High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost. The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers. The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller. The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications. The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres. From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface. For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites. Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan  and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan  values were calculated with duration of aging. It was observed that the tan  values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.

Submitted in fulfillment of the requirements for the degree of Master of Engineering in Chemical Engineering, Durban University of Technology. Durban. South Africa, 2015. / Several areas in the world such as the United States of America, Sri Lanka, China, Argentina, Canada, Tanzania, Kenya, South Africa and many others have a problem of high fluoride content in drinking water. Generally fluoride levels above 1.5 ppm in water may result in dental and skeletal fluorosis in humans depending on quantity consumed (Fan et al., 2003; Meenakshi, 2004). Remote rural areas where there are no water treatment facilities are more vulnerable to this problem. Adsorbents such as activated alumina and FR-10 resin seem to have a potential for successful application in rural areas. These methods however require pre-treatment if the feed has high turbidity. A membrane based system called woven fabric microfiltration gravity filter (WFMFGF) developed by Durban University of Technology proved to be suitable for turbidity removal. The main objective of this research was to develop a small water treatment system for fluoride removal. The small water treatment system developed in this study consists of WFMFGF for pre-treatment and an adsorption column. The WFMFGF is made up of a 40 L container packed with 15 immersed flat sheet membrane elements. The operation of the WFMFGF is in batch mode, driven by varying static head. The static head variation results in flow rate variation through the system. This in turn result in variation of contact time, velocity as well as pressure drop in the fluoride removal unit. Specific objectives of the study were: (1) to establish the maximum and minimum flow rates through the WFMFGF system, the total run time before cleaning is required and the best cleaning method for this particular membrane system. (2) to evaluate and compare the performance of activated alumina and FR-10 resin on varying contact time, velocity and pressure drop on the fluoride removal unit. The adsorbents were also compared on adsorption capacity, cost and ease of operation. The minimum and maximum flow rates through the WFMFGF were found to be 5 l/hr and 100 l/hr respectively. It was found that the system can be run for more than a month before requiring cleaning. The suitable cleaning method was found to be soaking the membranes in 0.0225 percent sodium hypochlorite solution overnight and brushing them using a plastic brush. The comparison of the performance of FR-10 resin to activated alumina found that the adsorbents gave equal performance based on the given criteria. FR-10 resin had higher adsorption capacity, gave good quality treated water even with shorter contact time and operated at wider velocity range. Activated alumina on the other hand had an advantage of lower costs, lower pressure drop and ease of use. According to Pontius (1990), the performance of activated alumina can be improved by intermittent operation. Point of use (POU) systems are generally operated intermittently. This improves the fluoride removal efficiency of activated alumina giving it more advantage over FR-10 resin. Based on this activated alumina was selected as the best adsorbent for the system. After the adsorbent was selected, the adsorption column was designed. The column operation regime was 3.5 minutes minimum contact time and 1.17 to 7.8 m/hr velocity range. The activated alumina adsorption capacity was 1.53mg/g. The column had an inside diameter of 70 mm. It was packed with activated alumina to a bed height of 400 mm. The column inlet and outlet pipes were made of PVC with a standard pipe size of 20 mm outside diameter. A valve at the column inlet pipe allowed water to flow through the system.

The work presented in this thesis deals with experimental and theoretical studies related to alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. However, controlling thin film growth of this material, in particular at low substrate temperatures, is not straightforward. The aim of this work is to increase the understanding of the basic mechanisms governing alumina growth and to investigate novel ways of synthesizing alumina coatings. The thesis can be divided into two main parts, where the first part deals with fundamental studies of mechanisms affecting alumina growth and the second part with more application-oriented studies of high power impulse magnetron sputter (HiPIMS) deposition of the material. In the first part, it was shown that the thermodynamically stable α phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of merely 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α-alumina (in addition to the effect of the chromia nucleation layer). Moreover, the effects of residual water on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1*10-5 Torr was introduced, the columnar α-alumina growth was disrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the γ-alumina content was found to increase with increasing film thickness. To gain a better understanding of the atomistic processes occurring on the surface, density functional theory based computational studies of adsorption and diffusion of Al, O, AlO, and O2 on different α-alumina (0001) surfaces were also performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites and also show how adsorbed hydrogen might inhibit further growth of α-alumina crystallites. In addition, it was shown that the Al surface diffusion activation energies are unexpectedly low, suggesting that limited surface diffusivity is not the main obstacle for low-temperature α-alumina growth. Instead, it is suggested to be more important to find ways of reducing the amount of impurities, especially hydrogen, in the process and to facilitate α-alumina nucleation when designing new processes for low-temperature deposition of α-alumina. In the second part of the thesis, reactive HiPIMS deposition of alumina was studied. In HiPIMS, a high-density plasma is created by applying very high power to the sputtering magnetron at a low duty cycle. It was found, both from experiments and modeling, that the use of HiPIMS drastically influences the characteristics of the reactive sputtering process, causing reduced target poisoning and thereby reduced or eliminated hysteresis effects and relatively high deposition rates of stoichiometric alumina films. This is not only of importance for alumina growth, but for reactive sputter deposition in general, where hysteresis effects and loss of deposition rate pose a substantial problem. Moreover, it was found that the energetic and ionized deposition flux in the HiPIMS discharge can be used to lower the deposition temperature of α-alumina. Coatings predominantly consisting of the α phase were grown at temperatures as low as 650 °C directly onto cemented carbide substrates without the use of nucleation layers. Such coatings were also deposited onto cutting inserts and were tested in a steel turning application. The coatings were found to increase the crater wear resistance compared to a benchmark TiAlN coating, and the process consequently shows great potential for further development towards industrial applications.

In this master thesis, performed at Sandvik Coromant Västberga (Stockholm), a comprehensive study has been made to investigate the wear on textured alumina (Inveio™) coated cutting tools when turning low-alloy steels. Specifically, wear studies have been made on tools’ rake faces when turning two separate batches of SS2541, after an initial turning time of 4 min. A particular focus has been given to elucidate what particular role the inclusions might have for the wear of the alumina coating onthe tools. Evaluation of tool wear has been made by employing several different analytical techniques, such as LOM, SEM, Wyko, Auger-spectrometry (AES), EPMA and XRD. The results shows that the arisen wear marks on both tested tool types may be divided into three separate and highly distinguishable wear zones, denoted here in thiswork as “wear bands”. Largest amount of wear tended to occur initially at the topmost part of the 3rd wear band. This was true for both tested tool types. This area demonstrated a characteristic 'lamellar' wear pattern, composed of narrow andstructured ridges. All the tools tested demonstrated the adhesion of workpiece materials of various composition that formed into smeared layers in these formed ridges. Depth-profiling Auger-spectrometry revealed that a significant amount of calcium was present in the machined alumina coating layers. This suggests that a reaction between the calcium-containing inclusions found in the steel and the aluminacoating layer had occurred during the performed turning tests.These results arecontradictory to the general belief that alumina is chemical inert during machiningand has previously, to the authors knowledge, not yet been published. Based on the results from this thesis and from a literature review concerning thebehavior of α-alumina during deformation, a new theoretical wear model has been developed. In this model, it is emphasised that the sliding of hard inclusions from the steel may activate pyramidal slip systems in the textured alumina coating. This causes a nano-crystallisation and/or amorphisation in the topmost part of the coating, which facilitates the further wear of these coated tools. / I detta examensarbete, som har utförts vid Sandvik Coromant i Västberga (Stockholm), har en omfattande studie gjorts i syfte att undersöka slitaget på texturerad aluminiumoxid-belagda skärverktyg (Inveio™) vid svarvningen av låglegerade stålsorter. Förslitningsstudier har framförallt gjorts på verktygens spånsidor vid svarvningen av två separata batcher av stålsorten SS2541 efter en inledande ingreppstid på 4 min. Ett särskilt fokus har även ägnats åt att belysa vilken roll stålets inneslutningar kan ha för slitaget av aluminiumoxidbeläggningen. Utvärderingen av verktygsslitaget har gjorts med hjälp av flera olika analytiska tekniker, däribland LOM, SEM, Wyko, Auger-spektrometri (AES), EPMA samt XRD. Resultaten från detta examensarbete visar på att det uppkomna slitaget på de verktyg som har testats kan uppdelas till tre separata och mycket distinkta ”slitagezoner”. Dessa zoner har för detta arbete benämnts som ”nötningsband”. Störst förslitning framträdde initialt i den översta delen av det 3:e nötningsbandet på de testade skärverktygen. Detta område uppvisade ett karaktäristiskt ”lamell”-liknande utseende, bestående av smala och strukturerade åsar och skåror. Vidare uppvisade samtliga undersökta verktyg på förekomsten av påsmetat arbetsmaterial av varierande sammansättning i dessa bildade åsar. När de slitna verktygen undersöktes med djuprofilerande Auger-spektrometri påvisades det att en signifikant mängd kalcium fanns inuti aluminiumoxidbeläggningen. Detta tyder på att en reaktion mellan de kalciuminnehållande inneslutningarna (som finns inuti stålet) och aluminiumoxidbeläggningen har reagerat med varandra under bearbetningsförloppet. Dessa resultat är motsägande till den allmänna uppfattningen om att aluminiumoxid är kemiskt inert vid bearbetningen av stål. Därutöver har dessa resultat även, till författarens kännedom, aldrig tidigare publicerats. Baserat på de resultat som har erhållits från detta examensarbete, och från en omfattande litteraturstudie gällande deformationen av α-aluminiumoxid, har en ny teoretisk förslitningsmodell utarbetats. I denna modell betonas det särskilt att glidningen av hårda inneslutningar från stålet kan aktivera s.k. pyramidala glidsystem i den texturerade aluminiumoxidbeläggningen. Detta orsaker en nano-kristallisering och/eller amorfisering av den översta delen av aluminiumoxidbeläggningen.  Denna omvandling tros kunna underlätta den fortsatta förslitningen av dessa belagda skärverktyg.

L’objectif de ce travail est d’évaluer l’effet de la nature du support et l’effet de promotion sur les propriétés catalytiques des catalyseurs d’HDS à base de Mo. Pour obtenir les systèmes catalytiques adéquats, nous avons appliqué la préparation par « voie acac », qui consiste à faire réagir le promoteur sous forme de complexe acétylacétonate (de Co, Ni ou Fe) sur le sulfure de molybdène supporté (sur γ-Al2O3, SiO2, TiO2 ou ZrO2). Les différents solides obtenus ont été caractérisés par MET, IR(CO) et SPX notamment pour tenter de quantifier les phases actives, puis ils ont été testés dans les réactions d’HDS du thiophène et du 4,6-DMDBT. L’activité catalytique a pu être corrélée aux résultats de caractérisation par une nouvelle approche qui consiste à calculer l’activité apparente par site NiMoS ou CoMoS. Cette approche montre que la qualité des sites actifs CoMoS et NiMoS est la meilleure sur SiO2 et comparable sur les supports γ-Al2O3, TiO2 et ZrO2. Par la même méthode nous avons préparé de nouveaux catalyseurs de type CoNiMoS supportés, en ajoutant les promoteurs Co et Ni soit simultanément soit successivement au MoS2. Cette étude permet un fort apport expérimental aux études théoriques qui avancent l’hypothèse de différentes affinités du Co et du Ni pour les deux type de bords S-edge et Mo-edge sur γ-Al2O3 et TiO2. / The main objective of this work was to evaluate the support and the promoting effect on the catalytic properties of HDS catalysts. In order to obtain appropriate catalytic systems, we applied the “acac method” which consists to add the promoter as an acetylacetonate complex (of Co, Ni or Fe) onto the supported molybdenum sulfide (on γ-Al2O3, SiO2, TiO2 and ZrO2). The various solids obtained were characterized by TEM, IR(CO) and XPS in particular to quantify the active phases, and then they have been tested in the HDS reactions of thiophene and 4,6-DMDBT. The catalytic activity has been correlated to the characterization datas by a new approach which consists in calculating the apparent catalytic activity by NiMoS or CoMoS site. This approach showed that the quality of the active sites is the best on SiO2 and comparable on γ-Al2O3, TiO2 and ZrO2. Moreover, this “acac method” allowed us to study supported CoNiMoS catalysts synthesized by adding Co and Ni either simultaneously or successively to MoS2. This study represents an important experimental contribution which allow to discuss the hypothesis developped in theoretical studies about the different affinities of Co and Ni for the S-edge and Mo-edge on γ-Al2O3 and TiO2.

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs. / <p>QC 20111014</p>

La préparation de matériaux catalytiques, à base de métaux de transition (Ni, Co, Cu) supportés sur des supports à porosité organisée, performants pour la réaction d’hydrogénation chimiosélective du cinnamaldéhyde, a été étudiée. L’étude peut être divisée en deux parties distinctes, selon la nature du support, silicique ou aluminique. La première partie traite de la dispersion de métaux de transition sur des supports de type SBA-15.Dans le premier chapitre est présentée la préparation des catalyseurs par la méthode IWI-MD (Incipient Wetness Impregnation – Mild Drying). Plusieurs études, afin de valider l’efficacité de cette méthode, ont été menées : (i) influence de la texture du support, (ii) influence de la température et du temps de séchage; (iii) influence de la teneur en métal. Le deuxième chapitre rapporte l’étude de la préparation par la voie de déposition par précipitation. L’étude de la méthode d’infiltration des sels fondus, dite de Melt Infiltration (MI), optimisée afin d’assurer une infiltration complète du précurseur dans la porosité du support préalablement à la formation de la phase oxyde, est présentée dans le Chapitre 3. Finalement, le dernier chapitre du document traite de la dispersion sur des supports aluminiques mésoporeux ordonnés (AMO). Les matériaux catalytiques ont été préparés sur des supports AMO, obtenus par la voie d’auto-assemblage induit par évaporation (AAIE). Les paramètres étudiés sont : (i) l’effet de la texture du support, à partir d’alumines de différentes tailles de pores et (ii) l’effet du mode de déposition des métaux (par IWI-MD, MI ou TS). / The development of efficient transition metal based catalysts for the chemoselective hydrogenation reaction of cinnamaldehyde is studied. The active phases, studied in this work, are among the transition metals (Ni, Co and Cu), supported on porous ordered materials. This study can be divided in two different sections, according to the support nature. The first part concerns the dispersion of transition metals on SBA-15 type silica support. In the first chapter is presented the transition metal dispersion (Ni, Co and Cu) using IWI-MD (Incipient Wetness Impregnation –Mild Drying) method. Studies performed, to optimize active phase dispersion, are: (i) influence of support texture, (ii) influence of drying temperature, (iii) influence of drying time, (iv) influence of metal loading. In the second chapter, Ni, Co and Cu catalytic materials are prepared using deposition precipitation method. In the third chapter is described the transition metal dispersion using melt infiltration method (MI), optimized to ensure a complete infiltration of metallic precursors in the support porosity before oxide phase formation. The second section of the Ph.D. is related to the dispersion of transition metal over ordered mesoporous alumina (AMO) supports. Catalytic materials, based on Ni and Cu over AMO (obtained by EISA process - Evaporation Induced by Self-Assembly), are produced. Parameters studied are: effect of support texture, effect of preparation route (IWI-MD, MI and TS).

Dans ce travail réalisé au Centre de Morphologie Mathématique and IFPEN, on s'intéresse à la microstructure et aux propriétés physiques d'alumines mésoporeuses. Il s'agit d'un supporte de catalyseur utilisés notamment dans les processus industriels de raffinage du pétrole. Fortement poreux, ce matériau est formé de ''plaquettes'' distribuées de manière désordonnée à l'échelle de la dizaine de nanomètres. Les propriétés de transport de masse du support de catalyseur sont fortement influencées par la morphologie de la microstructure poreuse. Ce travail porte sur la modélisation de la microstructure et des propriétés de transport des alumines mésoporeuses, à l'aide d'outils numériques et théoriques dérivés de l'analyse d'image et de la théorie des ensembles aléatoires. D'une part, on met en place des méthodes de caractérisation et de modélisation des microstructures, qui s'appuient sur, entre autre, des images obtenues par microscopie électronique en transmission (MET) et des courbes de porosimétrie azote. D'autre part, on utilise des méthodes d'homogénéisation numérique à champs complets par transformées de Fourier rapide (FFT).Dans un premier temps, le matériau est caractérisé expérimentalement par porosimétrie azote et résonance magnétique nucléaire à gradient de champ pulsé (RMN-GCP). Les images MET sont obtenus sur des échantillons d'épaisseur variable, filtrées et caractérisés par des fonctions de corrélation, notamment. Le bruit à haute fréquence issu de la membrane de carbone est identifié et pris en compte dans la modélisation de l'imagerie MET. À partir des images MET 2D, un modèle aléatoire à deux échelles est proposé pour représenter la microstructure 3D. Il prend en compte la forme des plaquettes d'alumines, leurs tailles, les effets d'alignement locaux et d'agrégation, qui sont identifiés numériquement. La procédure est validée à l'aide de comparaisons entre modèle et images expérimentales, en terme notamment de fonctions de corrélation et de surface spécifique, mesurées par porosimétrie azote.Dans un deuxième temps, une méthode de simulation des courbes d'isothermes de porosimétrie dans des milieux poreux périodiques ou aléatoires est développée. Basée sur des opérations morphologiques simples, elle étend un travail antérieur sur la porosimétrie au mercure. L'adsorption multicouche à basse pression est simulée à l'aide d'une dilatation tandis que les ménisques de l'interface vapeur-liquide intervenant pendant l'adsorption sont simulés à l'aide de fermetures de la phase solide par des éléments structurants sphériques. Pour simuler la désorption, une combinaison de fermetures et de bouchages de trou est utilisée. Le seuil de désorption est obtenu par une analyse de la percolation de la phase gazeuse. La méthode, d'abord validée sur des géométries simples, est comparée à des résultats antérieurs. Elle prédit une hystérésis et les distributions de pores associées à la porosimétrie. Nous l'appliquons aux modèles de microstructures 3D d'alumines mésoporeuses et proposons un modèle à trois échelles afin de rendre compte du seuil de pression pendant la désorption. En plus de la courbe de désorption, ce modèle reproduit les fonctions de corrélation mesurées sur les images MET.Dans un troisième temps, la diffusion de Fick, la perméabilité de Darcy, et les propriétés élastiques sont prédits à l'aide de calculs de champs complets par FFT sur des réalisations des modèles d'alumines mésoporeuses à deux et trois échelles. Les coefficients de diffusion effectifs et les facteurs de tortuosité sont prédits à partir de l'estimation du flux. Sont étudiés les effets de forme, d'alignement et d'agrégation des plaquettes sur les propriétés de diffusion à grande échelle. Les prédictions numériques sont validées au moyen des résultats expérimentaux obtenus par méthode RMN-GCP. / In a work made at Centre de Morphologie Mathématique and IFPEN, we study the microstructure and physical properties of mesoporous alumina. This is a catalyst carrier used in the petroleum refining industry. Highly porous, it contains disordered ''platelets'' at the nanoscale. The mass transport properties of the catalyst carrier are strongly influenced by the morphology of the porous microstructure. We focus on the modeling of the microstructure and of transport properties of mesoporous alumina, using numerical and theoretical tools derived from image analysis and random sets models. On the one hand, methods are developed to characterize and model the microstructure, by extracting and combining information from transmission electron microscope (TEM) images and nitrogen porosimetry curves, among others. On the other hand, the numerical homogenization relies on full-field Fourier transform computations (FFT).The material is first characterized experimentally by nitrogen porosimetry and pulse-field gradient nuclear magnetic resonance (PFG-NMR). TEM images, obtained on samples of various thicknesses are filtered and measured in terms of correlation function. The high-frequency noise caused by carbon membrane support is identified and integrated in the TEM image model. Based on the 2D TEM images, a two-scale random set model of 3D microstructure is developed. It takes into account the platelet shape, platelet size, local alignments and aggregations effects which are numerically identified. The procedure is validated by comparing the model and experimental images in terms of correlation function and specific surface area estimated by nitrogen porosimetry.Next, a procedure is proposed to simulate porosimetry isotherms in general porous media, including random microstructures. Based on simple morphological operations, it extends an earlier approach of mercury porosimetry. Multilayer adsorption at low pressure is simulated by a dilation operation whereas the menisci of the vapor-liquid interface occurring during adsorption are simulated by closing the solid phase with spherical structuring elements. To simulate desorption, a combination of closing and hole-filling operations is used. The desorption threshold is obtained from a percolation analysis of the gaseous phase. The method, validated first on simple geometries, is compared to previous results of the literature, allowing us to predict the hysteresis and pore size distribution associated to porosimetry. It is applied on 3D microstructures of mesoporous alumina. To account for the pressure threshold during desorption, we propose a refined three-scale model for mesoporous alumina, that reproduces the correlation function and the desorption branch of porosimetry isotherms.Finally, Fick diffusion, Darcy permeability, and elastic moduli are numerically predicted using the FFT method and the two-scale and three-scale models of mesoporous alumina. The hindering effects in diffusion are estimated by the Renkin's equation. The effective diffusion coefficients and the tortuosity factors are estimated from the flux field, taking into account hindering effects. The effects of platelet shape, alignment and aggregation on the diffusion property are studied. The numerical estimation is validated from experimental PFG-NMR results.

Le principe de la projection dynamique par gaz froid ou « cold spray » repose sur la projection de particules de poudres convoyées par un gaz à des vitesses supersoniques vers un substrat. La déformation des particules à l’impact avec ce dernier permet la construction d’un dépôt. Ce procédé permet de conserver la microstructure des particules de poudre et de produire des dépôts peu poreux. Cette dernière caractéristique est essentielle dans le cadre d’applications anticorrosion. L’ambition de la thèse est de comprendre le rôle de la microstructure sur les mécanismes de corrosion marine d’un dépôt à base d’aluminium élaboré par cold spray. Pour atteindre cet objectif sont projetées des poudres à base d’aluminium (aluminium pur, alliages d’aluminium et mélanges avec ajout d’alumine) sur un substrat en acier. Les microstructures des dépôts sont étudiées jusqu’à l’échelle nanométrique (MET). L’adhérence des dépôts est mesurée par l’essai de plot collé. A partir des microstructures sont proposés plusieurs mécanismes de formation de la porosité dans un dépôt cold spray à différentes échelles. Une étude numérique par éléments finis complète cette analyse microstructurale. Grâce aux mesures de la vitesse (DPV-2000) et de la température (caméra thermique) d’impact des particules, les paramètres de nouveaux modèles matériau sont optimisés pour simuler le comportement de l’aluminium et de l’alumine à l’impact. De plus, plusieurs essais de corrosion marine (immersion et brouillard salin) sont conduits. L’étude des microstructures corrodées permettent d’établir différents mécanismes de corrosion du dépôt cold spray. Un lien entre la porosité du dépôt et son comportement en corrosion est notamment montré. Enfin, une première approche du transfert de technologie du procédé à l’échelle industrielle est décrite. / Cold spray process is based on spraying particles carried by a gas at a supersonic speed onto a substrate. Particle deformation during impact with the substrate creates a coating. This spraying process can retain particle microstructure and produce very dense coating. This property is crucial for anticorrosion applications. The aim of this work is to understand the effect of cold spray aluminum coating microstructure on marine corrosion mechanisms. To achieve this goal, several aluminum powders (including pure aluminum, aluminum alloys and mixtures with alumina) are sprayed onto a steel substrate. Coating microstructure is studied down to a nanoscale (TEM). The coating-substrate bond strength is determined using pull-off testing. From a thorough microstructure study, various mechanisms are proposed to explain multiscale porosity formation in coatings. A numerical study using finite elements modeling complements this microstructure analysis. From particle speed (DPV-2000) and temperature (thermal camera) measurements during impact, new material models are optimized to model aluminum and alumina behavior at particle impact. Moreover, corrosion tests are conducted (including immersion and salt spray tests). The study of corroded coating microstructures is used to identify corrosion mechanisms which occur in the coating. A relationship between coating porosity and its corrosion behavior is particularly brought into light. Finally, a first approach to a technological transfer of this process to an industrial application is proposed.

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