Nous étudions ici l’heteroepitaxie du silicium-germanium (SiGe), un système qui est couramment considéré comme le stéréotype de l’´épitaxie des semi-conducteurs. Bien que ce système ait déjà attiré une attention considérable en raison de ses applications pour l’ingénierie des bandes dans l’industrie microélectronique, le défi majeur du développement de nouveaux dispositifs à base de SiGe reste la croissance épitaxiale contrôlable des nanostructures auto-assemblées. Il est bien connu que SiGe suit un mode de croissance de Stranski-Krastanov, qui passe par la croissance de couches bidimensionnelles suivie par la croissance d’ılots tridimensionnels. Sous cette dénomination générique ”Stranski-Krastanov”, plusieurs comportements différents peuvent être identifiés. Une compréhension globale de tous ces comportements est encore partiellement manquante en raison de la complexité et de l’interaction de la cinétique et des forces motrices dynamiques, empêchant le d´développement de nouveaux dispositifs. Dans ce travail, nous nous concentrons sur l’auto- assemblage des nanostructures SiGe à la suite de la quête de l’émission de lumière pour les dispositifs photoniques, optoélectroniques et nanoélectroniques à base de Si. Par Même si l’innovation dans les dispositifs à base de Si a été stimulée récemment par le d´développement de silicium complétement épuisé sur les transistors isolants, une véritable percée serait la démonstration de l´émission de lumière et / ou l’absorption par les éléments du groupe IV, car il permet une intégration pratique dans les semi-conducteurs actuels. Dans ce travail, nous montrons d’abord les différents régimes de croissance des films contraints, c’est-à-dire l’instabilité par rapport aux régimes de nucléation. Nous d´développons un modèle qui résout la course de ces deux voies de croissance et d´dévoile les mécanismes des différents modes d’évolution morphologique entrainés par l’élasticité. Dans la seconde partie, nous examinons en détail l’auto-organisation naturelle des îles cohérentes. L’effet élastique direct induit la répulsion entre les îles cohérentes. Cependant, l’énergie de surface dépendant de la déformation qui a été négligée précédemment dans l’analyse de l’interaction île-île est révélée pour provoquer une attraction entre les iles. Il peut compenser la répulsion élastique directe au cours de l´état initial de la nucléation et conduire au regroupement d’îlots cohérents. Dans une troisième partie, nous étudions l’influence des échelons du substrat vicinal sur la formation et l’auto-organisation des îles. Nous démontrons que l’anisotropie de relaxation de la contrainte produite par les bords des gradins est à l’origine de l’allongement de l’instabilité perpendiculaire aux marches. Un accord quantitatif entre l’allongement de l’instabilité et l’anisotropie de relaxation de la souche est trouvé, ce qui approfondit les compréhensions de la croissance hétéroépitaxiale sur le substrat vicinal. Dans la quatrième partie, nous développons un nouveau procédé basé sur la condensation Ge lors de l’oxydation thermique du SiGe dilué. On étudie la cinétique du procédé de condensation SiGe et on fabrique la couche épandeuse de SiGe totalement contrainte par ce procédé de condensation particulier. / We investigate here the heteroepitaxy of silicon-germanium (SiGe), a system which is commonly regarded as the stereotype of semiconductor epitaxy. While this system has already attracted a tremendous amount of attention due to its applications for band-gap engineering in microelectronic industry, the major challenge facing the development of new SiGe-based devices remains the con- trollable epitaxial growth of self-assembled nanostructures. It is well-known that SiGe follows a Stranski-Krastanov growth mode, which proceeds via the growth of bi-dimensionnal layers followed by the growth of three-dimensional islands. Under this generic “Stranski-Krastanov” designation, several different behaviors can be identified. An overall understanding of all these behavior is still partially missing due to the complexity and the interplay of kinetics and energetic driving forces, preventing the development of new devices.In this work we focus on the self-assembly of SiGe nanostructures following the quest of light emission for integrated Si-based photonic, optoelectronic and nanoelectronic devices.Even if the innovation in Si-based devices has been boosted recently by the development of ultra-thin body fully depleted silicon on insulator transistors, a real breakthrough would be the demonstration of light emission and/or absorption by group IV elements since it allows the conve- nient integration into the nowadays semiconductors.In this work we first demonstrate the different growth regimes of strained films, i.e. instability versus nucleation regimes. We develop a model which resolves the race of these two growth pathways and unveil the mechanisms of different modes of morphological evolution driven by elasticity.In the second part, we examine in details the natural self-organisation of coherent islands. The direct elastic effect induces repulsion between coherent islands. However, the strain-dependent surface energy which has been overlooked previously in analysis of the island-island interaction is revealed to cause an attraction between islands. It may compensate the direct elastic repulsion during the initial state of nucleation and lead to the clustering of coherent islands.In a third part we study the influence of miscut steps of vicinal substrate on the formation and self-organisation of islands. We demonstrate that the strain relaxation anisotropy produced by the step edges, is at the origin of the instability elongation perpendicular to steps. Quantitative agreement between the instability elongation and the anisotropy of strain relaxation is found, which deepens the understandings of hetero-epitaxial growth on vicinal substrate.In the fourth part we develop a new process based on Ge condensation during thermal oxidation of dilute SiGe. The kinetics of SiGe condensation process is investigated and the fully strained SiGe epilayer is fabricated via this particular condensation process. This process can be applied in fabrication of SiGe core-shell nanostructures, for which the direct deposition and growth process is found to be cumbersome in terms of the control of morphology and composition.As a whole, we studied the nanostructures of SiGe driven by its hetero-epitaxial elasticity. We proposed a model to compare two pathways of morphological evolution of SK growth and unearthed the mechanisms of the race and transition. We studied kinetics of island nucleation under the impact of elastic filed produced by an existing island. The peculiar role of strain-dependent surface energy is highlighted. Then the elasticity anisotropy induced by miscut steps on vicinal substrate is studied theoretically and experimentally. This anisotropy effectively induces the elongation of islands in one direction to form nanowires in good alignment. Then the kinetics of condensation of SiGe is studied, which is found to be an effective method in fabricating strained SiGe nanostructures.

Ligas de alumínio que contém lítio são conhecidas por serem materiais atraentes devido à sua baixa densidade, alta elasticidade, alta resistencia mecânica e boa resistência à corrosão. A degradação do material devido à fadiga e corrosão são os dois principais fatores que contribuem para o envelhecimento de uma aeronave, e a previsão de corrosão e fadiga sob corrosão são muito importantes para sua integridade estrutural. A ocorrencia de pites de corrosão pode reduzir significativamente a iniciação da trinca de fadiga e diminuir a variação da intensidade de tensão limite destas ligas em até 50%. Com o objetivo de analisar novas ligas Al que estão no mercado, este trabalho compara o comportamento mecânico, de fadiga de baixo ciclo e eletroquímico das ligas de aluminio 2525 T3 e 7050 T7451 utilizadas pela EMBRAER, com o das ligas T851 2198 e 7081 T73511. Assim, ensaios de nucleação de trinca por fadiga foram realizados ao ar e em espécimes pré-condicionadas por 15 dias em névoa salina 5%, para a obtenção de curvas S-N. Curvas de polarização potenciodinâmicas foram obtidas para a investigação eletroquímica do comportamento destas ligas em um ambiente corrosivo. Também foram feitos ensaios de resistência à tração e dureza. Os resultados obtidos da série 2XXX mostram que as ligas são menos susceptíveis à corrosão por pites por apresentarem valores de Epite mais positivos que as ligas da série 7XXX. Porém, seus valores de jcorr também são mais positivos, o que aumenta a velocidade de corrosão das ligas, uma vez iniciado o processo. Tal fato se deve à presença de precipitados e elementos de liga que agem de modo a elevar o potencial para valores mais altos. Análises metalográficas por microscopia ótica e de varredura foram realizadas para se determinar os precipitados presentes em cada uma das ligas estudadas. O comportamento em fadiga das ligas pré-condicionadas em ambiente salino foi inferior em relação ao comportamento das ligas mantidas ao ar. Os pites funcionaram como concentradores de tensão, aumentando a ocorrência de nucleação de trincas de fadiga. A resistência à fadiga ao ar das ligas estudadas foi ligeiramente inferior ao das ligas bases. Entretanto, as quatro curvas obtidas para os espécimes pré-condicionados apresentaram-se superpostas. Isso indica que a ação dos pites rege o mecanismo de nucleação das trincas, enquanto que em ar, adiciona-se a ação do acabamento superficial. / Lithium-containing aluminum alloys are known to be attractive materials because of their low densities, high elastic modulus, high strengths and good corrosion resistance. Material degradation due to fatigue and corrosion are two major factors that contribute to the aging of an aircraft, and the prediction of corrosion and corrosionfatigue are very important for the structural integrity of aircrafts. The presence of corrosion pits can significantly shorten the fatigue crack initiation life and decrease the threshold stress intensity of an alloy by as much as 50%. The purpose of this work was to compare mechanical, fatigue and electrochemical behavior of the new \'AL\' alloys, 2198 T851 and 7081 T73511 that are on the market, with those used by EMBRAER, named 2525 T3 and 7050 T7451. The comparisons also considered fatigue resistance in pre-corrosion confining in salt environment. Therefore, air and 15-day-confined 5% salt environment specimens were submitted to crack nucleation tests to obtain S-N curves. Potentiodynamic polarization curves were also plotted to study the electrochemical behavior of this alloys in a corrosion environment. Tensile and hardness tests were performed. The obtained results for the 2XXX series showed that these alloys are less susceptible to pitting corrosion due to more positives Epite compared to 7XXX series. However, their jcorr values are also more positive, increasing the corrosion speed once it has begun. This happens due to the presence of some precipitates and a few elements that react in a way to increase the potential to higher values. Optical and electronic microscopy analyses were performed to determine the nature of precipitates of each alloy. The fatigue behavior of the salty-pre-confined environment specimens was much inferior compared to air test specimens according to each corrosion environment. Pits work as tension concentration, increasing fatigue crack nucleation. Air fatigue resistance of the new alloys was slightly inferior than the base alloys, but when the tests under pre-confined environment were conducted, the four curves overlapped. This implies that the pit action governs crack nucleation mechanism, while in air, surface finishing is an additional factor.

Este projeto faz parte de uma Rede Interdisciplinar de Pesquisa em Superligas no Brasil (Projeto Pró-Engenharias - CAPES), que tem como objetivo o desenvolvimento técnico e científico do Brasil nesta classe de materiais. A rede é composta por especialistas de estabelecida competência em assuntos fundamentais para o desenvolvimento de materiais estruturais, tais como: fusão em vácuo, solidificação direcional, relações orientação-propriedade, tratamentos térmicos, fluência, fadiga em alta temperatura, oxidação e corrosão a quente. Assim, na parte que compete a este pesquisador, foram estudadas as propriedades de fadiga em altas temperaturas da liga MAR-M247 e de uma nova liga, a liga MAR-M247 modificada pela substituição do Ta pelo Nb, e sendo doravante denominada MAR-M247(Nb). Foram desenvolvidos estudos correlacionando parâmetros intrínsecos do material, como composição química e microestrutura adicionalmente a parâmetros extrínsecos, tais como: temperatura, estudo de oxidação, propriedades de fadiga, ensaios de tração em temperatura ambiente, 250, 500, 700, 800, 900 e 1000ºC, conforme as normas AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) E 8M-00 e ASTM E 21-00. Em relação aos ensaios de fadiga foram realizados ensaios de nucleação de trincas , conforme a norma ASTM E466-07 e os resultados foram apresentados na forma de curvas S-N e analisados estatisticamente segunda a norma ASTM E739-10. Para auxiliar na definição dos micromecanismos de fadiga, as superfícies de fratura foram analisadas utilizando o microscópio eletrônico de varredura (MEV) e microscópio ótico estereoscópico (MO). Foi realizado ensaio de oxidação para verificar a susceptibilidade a oxidação das ligas, sendo este um dos fatores que afetam a vida em fadiga em alta temperatura. / This project is part of an interdisciplinary network of Research in Super League in Brazil (Project Pro-Engineering - CAPES), which aims to technical and scientific development of Brazil in this class of materials. The network is composed of experts of established competence in matters fundamental to the development of structural materials, such as: vacuum melting, directional solidification, relationships property-oriented, heat treatment, creep, fatigue in high temperature oxidation and hot corrosion. Thus, at the racing this researcher, were studied the fatigue properties at high temperatures MAR-M247 alloy and a new league, which in reality is the MAR-M247 alloy modified by replacing the Ta by Nb, and being hereinafter referred to as MAR-M247 (Nb). Were designed studies correlating parameters intrinsic material, such as chemical composition and microstructure, with extrinsic parameters such as: temperature and type of loading, with the properties fatigue. Thus, tensile tests at room temperature environment, 250, 500, 700 and 900ºC, and tests for compression at temperatures of 700 and 900ºC were performed to determine the elastic behavior and elastoplastic material, according to the ASTM E-8M 00, ASTM E 21-00 and ASTM E209-00. Were also conducted testing of fatigue crack nucleation, as ASTM E466-07. The results were presented at form of SN curves and statistically analyzed the second ASTM E739-10. To assist in the definition of micromechanics of fatigue, the fracture surfaces were examined in a scanning electron microscope (SEM) and stereoscopic optical microscope (OM). Was oxidation test performed to check susceptibility to oxidation of the alloy, which is the factor affecting the fatigue life.

Pseudomonas syringae produz núcleos de gelo biológicos de grande eficiência. Bioaerossóis destas células tem potencial de participar na glaciação de nuvens, podendo influenciar a precipitação. Foram estudadas como as condições as quais P. syringae está sujeita em suspensão na atmosfera afetam sua sobrevivência e sua atividade de nucleação de gelo. Duas cepas foram testadas, e ambas apresentaram baixa tolerância ao UV-C e ao UV-B, mas exibiram uma maior resistência quando expostas a um espectro semelhante ao encontrado no ambiente. A atividade de congelamento de uma das cepas (pv. syringae) não foi afetada pelo UV, enquanto que para a outra (pv. garcae) houve uma redução moderada. Em resposta à dessecação, pv. garcae foi substancialmente mais resistente que pv. syringae. Isto também afetou a nucleação de gelo das cepas. Em ensaios adicionais, estas bactérias foram expostas em um voo de balão estratosférico, e a uma simulação em laboratório das condições no topo da troposfera. Nestes dois experimentos, sobreviventes protegidos do UV foram recuperados. / Pseudomonas syringae produces biological ice nuclei of great efficiency. Bioaerosols of these cells have the potential to take part in cloud glaciation, possibly influencing the precipitation. It was studied how the conditions to which P. syringae is subjected while in suspension in the atmosphere affect its survival and its ice nucleation activity. Two strains were tested, and both showed a low tolerance to UV-C and UV-B, but exhibited a higher resistance when exposed to a spectrum similar to the one found in the environment. The freezing activity of one of the strains (pv. syringae) was not affected by the UV, while that for the other (pv. garcae) there was a moderate reduction. In response to desiccation, pv. garcae was substantially more resistant than pv. syringae. This also affected the ice nucleation by the strains. In additional assays, these bacteria were exposed in a stratospheric balloon flight, and to a laboratory simulation of the conditions at the top of the troposphere. After these two experiments, survivors protected from the UV were recovered.

Um modelo matemático multifásico para a solidificação equiaxial de ligas binárias capaz de prever o efeito de taxa de resfriamento e da concentração de soluto no tamanho médio final de grãos foi proposto no presente trabalho. O modelo matemático foi desenvolvido através do conceito de envelope envolvendo os grãos, utilizando as equações de conservação de energia, massa e espécies químicas. O modelo de nucleação utilizado possibilita que novos núcleos possam surgir durante todo o período de resfriamento. As equações diferenciais foram obtidas através de uma média volumétrica das equações de conservação em um volume elementar representativo contendo três \"pseudofases\": sólido, líquido interdendrítico e líquido extradendrítico. O efeito de algumas variáveis de processamento sobre o tamanho médio final de grão foi analisado. Os resultados do modelo proposto foram comparados com resultados de alguns modelos disponíveis na literatura. / A multiphase mathematical model for the equiaxed solidification of binary alloys was proposed in the present work to predict the effects of the cooling rate and the average solute concentration on the final average grain size. The mathematical model was based on the concept of the grain envelope and on the conservation of energy, mass and chemical species. A nucleation model was adopted to consider the nucleation of new grains during the whole solidification time. The differential equations were derived from the volume average of conservation equations within a representative elementary volume that consisted of three pseudophases: solid, interdendritic liquid, and extradendritic liquid. The effect of some processing variables on the final average grain size was studied. The results from the proposed model were compared with those available in the literature from other models.

Cientes de que o histórico, a intensidade e a expansão espacial das atividades antrópicas afetam a resiliência e as taxas de recuperação de um ecossistema florestal, existe atualmente o desafio de determinar qual ou quais métodos de restauração ecológica serão os mais eficientes em termos de recursos em metas para cada local. Isso porque existem diversos tipos de métodos e estratégias de restauração ecológica, os quais variam desde apenas assistir um ecossistema se reestabelecer à alta intervenção as quais mudarão os rumos da sucessão ecológica. Neste contexto, o presente trabalho busca analisar se a nucleação aplicada, um método de restauração florestal de baixo custo e intervenção na área, restaurou e ocupou um antigo pasto abandonado numa área de preservação permanente dentro do campus da Escola Superior de Agricultura \"Luiz de Queiroz\". Para isso, foi implantado um experimento de nucleação aplicada, vizinho a um fragmento de floresta estacional semidecidual em maio de 2008 onde foram plantados 40 núcleos. Foram testadas 4 espécies (Inga laurina, Cordia trichotoma, Albizia niopoides e Jacaratia spinosa) com dez repetições cada e com apenas uma espécie por núcleo. Os núcleos foram então mensurados anualmente até 2013 e posteriormente no ano de 2016. Mensuramos o diâmetro na altura do peito (DAP), altura, área basal, biomassa, índice de área de vegetação (via fotografias hemisféricas) e área de copa (calculado como uma elipse). Depois, em 2017 alocamos 24 parcelas de 2 metros de raio no entorno dos núcleos para avaliar a densidade, riqueza e diversidade dos indivíduos regenerantes. Na análise dos dados comparamos os diferentes tratamentos através de análises de variância e dos testes de comparações de média de tukey para o último período de medição nos diferentes parâmetros dendrométricos. Procurando entender se alguma espécie plantada em núcleos monoespecíficos conseguiu atrair maior quantidade de regenerantes, espécies e diversidade comparamos entre os diferentes tratamentos esses parâmetros. Posteriormente, realizamos um modelo linear generalizado a fim de encontrar possíveis relações entre densidade e a riqueza dos indivíduos regenerantes com as variáveis dos núcleos, como altura máxima, área basal, índices de área de vegetação e área de copa. Os resultados encontrados nos dizem que existem diferenças no desenvolvimento dos diversos parâmetros analisados incluindo a ocupação da área pelas diferentes espécies plantadas na nucleação aplicada. Encontramos também para o presente projeto que a densidade de regenerantes no entorno dos núcleos é significantemente relacionada com a área basal e altura das árvores dos núcleos e a riqueza de espécies dos indivíduos em regeneração é significantemente relacionada com apenas a área área basal das árvores presentes nos núcleos. Sugerimos o uso de nucleação aplicada para restaurar áreas com grau médio de degradação usando uma espécie pioneira com altas taxas de crescimento. Os núcleos monoespecíficos devem ser utilizados apenas em paisagens com abundância de propágulos para que não haja baixa diversidade de espécies a médio prazo. / Despite the history that intensity and spatial expansion of anthropogenic activities affect the resilience and recovery rates of a forest ecosystem, we have the current challenge in forest restoration to determine which ecological restoration methods will be most efficient for each specific area, this in terms of resources and goals. In this context, the ecological restoration of degraded ecosystems must be specific to each site. The present work aimed to analyze applied nucleation, a method of low cost and low intervention in the area of forest restoration, occupied an abandoned pasture in a permanent preservation area inside the campus \"Luiz de Queiroz\" College of Agriculture in Piracicaba, São Paulo. For this, an applied nucleation experiment was implanted next to a semideciduous seasonal forest fragment in May 2008, where 40 nuclei were planted. Four species (Inga laurina, Cordia trichotoma, Albizia niopoides and Jacaratia spinosa) were tested with ten replicates each, with only one specie per nuclei. The nuclei were then measured annually until 2013 and later in 2016. In the individual\'s data, we measured the diameter at the chest height (DBH), height, basal area, biomass, vegetation area index (via hemispheric photographs) and Crown area (calculated as an ellipse). After that, in 2017, 24 subplots were allocated around the nuclei to evaluate the density, specie richness and diversity of regenerating individuals. In order to compare the different treatments used, we performed analysis of variance and the Tukey mean comparison test for the different dendrometrical parameters between species. Later, in order to understand the facilitation of density and specie richness by the different treatments of nuclei, we related the height, basal area, vegetation area index and area with these parameters through a generalized linear model. The results show that there are differences in the development of the various parameters analyzed including the occupation of the area by the different species planted in the applied nucleation. We also found for the present project that the density of regenerants found near the nuclei are significantly related to the sum of basal area and height of the nuclei and the species richness of regenerants are significantly related to the sum of the basal area of the individuals\' nuclei. We suggest the use of applied nucleation to restore areas with a medium degree of degradation using a pioneer species with high grown rates. The mono specific nuclei should be use just only in landscapes with plenty of propagules. So that there is no low diversity of species in the medium term.

Um modelo matemático multifásico para a solidificação equiaxial de ligas binárias capaz de prever o efeito de taxa de resfriamento e da concentração de soluto no tamanho médio final de grãos foi proposto no presente trabalho. O modelo matemático foi desenvolvido através do conceito de envelope envolvendo os grãos, utilizando as equações de conservação de energia, massa e espécies químicas. O modelo de nucleação utilizado possibilita que novos núcleos possam surgir durante todo o período de resfriamento. As equações diferenciais foram obtidas através de uma média volumétrica das equações de conservação em um volume elementar representativo contendo três \"pseudofases\": sólido, líquido interdendrítico e líquido extradendrítico. O efeito de algumas variáveis de processamento sobre o tamanho médio final de grão foi analisado. Os resultados do modelo proposto foram comparados com resultados de alguns modelos disponíveis na literatura. / A multiphase mathematical model for the equiaxed solidification of binary alloys was proposed in the present work to predict the effects of the cooling rate and the average solute concentration on the final average grain size. The mathematical model was based on the concept of the grain envelope and on the conservation of energy, mass and chemical species. A nucleation model was adopted to consider the nucleation of new grains during the whole solidification time. The differential equations were derived from the volume average of conservation equations within a representative elementary volume that consisted of three pseudophases: solid, interdendritic liquid, and extradendritic liquid. The effect of some processing variables on the final average grain size was studied. The results from the proposed model were compared with those available in the literature from other models.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVIALABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 118-119. / by Jane Ellen Martini. / M.S.

P-aminobenzoic acid (PABA) is a polymorphic compound with two known polymorphs - alpha with a needle morphology and β with a rhombic morphology. It is an enantiotropic compound with a transition temperature at 13.8oC, where alpha is more thermodynamically stable above transition temperature and β is more thermodynamically stable below. At the beginning of this project, crash-cooling crystallisation experiments were conducted to determine the effect of solvent, temperature and supersaturation on the nucleating polymorphs of PABA. Three solvents were tested (water, ethanol and isopropyl alcohol) over a range of supersaturations and temperatures. The results suggested that polymorph appearance of PABA was heavily influenced by kinetics, as opposed to thermodynamics of the system, disagreeing with Ostwald's rule of stages. The project then focussed on the ability of tailor-made additives to select the crystallising polymorph of PABA from supersaturated solutions of PABA in isopropyl alcohol. Crash-cooling crystallisation experiments were performed using two additives: 4-amino-3-nitrobenzoic acid, and 4-amino-3-methoxybenzoic acid. Results showed that alpha PABA crystallised below a critical concentration of either additive, and above that critical concentration, β PABA would crystallise. To determine whether the additives were affecting the nucleation and/or growth kinetics of alpha PABA and β PABA, a series of nucleation and growth experiments were conducted using a Crystal16 multiple stirred reactor and a crystal growth cell respectively. The results showed that both additives greatly reduced the attachment frequency of growth units to alpha PABA nuclei, and inhibited the growth rate of alpha PABA seed crystals. Nucleation data could not be obtained for β PABA, but in terms of crystal growth, both additives did not affect growth rate of β PABA to a noticeable degree. Gravimetric and HPLC experiments were also employed to measure the solubility effects of both additives on PABA in isopropyl alcohol. Results showed that both additives did not appear to affect PABA's solubility to a noticeable degree.

Afin de parvenir à une meilleure compréhension de la dynamique d’ascension et d’éruption des magmas basaltiques, nous avons réalisé des expériences de décompression à haute pression (200–25 MPa) et haute température (1200°C) spécifiquement orientées pour documenter la nucléation des bulles de gaz ; ce processus, qui constitue la première étape du dégazage magmatique, conditionne l’évolution de la phase gazeuse (force motrice des éruptions explosives) dans le conduit volcanique. Quatre principaux ensembles d’expériences ont été menés afin de mieux comprendre le rôle des volatils majeurs (H2O, CO2, S), ainsi que les effets de la vitesse d’ascension et de la présence de cristaux sur la cinétique de vésiculation (nucléation, croissance, coalescence) des bulles dans les magmas basaltiques. L’objectif est de comprendre les mécanismes qui contrôlent les caractéristiques texturales (nombre, taille, forme des bulles) et chimiques (teneur en volatils dissous, composition des gaz) des produits naturels et de les approcher expérimentalement. Dans ce sens, les verres expérimentaux ont été analysés avant et après décompression sur le plan textural (microtomographie par rayons X, MEB) et chimique (FTIR, microsonde électronique). Nos résultats démontrent une forte influence du CO2 sur les processus ainsi que sur le mode (équilibre vs. déséquilibre) de dégazage des magmas basaltiques, en lien avec des différences de solubilité et de diffusivité entre les espèces volatiles. Nos données, obtenues dans des conditions voisines des conditions naturelles, ont des implications volcanologiques pour l’interprétation des textures de bulles et des mesures de gaz en sortie de conduit, ainsi que, plus spécifiquement, pour la dynamique des éruptions paroxysmales au Stromboli. / For a better understanding of the dynamics of ascent and eruption of basaltic magmas, we have performed high pressure (200–25 MPa) and high temperature (1200°C) decompression experiments specifically oriented to document gas bubble nucleation processes. Bubble nucleation occurs first during magma degassing and, so, it is critical to understand bubble nucleation processes to constrain the evolution of the gas phase (which is the driving force of explosive eruptions) in the volcanic conduit. Four main sets of experiments were conducted to better assess the role of the major volatiles (H2O, CO2, S), as well as the effects of ascent rate and crystals, on bubble vesiculation (nucleation, growth, coalescence) kinetics in basaltic magmas. The aim of the study is to understand the mechanisms which control the textural (number, size, shape of bubbles) and the chemical (dissolved volatile concentrations, gas composition) characteristics of natural products, and also to approach them experimentally. In this way, experimental melts, before and after decompression, were analysed texturally (by X-ray microtomography and MEB) and chemically (by FTIR and electron microprobe). Our results demonstrate a strong influence of CO2 on degassing mode (equilibrium vs. disequilibrium) and mechanisms, which are shown to be controlled by differences in solubility and diffusivity between the main volatile species. Finally, our data, obtained under conditions closely approaching natural eruptions, have volcanological implications for the interpretation of bubble textures and gas measurements, as well as, more specifically, for the dynamics of Strombolian paroxysms.