[abstract] In the process of nucleation, the decay of a metastable state is initiated by the formation of a spatially localised region called a nucleus of critical size. In many realistic situations nucleation is initiated at an impurity or defect; such as a dust particle, an irregularity in a sample, or a crack in the wall of a container. The aim of this thesis is to identify and understand the fundamental changes different types of defect make to nucleation by studying a one-dimensional continuum model used to describe solitons. A well established theory due to Langer is extended to calculate the rate of decay of a metastable state due to the nucleation of solitons at defects. Results are used to find the rate of thermally activated magnetisation reversal for a ferromagnetic nanowire with defects in the uniaxial anisotropy. Defects which are narrower than the soliton width (point-like defects) and wider than the soliton width (step defects) are both modelled. An attractive defect breaks the translational symmetry of a soliton and leads to pinning. The pinning of solitons is found to reduce the activation energy required for nucleation, reduce the critical field above which a metastable state becomes unstable, alter the mechanism by which a metastable state decays, and modify the prefactor for the rate of decay. Changes to the prefactor are interpreted in terms of entropy and the dynamics of metastable decay when a defect is present.

The purpose of this thesis is to improve predictions of irradiation hardening in metals with a focus on coarse-graining via meso-scale simulations. Increasing hardness and decreasing in ductility in nuclear reactor pressure vessel steel is the limiting factor of nuclear reactor life, and accurately predicting reactor life is of the utmost importance for the safe operation of nuclear facilities. This is an inherently multi-scale problem with primary damage occurring at the atomic scale and its effects propagating across ten orders of magnitude in length and time scale to changes in macroscopic material properties, which must be reflected in its methods of prediction. To achieve this goal, this thesis develops two novel approaches to simulate the motion of dislocations in irradiated alpha-iron. First, a dislocation dynamics simulation coarse-graining insight from atomistic dislocation-defect simulations is used to guide the selection of proposed constitutive models. Several studies investigating the effect of size distribution show that the mean defect size can be used with the selected models to predict material hardening without a complex treatment for the defect size distribution. The hardening effect of the commonly observed defect types are found independently and a superposition principle is proposed for materials with both defect types. Second, a link to transition state theory and thermally activated reactions is established using a new method augmenting a discrete dislocation dynamics simulations with the nudged elastic band method to characterise the minimum energy pathways of dislocation reactions. This development enables calculations of activation energy for dislocation events using a continuum method as well as the numerical calculations of dislocation attempt frequency. The thesis concludes with an extension to the analysis of coarse-graining unit events to large scale dislocation-obstacle bypass phenomena.

Perlite is a volcanic mineral. The latest investigations on ground perlite showed that it is suitable for pozzolanic usage. Thus, it is of vital importance especially for countries rich in perlite such as Turkey. The aim of this study is to investigate the advantages and problems associated with using perlite in concrete and to identify accurate methods and amounts of use for producing durable cementitious mixtures. Within the scope of this study, the alkali-silica reactivity of perlite containing cementitious mixtures were compared using four different methods. Expansion mechanism of the mixtures were tried to be understood by measuring the alkalinity of bath waters. In order to cope with early strength decreases caused by perlite addition, activation of the mixtures by chemical and thermal methods were attempted. It was found that chloride containing chemicals are very effective at later ages and sodium containing chemicals are more effective at early ages. Sodiumhydroxide addition to the perlite containing mixtures was found to be detrimental to both the initial and late-age strengths of mortars. It was concluded that perlite addition generally results in a decrease in alkali-silica expansions. However, the expansion of concrete samples should be investigated comprehensively. Thermal curing at high temperatures resulted in a rapid increase at 1-day strengths, however, for better ultimate strengths lower thermal treatments or no-thermal curing were found to be more effective. Compared to the traditional portland cement concretes, high-volume ground perlite concretes have environmental and economical advantages.

Durant cette thèse, nous avons d'abord développé un dispositif expérimental permettant de mesurer la dynamique de l'angle de contact avec une précision record de 0,01° sur 7 décades de vitesses de la ligne triple, gamme jamais atteinte auparavant. Pour la première fois, la résolution numérique des équations de lubrification a permis de déduire l'angle de contact à l'échelle microscopique de ces mesures macroscopiques, découplant donc le problème hydrodynamique multi-échelles de la physique de la ligne de contact à petite échelle. Avec ces outils, nous avons montré qu'une pseudo-brosse - une couche nanométrique de polymères - peut complètement piloter la dynamique, en produisant des hystérésis les plus faibles jamais mesurées (<0,07° !) et des surdissipations massives provenant de la nature visco-élastique de la couche. Cette étude ouvre la voie à la nano-rhéologie, permettant de sonder la dynamique extrêmement rapide (~100 ns) de polymères confinés à l'échelle nanométrique. Grâce à un travail collaboratif fructueux, nous avons ensuite développé un modèle permettant de décrire quantitativement et de façon unifiée la dissipation hydrodynamique, l'hystérésis et l'activation thermique. Enfin, beaucoup d'efforts ont été fournis pour la fabrication de surfaces aux défauts nanométriques contrôlés en taille, forme et concentration. La dynamique s'est révélée insensible à cette échelle de désordre, la présence des défauts n'affectant que l'hystérésis. Ces résultats ont été interprétés semi-quantitativement avec des lois d'échelle, et la caractérisation complète des défauts devrait permettre à terme de développer des modèles plus quantitatifs. / During this thesis, we first developed an experimental set-up to measure contact angle dynamics with a record precision of 0.01° over 7 decades of velocity of the triple line, a range never before attained. For the first time, numerically solving the lubrication equations has allowed us to deduce the contact angle at the microscopic scale from these macroscopic measurements, and thus enabled the multi-scale hydrodynamic problem to be disentangled from the physics of the contact line at small scales. With these tools we have shown that the dynamics can be completely piloted by a pseudo-brush -a nanometric layer of polymers-, producing the lowest ever reported hysteresis (<0.07°!) and giving rise to a huge source of dissipation originating from the viscoelasticity of the coating. This study points the way towards nano-rheology, to probe extremely fast dynamics (~100 ns) of polymers confined at the nano-scale. Thanks to a fruitful collaborative work, we then developed a model that provides a single quantitative framework to account for hydrodynamic dissipation, hysteresis and thermal activation. Finally, a great deal of effort has been made to produce nano-defects whose size, shape and density are controlled. The dynamics appears to be insensitive to this scale of disorder, and the presence of defects is observed to only modify the hysteresis. These results have been interpreted semi-quantitatively with scaling laws, and we expect that the complete characterization of the defects should eventually allow the development of more quantitative models.

In the beginning of the twenty-first century, educational and commercial institutions have driven the demand for cheap and efficient data storage. The storage medium known as magnetic recording media has remained the mainstay for most computer systems due to its large storage capacity per dollar. With the recording media's ever-increasing storage density has come reductions in the magnetic grain size per bit. At the recording bit's density threshold, the magnetic grains become more susceptible to thermal activation, which can render the storage medium unusable. An accurate characterisation of the recording layer's sub-granular structure is essential for understanding the magnetic and thermal mechanisms of high-density recording media. Small-Angle Neutron Scattering (SANS) studies have been performed to investigate the magnetic and physical properties of longitudinal and perpendicular recording grains. The SANS studies of longitudinal magnetic recording media have probed the recording layer's magnetic grain size at a sub-nanometer resolution. In conjunction with these studies, SQUID magnetometry was used to characterise the recording grain's bulk magnetism. Measurements showed that the recording grain was composed of a ferromagnetic hard core (Co-enriched) and a weakly magnetic shell (Cr-enriched). These results provided important information on the grain's magnetic anisotropy, which determines the recording media's magnetic stability. The polarised SANS studies were used to characterise the recording layer's physical granular structure. It was shown that the physical grain size was comparable to its magnetic counterpart. These physical measurements provided insight into the recording grain's chemical composition. The magnetic properties of perpendicular magnetic recording media were studied using SANS and VSM measurements. The neutron scattering studies revealed that the recording grain was composed of a hard ferromagnetic centre enriched with cobalt. The VSM studies showed that the magnetic recording grains exhibited a large perpendicular magnetic anisotropy. These combined studies provided information on the recording grain's ferromagnetic composition and magnetic stability. The polarised SANS measurements showed the physical grain size to be slightly smaller than its magnetic counterpart. This size difference was attributed to the non-magnetic grain boundary composed of SiO2. The boundary thickness determined the degree of inter-granular exchange coupling. Further polarised studies investigated the recording layers switching behaviour, which revealed more information on the grain's magnetic stability.

<p>Predmet ovog istraživanja je razvoj nove generacije<br />mineralnih dodataka, dobijenih termičkom i<br />mehanohemijskom aktivacijom kaolinske gline i ispitivanje<br />svojstava kompozita, u kojima je deo portland cementa<br />zamenjen dobijenim pucolanskim materijalima,<br />metakaolinom i amorfnim kaolinom, za različite režime<br />nege. Rezultati su pokazali da su termička i mehanohemijska<br />aktivacija kaolinske gline jednako pogodne metode za<br />dobijanje pucolanskih materijala. Pozitivni efekti na<br />čvrstoće pri pritisku postižu se primenom do 30 %<br />metakaolina u kompozitima pri normalnom režimu nege, a uz<br />dodatno mlevenje, sadržaj metakaolina se može povećati do<br />40 %, uz dodatak CH. Amorfni kaolin se može primeniti u<br />kompozitima, sa stepenom zamene portland cementa do 10 %,<br />pri normalnom i autoklaviranom režimu nege.</p> / <p>The subject of this research is development of a new generation<br />of mineral admixtures, obtained by thermal and<br />mechanochemical activation of kaolin clay, and testing of the<br />properties of the cement based composites, where a part of the<br />portland cement is replaced by pozzolanic materials, metakaolin<br />and amorphous kaolin, for different curing conditions. The<br />results showed that thermal and mechanochemical activation of<br />kaolin clay were equally suitable for obtaining pozzolanic<br />materials. Positive effects on the compressive strength could be<br />achieved by using up to 30 % of MK, and with additional grinding<br />after thermal activation, content of MK could be increased up to<br />40 %, with the addition of CH, under the normal curing<br />conditions. Amorphous kaolin could be used in composites with<br />a cement replacement level of 10 %, under the normal and<br />autoclave curing conditions.</p>

Ce travail de thèse met en évidence deux phénomènes microscopiques dissipatifs au voisinage de la ligne de contact dans les phénomènes de capillarité et d'adhésion. L'étude s'appuie sur des expériences dynamiques et des modélisations théoriques. La mesure expérimentale de quantités macroscopiques et la théorie hydrodynamique permettent d'extraire les informations dynamiques localisées au voisinage la ligne de contact. Les différents phénomènes dissipatifs localisés au voisinage de la ligne de contact ont pour origines les propriétés des substrats sur lesquels se déplace la ligne de contact. Pour une surface rigide hétérogène, nous avons développé un modèle rhéologique de la ligne de contact fondé sur l'hydrodynamique, permettant d'établir théoriquement l'évolution temporelle de la ligne de contact et de ses déformations. Une décomposition modale fondée sur la réduction de l'énergie par la théorie du chemin de réaction fournit une prédiction quantitative de la dynamique thermiquement activée de la ligne de contact, en accord avec l'expérience réalisée. Pour un substrat déformable, à partir de l'analyse de deux expériences différentes de mouillage dynamique et de l'estimation de la dissipation dans le substrat, fondée sur sa viscoélasticité, nous avons développé une compréhension générale du comportement dynamique d'une ligne de contact sur un substrat viscoélastique. Pour finir, ce modèle de dissipation viscoélastique est appliqué au cas de l'adhésion réversible, où expérimentalement nous mesurons la dynamique de pelage et de recollement sur un substrat viscoélastique. Cette extension à l'adhésion permet de relier les phénomènes interfaciaux en une compréhension générale / This thesis reveals two dissipative microscopic phenomena close to the contact line in the fields of capillarity and adhesion. The study is based on dynamic experiments and theoretical predictions. Experimental measurement of macroscopic quantities and the hydrodynamic theory give access to dynamic information located close to the contact line. The different dissipative phenomena, located close to the contact line, originate from the properties of the substrates on which the contact line moves. For a heterogeneous rigid surface, we have developed a rheological model of the contact line based on hydrodynamics, in order to theoretically establish the temporal evolution of the contact line and its deformations. A modal decomposition based on the reduction of the energy by the reaction path theory allows a quantitative prediction of the thermally activated dynamics of the contact line, in agreements with the experiment carried out. For a deformable substrate, based on the analysis of two different experiments of wetting dynamics and on the estimation of the dissipation in the substrate founded on its viscoelasticity, a general understanding of the dynamical behavior of contact lines on viscoelastic substrates is achieve. Finally, this viscoelastic model is applied to the case of weak adhesion, where experimentally we measured the peeling dynamics from a viscoelastic substrate. This extension to adhesion bridge the gap between different interfacial phenomena into a general understanding

Submitted by Bruna Rodrigues (bruna92rodrigues@yahoo.com.br) on 2016-09-15T19:43:41Z No. of bitstreams: 1 TeseMA.pdf: 4330905 bytes, checksum: 6cb5f6465c74b22135d461ab86d86511 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:55:34Z (GMT) No. of bitstreams: 1 TeseMA.pdf: 4330905 bytes, checksum: 6cb5f6465c74b22135d461ab86d86511 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:55:39Z (GMT) No. of bitstreams: 1 TeseMA.pdf: 4330905 bytes, checksum: 6cb5f6465c74b22135d461ab86d86511 (MD5) / Made available in DSpace on 2016-09-16T19:55:47Z (GMT). No. of bitstreams: 1 TeseMA.pdf: 4330905 bytes, checksum: 6cb5f6465c74b22135d461ab86d86511 (MD5) Previous issue date: 2015-08-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / This paper describes an integrated process for recovering aluminum, iron, titanium, sodium and silica from red mud through a hydrometallurgical treatment sequence. The disposal of red mud, which is the largest waste produced by the aluminum industry, causes considerable environmental problems, and impacts costs greatly. This work presents a proposal to deal with it. Firstly, red mud is subjected to calcination at the 500-600°C range (thermal activation) so as to modify the structure of the metals present in red mud and make the attack with sulfuric acid easier. Next, the red mud is mixed with sulfuric acid and calcinated at 250- 300 °C (acid calcination). After digestion, the metal sulfates in the cake are dissolved by leaching with water and separated from the silica by filtration . Two routes to recuperate the leached metals are presented here, and the second one is analyzed economically. In this second method, silica is separated by filtration and all other metals in the leached solution are precipitated through a hydrometallurgical process in the form of their oxides. The remaining products present high purity level, thus being more easily marketed. / Este documento descreve um processo integrado para a recuperação de alumínio, ferro, titânio,sódio e sílica numa sequência de tratamento hidrometalúrgico da lama vermelha. A eliminação de lama vermelha, que é a maior resíduos produzidos pela indústria de alumínio, provoca consideráveis problemas ambientais e impactos custa muito. Este trabalho apresenta uma proposta para lidar com eles. Em primeiro lugar, a lama vermelha é submetida a calcinação no intervalo de 500-600 ° C(ativação térmica), para modificar a estrutura de metais presentes na lama vermelha, o que facilita o ataque com ácido sulfúrico. Em seguida, a lama vermelha e misturada ,com ácido sulfúrico, e levada à calcinação com ácido sulfúrico, a 250- 300 ° C (calcinação ácida). Após a digestão, os sulfatos de metal no bolo são dissolvidos por lixiviação com água, e separados da silica por filtração. São apresentados dois métodos para recuperação dos metais que foram lixiviados,sendo que a segunda alternativa, apresentada é avaliada ecônomicamente. A sílica é separada por filtração , e todos metais da solução lixiviada , são separados por processos hidrometalurgicos, na forma dos seus respectivos óxidos, apresentam grande pureza ,sendo facilmente comercializáveis

Les matériaux composants les réacteurs nucléaires subissent des conditions d’irradiationsévères, donnant lieu à des modifications de leurs propriétés mécaniques. Le vieillissement de cesmatériaux soulève des questions aussi importantes que celles liées à la sécurité des centrales existantes etaux futurs réacteurs à fission et à fusion. Dans plusieurs situations les matériaux de structure cristallinecubique centrée CC sont utilisés ayant pour base le fer, le tungstène, le vanadium et le tantale. Lescollisions entre les particules irradiantes et les atomes constituants les matériaux engendrent des défautsponctuels dont la migration mène à la formation d’amas responsables du vieillissement. Dans cette thèsenous avons étudié les propriétés énergétiques des défauts ponctuels dans les métaux CC citésprécédemment à l’échelle atomique. La modélisation des défauts ponctuels à l’échelle atomique peut êtreréalisée avec différentes méthodes se différenciant uniquement par la qualité de la description del’interaction entre atomes. Les études utilisant des interactions atomiques exactes, type ab initio,nécessitent des calculs lourds rendant impossible l’étude directe des amas de grandes tailles. Avec lamodélisation des interactions atomiques via les potentiels semi-empiriques on réduit la fiabilité et lecaractère prédictif du calcul. Ceux-ci permettent toutefois de réaliser une étude des amas en fonction deleur taille. Dans cette thèse nous avons développé un modèle énergétique original pour les boucles dedislocation ainsi que pour les amas interstitiels tridimensionnels de type C15. Le modèle obtenu est sanslimite de taille et peut être paramétré entièrement par les calculs ab initio. Afin de tester sa robustessepour les grandes tailles d’amas nous avons également paramétré ce modèle par rapport à des calculs enpotentiels semi-empiriques et comparé les prédictions du modèle aux simulations atomiques. Grâce ànotre développement nous avons pu déterminer : (i) la stabilité relative des boucles de dislocationd’interstitiels d’après leur vecteur de Burgers. (ii) La stabilité des amas C15 par rapport aux amas de typeboucle. Nous avons montré que les amas de type C15 étaient plus stables lorsqu’ils impliquent moins de41 interstitiels dans le fer. (iii) Dans le Ta nous avons pu mettre en évidence la même stabilité jusqu’à 20interstitiels. Les expériences dans le fer irradié montrent qu’en fonction de la température d’irradiation, ilse forme des boucles de dislocation très mobiles de vecteur de Burgers ½<111> ou immobiles ayant unvecteur de Burgers <100>. Les mécanismes de formation sous irradiation en fonction de la température,des amas de type <100> étaient une question restée sans explication théorique depuis 50 ans. Dans cettethèse, grâce à la précision de notre modèle énergétique, nous avons pu tester plusieurs théories.Notamment nous avons montré que les amas C15 constituent un catalyseur dans la formation des boucles<100>. Les clusters C15 peuvent se former, par germination, directement dans le processus d’irradiation.Ces clusters sont immobiles et peuvent croitre. A partir d’une certaine taille les amas C15 se dissocienten boucles ½ <111> ou <100>. Nous avons étendu notre modèle au calcul d’énergie libre de formationdes défauts permettant ainsi des prédictions à température finie que nous avons comparées auxsimulations atomiques. Les lois établies dans cette thèse en utilisant notre modéle pour calculer l’énergielibre de formation en fonctions de la taille des amas, ont été ensuite utilisées dans une simulation dedynamique d’amas. Nous avons ainsi pu prédire avec un très bon accord expérience-théorie laconcentration des amas d’interstitiels en fonction de leurs tailles au cours du murissement d’Oswald postirradiationdans un échantillon de Fer sous atmosphère d’Hélium. Le succès d’une telle approche nouspermet d’espérer étendre ce type d’étude à des matériaux plus complexes. / The structural materials in nuclear reactors are subjected to severe irradiation conditions,leading to changes in their mechanical properties. The aging of these materials raises important issuessuch as those related to the safety of existing plants and future reactors. In many cases, materials withbody-centered cubic bcc crystal structure are used with iron, tungsten, vanadium and tantalum as basemetal. Collisions between irradiating particles and atoms constituting materials generate point defectswhose migration leads to the formation of clusters responsible for aging. In this thesis, we studied theenergetic properties of point defects in the bcc metals mentioned above at the atomic scale. Modelingpoint defects at the atomic scale can be achieved with different methods that differ only in the quality ofthe description of the interaction between atoms. Studies using accurate atomic interactions such ab initiocalculations are computationally costly making it impossible to directly study clusters of large sizes. Themodeling of atomic interactions using semi-empirical potentials reduces the reliability of predictivecalculations but allow calculations for large-sized clusters. In this thesis we have developed a uniqueenergy model for dislocation loops as well as for three-dimensional interstitial cluster of type C15. Theresulting model has no size limit and can be set entirely by ab initio calculations. To test its robustness forlarge sizes of clusters we also set this model with semi-empirical potentials calculations and comparedthe predictions of the model to atomic simulations. With our development we have determined: (i) Therelative stability of interstitial dislocation loops according to their Burgers vectors. (ii) The stability of theclusters C15 compared to the type of cluster loop. We showed that the C15 type clusters are more stablewhen they involve less than 41 interstitials in iron. (iii) In Ta we were able to show the same stability till20 interstitials. The experiments involving iron show that depending on the irradiation temperature,highly mobile dislocation loops of Burgers vector ½ <111> or loops with Burgers vector <100> areformed. Considering formation mechanisms under irradiation as a function of temperature, formation ofthe <100>-type clusters lacked an acceptable theoretical explanation for about 50 years. In this thesis, theaccuracy of our energy model enabled validation of several theories proposed in the last 50 years. Inparticular we have shown that the formation of loops <100> at high temperatures can be formed fromC15 clusters which may be created directly in the irradiation process. These clusters are immobile andcan grow. Beyond a certain size, the C15 clusters dissociate into loops ½ <111> or <100>. We haveextended our model to free energy calculation of defect formation allowing for finite temperaturepredictions which is further compared to atomic simulations. The laws established in this thesis using ourmodel to calculate the free energy of formation of the cluster size functions were then used in a clusterdynamics simulation. On comparison with experiments involving post-irradiation Oswald ripening in asample of iron exposed to an atmosphere of helium, our energy model showed significant improvementsover older energy laws, such as the capillary law widely-used in multiscale computation cluster dynamicsor Monte Carlo kinetics. We conclude that the new laws established from our calculations are essential topredict the concentration of dislocation loop under irradiation, depending on their sizes. The success ofsuch an approach encourages extension of a similar study in more complex materials.