surfactant dosage (e.g. hydroxamate) used for the surface treatment. The results showed that the magnitude of the contact angle and, hence, the surface free energy and its components on anatase surface varies significantly with the amount of surfactant used for the surface treatment.Ph. D.
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Carré, Sonia. "Développement de réactions modèles pour la caractérisation de l'acido-basicite de catalyseurs et d'adsorbants." Poitiers, 2008. http://theses.edel.univ-poitiers.fr/theses/2008/Carre-Sonia/2008-Carre-Sonia-These.pdf.
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Les alumines sont très largement utilisées dans les procédés industriels, les propriétés acido-basiques de ces solides jouent un rôle dans le développement de nouveaux catalyseurs, il est donc important de bien connaître leurs propriétés. Ces oxydes sont généralement caractérisés par des méthodes physico-chimiques classiques, la plus employée étant l’adsorption (désorption) de molécules sondes suivie par spectroscopie infrarouge. Cependant les conditions étant assez éloignées des conditions de catalyse, il est souvent difficile de prévoir le comportement réel d’un catalyseur. L’utilisation de réactions modèles, dont les conditions de caractérisation sont plus proches de la catalyse, permet de mieux appréhender les propriétés acido-basiques des catalyseurs. L’objectif de cette étude est de développer des réactions modèles permettant de caractériser simultanément l’acidité et la basicité de diverses alumines de transition. Des études ont montré que les réactions de transformation du mélange cyclopentanol et cyclohexanone permettent d’estimer l’acido-basicité de catalyseurs. En effet deux réactions se produisent, d’une part un transfert d’hydrogène (TH) sur les sites basiques, et d’autre part les deux alcools présents se déshydratent sur les sites acides (DES). Les résultats ont montré qu’à 250°C, il est possible en une seule réaction de déterminer les propriétés acide et basique des alumines de transition et qu’il est possible de distinguer les alumines en 2 groupes : d’une part les alumines ŋ, γ et δ qui possèdent un caractère acido-basique voisin, et d’autre part les alumines θ et α qui possèdent un caractère basique plus marquéOxides are important materials as industrial catalyst support, adsorbent or catalyst, and are often characterized by physicochemical methods. The most technique commonly used is adsorption-desorption of acid and base probe molecules followed by IR spectroscopy. However, the experimental conditions are far from conditions used in catalysis, the results obtained are not always in agreement with the catalytic performance. Model reactions, for which the experimental conditions are close to that for catalysis use, allow a better understanding for the acid-base properties of catalysts. The aim of this work was to develop model reactions to estimate simultaneously the acidity and the basicity of transition aluminas. Cyclopentanol/cyclohexanone mixture transformation makes it possible in simple reaction to estimate the acidic and basic properties of catalyst. Indeed two reactions take place: hydrogen transfer (HT) between cyclopentanol and cyclohexanone to form cyclopentanone and cyclohexanol on basic sites, and alcohol dehydratation (cyclopentanol and cyclohexanol) (DEH) on acid sites. The HT/DEH ratio is also characteristic of the acid-base properties of catalyst. From this transformation, different crystallographic phases of transition aluminas can be divided into two groups: one,θ and alpha, which possess a basic character close to the one observed on MgO and η, γ and δ, which appear less basic, and possess an acidic character
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Vittoz, Christelle. "Étude de l'acido-basicité des surfaces par mouillabilité et XPS : application aux aciers inoxydables." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0042.
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Les aciers inoxydables sont des materiaux caracterises en surface par une couche passive, protectrice vis-a-vis de la corrosion, dont la composition chimique et la structure varie en fonction de la composition de l'alliage et de l'histoire de l'echantillon (nature du recuit, du vieillissement, du traitement de surface). Dans de nombreux domaines d'applications, la connaissance des proprietes d'adhesion de ces surfaces est necessaire. L'objet de cette etude consiste de determiner en particulier les caracteristiques acido-basiques de ces surfaces. Pour cela, nous avons utilise une methode originale basee sur la methode de la goutte posee dont le principe consiste a analyser l'evolution des angles de contact en fonction du ph de la solution aqueuse. A partir des proprietes des oxydes en presence d'une solution aqueuse, on a pu demontrer que cette evolution permet d'obtenir le point de charge nulle (pcn) et la charge maximale de la surface etudiee, ces parametres etant directement relies aux proprietes acido-basiques des surfaces au sens de brnsted. Dans un premier temps, l'application de cette methode pour la caracterisation des proprietes acido-basiques de surfaces modeles (silice, alumine) a permis de valider le principe et l'approche theorique proposee. Ensuite, des surfaces d'aciers inoxydables (aisi 304, fecrsi) ayant subi differents traitements ont ete ainsi caracterisees. Une etroite correlation a ete mis en evidence entre le comportement acido-basique et la composition chimique de la surface determinee par les spectroscopie d'electrons (xps, aes). Au regard de ces premiers resultats, il semble que les proprietes acido-basiques des aciers inoxydables peuvent etre modifier en modifiant la chimie des films passifs.
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Albertsson, Galina. "Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation." Doctoral thesis, KTH, Materialens processvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133480.
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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.QC 20131114
Steel Eco-Cycle
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Maria, Pierre-Charles. "Chimiométrie de la basicité contribution à l'étude de la solvatation /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376076659.
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Abiuso, Maria. "Pentaalkylguanidines : étude par RMN de la basicité ; synthèse et activité catalytique de résiines polystyrène modifiées." Lyon 1, 1995. http://www.theses.fr/1995LYO10310.
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Ce travail a pour objectif l'elaboration de pentaalkylguanidines supportees sur polystyrene et l'etude de leur activite catalytique basique. Afin de mieux comprendre la relation entre la basicite et la structure de la guanidine, nous avons dans un premier temps, etudie par rmn du carbone 13, le mode d'association des pentaalkylguanidines avec des composes a hydrogene mobile. Cette technique nous a permis de mettre en evidence la formation simultanement au sel de guanidinium, d'un complexe mettant en jeu deux molecules d'acides. Les valeurs des constantes d'equilibre mises en jeu ont ete determinees. Dans un deuxieme temps, nous avons elabore et caracterise differentes pentaalkylguanidines supportees sur polystyrene. Ces resines ont ete testees dans une reaction d'addition 1,4 de michael. Deux voies de synthese, la copolymerisation et la post-fonctionnalisation, ont ete envisagees et leur efficacite comparee. L'influence de la morphologie du support et de la nature de la pentaalkylguanidine ont de meme ete analyses. Au terme de cette etude, nous avons selectionne la resine presentant l'activite catalytique la meilleure et la morphologie la plus adaptee a une application industrielle. Cette derniere donne d'excellents resultats qui laissent presager son utilisation dans de nombreuses applications en chimie organique fine
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Goeppert, Alain. "[Sigma]-basicité et réactivité des petits alcanes en présence de superacides liquides et acides solides." Université Louis Pasteur (Strasbourg) (1971-2008), 2002. http://www.theses.fr/2002STR13045.
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Pommier, Catherine. "Influence de la basicité de la zéolithe faujasite sur les propriétés du platine dispersé et sur son activité catalytique en oxydation du dichlorométhane." Paris 6, 2003. http://www.theses.fr/2003PA066264.
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Chizallet, Céline. "Nature et réactivité des sites basiques de l'oxyde de magnésium : rôle des hydroxyles : approche mixte expérimentale et théorique." Paris 6, 2006. http://www.theses.fr/2006PA066350.
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Lopez, Sébastien. "Acido-basicité et hydroxylation/hydratation de surfaces d'aluminium : lien avec leur adhérence à un revêtement organique." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0145.
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Les propriétés des oxydes de surface sur aluminium influencent la performance du métal en formabilité, résistance à la corrosion, aspect de surface, et adhésion de revêtements organiques. Le but de cette thèse est de montrer que la comparaison de diverses techniques d'analyses de surface entraîne une meilleure connaissance des surfaces d'aluminium. Les films passifs sur aluminium apparaissent habituellement sous forme de mélanges complexes d'oxydes, oxyhydroxydes et hydroxydes d'aluminium plus ou moins hydrates. L’hydroxylation / hydratation a été étudiée par spectroscopie infrarouge (ft-ir/ras) et photoémission x (xps), essentiellement. L’hydratation globale peut être quantifiée par le nombre de molécules d'eau par équivalent de molécule d'alumine. L’hydroxylation et l'hydratation peuvent aussi être décrites dans un diagramme quaternaire (oxyde, oxyhydroxyde, hydroxyde, eau), par comparaison avec des matériaux de référence. Les propriétés acido-basiques des films passifs sur aluminium sont un facteur important pour la performance en adhésion. L’acido-basicité de Lewis a été caractérisée par photoélectrochimie (approche nouvelle basée sur la mesure de la courbure de bandes dans le film passif), photoémission x (déplacement du niveau de fermi), et par absorption x (xanes) (adsorption de molécules-sondes). Les surfaces d'aluminium étudiées ont montre leur caractère basique. L’adhésion des diverses surfaces avec un revêtement organique a été évaluée à l'aide d'un test de pelage a 180 simplifie (ruban adhésif). Il apparaît que l'adhésion soit meilleure pour des surfaces plus basiques
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CHARDIN, AURELIE. "Etude de la super-basicite de liaison hydrogene par spectrometrie irtf. Construction de l'echelle pk#h#b." Nantes, 1997. http://www.theses.fr/1997NANT2002.
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Afin d'etudier la partie haute de l'echelle de basicite de lewis particuliere que constitue l'echelle pk#h#b de basicite de liaison hydrogene, nous avons utilise ch#2cl#2 comme solvant de mesure a la place du solvant standard ccl#4 lorsque ce dernier ne solubilise pas les super-bases tres polaires, et le methanol comme donneur de liaison hydrogene de reference a la place du 4-fluorophenol, donneur standard, lorsque les equilibres sont trop deplaces vers la formation du complexe de liaison hydrogene. Au total l'usage du systeme ch#2cl#2/methanol rend possible l'obtention de valeurs pk#h#b proches de 12. L'etude par spectrometrie infrarouge du vibrateur o-h des donneurs de liaison hydrogene et des vibrateurs de la base, ainsi que le calcul des potentiels electrostatiques, permettent de s'assurer que les pk#h#b mesures correspondent bien a la formation d'un complexe 1 : 1 entre la base et le donneur de liaison hydrogene. Grace a la recherche des facteurs structuraux permettant d'atteindre les sommets de l'echelle pk#h#b, nous avons trouve que : (i) les oxydes des elements du groupe v conduisent aux valeurs les plus elevees de l'echelle pk#h#b (me#3no, pk#h#b egal a 6,28), (ii) la cyclisation des substituants alkyles autour du site basique permet une combinaison optimale de leurs effets electrodonneurs et steriques pour atteindre des guanidines et des imines super-basiques, (iii) le substituant (neutre) zwitterionique r#3n#+n#- donne les elevations de basicite les plus impressionnantes avec les carboxamidates, les cyanamidates, les nitramidates et les sulfonamidates, (iv) dans la famille des 1,10-phenanthrolines, en associant l'effet de synergie des paires libres des azotes a l'effet du substituant pyrrolidino, nous obtenons la base azotee la plus forte decrite a ce jour (4,7-dipyrrolidino-1,10-phenanthroline, pk#h#b egal a 3,90).
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Auerbacher, Valérie. "Etude d'une relation entre la basicité de l'azote et l'affinité au récepteur dans une série de quinoléines substituées." Paris 5, 1990. http://www.theses.fr/1990PA05P178.
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