Introdução. Não há dados que atestem, no contexto brasileiro das primeiras décadas do século XXI, que a fluoretação das águas de abastecimento público agrega benefício preventivo com relação à cárie dentária, em pequenos municípios, aos proporcionados pelo uso generalizado dos dentifrícios fluoretados. Objetivo. Analisar o grau do benefício preventivo da exposição à água fluoretada em relação à cárie dentária e sua distribuição segundo grupamentos dentais, em contexto de uso generalizado de creme dental fluoretado, no Brasil. Metodologia. Foi realizado estudo observacional transversal, de tipo censitário, na modalidade de duplo inquérito epidemiológico populacional. As populações avaliadas residem em municípios da mesma região geográfica, de pequeno porte demográfico e com classificação socioeconômica similar, diferenciando-se apenas pela condição de exposição, há pelo menos 5 anos, à água fluoretada (Silveiras) ou de não exposição (São José do Barreiro). A experiência e a magnitude da cárie dentária nessas populações foram avaliadas utilizando-se os índices ceod (aos 5 e 6 anos de idade; N=233), CPOD (aos 11 e 12 anos; N=312) e SiC (aos 11 e 12 anos; N=105) e a associação foi testada empregando-se as estatísticas qui-quadrado de Pearson e razão de prevalência (RP) entre não expostos (NE) e expostos (E) à água fluoretada. A partir dos valores do ceod, CPOD e SiC, foram obtidas as razões de magnitude entre os grupamentos dentários posteriores e anteriores (RM-PA), em ambas as dentições, segundo exposição ou não à água fluoretada. Os grupamentos dentários foram assim definidos: anteriores-estéticos (incisivos centrais e laterais e caninos, superiores e inferiores, em ambas as dentições) e posteriores (primeiros e segundos pré-molares e primeiros e segundos molares, superiores e inferiores na dentição permanente e primeiros e segundos molares superiores e inferiores na dentição decídua). Resultados. Dentição decídua- Embora a experiência de cárie (ceod1) não tenha se associado com a exposição à água fluoretada (qui-quadrado=2,77; p=0,96; =5 por cento ),observou-se expressiva diferença na magnitude com que a doença atingiu a população: as médias ceod foram de 2,74 em expostos e 4,17 em não expostos. O grau da polarização, indicado pela porcentagem de indivíduos com ceod=0, foi diferente, sendo maior (43,0 por cento ) em expostos e menor (31,0 por cento ) em não expostos. A RP (NE/E) foi de 1,21 indicando que a exposição à água fluoretada correspondeu a uma taxa de prevalência 21 por cento menor, comparativamente aos não expostos. As razões de magnitude para dentição decídua (RM-PAd) foram de 4,2 em expostos e 4,8 em não expostos. Dentição permanente- Embora a experiência de cárie (CPOD1) não tenha se associado com a exposição à água fluoretada (qui-quadrado=1,78; p=0,18; =5 por cento ), observou-se expressiva diferença na magnitude com que a doença atingiu a população: as médias CPOD foram de 1,76 em expostos e 2,60 em não expostos. O grau da polarização, indicado pela porcentagem de indivíduos com CPOD=0, foi diferente, sendo maior (41,8 por cento ) em expostos e menor (34,3 por cento ) em não expostos. A RP (NE/E) foi de 1,13 indicando pouca expressividade na diferença das prevalências. Para a dentição permanente as razões de magnitude na população total (RM-PAp) foram de 22,1 em expostos e 6,1, em não expostos. O valor médio do SiC foi de 4,04 em expostos e 6,16 em não expostos, enquanto as razões de magnitude (RM-PA-SiC) foram 23,8 e 5,9, respectivamente. Conclusão. A exposição à água fluoretada implicou menores valores médios dos índices ceod, CPOD e SiC, ainda que em presença de exposição concomitante a dentifrício fluoretado, em cenário de baixa prevalência da doença e padrão similar de distribuição de cárie nas populações analisadas. As menores experiência e magnitude da cárie nos grupamentos dentários anteriores, em situação de exposição à água fluoretada em comparação com a não exposição, corrobora estudos anteriores. No contexto brasileiro, ainda que em presença de exposição simultânea a dentifrício fluoretado, a fluoretação das águas segue produzindo efeitos epidemiológicos relevantes / Introduction. In the Brazilian context of the first decades of the 21st century, there is no evidence that the fluoridation of public water supplies adds preventive benefit in relation to dental caries, in small municipalities, to those provided by the widespread use of fluoridated dentifrices. Objective. To analyze the degree of the preventive benefit of exposure to fluoridated water in relation to dental caries and its distribution according to dental groups, in a context of widespread use of fluoride toothpaste in Brazil. Methodology. A cross - sectional observational study, census type, was conducted in a double epidemiological population survey. The populations studied live in municipalities of the same geographic region, with a small demographic and similar socioeconomic classification, differing only by the condition of exposure to fluoridated water (Silveiras) or no exposure (São José do Barreiro), for at least 5 years. The experience and magnitude of dental caries in these populations were evaluated using the dmft indice (at 5 and 6 years of age, N=233), DMFT (at 11 and 12 years old, N=312) and SiC (at 11 and 12 years, N=105), and the association was tested using Pearson\'s chi-square statistic and prevalence ratio (PR) between no-exposed (NE) and exposed (E) to fluoridated water. From the values of dmft, DMFT and SiC, the magnitude ratios between the posterior and anterior dental groups (MR-PA) were obtained in both dentitions according to exposure to fluoridated water. Dental groups were defined: anterior-esthetic (central and lateral incisors and canines, upper and lower, in both dentitions) and posterior (first and second premolars and first and second molars, upper and lower, in the permanent dentition and first and second molars upper and lower in the deciduous dentition). Results. Deciduos Dentition- Although the caries experience (dmft1) wasnt associated with exposure to fluoridated water (chi-square=2.77, p=0.96, =5 per cent ), there was a significant difference in Magnitude with which the disease reached the population: the mean dmft were 2.74 in exposed and 4.17 in no exposed. The degree of polarization, indicated by the percentage of individuals with dmft=0, was different, being higher (43.0 per cent ) in exposed and lower (31.0 per cent ) in no exposed. PR (NE / E) was 1.21 indicating that exposure to fluoridated water corresponded to a 21 per cent lower prevalence rate compared to those not exposed. The magnitude ratios for deciduous dentition (MR-PAd) were 4.2 in exposed and 4.8 in no exposed. Permanent Dentition - Although the caries experience (DMFT1) was not associated with exposure to fluoridated water (chi-square=1.78, p=0.18, =5 per cent ), there was a significant difference in Magnitude with which the disease reached the population: DMFT means were 1.76 in exposed and 2.60 in no exposed. The degree of polarization, indicated by the percentage of individuals with DMFT=0, was different, being higher (41.8 per cent ) in exposed and lower (34.3 per cent ) in no exposed. PR (NE / E) was 1.13 indicating little expressiveness in the difference in prevalence. For permanent dentition the magnitude ratios in the total population (MR-PAp) were 22.1 in exposed and 6.1 in no exposed. The DMFT value for the SiC was 4.04 in exposed and 6.16 in no exposed, while the magnitude ratios (MR-PA-SiC) were 23.8 and 5.9, respectively. Conclusion. Exposure to fluoridated water implied lower mean values of dmft, DMFT and SiC indexes, although in the presence of concomitant exposure to fluoridated dentifrice, in a scenario of low disease prevalence and a similar pattern of caries distribution in the populations analyzed. The lower experience and magnitude of caries in the anterior-esthetic dental groups, in situations of exposure to fluoridated water compared to no exposure, corroborates previous studies. In the Brazilian context, even in the simultaneous exposure to fluoridated dentifrice, the fluoridation of water continues to produce relevant epidemiological effects

Introdução. Não há dados que atestem, no contexto brasileiro das primeiras décadas do século XXI, que a fluoretação das águas de abastecimento público agrega benefício preventivo com relação à cárie dentária, em pequenos municípios, aos proporcionados pelo uso generalizado dos dentifrícios fluoretados. Objetivo. Analisar o grau do benefício preventivo da exposição à água fluoretada em relação à cárie dentária e sua distribuição segundo grupamentos dentais, em contexto de uso generalizado de creme dental fluoretado, no Brasil. Metodologia. Foi realizado estudo observacional transversal, de tipo censitário, na modalidade de duplo inquérito epidemiológico populacional. As populações avaliadas residem em municípios da mesma região geográfica, de pequeno porte demográfico e com classificação socioeconômica similar, diferenciando-se apenas pela condição de exposição, há pelo menos 5 anos, à água fluoretada (Silveiras) ou de não exposição (São José do Barreiro). A experiência e a magnitude da cárie dentária nessas populações foram avaliadas utilizando-se os índices ceod (aos 5 e 6 anos de idade; N=233), CPOD (aos 11 e 12 anos; N=312) e SiC (aos 11 e 12 anos; N=105) e a associação foi testada empregando-se as estatísticas qui-quadrado de Pearson e razão de prevalência (RP) entre não expostos (NE) e expostos (E) à água fluoretada. A partir dos valores do ceod, CPOD e SiC, foram obtidas as razões de magnitude entre os grupamentos dentários posteriores e anteriores (RM-PA), em ambas as dentições, segundo exposição ou não à água fluoretada. Os grupamentos dentários foram assim definidos: anteriores-estéticos (incisivos centrais e laterais e caninos, superiores e inferiores, em ambas as dentições) e posteriores (primeiros e segundos pré-molares e primeiros e segundos molares, superiores e inferiores na dentição permanente e primeiros e segundos molares superiores e inferiores na dentição decídua). Resultados. Dentição decídua- Embora a experiência de cárie (ceod1) não tenha se associado com a exposição à água fluoretada (qui-quadrado=2,77; p=0,96; =5 por cento ),observou-se expressiva diferença na magnitude com que a doença atingiu a população: as médias ceod foram de 2,74 em expostos e 4,17 em não expostos. O grau da polarização, indicado pela porcentagem de indivíduos com ceod=0, foi diferente, sendo maior (43,0 por cento ) em expostos e menor (31,0 por cento ) em não expostos. A RP (NE/E) foi de 1,21 indicando que a exposição à água fluoretada correspondeu a uma taxa de prevalência 21 por cento menor, comparativamente aos não expostos. As razões de magnitude para dentição decídua (RM-PAd) foram de 4,2 em expostos e 4,8 em não expostos. Dentição permanente- Embora a experiência de cárie (CPOD1) não tenha se associado com a exposição à água fluoretada (qui-quadrado=1,78; p=0,18; =5 por cento ), observou-se expressiva diferença na magnitude com que a doença atingiu a população: as médias CPOD foram de 1,76 em expostos e 2,60 em não expostos. O grau da polarização, indicado pela porcentagem de indivíduos com CPOD=0, foi diferente, sendo maior (41,8 por cento ) em expostos e menor (34,3 por cento ) em não expostos. A RP (NE/E) foi de 1,13 indicando pouca expressividade na diferença das prevalências. Para a dentição permanente as razões de magnitude na população total (RM-PAp) foram de 22,1 em expostos e 6,1, em não expostos. O valor médio do SiC foi de 4,04 em expostos e 6,16 em não expostos, enquanto as razões de magnitude (RM-PA-SiC) foram 23,8 e 5,9, respectivamente. Conclusão. A exposição à água fluoretada implicou menores valores médios dos índices ceod, CPOD e SiC, ainda que em presença de exposição concomitante a dentifrício fluoretado, em cenário de baixa prevalência da doença e padrão similar de distribuição de cárie nas populações analisadas. As menores experiência e magnitude da cárie nos grupamentos dentários anteriores, em situação de exposição à água fluoretada em comparação com a não exposição, corrobora estudos anteriores. No contexto brasileiro, ainda que em presença de exposição simultânea a dentifrício fluoretado, a fluoretação das águas segue produzindo efeitos epidemiológicos relevantes / Introduction. In the Brazilian context of the first decades of the 21st century, there is no evidence that the fluoridation of public water supplies adds preventive benefit in relation to dental caries, in small municipalities, to those provided by the widespread use of fluoridated dentifrices. Objective. To analyze the degree of the preventive benefit of exposure to fluoridated water in relation to dental caries and its distribution according to dental groups, in a context of widespread use of fluoride toothpaste in Brazil. Methodology. A cross - sectional observational study, census type, was conducted in a double epidemiological population survey. The populations studied live in municipalities of the same geographic region, with a small demographic and similar socioeconomic classification, differing only by the condition of exposure to fluoridated water (Silveiras) or no exposure (São José do Barreiro), for at least 5 years. The experience and magnitude of dental caries in these populations were evaluated using the dmft indice (at 5 and 6 years of age, N=233), DMFT (at 11 and 12 years old, N=312) and SiC (at 11 and 12 years, N=105), and the association was tested using Pearson\'s chi-square statistic and prevalence ratio (PR) between no-exposed (NE) and exposed (E) to fluoridated water. From the values of dmft, DMFT and SiC, the magnitude ratios between the posterior and anterior dental groups (MR-PA) were obtained in both dentitions according to exposure to fluoridated water. Dental groups were defined: anterior-esthetic (central and lateral incisors and canines, upper and lower, in both dentitions) and posterior (first and second premolars and first and second molars, upper and lower, in the permanent dentition and first and second molars upper and lower in the deciduous dentition). Results. Deciduos Dentition- Although the caries experience (dmft1) wasnt associated with exposure to fluoridated water (chi-square=2.77, p=0.96, =5 per cent ), there was a significant difference in Magnitude with which the disease reached the population: the mean dmft were 2.74 in exposed and 4.17 in no exposed. The degree of polarization, indicated by the percentage of individuals with dmft=0, was different, being higher (43.0 per cent ) in exposed and lower (31.0 per cent ) in no exposed. PR (NE / E) was 1.21 indicating that exposure to fluoridated water corresponded to a 21 per cent lower prevalence rate compared to those not exposed. The magnitude ratios for deciduous dentition (MR-PAd) were 4.2 in exposed and 4.8 in no exposed. Permanent Dentition - Although the caries experience (DMFT1) was not associated with exposure to fluoridated water (chi-square=1.78, p=0.18, =5 per cent ), there was a significant difference in Magnitude with which the disease reached the population: DMFT means were 1.76 in exposed and 2.60 in no exposed. The degree of polarization, indicated by the percentage of individuals with DMFT=0, was different, being higher (41.8 per cent ) in exposed and lower (34.3 per cent ) in no exposed. PR (NE / E) was 1.13 indicating little expressiveness in the difference in prevalence. For permanent dentition the magnitude ratios in the total population (MR-PAp) were 22.1 in exposed and 6.1 in no exposed. The DMFT value for the SiC was 4.04 in exposed and 6.16 in no exposed, while the magnitude ratios (MR-PA-SiC) were 23.8 and 5.9, respectively. Conclusion. Exposure to fluoridated water implied lower mean values of dmft, DMFT and SiC indexes, although in the presence of concomitant exposure to fluoridated dentifrice, in a scenario of low disease prevalence and a similar pattern of caries distribution in the populations analyzed. The lower experience and magnitude of caries in the anterior-esthetic dental groups, in situations of exposure to fluoridated water compared to no exposure, corroborates previous studies. In the Brazilian context, even in the simultaneous exposure to fluoridated dentifrice, the fluoridation of water continues to produce relevant epidemiological effects

As cerâmicas de carbeto de silício, SiC, possuem excelentes propriedades físicas, químicas e mecânicas, fazendo com que as mesmas tenham um vasto campo de aplicações. Devido à natureza altamente covalente do SiC, este possui baixo coeficiente de autodifusão, dificultando sua sinterização via fase sólida. Por esse motivo as cerâmicas de SiC devem ser sinterizadas via fase líquida, usando aditivos. A dificuldade para a expansão das aplicações das cerâmicas de SiC é a baixa tenacidade à fratura, 3-4 MPa√m . Neste trabalho foi estudada a sinterização de cerâmicas de SiC aditivadas com o sistema La2O3 - Al2O3, obtido por mistura mecânica e mistura química. Foram preparadas misturas de SiC com 10% em volume de aditivos. As amostras foram prensadas e sinterizadas; e as que apresentaram melhores resultados de densificação foram tratadas termicamente com o objetivo de reforçar in situ essas cerâmicas. Tanto as amostras somente sinterizadas quanto as sinterizadas e tratadas termicamente foram submetidas as análises de microscopia eletrônica de varredura, difração de raios X, tenacidade à fratura e energia de fratura. Foram correlacionados os resultados de microestrutura e resistência à propagação de trincas. Além do aprofundamento científico na sinterização e caracterização das cerâmicas de SiC, foram também obtidas resultados de tenacidade à fratura da ordem de 6 MPa√m. / Silicon carbide, SiC, ceramics have excellent physical, chemical and mechanical properties, allowing them to be used in a vast range of applications. However, due to the highly covalent nature of SiC, its self-diffusion coefficient is low, making its solid phase difficult to sinter without additives. SiC ceramics should therefore be sintered via liquid phase using densifying additives. The expansion of SiC ceramic applications, however, is hampered by its low fracture toughness of 3-4 MPa √m . The purpose of this work was to study SiC ceramics sintered with La2O3 - Al2O3 as additive system produced by mechanical and chemical mixing. To this end, SiC mixtures were prepared containing 10% in volume of additives. The samples were pressed and sintered. The samples displaying the highest densification were heat-treated to improve their properties. All the samples, both sintered and sintered followed by heat-treatment, were subjected to analyses by scanning electron microscopy, X-ray diffraction, fracture toughness and fracture energy. The result of microstructure, fracture energy and fracture toughness among them selves were then correlated. In addition to contributing to the body of scientific knowledge on the sintering and characterization of SiC ceramics, the goal of reaching fracture toughness in the order of 6 MPa √m was also achieved.

This thesis focuses on the design of high voltage MOSFET on SiC and its application in power electronic systems. Parameters extraction for 4H SiC MOS devices is the main focus of the first topic developed in this thesis. Calibration of two-dimensional (2-D) device and circuit simulators (MEDICI and SPICE) with state-of-the-art 4H SiC MOSFETs data are performed, which includes the mobility parameter extraction. The experimental data were obtained from lateral N-channel 4H SiC MOSFETs with nitrided oxide-semiconductor interfaces, exhibiting normal mobility behavior. The presence of increasing interface-trap density (Dit) toward the edge of the conduction band is included during the 2-D device simulation. Using measured distribution of interface-trap density for simulation of the transfer characteristics leads to good agreement with the experimental transfer characteristic. The results demonstrate that both MEDICI and SPICE simulators can be used for design and optimization of 4H SiC MOSFETs and the circuits utilizing these MOSFETs. Based on critical review of SiC power MOSFETs, a new structure of SiC accumulation-mode MOSFET (ACCUFET) designed to address most of the open issues related to MOS interface is proposed. Detailed analysis of the important design parameters of the novel structure is performed using MEDICI with the parameter set used in the calibration process. The novel structure was also compared to alternative ACCUFET approaches, specifically planar and trench-gate ACCUFETs. The comparison shows that the novel structure provides the highest figure of merit for power devices. The analysis of circuit advantages enabled by the novel SiC ACCUFET is given in the final part of this thesis. The results from circuit simulation show that by utilizing the novel SiC ACCUFET the operating frequency of the circuit can be increased 10 times for the same power efficiency of the system. This leads to dramatic improvements in size, weight, cost and thermal management of power electronic systems.

<p>The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany.</p><p>Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements.</p><p>When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m²) and the peak wavelength were maximum luminescence occurred.</p><p>The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected.</p><p>When irradiance of the excitation light was approx. 8 W/m² the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m². The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample.</p><p>The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.</p>

The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany. Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements. When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m2) and the peak wavelength were maximum luminescence occurred. The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected. When irradiance of the excitation light was approx. 8 W/m2 the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m2. The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample. The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.

Le carbure de silicium est en théorie un des meilleurs candidats pour les applications aussi stratégiques que sont l'électronique forte puissance, haute température, haute fréquence ou encore fonctionnant en environnement hostile. Cependant, les difficultés de cristallogenèse de ce matériau ralentissent le développement de cette filière. Par exemple, l'épitaxie en phase vapeur (EPV) de couches minces de SiC nécessite des températures élevées, supérieures à 1400°C, ce qui compliquent la mise en oeuvre et le contrôle du procédé de croissance. Faire<br />croître SiC en dessous de cette température tout en gardant une qualité de matériau (cristallinité et dopage) satisfaisante est un véritable défi dont les intérêts industriels sont évidents.<br />Cet objectif peut être atteint en utilisant des techniques en solution, sous gradient thermique<br />ou par mécanisme vapeur-liquide-solide (VLS). Différents bains et différentes configurations<br />de croissance ont été envisagés. Cette étude a permis de mieux cerner les difficultés de mise en oeuvre, de justifier les solutions techniques proposées et de sélectionner les alliages Al-Si comme meilleurs candidats. A partir de ces bains, l'homoépitaxie des polytypes hexagonaux (4H et 6H-SiC) a été démontrée pour des températures aussi basses que 1100°C. Les couches sont très fortement dopées p, par l'incorporation massive d'Al, de bonne qualité cristalline et assez rugueuses. Ce fort dopage p confère des propriétés électriques très intéressantes<br />notamment en terme d'abaissement de la résistivité de contact.<br />Le polytype cubique (ou 3C-SiC) ne disposant pas de substrats commerciaux de qualité suffisante, sa croissance a été réalisée par hétéroépitaxie sur substrat de Si(100) et a-SiC(0001) non désorientés, respectivement par EPV et VLS. L'EPV sur substrat de Si produit des couches de qualité cristalline médiocre en raison du fort désaccord de maille. La courbure<br />importante des plaques, résultant des contraintes thermiques, peut être diminuée en modifiant<br />l'étape de carburation. Un tel matériau pourra trouver des débouchés avec des composants peu<br />exigeants en qualité cristalline. Enfin, les alliages à base de Ge et Sn se sont montrés adaptés à<br />la germination du polytype 3C-SiC sur substrats hexagonaux. Des conditions de croissances<br />permettant d'éliminer les parois d'inversions dans les couches, ont été déterminées. Le matériau 3C ainsi épitaxié n'a pas d'équivalent ailleurs et est très prometteur pour développer un filière basée sur ce polytype.

Les polymères précéramiques à base de silicium ont été proposés vers la fin des années 50 comme précurseurs de céramiques non oxydes, matériaux que l’on définira plus tard par « Polymer Derived Ceramics (PDCs)». Comparées aux méthodes de synthèses traditionnelles, la voie dite des polymères précéramiques ou encore PDCs offre de nombreux avantages en terme de composition, structure et texture des céramiques. Grâce à ses propriétés intrinsèques, (thermiques, résistances chimiques et mécaniques, comportement semi-conducteur...) le carbure de silicium (SiC) et ses dérivés azotés (carbonitrure de silicium SiCN) peuvent être considérés comme des matériaux appropriés pour la préparation de nouvelles générations de membranes céramiques dédiées en particulier aux procédés de production de l’hydrogène (à partir du CO2, CH4 ou de la réaction de dissociation de l’eau par exemple). En mettant en oeuvre la voie PDCs, un matériau SiC hydrophobe et amorphe adapté aux procédés de séparation de l’hydrogène, possédant un bon couplage perméance/sélectivité associé à une excellente stabilité thermostructurale au delà de 500°C peut être proposé. Néanmoins, l’utilisation de polymères précéramiques induit un changement dimensionnel important au cours de la pyrolyse permettant la conversion du polymère en céramique. Des contraintes mécaniques résiduelles induites par ce retrait volumique entraînent la formation de défauts, de fissures et parfois l’effondrement de la structure lorsque le polymère précéramique est mis en forme. Dans le cadre de cette étude, nous proposons d’élaborer des supports macroporeux ou mousses microcellulaires, des revêtements mésoporeux ainsi que des revêtements microporeux à base de SiC pour, à terme, proposer un matériau à base de SiC et à porosité hiérarchisée pour une utilisation en séparation gazeuse. l’allylhydridopolycarbosilane (AHPCS) est utilisé comme précurseur SiC. Après avoir fait un état de l’art dans le chapitre I et décrit les matériaux et méthodes dans le chapitre II, deux stratégies sont mises en œuvre dans les chapitres III et IV pour générer ces différents matériaux avec un meilleur contrôle du changement dimensionnel du polymère. Dans une première stratégie (chapitre III), des charges passives (nanodiamants) et actives (particules de bore) sont introduites dans l’AHPCS pour générer des formulations avec différentes proportions de charges et s’opposer ainsi au retrait volumique du polymère au cours de la pyrolyse et élaborer des matériaux composites. Dans une seconde stratégie qui fait l’objet du chapitre IV, une approche moléculaire à source unique est proposée. Elle consiste à introduire l’élément bore à l’échelle moléculaire dans l’AHPCS pour en augmenter son rendement céramique et donc réduite la perte de masse que subira l’AHPCS modifié au cours de la pyrolyse. Dans ces chapitres III et IV, des structures monolithiques denses sont élaborées pour mieux observer le changement dimensionnel au cours de la conversion polymère-céramique. Les formulations et précurseurs synthétisés et sélectionnés serviront alors de précurseurs de matériaux macroporeux, mésoporeux et microporeux dans le chapitre V. / Preceramic polymers have been proposed in the late fifty’s as non-oxide silicon based ceramic precursors generally called PDCs for “Polymer Derived Ceramics”. Compared to traditional synthesis ways, the PDCs route can offer many advantages in terms of compositions, structures and textures of ceramics. Due to its intrinsic properties (thermal, chemical and mechanical resistance, semi-conductor behavior,...), silicon carbide (SiC) and their derivatives with nitrogen (silicon carbonitride, SiCN) can be considered as one of the best materials for the next generation of ceramic based membranes, in particular in the hydrogen production processes (from CO2, CH4 or through the water gas shift reaction for example). By investigating the PDCs route, a hydrophobic and amorphous SiC material suitable for hydrogen separation process exhibiting good permeability/selectivity ratio, high thermal mechanical and chemical resistance coupled with a good stability under wet atmosphere up to 500°C can be proposed. However, the use of preceramic polymrers induces an important dimensional modification during the pyrolysis allowing the conversion from polymer to ceramic. Residual stresses caused by the volume shrinkage leads to the formation of cracks or even collapses of the structure of shaped preceramic polymers. This study is focused on the elaboration of SiC based macroporous substrates or microcellular foams, mesoporous and microporous coatings in the aim to propose a SiC based material showing a hierarchized porosity dedicated to gaseous separation applications. The AllylHydridoPolycarbosilane (AHPCS) is used as SiC precursor. After the chapters I and II, respectively dedicated to a literature review and the materials and methods used, two strategies are enforced in the chapters III and IV to generate these materials with a better control of the polymer dimensional change. In the first strategy (chapter III), passive (nanodiamonds) and active (boron particles) fillers are introduced in the AHPCS to generate some formulations with different fillers proportions and opposing to the volume shrinkage of the polymer during the pyrolysis and create composite materials. In the second strategy (chapter IV), a single molecular source approach consisting of the introduction of boron at the molecular state in the AHPCS is proposed. This introduction of boron leads to increase the ceramic yield and to reduce the mass loss of the modified AHPCS during the pyrolysis. In the chapters III and IV, monolithic dense structures are developed to better understand the dimensional change occurring during the pyrolysis. Synthetized and selected formulations and polymers will serve as precursors for macroporous, mesoporous and microporous materials in the chapter V.

Introduzido na década de 1970, o glifosato figura entre os herbicidas mais consumidos em todo mundo. Devido a características como baixa toxicidade aguda a organismos não-alvo e alta eficiência na eliminação de plantas daninhas, o herbicida se tornou um sucesso de vendas, com um substancial incremento em sua utilização após o desenvolvimento de culturas geneticamente modificadas para tolerar o ingrediente ativo. O elevado consumo do glifosato vem se tornando uma preocupação para diferentes agências ambientais e de saúde. Consequentemente, métodos eficientes para a determinação e quantificação do herbicida se fazem necessários. Na presente dissertação, aprimorou-se um método que utiliza um sistema de análise de injeção sequencial por cromatografia líquida (SIC) com detecção por fluorescência para a determinação de glifosato e seu principal produto de degradação, o ácido aminometilfosfônico (AMPA), em amostras ambientais. Os limites de detecção (LD) e quantificação (LQ) para o glifosato foram 0,10 e 0,33 &#1281;mol L-1, respectivamente. Já para o AMPA, LD foi de 0,07 &#181;mol L-1 e LQ de 0,22 &#181;mol L-1. O método foi empregado na determinação das espécies em amostras de água fortificadas e gerou valores de recuperação entre 97,2 a 151,5% para o AMPA e 74,6 a 140,5% para o glifosato. Quando empregado em um estudo de adsorção-dessorção, o método foi capaz de produzir valores dos parâmetros de Freundlich e Langmuir comparáveis aos encontrados na literatura. Com qmax = 2,1 ± 0,1 &#181;mol g-1 e KF = 0,53 ± 0,07 &#181;mol1-1/n L1/n g-1, o Latossolo B se mostrou como o solo com maior capacidade de adsorver o glifosato. Em termos de dessorção, o percentual dessorvido ficou abaixo de 55% da quantidade inicialmente adsorvida para as concentrações trabalhadas. / Introduced in the 1970, glyphosate figures among the most used herbicides in the world. Due to characteristics such as low acute toxicity to non-target organisms and high efficiency regarding the elimination of weeds, the herbicide has experienced a huge success in terms of safes. Since genetically modified crops that tolerate the active ingredient have been developed, these safes have continued to increase. Glyphosate\'s high consumption has become a concern to different environmental and health agencies. As a result, efficient methods for the determination of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), are necessary. This dissertation describes improvements in a sequential injection chromatography method for the determination of glyphosate and aminomethylphosphonic acid in environmental samples. The limits of detection (LOD) and quantification (LOQ) for glyphosate is 0.10 e 0.33 &#181;mol L-1, respectively. LOD of 0.07 &#181;mol L-1 and LOQ of 0,22 &#181;mol L-1 is registered for AMPA. The method was employed for the determination of both species in spiked water samples and recovery values between 97.2 a 151.5% was obtained for AMPA and between 74.6 a 140.5% for glyphosate. When used in an adsorption-desorption study, the method was capable of generating values for the Freundlich and Langmuir parameters that are similar to those found in the scientific literature. With a qm\" of 2.1 ± 0.1 &#181;mol g-1 and KF = 0.53 ± 0.07 &#181;mol1-1/n L1/n g-1, Latossolo B was the soil sample with the largest glyphosate adsorption capacity. Regarding desorption, the percentages desorbed were beiow 55% of the initial mass of glyphosate adsorbed for the concentrations used.

Descreve-se o desenvolvimento de um método de análise por injeção sequencial para determinação de glifosato em formulações comerciais por voltametria de onda quadrada em eletrodo de gota de mercúrio. O glifosato foi derivatizado em modo estacionário com ácido nitroso para produção de N-nitroso glifosato, que é eletroativo. Os limites de detecção (LD) e quantificação (LQ) foram 0,7 e 2,4 mg L-1 (4 e 14 &#181;mol L-1), respectivamente. O método foi aplicado a três formulações, obtendo resultados que diferiram do valor indicado pelo fabricante por -2,6, -0,8 e -28%. Em seguida descreve-se o desenvolvimento de um método de injeção seqüencial para a determinação fluorimétrica de glifosato, Esse método baseou-se em uma primeira etapa de conversão de glifosato a glicina por reação com hipoclorito de calcio, seguida por reação com o-ftaldialdeído na presença de 2-mercaptoetanol (OPA-MCE) em tampão borato (pH> 9) para produzir o composto fluorescente (2\'-hidroxietiltio)-2-N-alkilisoindol (excitação em 340 nm e emissão em 450 nm). O método apresentou resposta linear para concentrações entre 0,25 e 25,0 &#181;mol L-1, com LD e LQ de 0,08 e 0,25 &#181;mol L-1 (14 e 42 &#181;g L-1), respectivamente, e frequência de amostragem de 18 análises por hora. O método foi aplicado para estudar as propriedades de adsorção / dessorção em um solo e em uma amostra de sedimento. Os dados das isotermas de adsorção e dessorção foram tratados pelas equações de Freundlich e Langmuir, que permitiram estimar uma capacidade de adsorção de 1384 ± 26 e 295 ± 30 mg kg-1 para as amostras de solo e sedimento, respectivamente. A determinação de glifosato e AMPA em amostras de água foi realizada por cromatografia por injeção sequencial com detecção fluorimétrica explorando as mesmas reações com hipoclorito e OPA-MCE. A solução transportadora com papel de fase móvel foi composta por mistura metanol: tampão fosfato 10 mmol L-1 (pH 6,8) na proporção 25:75 (v v-1). A frequência de amostragem foi de 6 análises por hora, com LD e LQ de 0,14 e 0,42 &#181;mol L-1 para AMPA e 0,11 e 0,33 &#181;mol L-1 para glifosato, respectivamente. Testes de adição e recuperação em amostras de águas naturais enriquecidas com 0,50 &#181;mol L-1 desses compostos levaram a taxas de recuperação de 82 a 140% para AMPA e de 84 a 96% para glifosato. Investigou-se o efeito do herbicida em cultivos de duas espécies de microalgas marinhas - a Chlorophyta, Tetraselmis gracilis e a diatomácea, Phaeodactilum tricornutum. Para isso adicionou-se diferentes concentrações de glifosato (2 a 1000 mg L-1) a cultivos crescendo em fase exponencial. Doses de 2 e 50 mg L-1 provocaram leve aumento de crescimento algal quando comparados com o cultivo controle sem glifosato. O rendimento quântico da fotossíntese aumentou levemente em alguns dias no cultivo de P. tricornutum em concentrações baixas de glifosato. Na concentração de glifosato de 200 mg L-1 houve declínio do crescimento e acentuada queda do rendimento quântico da fluorescência da fotossíntese. Perfis dos aminoácidos aromáticos, tirosina, triptofano e fenilalanina apresentaram diferenças nas algas. / We describe a development of a voltammetric method for determination of glyphosate in commercial formulations using sequential injection analysis to carry the sample to a flow cell adapted to the capillary of a mercury drop electrode. Glyphosate is batch-derivatized with nitrous acid in hydrochloric acid to produce N-nitroso glyphosate, which is electroactive. The limits of detection (LOD) and quantification (LOQ) were 0.7 and 2.4 mg L-1, respectively. The method was applied to three formulations, obtaining results that differed from the value indicated by the manufacturer by -2.6, -0.8 and -28%. Next, the thesis describes the development of a sequential injection method to automate the fluorimetric determination of glyphosate based on a first step of oxidation to glycine by hypochlorite, followed by reaction with o-phthaldialdehyde in presence of 2-mercaptoethanol (OPA-MCE) in borate buffer (pH>9) to produce a fluorescent 1-(2´-hydroxyethylthio)-2-N-alkylisoindole. The proposed method exhibited a linear response for glyphosate concentrations between 0.25 and 25.0 &#181;mol L-1, with LOD and LOQ of 0.08 and 0.25 &#181;mol L-1, respectively. The sampling rate of the method was 18 samples per hour. The method was applied to study adsorption/desorption properties in a soil and in a sediment sample. Adsorption and desorption isotherms were properly fitted by Freundlich and Langmuir equations, leading to adsorption capacities of 1384 ± 26 and 295 ± 30 mg kg-1 for the soil and sediment samples, respectively. Determination of glyphosate and AMPA in water samples was performed by sequential injection chromatography (SIC) with fluorimetric detection by exploiting the same reactions with hypochlorite and OPA-MCE. The carrier solution plays a role of mobile phase, being composed of 25:75 (v v-1) methanol : 10 mmol L-1 phosphate buffer (pH 6.8). The chromatographic step enhanced the method selectivity. The sampling throughput was 6 analyzes per hour with LOD and LOQ of 0.14 and 0.42 &#181;mol L-1 for AMPA and 0.11 and 0.33 &#181;mol L-1 for glyphosate, respectively. Recovery tests in natural water samples enriched with 0.50 &#181;mol L-1 in the compounds led to recovery rates from 82 to 140% for AMPA and 84 to 96% for glyphosate. We investigated the effect of the herbicide on cultivation of two species of marine microalgae - the Chlorophyta, Tetraselmis gracilis and the diatomaceous Phaeodactilum tricornutum. To achieve this goal, different concentrations of glyphosate (2 to 1000 mg L-1) were added to cultures growing in exponential phase. Doses between 2 and 50 mg L-1 caused a slight increase in algal growth compared to the control culture without glyphosate. The quantum yield of photosynthesis increased slightly in some days in the cultivation of P. tricornutum at low concentrations of glyphosate. The glyphosate concentration of 200 mg L-1 decreases the cell growth and caused a marked decline in the fluorescence quantum yield of photosynthesis. Profiles of aromatic amino acids, tyrosine, tryptophan and phenylalanine differed in the algae