Nonlinear ultrasonic waves have demonstrated high sensitivities to various microstructural changes in metal including coherent precipitates; these precipitates introduce a strain field in the lattice structure. The thermal aging of certain alloy steels leads to the formation of coherent precipitates, which pin dislocations and contribute to the generation of a higher harmonics in an initially monochromatic wave. The objective of this research is to develop a robust technique to perform nonlinear Rayleigh wave measurements in metals using a non-contact receiving transducer. In addition a discussion about the data processing based on the two-dimensional diffraction and attenuation model is provided in order to calculate the relative nonlinearity parameter. A precipitate hardenable material, 17-4 PH stainless steel, is used to obtain different precipitation stages by thermal treatment and the influence of precipitates on the ultrasonic nonlinearity is assessed. Conclusions about the microstrucutural changes in the material are drawn based on the nonlinear Rayleigh surface wave measurement and complementary measurements of thermo-electric power, mircohardness and ultrasonic velocity. The results show that the nonlinearity parameter is sensitive to coherent precipitates in the material and moreover that precipitation characteristics can be characterized based on the obtained experimental data.

Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.

Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.

Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with similar matrix but varying contents of niobium, vanadium and nitrogen were prepared. Sample preparation process included melting, hot forging, solution annealing and finally aging for 500 h at 700, 800 and 850 ºC. Light optical and scanning electron microscopy revealed micron-scale precipitates on grain and twin boundaries as well as sub-micron intragranular precipitates in all samples. Characterization of precipitates was carried out by means of energy dispersive X-ray spectroscopy (EDS). Among micron-scale precipitates M23C6 carbide was the dominant phase at 700 ºC aging temperature; whereas silicon-rich eta phase (M5SiC) was the main precipitate in samples aged at 800 and 850 ºC. A few sigma phase particles were found in one of the niobium containing samples aged at 700 and 800 ºC. Sub-micron intragranular precipitates were analyzed using low voltage EDS. The spatial resolution of EDS microanalysis at 5 kV accelerating voltage was estimated as almost 100 nm which was at least eight times better than that using the ordinary 20 kV voltage. Also, low voltage EDS revealed the presence of light elements (carbon, nitrogen and boron) in the composition of sub-micron particles thanks to the less matrix effect in absorption of low energy X-rays of light elements. In samples aged at 700 ºC niobium-rich and vanadium-rich carbonitrides were found as the dominant precipitates; whereas they contained much less carbon in samples aged at 800 ºC and mostly became carbon-free nitrides with well-defined cuboidal shapes at 850 ºC aging temperature. This showed that niobium/vanadium-rich nitride phases are stable precipitates at aging temperatures above 700 ºC. The drawbacks of low voltage EDS were indicated as high detection limit (no detection of low- content elements), poor accuracy of quantitative analysis and high sensitivity to surface contamination. Some possible ways to improve the accuracy of low voltage EDS, e.g. longer acquisition time were examined and some other suggestions are proposed for future works.

Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with similar matrix but varying contents of niobium, vanadium and nitrogen were prepared. Sample preparation process included melting, hot forging, solution annealing and finally aging for 500 h at 700, 800 and 850 ºC.Light optical and scanning electron microscopy revealed micron-scale precipitates on grain and twin boundaries as well as sub-micron intragranular precipitates in all samples. Characterization of precipitates was carried out by means of energy dispersive X-ray spectroscopy (EDS). Among micron-scale precipitates M23C6 carbide was the dominant phase at 700 ºC aging temperature; whereas silicon-rich eta phase (M5SiC) was the main precipitate in samples aged at 800 and 850 ºC. A few sigma phase particles were found in one of the niobium containing samples aged at 700 and 800 ºC. Sub-micron intragranular precipitates were analyzed using low voltage EDS. The spatial resolution of EDS microanalysis at 5 kV accelerating voltage was estimated as almost 100 nm which was at least eight times better than that using the ordinary 20 kV voltage. Also, low voltage EDS revealed the presence of light elements (carbon, nitrogen and boron) in the composition of sub-micron particles thanks to the less matrix effect in absorption of low energy X-rays of light elements. In samples aged at 700 ºC niobium-rich and vanadium-rich carbonitrides were found as the dominant precipitates; whereas they contained much less carbon in samples aged at 800 ºC and mostly became carbon-free nitrides with well-defined cuboidal shapes at 850 ºC aging temperature. This showed that niobium/vanadium-rich nitride phases are stable precipitates at aging temperatures above 700 ºC.The drawbacks of low voltage EDS were indicated as high detection limit (no detection of low- content elements), poor accuracy of quantitative analysis and high sensitivity to surface contamination. Some possible ways to improve the accuracy of low voltage EDS, e.g. longer acquisition time were examined and some other suggestions are proposed for future works.

Studies of seafloor hydrothermal activity and its associated geochemical and mineralogical effects have primarily focused on deep sea systems. These processes are not limited to deep sea locations. Numerous shallow hydrothermal systems have been identified along the submerged flanks of volcanic islands such as Vulcano Island, Italy and Ambitle Island, Papua New Guinea. This study investigates the Champagne Hot Springs shallow marine hydrothermal system, located along the submerged flank of the Plat Pays volcanic system on the southwest section of the island of Dominica, Lesser Antilles. The main objective is determine the source of the hydrothermal fluids and gases and their related effect on sediment and precipitate chemistry. A detailed map of the vent field will also be generated to accurately present vent locations and distribution. Geochemical and mineralogical analyses of vent waters, pore waters, gases, sediments and precipitates were determined by High Pressure Liquid Chromatography (HPLC), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Neutron Activation Analysis (NAA), Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Analysis (EDX), Powder X-Ray Diffraction (XRD), Gas Chromatography and Mass Spectrometry. These analyses have revealed the following: (1) The vent waters and pore waters are mixtures of seawater and meteoric derived hydrothermal fluids in varying proportions. The relative input of each component is both temperature and flow rate dependent. (2) The simultaneous increase in pH and Eh caused by mixing between Fe2+ rich vent fluids and seawater forms precipitates and sediment coatings of hydrous ferric oxides. The elevated concentrations of As and Sb in the precipitates and sediments relative to average Caribbean seafloor sediments is a function of adsorption to the surface of the hydrous ferric oxide, (3) Pore waters in the immediate vicinity of sediment covered vents carry Fe2+ rich fluid to the sediment/seawater interface, where rapid oxidation of soluble Fe2+ to insoluble Fe3+ leads to precipitation of hydrous ferric oxide coatings on sediment grains and subsequent formation of hydrothermally altered sand patches, (4) The gas samples are typical arc-type gases and have both meteoric and magmatic signatures.

Leachate collection systems consist of a series of pipes installed beneath the waste at the base of a landfill. The liquid drains toward a central location where it is pumped and then treated, discharged, or recirculated. In some landfills, solid precipitates form in the collection system resulting in clogging and malfunctions of the drainage system. The formation of the precipitates is linked to the chemical and biological stability of the leachate generated within the landfill. To control the formation of precipitates and prevent clogging of leachate collection systems, it is important to understand factors that influence leachate characteristics. Ashes from municipal solid waste (MSW) combustion are either placed in monofills or combined with traditional solid waste, and sludges and biosolids from wastewater and drinking water treatment plants when landfilled. The ashes, depending on the type of combustion process, contain high concentrations of metals and non-biodegradable materials. As the waste degrades, oxygen in the landfill is consumed and the leachate becomes anaerobic. The reducing environment allows for greater solubility of metals. This research tested ashes from three different Waste-to-Energy (WTE) facilities to understand better the role MSW fly ash and MSW bottom ash in the chemical make-up of landfill leachate. Two different types of batch tests were used to analyze the leaching behavior. First, a contact time batch test with a range of different contact times was used to assess the rate at which different elements reach equilibrium. This was followed by a sequential extraction batch test that predicted the total amount of soluble material in the ashes. The chemical characteristics of the leachate produced by the ashes were understood and the leaching behaviors analyzed, dominant chemical factors that influence the formation of precipitates were identified. This data produced a better understanding of the roles of WTE ashes in the production of precipitates in leachate collection systems.

Oriented needle-shaped or rod-shaped quartz precipitates occur in clinopyroxenes have been commonly observed in eclogites or garnet peridotites from the high pressure or ultra-high pressure (HP/UHP) metamorphic belts, and their occurrence has been used as an indicator of UHP metamorphism. However, the origin of those quartz precipitates and their crystallographic orientation relationships with clinopyroxene hosts are still not clear. In order to understand the formation mechanisms and environments of the quartz precipitates, the present study has used electron backscattered diffraction (EBSD) analysis, petrographic and scanning electron microscopy, and electron microprobe analysis to study textural features, mineral assemblages, mineral compositions, and crystallographic orientation relationships of mineral precipitates in the omphacite from Xitieshan, North Qaidam UHP metamorphic belt. The results show that the oriented rod-like precipitates in the omphacite hosts are mainly composed of quartz + edenite, and the rods are 5~20

Cette thèse est axée sur la caractérisation microstructurale des précipités dans les oxydes des alliages binaires de zirconium (1 wt.% Fe, Cr , Ni ou 0.6 wt.% Nb). La température d'oxydation est fixée au 415°C. Les échantillons sont oxydés dans l'air et dans l'autoclave sous des pressions différentes et dans un microscope électronique à balayages environnemental sous vapeur d'eau. Les résultats des recherches peuvent être résumés ci-dessous : -Deux types d'oxydation (retardée et non retardée) ont été observés pour les précipités. -Le facteur de Pilling-Bedworth des précipités est plus élevé par rapport à celui de zirconium. -Les précipités contenant du fer entrainent une formation des cristaux de l'oxyde de fer pur à la surface du matériau, quand les précipités sont à la surface ou à la proximité. Ces observations mènent à la conclusion que le comportement d'oxydation des précipités peut être corrélé à leurs compositions et à la tendance d'oxydation de leurs éléments constituants. / This thesis is focused on the microstructural characterisation of precipitates in the oxide of binary zirconium alloys (1 wt.% Fe, Cr or Ni or 0.6 wt.% Nb) under different oxidation conditions at 415°C. The samples were oxidised in autoclave in air and steam and in an environmental scanning electron microscope in water vapour. The microstructural evolution of the precipitates during oxidation was characterised using electron microscopy. The findings from the analysis are the following: -Two types of oxidation behaviour are observed for precipitates. -Pilling-Bedworth ratio of precipitates is higher than that of the zirconium matrix. -Formation of pure iron oxide crystals on the surface for iron bearing precipitates close to or at the surface. From these observations it is concluded that the precipitate oxidation behaviour can be correlated to precipitate composition and oxidation tendency of the elements in the precipitates. Iron exhibits clearly different behaviour.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Os aÃos Fe-Cr-Mo sÃo amplamente usados em tubulaÃÃes e componentes que estÃo constantemente sujeitos a processos de degradaÃÃo nas indÃstrias petroquÃmicas. A exposiÃÃo desses aÃos em ambientes agressivos por um perÃodo prolongado quando submetidos a elevadas temperaturas tem como consequÃncias alteraÃÃes microestruturais, precipitaÃÃes na forma de carbonetos que atuam nos aÃos afetando sua resistÃncia a fluÃncia e a corrosÃo. Os aÃos Fe-Cr-Mo possuem propriedades ferromagnÃticas que podem ser exploradas com o objetivo de fornecer informaÃÃes sobre essas alteraÃÃes microestruturais. Nesse trabalho foram analisadas as propriedades magnÃticas das ligas Fe-9Cr-XMo (X = 1%, 5%, 7% e 9%) e a relaÃÃo dessas propriedades com a formaÃÃo de precipitados. Para isso as amostras foram submetidas a tratamentos tÃrmicos de solubilizaÃÃo (com exceÃÃo da liga contendo 1% de Mo) e envelhecimento. As anÃlises das propriedades magnÃticas foram feitas usando ciclos de histerese obtidos pela tÃcnica de magnetometria de amostra vibrante. Os parÃmetros magnÃticos analisados foram o campo coercivo, a magnetizaÃÃo residual e a magnetizaÃÃo de saturaÃÃo. A anÃlise dos precipitados foi feita usando micrografias obtidas por microscopia eletrÃnica de varredura e espectros de EDS, alÃm de histogramas obtidos com auxÃlio do software ImageJ que mostram a distribuiÃÃo e o tamanho mÃdio de precipitados. Os resultados obtidos permitem concluir que existe uma relaÃÃo entre a distribuiÃÃo e tamanho mÃdio dos precipitados com o campo coercivo. Em geral, o aumento na densidade de precipitados contribui de forma significativa para o aumento na dureza magnÃtica do material, esse mecanismo està relacionado a um processo de ancoragem das paredes de domÃnio magnÃtico. A magnetizaÃÃo de saturaÃÃo à afetada tanto pela formaÃÃo de precipitados quanto pelo teor de molibdÃnio na liga. / Cr-Mo steels are widely used in pipes and components constantly subjected to degradation processes in the petrochemical industries. The exposure of these steels in harsh environments for extended periods when subjected to elevated temperatures lead to microstructural changes, such as carbide precipitation which affect its creep and corrosion resistance. Fe-Cr-Mo steels have ferromagnetic properties that can be investigated in order to provide information on these microstructural changes. In this work we analyzed the magnetic properties of Fe-9Cr-Xmo (X = 1%, 5%, 7% and 9%) alloys and the relation between these properties and related to the formation of precipitates. For this, the samples were first subjected to solution heat treatments (except alloy containing 1% Mo) and then aged. The analysis of the magnetic properties was carried out by hysteresis loops obtained by vibrating sample magnetometry. The magnetic parameters analyzed were the coercive field, the residual magnetization and the saturation magnetization. The precipitates were analyzed by scanning electron microscopy and EDS spectra, and their distribution and average size were calculated through histograms obtained by the ImageJ software. The results indicate that the distribution and average size of the precipitates are related to the coercive field. In general, the increase in the density of precipitates contributes signicantly to the increase in the magnetic hardness of the material. This mechanism is related to a process of pinning the magnetic domain walls. The saturation magnetization is affected both by the formation of precipitates and by the molybdenum content in the alloy.