Dissertations / Theses on the topic 'Metallic hydrides'

Nowadays proton exchange membrane fuel cell (PEMFC) using hydrogen as fuel is considered as one of the most promising alternative to combustion engines due to its zero emissions. In order to operate a PEMFC successfully, a safe and convenient hydrogen storage and production system is necessary. A stabilized aqueous solution of metal hydride is considered appropriate for use as hydrogen storage material. In particular, NaBH4 is the preferred hydride due to its high hydrogen storage capacity (10.8 wt%). Moreover, sodium borohydride is non-flammable and non-toxic. The by-products of hydrolysis reaction are environmentally friendly and can be recycled in order to re-synthesizing NaBH4. Sodium borohydride reacts with water, forming 4 moles of hydrogen and 1 mol of sodium metaborate, according with the following exothermic reaction: NaBH4 + 2H2O ¡ú NaBO2 + 4H2 + 217 KJ/mol To inhibit the self-hydrolysis reaction, NaBH4 solution must be maintained at pH > 13. At this pH, NaBH4 solution is very stable and the hydrogen release occurs only if the solution is in contact with specific catalysts permitting the ideation of HOD (hydrogen on demand) systems. Considering our preliminary experiments and data of literature showing that catalysts based on ruthenium metal have a good catalytic activity, for this study, ruthenium metal catalysts on different supports such as ¦Ã-Al2O3, CeO2, TiO2, activated carbon (a mineral carbon with high surface area) were prepared. We found that Ru supported on an activated carbon of mineral origin with high surface area, is more active with respect to Ru on other supports. The best performances of Ru/activated carbon were related both to the high surface area of the activated carbon and to its high chemical inertness in the strong basic environment. Considering that activated carbon (mineral carbon with surface area of 1059m2g-1) resulted the more suitable support for the reaction under study, we investigated the NaBH4 hydrolysis over Ru catalysts supported on activated carbons with different origin and morphological characteristics. The influence of two different Ruthenium precursors (RuCl3 or Ru(NO)(NO3)3) was also studied. We found that a higher surface area leads to smaller Ru nanoparticles, whereas the presence of alkali metals on the support (mainly potassium) and the use of RuCl3 as precursor (containing chlorine), promote the formation of larger Ru clusters. In this context, it was found that the best catalytic performance was obtained using the activated carbon of vegetable origin as support and Ru(NO)(NO3)3 as precursor that give Ru clusters with 3nm as diameter size.

Structural defects play a major role in nanotechnology as they influence most properties, thus largely motivating the special interest in studying materials at the nano scale. The present Thesis work contributes to this broad and diversified research field with emphasis on the characterization of nanocrystalline ceramic materials and their lattice defects. In particular, main efforts were addressed to develop new and more comprehensive approaches to the study of nanocrystalline powders, combining different techniques for a better and deeper understanding of materials. The specific applications selected in this work are basically two: nanocrystalline fluorite as a promising ionic conductor and nanocrystalline magnesium hydride for hydrogen storage applications. Chapters II and III were dedicated to investigate nanocrystalline fluorite produced by two different methods: a bottom-up approach based on co-precipitation of Ca and F precursors yielding loosely bound nanocrystals, and a popular top-down approach, high energy ball milling, giving nanocrystals of comparable sizes but strongly agglomerated and densely populated with dislocations. As a major achievement reported in this part of the Thesis work, a new approach was proposed and tested for the simultaneous modelling of X-ray Diffraction (XRD) peak profiles and solid state NMR spin-lattice relaxation data. With the valuable support of Transmission Electron Microscopy (TEM), this work offers a new understanding of the complex defect structure of nanocrystalline fluorite, and is also a demonstration of the power of combining different techniques in a consistent way. One of the most debated aspects of nanotechnology concerns the stability of the nanostructure, and the mechanisms of defect annealing and grain growth with temperature. This topic was the object of chapter V, dedicated to study the influence of lattice defects on the grain growth kinetics of nanocrystalline fluorite. This chapter was preceded by chapter IV, on the furnace recently installed at the MCX beamline for in-situ high temperature fast data collection; besides providing useful details for the in-situ study on nanocrystalline fluorite shown in the following chapter, the activity reported in chapter IV is a tangible sign of the special involvement during the Thesis work in supporting standard operation as well as development of the ELETTRA beamline MCX. The growth kinetics was studied on two samples, among those discussed in Chapter III, with comparable crystalline domain size but drastically different lattice defect content, so to highlight the role lattice defects – dislocations in this case – in the growth process. 14 Last two chapters (chapter VI and VII) were dedicated to nanocrystalline magnesium hydride, and how the performance, in particular the hydrogen desorption kinetics, can be improved by adding a nanocrystalline tin oxide. Besides general aspects on phase composition of the system and hydrogen storage capability, the work also addressed the problem of obtaining activation energy values in the thermal decomposition of magnesium hydride powders, presenting an interesting review of results given by the most known and well-assessed TG-MS coupled measurements, with details on the use of different equations of the literature on thermal analysis. Although research work can rarely be considered as finished, a sound conclusion of this Thesis work is toward the use of different characterization techniques, also within the same data analysis procedure, to support a better, and more reliable investigation of nanomaterial properties.

Structural defects play a major role in nanotechnology as they influence most properties, thus largely motivating the special interest in studying materials at the nano scale. The present Thesis work contributes to this broad and diversified research field with emphasis on the characterization of nanocrystalline ceramic materials and their lattice defects. In particular, main efforts were addressed to develop new and more comprehensive approaches to the study of nanocrystalline powders, combining different techniques for a better and deeper understanding of materials. The specific applications selected in this work are basically two: nanocrystalline fluorite as a promising ionic conductor and nanocrystalline magnesium hydride for hydrogen storage applications. Chapters II and III were dedicated to investigate nanocrystalline fluorite produced by two different methods: a bottom-up approach based on co-precipitation of Ca and F precursors yielding loosely bound nanocrystals, and a popular top-down approach, high energy ball milling, giving nanocrystals of comparable sizes but strongly agglomerated and densely populated with dislocations. As a major achievement reported in this part of the Thesis work, a new approach was proposed and tested for the simultaneous modelling of X-ray Diffraction (XRD) peak profiles and solid state NMR spin-lattice relaxation data. With the valuable support of Transmission Electron Microscopy (TEM), this work offers a new understanding of the complex defect structure of nanocrystalline fluorite, and is also a demonstration of the power of combining different techniques in a consistent way. One of the most debated aspects of nanotechnology concerns the stability of the nanostructure, and the mechanisms of defect annealing and grain growth with temperature. This topic was the object of chapter V, dedicated to study the influence of lattice defects on the grain growth kinetics of nanocrystalline fluorite. This chapter was preceded by chapter IV, on the furnace recently installed at the MCX beamline for in-situ high temperature fast data collection; besides providing useful details for the in-situ study on nanocrystalline fluorite shown in the following chapter, the activity reported in chapter IV is a tangible sign of the special involvement during the Thesis work in supporting standard operation as well as development of the ELETTRA beamline MCX. The growth kinetics was studied on two samples, among those discussed in Chapter III, with comparable crystalline domain size but drastically different lattice defect content, so to highlight the role lattice defects – dislocations in this case – in the growth process. 14 Last two chapters (chapter VI and VII) were dedicated to nanocrystalline magnesium hydride, and how the performance, in particular the hydrogen desorption kinetics, can be improved by adding a nanocrystalline tin oxide. Besides general aspects on phase composition of the system and hydrogen storage capability, the work also addressed the problem of obtaining activation energy values in the thermal decomposition of magnesium hydride powders, presenting an interesting review of results given by the most known and well-assessed TG-MS coupled measurements, with details on the use of different equations of the literature on thermal analysis. Although research work can rarely be considered as finished, a sound conclusion of this Thesis work is toward the use of different characterization techniques, also within the same data analysis procedure, to support a better, and more reliable investigation of nanomaterial properties.

Les accumulateurs Ni-MH (Nickel-Métal-Hydrure) sont un sujet prometteur et largement étudié dans les recherches d’une énergie propre et durable. Trouver le matériau idéal pour l'électrode négative à haute densité volumétrique et gravimétrique est la clé pour l’application de cette technologie. Les hydrures métalliques à base de Ti-Ni ont des propriétés équilibrées entre la capacité d’hydrogène et les performances électrochimiques.L’objectif de cette thèse est d’étudier les effets de substitutions/additions d’éléments et de la mécanosynthèse sur la structure et les propriétés d’hydrogène des alliages Ti-Ni. Dans cette étude, une série d’alliages à base de Ti-Ni avec des substitutions/additions de Mg ou de Zr ont été systématiquement étudiés.Les alliages (TiNi)1-xMgx, (TiH2)1.5Mg0.5Ni, and Ti2-xZrxNi ont été synthétisés par mécanosynthèse à partir de poudres élémentaires. Dans un premier temps, l’influence du temps de broyage et les effets de substitutions/additions sur les microstructures ont été caractérisés par des techniques telles que la DRX, le MEB et le MET. Dans un second temps, les propriétés d’hydrogénation des différents alliages ont été mesurées par des réactions solid-gaz et par cyclage électrochimique.La théorie de la fonctionnelle de la densité (DFT) en utilisant le programme CASTEP a permis de calculer les enthalpies de formation afin de comparer la stabilité thermodynamique des alliages obtenus. Dans ces travaux de recherche, nous avons identifié les priorités d’alliage des ternaires Ni-Ti-Mg et Ti-Ni-Zr dans des conditions de broyage. La transformation structurale du Ti en phase CFC, induite par l’introduction d’éléments étrangers, a été mise en évidence.Les courbes PCI (Pression-Composition-Isothermes) et les capacités de décharge en fonction du nombre de cycles indiquent les propriétés d’hydrogène des alliages obtenus, y compris TiNi, Ti2Ni (amorphe), Ti-Mg et Ti-Zr<br>Ni-MH (Nickel-Metal-Hydride) batteries have been a promising and extensively studied topic among clean and sustainable energy researches. Finding the ideal material for the negative electrode with high volumetric and gravimetric densities is the key to apply this technology on broader applications. Metal hydrides based on Ti-Ni have balanced properties between hydrogen capacity and electrochemical performances in cycling.The objective of this thesis is to study the effects of element substitution/doping and mechanical alloying on the structural and hydrogen properties of Ti-Ni alloys. In this study, a series of Ti-Ni based systems with Mg or Zr doping/substitution have been systematically investigated.The metallic compounds (TiNi)1-xMgx, (TiH2)1.5Mg0.5Ni, and Ti2-xZrxNi were synthesized by mechanically alloying from elemental powders.The milling time and effects of Mg, Zr substitution/doping were studied firstly in respect of their microstructures, using characterization techniques including XRD, SEM, TEM (EDX support), followed by the hydrogen properties measurements of the samples by hydrogen solid-gas reaction and electrochemical cycling.A first principle calculation tool based on DFT (Density Functional Theory) was carried out to further investigate the enthalpy of formation in order to compare the thermodynamical stability of the obtained compounds. In the study, we have found the alloying priorities in the ternary alloys Ti-Ni-Mg and Ti-Ni-Zr under milling conditions.A structure transformation of Ti to FCC induced by foreign elements is reported and investigated. Enthalpy of formation per atom of the compounds were obtained by DFT calculations, which helped interpreting the experimental results. PCI (Pressure Composition Isotherms) curves and discharge capacities as the function of cycling numbers revealed the hydrogen properties of the obtained compounds, including TiNi, Ti2Ni (amorphous), Ti-Mg and Ti-Zr

As a part of the production of nitride nuclear fuel for use in fast nuclear reactors, zirconium is hydrided followed by nitriding and mixing with uranium nitride. This work concludes a study of unwanted metallic particles present in a powder that is supposed to be a zirconium hydride. Sponge zirconium was hydrided at different temperatures and different time intervals, and the resulting hydride was milled into a powder. The powders were analyzed using SEM and XRD after which the powders were pressed into pellets for light optical microscopic study. The primary goals were determination of the structure of the particles and thereafter elimination of them. It was seen that hydriding at 500 C results in less metal particles but more experiments need to be conducted to confirm this.

Orientador: Marco Aurélio Zezzi Arruda<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química<br>Made available in DSpace on 2018-08-22T10:57:39Z (GMT). No. of bitstreams: 1 Galazzi_RodrigoMoretto_M.pdf: 2262907 bytes, checksum: fb6e92051f6858cd925c525071ce6540 (MD5) Previous issue date: 2013<br>Resumo: Nessa dissertação, otimizou-se um método para a determinação de estanho (Sn) em amostras biológicas empregando a técnica de Espectrometria de Absorção Atômica por Geração de Hidretos e Forno Metálico (MF-HG-AAS, do inglês Metallic Furnace Hydride Generation Atomic Absorption Spectrometry). Foram avaliadas algumas variáveis químicas como o tipo e concentração do carregador/diluente da solução padrão, concentração do redutor tetraidridoborato (-1) de sódio (THB) e concentração de hidróxido de sódio, bem como variáveis físicas do sistema dentre elas a vazão de carregador, proporção de acetileno:ar na chama, volume de solução injetado, vazão de argônio como gás de arraste, vazão de água no nebulizador e área total de furos no tubo metalico Inconel600®. Foi realizado um estudo do efeito de memória observado em condições de chama oxidante nas vazões de 1,5:9; 1,4:9; 1,3:9; 1,4:10; 1,4:8 e 1,5:11 L min de acetileno:ar, respectivamente. Em todas essas proporções de chama diferentes da otimizada (1,5:10 L min acetileno:ar) há efeito de memória, o que é extremamente indesejável. Após a otimização do sistema, foram realizados testes de exatidão e precisão do mesmo com os materiais PACS-2 (sedimento) e SRM 1643e (amostra de água) em que, em ambos, foi possível recuperar o Sn adicionado obtendo limites de detecção (LD) de 7,1 mg kg e 7,6 mg L, respectivamente. Um estudo com concomitantes foi realizado para avaliar se algum dos elementos em questão poderia interferir na determinação do Sn. Foram estudados como possíveis concomitantes o cobre, chumbo e zinco em três níveis diferentes. Somente o cobre, nas razões de 1:10 e 1:20 (Sn:concomitante), interferiu na detecção de Sn. Por fim, a morfologia do atomizador foi avaliada por meio da técnica de Microscopia Eletrônica de Varredura (SEM, do inglês Scanning Electron Microscopy). Mesmo após a realização de todos os experimentos envolvendo a otimização do sistema e análise das amostras, os principais constituintes do tubo metálico Inconel600® (ferro, níquel e cromo) permaneceram homogeneamente distribuídos, indicando que esses metais podem não participar da rota de atomização do Sn. Além disso, houve formação de óxidos no atomizador que, juntamente com o uso de uma chama oxidante, sugerem uma rota de atomização do Sn via formação de óxidos. Considerando os LD, bem como a exatidão e precisão por meio da recuperação de Sn obtida nas amostras, constata-se a potencialidade da MF-HG-AAS frente a outras técnicas empregadas na determinação de Sn<br>Abstract: In this work, a Metallic Furnace Hydride Generation Atomic Absorption Spectrometry (MF-HG-AAS) was optimized for tin (Sn) determination in biological samples. Chemical variables, such as the type and carrier concentration, the sodium tetrahydrideborate (-1) (THB), and the sodium hydroxide concentration, as well as physical variables, such as carrier flow-rate, ratio of acetylene and air in the flame, injection volume, argon flow-rate as carrier of stannane, water flow-rate in nebulizer and total hole area of a Inconel600® metallic furnace were evaluated. A study of a memory effect observed in oxidant flame conditions such as 1.5:9; 1.4:9; 1.3:9; 1.4:10; 1.4:8 e 1.5:11 L minof acetylene:air, respectively, was realized. In any other flame flow-rate, which the optimized flame ratio (1.5:10 L min acetylene:air) was observed a memory effect, which is very undesirable. After optimizing of the system, test of accuracy and precision were realized with the PACS-2 (sediment) and SRM 1643e (water sample) materials wherein, in both, a recovery of the Sn added to the samples was possible with limits of detection (LOD) as 7,1 mg kg and 7,6 mg L, respectively. A concomitant study was carried out for checking the interferences in the Sn determination. Copper, lead and zinc at three different levels were studied as possible concomitants. Only copper, at 1:10 and 1:20 (Sn:concomitant) ratios interfered in the determination of Sn. Finally, the morphology of the atomizer employed was evaluated through Scanning Electron Microscopy (SEM) technique. Even after carrying out all experiments involved in the optimization of the system and in the sample analysis, the main constituents of Inconel600® metallic furnace (iron, nickel and chromium) remained homogeneously distributed, indicating which these elements may not participate of the Sn atomization route. Moreover, the oxide formation in the atomizer was detected, which, together with an oxidant flame used, suggests the Sn atomization route via oxides formation. Considering the LOD, as well the accuracy and precision through the Sn recovery in the samples, the MF-HG-AAS potentially is well pointed out when it is compared to other techniques employed for Sn determination<br>Mestrado<br>Quimica Analitica<br>Mestre em Química

Heat generation plays an important role for energy storage systems like batteries in electric and hybrid vehicles. In order to investigate the thermal and electrical behaviour the nickel metal hydride batteries were exposed to cycling programs including various methods of battery cooling by flowing air. The second part of the paper describes the simulation of the temperature distribution by using finite element methods (FEM). The electric-thermal battery model was compared with results obtained from temperature measurements at four selected points during battery cycling. The results serve environmentalcareful battery employment for the general, system-oriented viewpoint of the battery condition and form the basis for energy and enviroment save used<br>Die Wärmeerzeugung spielt bei dem Einsatz von Batterien in Elektro- und Hybridfahrzeugen eine wichtige Rolle. In der Arbeit wird das thermische und elektrische Verhalten der Batterien bei der Belastung mit schnell aufeinander folgenden Höchststromladeimpulsen und -entladeimpulsen untersucht. Die Kühlung der Batterie erfolgte mit verschiedenen Methoden der Luftkühlung. Im zweiten Teil der Arbeit wird die Simulation der Temperaturverteilung mittels Finiter Element Methoden (FEM) beschrieben. Die mit einem elektrisch-thermischen Batteriemodell simulierten Temperaturen werden mit den an verschiedenen Punkten experimentell gemessenen Zelltemperaturen verglichen. Die Ergebnisse dienen zur ganzheitlichen, systemorientierten Betrachtungsweise des Batteriezustandes und bilden die Grundlage für einen energie- und umweltschonenden Batterieeinsatz

The sulfone group is a well-established activating moiety important in many organic transformations. Standard procedures for desulfonylation [Al(Hg), or Na(Hg)] were ineffective for the removal of the pyridin-2-ylsulfonyl group from the α-carbon of phosphonic esters. Prompted by these results, we undertook a study for the synthesis of α-(arylsulfonyl)phosphonates, and their fluorination with Selectfluor to produce α-fluoro-α-(arylsulfonyl)phosphonates, Radical mediated hydrogenolysis of α-fluoro-α-(arylsulfonyl)phosphonates using BujSnH gave (α-fluoro)phosphonates. We observed that the yield for the desulfonylation reaction depends on the n-deficiency effect and increase in the order pyrimidinyl > pyridinyl > phenyl sulfonyl. The (α-fluoro)phosphonates were employed as convenient precursors in the Homer-Wadsworth-Emmons (HWE) reaction to provide (α-fluoro)vinyl sulfones. The vinyl and (α-fluoro)vinyl sulfones underwent substitutive silyl and germyl- desulfonylation to yield vinyl and (α-fluoro)vinyl silanes and germanes via an addition-elimination mechanism. The vinyl tris(trimethylsilyl)silanes were employed as nucleophiles (under oxidative conditions) in palladium-catalyzed cross coupling reactions with iodobenzene and bromobenzene.

A promising alternative to hydrogen storage in high pressure cylinders and cryogenic tanks is the hydrogen storage in solid form as metal hydrides or complex metal hydrides. However, much research is still necessary in this direction. In particular, the optimal pressure and temperature of operation for the use of a hydride-based tank in a PEM fuel cell-powered vehicle should remain in the of 1-10 atm and 25-120 °C, respectively. The further difficulty is related to the weight of the storing materials, which is still too high for efficient mobile applications compared to the amount of stored hydrogen. The work reported in this thesis deals with systems belonging to several hydride classes such as complex hydrides, interstitial metal hydrides and magnesium-based hydrides. Improvements from the point of view of thermodynamic and kinetic properties are proposed and discussed on systems almost ready for niche applications and on other very promising systems but still far from hydrogen storage applications. Among the classical interstitial hydrides-forming alloys, the interaction of hydrogen with TiCr1.78-xMnx alloys, one of the most promising for the use in high pressure-solid state hybrid tanks, has been studied. Among the Mg-based hydrides, a compacted Mg-Al-based material is proposed in order to overcome the degradation problems found during the scaling up of MgH2 as hydrogen storage medium. Concerning the complex hydrides, the kinetics improvement of the Li-Mg-N-H system by high energy ball milling processing is discussed and the problem of reversibility and slow decomposition kinetics of LiBH4 has been faced.<br>Una promettente alternativa allo stoccaggio dell’idrogeno in bombole ad alta pressione e in contenitori criogenici è lo stoccaggio dell’idrogeno allo stato solido utilizzando idruri metallici o idruri complessi. In ogni caso, molta ricerca è ancora necessaria in questa direzione. In particolare, la pressione e la temperatura di lavoro ottimali per un serbatoio da utilizzare in una vettura basata su celle a combustibili PEM dovrebbero rimanere rispettivamente negli intervalli 1-10 atm e 25-120 °C. L’ulteriore difficoltà è legata al peso dei materiali assorbenti, che è ancora troppo elevato rispetto alla quantità di idrogeno stoccata per applicazioni veicolari efficienti. Il lavoro riportato in questa tesi riguarda sistemi appartenenti a diverse classi di idruri come idruri complessi, idruri metallici interstiziali, idruri a base di magnesio. Vengono proposti e discussi miglioramenti dal punto di vista termodinamico e cinetico apportati a sistemi ormai quasi pronti ad applicazioni di nicchia e ad altri molto promettenti ma ancora lontani da applicazioni per lo stoccaggio dell’idrogeno. Per quanto riguarda i classici idruri interstiziali, è stata studiata l’interazione dell’idrogeno con le leghe TiCr1.78-xMnx, tra le più promettenti per l’utilizzo in serbatoi ibridi ad alta pressione. Riguardo gli idruri a base di magnesio, un materiale basato su Mg-Al compattato in pastiglie viene proposto per ovviare ai problemi legati allo “scaling-up” del MgH2. Per quanto riguarda la classe degli idruri complessi, viene discusso il miglioramento delle cinetiche di assorbimento/desorbimento di idrogeno grazie al trattamento con macinazione ad alta energia e vengono affrontati i problemi della reversibilità e della lenta cinetica di decomposizione del LiBH4.

La demande en énergie ne cesse d'augmenter et elle satisfaite essentiellement par les énergies fossiles qui présentent une contrainte environnementale vue ses émissions de gaz à effet de serre. Considéré comme vecteur énergétique, l'hydrogène possède l'immense avantage de ne pas émettre de gaz à effet de serre et notamment du CO2. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques supérieures à celles obtenues en voie liquide ou sous pression. Dans ce travail, nous avons élaboré le composé intermétallique quaternaire LaCaMgNi9 par mécanosynthèse et ce selon différents schémas réactionnels. Ce procédés de synthèse est employé pour la première fois, pour la synthèse de cet intermétallique, afin de s'affranchir des difficultés que présentent les autres techniques de synthèse (co-fusion, frittage). Les caractérisations structurales et morphologiques des alliages obtenus ont été réalisées afin de tester leurs performances en tant que matériaux pour électrode négative d’accumulateur Ni-MH par divers techniques de caractérisation électrochimiques et solide-gaz<br>The increasing energy demand is mainly supplied by fossil sources which had environmental drawback essentially greenhouse gas emission. Considered as an energy carrier, hydrogen has the huge advantage to be clean. Its storage in intermetallic compound leads too higher hydration capacities than liquid and compressed storage. In this work, LaCaMgNi9 quaternary type alloy has been synthesized, for the first time, by mechanical alloying in order to avoid the inherent difficulties of the fusion technique. The structural and morphological characterization of the obtained alloys were performed. Their hydrogen related properties were examined (solid-gas and electrochemical reactions) in order to study their performance as negative electrode material in Ni-MH batteries

The research presented in this doctoral thesis concerns with the development of novel materials and systems for solid state hydrogen storage. The first group of works presented is on alkaline and alkaline-earth borohydrides. The possibility to enhance their properties with the help of nanosupports has been widely explored. An attempt to improve the dehydrogenation kinetics of lithium borohydride has been made dispersing this material on the surface of modified nanotubes and graphite. The resulting nanoconfined material displayed a decreased decomposition temperature in comparison with pure material and further decreasing was observed when the surface area of the supports was increased. An analogous experiment was performed to investigate this effect in combination with the assets of a reactive hydride composite, where two materials are mixed to obtain a compound with a lower decomposition enthalpy. The effect of the mixture was beneficial in presence of the support, due to lower temperature melting. For calcium borohydride an ordered mesoporous carbon was used after chemical activation. The increased properties of this support resulted in lower decomposition temperature and improved reversibility for a number of cycles at different pressure values. The second research line is focused on magnesium hydride. To improve its kinetic properties a zirconium-nickel alloy was investigated to evaluate its influence on the reaction rate, both in absorption and desorption. The degradation observed in experimental reactors, of different magnesium hydride powders catalyzed with a transition metal oxide, motivated the fabrication of pellets with the addition of a binding agent, to obtain mechanical resistance, still allowing hydrogen diffusion. Each pellet was supposed to behave as an independent system, so they were also tested in a small reactor. Several hydrogen absorption/desorption cycles were performed to compare the behaviour of the small reactor with the laboratory data obtained on smaller quantity of powdered and pelletized specimens. Finally, the feasibility of a vehicular hydrogen tank system was investigated using an interstitial metal hydride as storage material. Apart from material basic characterization, two different kinds of experiment were performed. Static tests (measurements with automatic flow control and constant settings) were used to evaluate wether the requirements for desorption are met by the tank set-up. Then, dynamic tests were designed and applied on the tank, where the hydrogen flow was fluctuating following a hypothetical on-road trial. It was possible to underline the heat management issues of high-demanding performances and to analyze some solutions for that. Different cycles were carried out on the tank to find the ideal setting for high average and peak flows in a realistic experiment.<br>L’attività di ricerca presentata in questa tesi di dottorato riguarda lo sviluppo di nuovi materiali e sistemi per lo stoccaggio di idrogeno allo stato solido. Il primo gruppo di attività presentate è sui boroidruri di metalli alcalini e alcalinoterrosi. È stata ampiamente esplorata la possibilità di migliorare le loro proprietà con l’ausilio di nanosupporti. Un tentativo di migliorare la cinetica di decomposizione del litio boroidruro è stato fatto disperdendo tale materiale sulla superficie di nanotubi di carbonio e grafite modificati.Il materiale nanoconfinato risultante ha mostrato una temperatura di decomposizione inferiore, se paragonato al materiale puro e un’ulteriore diminuzione è stata osservata aumentando l’area superficiale del supporto. Un esperimento analogo è stato eseguito per osservare questo effetto in combinazione con i vantaggi di un reactive hydride composite, nel quale due materiali sono combinati per ottenere un composto con una minor entalpia di decomposizione. L’effetto del composto è stato positivo in presenza del supporto, grazie alla minor temperatura di fusione. Per il calcio boroidruro è stato usato carbone mesoporoso dopo attivazione chimica. Le migliorate proprietà di questo supporto hanno dato una minor temperatura di decomposizione e una migliorata reversibilità per vari cicli a diverse pressioni. La seconda linea di ricerca si focalizza sull’idruro di magnesio. Per migliorare le sue proprietà cinetiche, è stata testata una lega zirconio-nickel, al fine di valutare la sua influenza sulla velocità di reazione in assorbimento e desorbimento. Il degrado di altre polveri di magnesio idruro catalizzate con un ossido metallico in reattori sperimentali ha motivato la produzione di pastiglie con l’aggiunta di un agente legante, per ottenere resistenza meccanica, consentendo comunque la diffusione dell’idrogeno. Era previsto che ogni pastiglia si comportasse come un sistema indipendente, infatti, sono state testate in un piccolo reattore. Diversi cicli di assorbimento e desorbimento sono stati effettuati per paragonare la risposta del reattore con dati di laboratorio ottenuti su minori quantità di polvere o pastiglie. Infine, è stata sperimentata la realizzabilità di un serbatoio di idrogeno veicolare usando un idruro di un metallo interstiziale. Oltre alla caratterizzazione di base del materiale, sono stati realizzati due tipi di esperimenti. Test statici (misure con controllo automatico di flusso e impostazioni costanti) sono stati usati per valutare se il serbatoio soddisfacesse i requisiti di rilascio di idrogeno. Test dinamici sono stati progettati e applicati al serbatoio, dove il flusso di idrogeno era variabile seguendo un’ipotetica prova su strada. È stato possibile evidenziare i problemi legati allo scambio di calore per le prestazioni di maggior consumo e analizzare alcune possibili soluzioni. Cicli diversi sono stati effettuati sul serbatoio in esperimenti realistici, per trovare le impostazioni ideali per alti valori di flusso medio e di picco.

Cette étude s’inscrit dans le cadre du stockage de l’hydrogène pour des applications mobiles de faibles puissances électriques. Elle a été réalisée dans le cadre du projet FUI HyCAN. L’objectif était la formulation et la fonctionnalisation d’un alliage métallique de structure cubique corps centrée. Ces solutions solides désordonnées sont à base de vanadium qui présente initialement une bonne réactivité vis-à-vis de l’hydrogène.Cependant la thermodynamique du système V-H ne permet pas une utilisation pour des températures inférieures à 40°C, son coût est prohibitif et sa mise en oeuvre en milieu industriel nécessite quelques précautions. Nous avons travaillé sur trois grandes familles d’alliages à base de vanadium. Les alliages de Ti-V-Cr ont été étudiés au rayonnement synchrotron par diffraction X in operando dans le but de comprendre les transformations structurales observables lors de l’hydruration et de les relier à la thermodynamique des composés. Dans unsecond temps, le cahier des charges du projet nous a orienté vers des composites à base de vanadium dans lesquels nous développons une structure intergranulaire permettant une meilleure activation et une déstabilisation contrôlée de l’hydrure pour atteindre des températures de fonctionnement proche de 0°C.L’utilisation du ferro-vanadium en tant que précurseur a motivé l’étude des alliages de type Ti-V-Fe et Ti-V-Fe-Cr. La viabilité des solutions de stockage sur la base de ces matériaux est discutée. Tout au long de ces travaux la relation microstructure/propriété de sorption de l’hydrogène est systématiquement discutée et des modèles empiriques décrivant l’équilibre de l’hydrure sont systématiquement confrontés à la base bibliographique.Enfin, une partie de l’étude est consacrée à l’étude et à la modélisation des réservoirs en condition de fonctionnement, d’un point de vue de la thermique, du respect des normes de sécurité et des contraintes mécaniques générées par le lit de poudre réactif<br>This study has been carried out in the framework of solid state hydrogen storage for mobile applications withlow electrical power. It was conducted under the FUI project HyCAN. The objective was to develop andfunctionalize a bcc alloy. Such disordered solid solutions are based on vanadium, which initially has a goodreactivity in relation to hydrogen. However, the thermodynamics of V-H system does not allow applicationsbelow 40 ° C, the cost is prohibitive and its implementation in industrial environments is not straightforward.We worked on three major families of vanadium alloys. Alloys Ti-V-Cr have been studied by in operandosynchrotron radiation X-ray diffraction in order to understand the observable structural transformations that takeplace during hydrogenation and then to link them to the thermodynamics of compounds. In a second step, thespecifications of the project directed us towards vanadium composites in which we develop an intergranularstructure for a better controlled activation and destabilization of the hydride so as to reach operatingtemperatures near 0 ° C. The use of ferro-vanadium as a precursor prompted the study of alloys in the Ti-V-Feand Ti-V-Cr-Fe systems. The viability of storage solutions on the basis of these materials is discussed.Throughout the course of this work the relationship between microstructure and hydrogen sorption properties issystematically discussed and empirical models describing the hydride equilibrium are routinely faced with thebibliographic database.Finally, part of the study is devoted to the study and modeling of reservoirs in operating condition, from thepoint of view of heat exchange, compliance with safety standards and mechanical stresses generated by the bedreactive powder

The general objective of this thesis is the analysis of selective reactions for group VI grafted metal complexes via methods and principles of SOMC. For this objective, three approaches have been chosen. The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing heterogeneous catalysis and more specifically the different approaches to support catalysts on surfaces. The concept of catalysis by design is introduced as a new way to use the surface as a ligand. Chapter 2 presents the results of a library of well-defined catalysts of group VI with identical catalytic functionality, but different ligand environment. The results reveal, that metal-carbynes are able to switch their catalytic reactivity based on the substrate that they are contacted with. The difference in reaction mechanisms and the differing reactivities towards the substrates are presented. It can be concluded that the classical ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas cyclic alkanes yield exclusively higher and lower homologues of the substrate without polymeric products. Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products is analyzed. It is presented, that the ligand environment of the catalysts is showing an influence in the selectivity. Rates of cis/trans isomerization of the products are high and are approaching thermodynamic equilibrium at high conversion. Product isomerization, thermodynamic equilibrium and reactivity differences between liquid phase and gas phase products are analyzed. Chapter 4 presents the full characterization of tungsten-hydrides by selective transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show, that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes. Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the generated tungsten-hydroxides of chapter 4.

Aluminium foams have high specific strength and higher stiffness than other contemporary packaging materials. They have important application as packaging material for critical applications that needs highest safety standards. Commercially, established processes for manufacturing of metal foam include Hydro/Alcan Process, Alporas Process, Gasar/Lotus process, Alulight/Foaminal process, Formgrip Process, ALUHAB and Powder Metallurgy route. In the above methods, control of the shape and size of pores is difficult. In these techniques significant changes in the chemistry of the melt is carried out to foam the metals. The Gap area of the above commercial processes is minimised by “Hollow sphere technique”. This process overcomes the limitations in achieving the cell wall thickness, shape of the pores, non-uniformity of pore size and its distribution in comparison to existing commercial established process. Moreover, it is easy to fabricate foams, with desired/tunable mechanical properties. This thesis discusses, the fabrication technique of hollow spheres using a special die by successive pressing of hollow tube through a series of ten die cavities. The fabricated hollow spheres are cured in the required shape using suitable bonding material (resin based or metal binder). The advantage of this process being, any asymmetrical shape is easier to fabricate and mechanical properties can be controlled by using spheres with different diameters and varying wall thickness. This process does not require any additional alloy nor does it require huge experimental facilities for fabrication. This mechanical processing method of hollow sphere technique can fabricate different diameter spheres with varying wall thickness. By arranging spheres in desired pattern, “graded foams” which is a new concept exhibiting peculiar properties is introduced. This work includes assessment of mechanical properties and its comparison with respect to commercially available foams. The main properties under consideration were yield strength, Young’s modulus, plateau stress, densification strain and energy absorption evaluation. This thesis also, discusses practical application of developed product in the field of engineering as base isolators, which is novel. The thesis concludes by highlighting advantages of this technique over the other existing commercially established fabrication routes: • Desired/tunable Mechanical properties can be achieved on case-to-case basis with ease and can be supported by impact simulations using finite element analysis. • It is the fastest and easiest way for production of High purity aluminium foam and in achieving any asymmetrical shapes. • Relative Densities of the order of 10%, 20%, 30%, 40%, 50 % and higher can be achieved by varying only the hollow sphere diameter or wall thickness of the sphere. • Cost effective and Environment/Eco-friendly and Recyclable This route of hollow spheres fabrication and the final product is different from the prevalent commercially established routes of metal foam fabrication using hollow sphere technique.

Dissertação de Mestrado Integrado em Engenharia Física apresentada à Faculdade de Ciências e Tecnologia<br>O armazenamento de hidrogénio tem sido tema de estudo por parte de diversos investigadores, nomeadamente o armazenamento de H2 em substâncias sólidas - geralmente metais. Um dos problemas apontados neste estudo passa pela variação significativa dos parâmetros de rede na formação do hidreto metálico, causando uma expansão no volume da célula unitária e, consequentemente, o inchaço dos grãos de pó do hidreto formado. Para viabilizar este estudo e com foco no armazenamento de hidrogénio, foi desenvolvida uma câmara para medidas de difracção de raios-X in-situ, que suporta pressões até 10 bar, considerando a geometria do método de análise de difração de Bragg-Brentano para o estudo de compostos metálicos hidrogenados.Muitas das decisões que influenciaram o seu desenho final passaram pelo estudo da geometria do próprio difractómetro e das propriedades dos materiais a serem escolhidos para a construção de todo o sistema.O trabalho de pesquisa sobre casos práticos, teve imensa importância para a identificação de erros cometidos no passado. Estes erros, depois de identificados e contornados, permitiu o melhoramento do instrumento final, com soluções concebíveis, seguras e ao mesmo tempo, economicamente viáveis.Esta câmara permite medições in-situ de difração de raios-X em pó, em função da concentração de hidrogénio. Essas medidas de difração com pressão são fundamentais na caracterização inicial de qualquer material novo. A reacção de absorção pode ser estudada através da alteração da cristalografia das fases envolvidas em resposta a uma alteração na pressão de hidrogénio. A câmara de difracção de raios-X foi integrada num sistema volumétrico que permitirá a quantificação da concentração do hidrogénio armazenado em qualquer momento. Todo o sistema foi inteiramente projectado para integrar o difractómetro D8 ADVANCE da Bruker. Os ensaios realizados para a validação da câmara nas medidas de difractometria foram feitos usando amostras de Corundum e Silício, enquanto que o hidreto padrão LaNi5Hx foi o hidreto escolhido para a validação do sistema Sieverts.<br>Hydrogen offers excellent prospects as potential energy carrier. It’s production and storing, as well as the recovery of the energy, are currently the object of many researchers attention. That being said, we propose the study of metal hydrides for the purpose of hydrogen storage, with in-situ XRD analysis applied to the Bruker D8 Advance diffractometer.In order to make this study feasible, the design and conception of a chamber that supports pressures up to 10 bar was developed taking into account all the physical aspects for its integration in the same diffractometer.The conception of a new chamber allows its use in the in-situ analysis of hydrogenated metallic compounds by powder X-rays diffraction. The hydriding reaction may be followed via the changing crystallography of the phases involved in response to a change in hydrogen pressure. Those aspects are points that we propose to study with the construction of this new instrument.This chamber was developed fulfilling a geometry of the Bragg-Brentano diffraction analysis method and allows in-situ measurements of X-rays diffraction as a function of the concentration of hydrogen.These diffraction measurements with pressure are fundamental in the initial characterization of any new material.The final design was achieved taking into account the many physical and mechanical aspects involved. One of them was the design of a low-cost window made of Kapton material. Our chamber is incorporated in a Sieverts system with valves and a reference volume that allow us to quantify the concentration of hydrogen at any time.Currently the metal hydrides are exploited to the maximum in the sense of their properties. An already well known example of the properties of these materials is the formation of different phases when the hydride is formed at different pressures. The use of the chamber for X-ray diffraction was validated with standard silicon and Corundum samples while the standard hydride LaNi5Hx was the hydride chosen for the validation of the Sieverts instrumentation.