Etude spectroscopique d’un plasma micro-onde à la pression atmosphérique et son application à la synthèse de nanostructures

L’objectif de ce mémoire de maîtrise est de caractériser la distribution axiale des plasmas tubulaires à la pression atmosphérique créés et entretenus par une onde électromagnétique de surface ainsi que d’explorer le potentiel de ces sources pour la synthèse de matériaux et de nanomatériaux. Un précédent travail de thèse, qui avait pour objectif de déterminer les mécanismes à l’origine de la contraction radiale du plasma créé dans des gaz rares, a mis en lumière un phénomène jusque-là inconnu dans les plasmas d’onde de surface (POS). En effet, la distribution axiale varie différemment selon la puissance incidente ce qui constitue une différence majeure par rapport aux plasmas à pression réduite. Dans ce contexte, nous avons réalisé une étude paramétrique des POS à la pression atmosphérique dans l’Ar. À partir de nos mesures de densité électronique, de température d’excitation et de densité d’atomes d’Ar dans un niveau métastable (Ar 3P2), résolues axialement, nous avons conclu que le comportement axial de l’intensité lumineuse avec la puissance n’est pas lié à un changement de la cinétique de la décharge (qui est dépendante de la température des électrons et de la densité d’atomes d’Ar métastables), mais plutôt à une distribution anormale de dissipation de puissance dans le plasma (reliée à la densité d’électrons). Plus précisément, nos résultats suggèrent que ce dépôt anormal de puissance provient d’une réflexion de l’onde dans le fort gradient de densité de charges en fin de colonne, un effet plus marqué pour de faibles longueurs de colonnes à plasma. Ensuite, nous avons effectué une étude spectroscopique du plasma en présence de précurseurs organiques, en particulier le HMDSO pour la synthèse de matériaux organosiliciés et l’IPT pour la synthèse de matériaux organotitaniques. Les POS à la PA sont caractérisés par des densités de charges très élevées (>10^13 cm^-3), permettant ainsi d’atteindre des degrés de dissociation des précurseurs nettement plus élevés que ceux d'autres plasmas froids à la pression atmosphérique comme les décharges à barrière diélectrique. Dans de tels cas, les matériaux synthétisés prennent la forme de nanopoudres organiques de taille inférieure à 100 nm. En présence de faibles quantités d’oxygène dans le plasma, nous obtenons plutôt des nanopoudres à base d’oxyde de silicium (HMDSO) ou à base de titanate de silicium (IPT), avec très peu de carbone.

Les effets de revêtements de surface sur la dissolution et la bioaccumulation de nanoparticules d'oxyde de zinc par l'algue unicellulaire, C. reinhardtii

Au cours de la dernière décennie, les nanoparticules ont connu un essor sans précédent dans plusieurs domaines. On peut retrouver ces nanoparticules dans des secteurs aussi variés tels que la médecine, l’électronique, les écrans solaires, les cosmétiques et les plastiques, pour ne nommer que ceux-là. Cette utilisation massive a eu un effet pervers sur l’environnement, sachant qu’une grande partie de ces produits se sont retrouvés inévitablement dans les milieux naturels. Plusieurs études révèlent qu’autant la présence des nanoparticules que leurs produits de dissolution sont à prendre en considération lorsque des travaux toxicologiques ou le devenir de ces matériaux sont étudiés. Il est désormais clair que les propriétés de surface de ces nanoparticules jouent un rôle central sur leur comportement dans les solutions aqueuses; que ce soit les interactions avec des organismes ou entre les particules elles-mêmes. Afin d’évaluer le devenir de nZnO, une étude sur la dissolution ainsi que la bioaccumulation a été réalisée avec l’algue modèle Chlamydomonas reinhardtii en présence de nanoparticules ayant différents enrobages. Les nanoparticules d’oxyde de zinc suivantes ont été étudiées : (i) nZnO sans enrobage (nZnO); (ii) nZnO avec enrobage d’acide polyacrylique (nZnO-PAA) et (iii) nZnO avec enrobage d’hexamétaphosphate de sodium (nZnO-HMP). La dissolution était mesurée à l’aide de trois techniques : ultrafiltration par centrifugation (CU); technique potentiométrique (scanned stripping chronopotentiometry, SSCP) et spectrométrie de masse – plasma à couplage inductif couplé à une résine échangeuse d’ions (resin-based inductively coupled plasma-mass spectrometry, resin-based ICP-MS). Les résultats obtenus démontrent une grande tendance à la dissolution pour le nZnO (presque totale) tandis que pour le nZnO-PAA et le nZnO-HMP, la dissolution est dépendante de la nature de l’enrobage le composant. Pour la bioaccumulation sur l’algue testée, les données montrent une grande dépendance au zinc libre issu de la dissolution pour nZnO et nZnO-PAA. À l’inverse, le nZnO-HMP démontre une bioaccumulation plus élevée par comparaison aux mêmes concentrations d’expositions du zinc libre, expliquée par la stimulation de l’internalisation du zinc provoqué par la présence de phosphate constituant l’enrobage de nZnO-HMP.

Effect of cycling on the magnetization of ion exchanged magnetic nanocomposite based on polystyrene

Magnetic nanocomposites containing iron oxide particles embedded in a polymer matrix have been synthesized using the method of ion exchange. They have been characterized by using low temperature and room temperature magnetic measurements and Mo¨ ssbauer spectroscopy. The iron content in these samples has also been determined. The results have been analysed and explained. The physical and chemical properties of these nanocomposite materials are different from those of the bulk. Some of the unique properties of these materials find application in information storage, color imaging, ferrofluids and magnetic refrigeration

Low temperature Mössbauer studies on magnetic nanocomposites

Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of g-Fe2O3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of g-Fe2O3 in the matrix

Synthesis, Characterization and Applications of Hybrid Nanocomposites of TiO2 With Conducting Polymers

A nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), or structures having nano-scale repeat distances between the different phases that make up the material. In the broadest sense this definition can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nanocomposite will differ markedly from that of the component materials. Size limits for these effects have been proposed, <5 nm for catalytic activity, <20 nm for making a hard magnetic material soft, <50 nm for refractive index changes, and <100 nm for achieving superparamagnetism, mechanical strengthening or restricting matrix dislocation movement. Conducting polymers have attracted much attention due to high electrical conductivity, ease of preparation, good environmental stability and wide variety of applications in light-emitting, biosensor chemical sensor, separation membrane and electronic devices. The most widely studied conducting polymers are polypyrrole, polyaniline, polythiophene etc. Conducting polymers provide tremendous scope for tuning of their electrical conductivity from semiconducting to metallic region by way of doping and are organic electro chromic materials with chemically active surface. But they are chemically very sensitive and have poor mechanical properties and thus possessing a processibility problem. Nanomaterial shows the presence of more sites for surface reactivity, they possess good mechanical properties and good dispersant too. Thus nanocomposites formed by combining conducting polymers and inorganic oxide nanoparticles possess the good properties of both the constituents and thus enhanced their utility. The properties of such type of nanocomposite are strongly depending on concentration of nanomaterials to be added. Conducting polymer composites is some suitable composition of a conducting polymer with one or more inorganic nanoparticles so that their desirable properties are combined successfully. The composites of core shell metal oxide particles-conducting polymer combine the electrical properties of the polymer shell and the magnetic, optical, electrical or catalytic characteristics of the metal oxide core, which could greatly widen their applicability in the fields of catalysis, electronics and optics. Moreover nanocomposite material composed of conducting polymers & oxides have open more field of application such as drug delivery, conductive paints, rechargeable batteries, toners in photocopying, smart windows, etc.The present work is mainly focussed on the synthesis, characterization and various application studies of conducting polymer modified TiO2 nanocomposites. The conclusions of the present work are outlined below, Mesoporous TiO2 was prepared by the cationic surfactant P123 assisted hydrothermal synthesis route and conducting polymer modified TiO2 nanocomposites were also prepared via the same technique. All the prepared systems show XRD pattern corresponding to anatase phase of TiO2, which means that there is no phase change occurring even after conducting polymer modification. Raman spectroscopy gives supporting evidence for the XRD results. It also confirms the incorporation of the polymer. The mesoporous nature and surface area of the prepared samples were analysed by N2 adsorption desorption studies and the mesoporous ordering can be confirmed by low angle XRD measurementThe morphology of the prepared samples was obtained from both SEM & TEM. The elemental analysis of the samples was performed by EDX analysisThe hybrid composite formation is confirmed by FT-IR spectroscopy and X-ray photoelectron spectroscopyAll the prepared samples have been used for the photocatalytic degradation of dyes, antibiotic, endocrine disruptors and some other organic pollutants. Photocatalytic antibacterial activity studies were also performed using the prepared systemsAll the prepared samples have been used for the photocatalytic degradation of dyes, antibiotic, endocrine disruptors and some other organic pollutants. Photocatalytic antibacterial activity studies were also performed using the prepared systems Polyaniline modified TiO2 nanocomposite systems were found to have good antibacterial activity. Thermal diffusivity studies of the polyaniline modified systems were carried out using thermal lens technique. It is observed that as the amount of polyaniline in the composite increases the thermal diffusivity also increases. The prepared systems can be used as an excellent coolant in various industrial purposes. Nonlinear optical properties (3rd order nonlinearity) of the polyaniline modified systems were studied using Z scan technique. The prepared materials can be used for optical limiting Applications. Lasing studies of polyaniline modified TiO2 systems were carried out and the studies reveal that TiO2 - Polyaniline composite is a potential dye laser gain medium.

Tubular Organization of SnO₂ Nanocrystallites for Improved Lithium Ion Battery Anode Performance

Porous tin oxide nanotubes were obtained by vacuum infiltration of tin oxide nanoparticles into porous aluminum oxide membranes, followed by calcination. The porous tin oxide nanotube arrays so prepared were characterized by FE-SEM, TEM, HRTEM, and XRD. The nanotubes are open-ended, highly ordered with uniform cross-sections, diameters and wall thickness. The tin oxide nanotubes were evaluated as a substitute anode material for the lithium ion batteries. The tin oxide nanotube anode could be charged and discharged repeatedly, retaining a specific capacity of 525 mAh/g after 80 cycles. This capacity is significantly higher than the theoretical capacity of commercial graphite anode (372 mAh/g) and the cyclability is outstanding for a tin based electrode. The cyclability and capacities of the tin oxide nanotubes were also higher than their building blocks of solid tin oxide nanoparticles. A few factors accounting for the good cycling performance and high capacity of tin oxide nanotubes are suggested.

Analysis of red and yellow ochre samples from Clearwell Caves and Catalhoyuk by vibrational spectroscopy and other techniques

Ochre samples excavated from the neolithic site at Qatalhoyuk, Turkey have been compared with "native" ochres from Clearwell Caves, UK using infrared spectroscopy backed up by Raman spectroscopy, scanning electron microscopy (with energy-dispersive X-rays (EDX) analysis), powder X-ray diffraction, diffuse reflection UV-Vis and atomic absorption spectroscopies. For the Clearwell Caves ochres, which range in colour from yellow-orange to red-brown, it is shown that the colour is related to the nature of the chromophore present and not to any differences in particle size. The darker red ochres contain predominantly haematite while the yellow ochre contains only goethite. The ochres from Qatalhoyuk contain only about one-twentieth of the levels of iron found in the Clearwell Caves ochres. The iron oxide pigment (haematite in all cases studied here) has been mixed with a soft lime plaster which also contains calcite and silicate (clay) minerals. (C) 2003 Elsevier B.V. All rights reserved.

Using aircraft measurements to determine the refractive index of Saharan dust during the DODO Experiments

Much uncertainty in the value of the imaginary part of the refractive index of mineral dust contributes to uncertainty in the radiative effect of mineral dust in the atmosphere. A synthesis of optical, chemical and physical in-situ aircraft measurements from the DODO experiments during February and August 2006 are used to calculate the refractive index mineral dust encountered over West Africa. Radiative transfer modeling and measurements of broadband shortwave irradiance at a range of altitudes are used to test and validate these calculations for a specific dust event on 23 August 2006 over Mauritania. Two techniques are used to determine the refractive index: firstly a method combining measurements of scattering, absorption, size distributions and Mie code simulations, and secondly a method using composition measured on filter samples to apportion the content of internally mixed quartz, calcite and iron oxide-clay aggregates, where the iron oxide is represented by either hematite or goethite and clay by either illite or kaolinite. The imaginary part of the refractive index at 550 nm (ni550) is found to range between 0.0001 i to 0.0046 i, and where filter samples are available, agreement between methods is found depending on mineral combination assumed. The refractive indices are also found to agree well with AERONET data where comparisons are possible. ni550 is found to vary with dust source, which is investigated with the NAME model for each case. The relationship between both size distribution and ni550 on the accumulation mode single scattering albedo at 550 nm (ω0550) are examined and size distribution is found to have no correlation to ω0550, while ni550 shows a strong linear relationship with ω0550. Radiative transfer modeling was performed with different models (Mie-derived refractive indices, but also filter sampling composition assuming both internal and external mixing). Our calculations indicate that Mie-derived values of ni550 and the externally mixed dust where the iron oxide-clay aggregate corresponds to the goethite-kaolinite combination result in the best agreement with irradiance measurements. The radiative effect of the dust is found to be very sensitive to the mineral combination (and hence refractive index) assumed, and to whether the dust is assumed to be internally or externally mixed.

Analysis of red and yellow ochre samples from Clearwell Caves and Catalhoyuk by vibrational spectroscopy and other techniques

Ochre samples excavated from the neolithic site at Qatalhoyuk, Turkey have been compared with "native" ochres from Clearwell Caves, UK using infrared spectroscopy backed up by Raman spectroscopy, scanning electron microscopy (with energy-dispersive X-rays (EDX) analysis), powder X-ray diffraction, diffuse reflection UV-Vis and atomic absorption spectroscopies. For the Clearwell Caves ochres, which range in colour from yellow-orange to red-brown, it is shown that the colour is related to the nature of the chromophore present and not to any differences in particle size. The darker red ochres contain predominantly haematite while the yellow ochre contains only goethite. The ochres from Qatalhoyuk contain only about one-twentieth of the levels of iron found in the Clearwell Caves ochres. The iron oxide pigment (haematite in all cases studied here) has been mixed with a soft lime plaster which also contains calcite and silicate (clay) minerals. (C) 2003 Elsevier B.V. All rights reserved.

Impact of gut passage and mucus secretion by the earthworm Lumbricus terrestris on mobility and speciation of arsenic in contaminated soil

Earthworms inhabiting arsenic contaminated soils may accelerate the leaching of As into surface and ground waters. We carried out three experiments to determine the impact of passage of As contaminated soil (1150 mgAs kg−1) through the gut of the earthworm Lumbricus terrestris on the mobility and speciation of As and the effects of earthworm mucus on As mobility. The concentration of water soluble As in soil increased (from 1.6 to 18 mg kg−1) after passage through the earthworm gut. Casts that were aged for 56 days still contained more than nine times greater water soluble As than bulk earthworm inhabited soil. Changes were due to increases in As(V) mobility, with no change in As(III). Dilute mucus extracts reduced As mobility through the formation of As-amino acid-iron oxide ternary complexes. More concentrated mucus extracts increased As mobility. These changes, together with those due to the passage through the gut, were due to increases in pH, phosphate and soluble organic carbon. The mobilisation of As from contaminated soils in the environment by cast production and mucus secretion may allow for accelerated leaching or uptake into biota which is underestimated when bulk soil samples are analysed and the influence of soil biota ignored.

Effects of calcining conditions on the microstructure of sugar cane waste ashes (SCWA): Influence in the pozzolanic activation

in this paper a study of calcining conditions on the microstructural features of sugar cane waste ash (SCWA) is carried out. For this purpose, some microparticles (< 90 mu m) of sugar cane straw ash and sugar cane bagasse ash of samples calcined at 800 degrees C and 1000 are studied by combining the bright field and the dark field images with the electron diffraction patterns in the transmission electron microscopy (TEM). It is appreciated that the morphology and texture of these microparticles change when silicon or calcium are present. Furthermore, it is observed that iron oxide (magnetite Fe(3)O(4)) is located in the calcium-rich particles. The microstructural information is correlated with the results of a kinetic-diffusive model that allows the computing of the kinetic parameters of the pozzolanic reaction (mainly the reaction rate constant). The results show that the sugar cane wastes ash calcined at 800 and 1000 degrees C have properties indicative of high pozzolanic activity. The X-ray diffraction patterns, the TEM images and the pozzolanic activity tests show the influence of different factors on the activation of these ashes. (c) 2008 Elsevier Ltd. All rights reserved.

An investigation of the activation process of high temperature shift catalyst

The aim of this work is to address the activation process of a high temperature shift (HTS) catalyst, composed of Fe2O3/Cr2O3/CuO, by analyzing it before activation (HTS-V) and after activation (HTS-A) using complementary characterization techniques. The textural and morphological characterizations were done by transmission electron rnicroscopy (TEM) and nitrogen physisorption at 77 K; crystallographic structure was confirmed by X-ray diffraction (XRD); electronic structure was analyzed by X-ray absorption spectroscopy (XAS) and the chemical composition of the catalyst`s surface was obtained by X-ray photoelectron spectroscopy (XPS). The investigation pointed out that the HTS-V catalyst presents good textural and morphological properties, which are not deeply affected by the activation process (sample HTS-A). The iron oxide phase in the HTS-V catalyst is hematite whereas in HTS-A catalyst is magnetite with Fe2+/Fe3+ ratio close to the expected value (0.5). For both samples, the Cr ions seem to be incorporated in the iron oxide lattice with higher concentration at particle surface. In the HTS-V catalyst, the Cu ions have oxidation number II and occupy in average distorted octahedral sites; after the activation, the Cu ions are partially reduced, suggesting that the reduction of the Cu species is complex. (C) 2007 Elsevier B.V. All rights reserved.

Contribuição ao beneficiamento de finos de fosfatos

Foram estudadas as características de floculação da hidro-xiapatita, calcita e quartzo com poliacrilamidas aniônicas. Tanto as suspensões de hidroxiapatita como a calcita foram completamente floculadas enquanto que o quartzo foi refratário a floculação com esses polimeros. Entretanto, observou-se que a floculação da calcita foi impedida com a utilização de um poliacrilato de sódio, enquanto que a hidroxiapatita continuou a ser floculada pela poliacrilamida num intervalo de concentração de O a 1000 g/ton de poliacrilato. Estes resultados permitiram estabelecer condições para a floculação seletiva de hidroxiapatita em misturas sintéticas com quartzo e calcita. Nestes sistemas foram estudados diversos parâmetros operacionais, tais como tipo de separação, efeito do teor da alimentação, e influência da moagem. Onde a separação estagiada apresentou melhor resultado, uma moagem adicional no sistema não favoreceu a seletividade. Por outro lado, o teor de P205 no concentrado é proporcional ao teor presente na alimentação. A hidroxiapatita, em estudo, de alta pureza (de acordo com técnicas de análise química, espectrofotometria de infravermelho e difração de raios X) apresentou um parto de carga zero em pH 6,77 na presença de diversos eletrólitos. A aplicação do sistema de floculação seletiva a fraçoes ultrafinas industriais foi estudada em detalhe e comparada com processos de flotação e floco-flatação. 0s resultados obtidos mostraram que a floculação seletiva somente foi eficiente nos sistemas sintéticos. A flotação, embora o minério apresente uma granulometria muito fina, foi mais eficiente que a floculação seletiva e a floco-flotação nos sistemas reais, em termos de taxa de enriquecimento e percentual de rejeição de massa. Entretanto com a floco-flotação foi possivel obter altas recuperações(-90%) para os minérios de Araxá e Itataia. Para o minério de Tapira, um aumento do teor de P2O5 foi obtido com a flotação da fração seletivamente floculada. As taxas de enriquecimento obtidas foram baixas (entre 1,35 e 2,101 em função das associações entre a apatita do minério com óxido de ferro e argila, o que revelou a caracterização mineralógica. Conclue-se que a concentração de minerios fosfatados de baixo teor é uma operação onerosa, onde o fator predominante é a absorção seletiva de reagentes e atransferência não específica de material de ganga nos respectivos concentrados.

Caracterização do concentrado de ilmenita produzido na Mina do Guaju, Paraíba, visando identificar inclusões de monazita e outros contaminantes

O presente estudo tem como proposta, identificar o modo como o mineral monazita se encontra no concentrado final de ilmenita. Este concentrado é o produto resultante do beneficiamento do minério extraído de depósitos do tipo pláceres, conhecidos como depósitos de areias pretas. Estes depósitos são formados por dunas litorâneas pertencentes à jazida do Guaju, no município de Mataraca-PB. Todo o processo de lavra e beneficiamento deste minério ocorre na Mina do Guaju, a qual é operada pela empresa Millennium Inorganic Chemicals do Brasil S/A, pertencente a Lyondell Chemical Company. A ilmenita é um mineral composto por óxido de ferro e titânio, FeTiO3. Quase toda a ilmenita produzida na mina é transferida para o processo de fabricação de pigmento. A exigência para o uso na fabricação de pigmento é de que o concentrado final de ilmenita tenha um teor mínimo de 53% de TiO2 e um teor máximo de 0,1% de P2O5, entre outras substâncias. A monazita é o principal mineral fonte de óxido de tório, que é radioativo. No processo de fabricação de pigmento, a monazita é um contaminante indesejado. De acordo com a proposta de trabalho, foi feito um estudo de caracterização mineralógica de amostras do concentrado final de ilmenita fornecidas pela empresa. Inicialmente foram feitas análises em lupa, onde muitos grãos de leucoxeno foram identificados. O leucoxeno é uma alteração da ilmenita que permanece com as mesmas características magnéticas e eletrostáticas, tornando impossível, assim, a sua separação no processo de concentração. Também foi verificada a existência de grãos de monazita liberados em pequenas quantidades neste concentrado, indicando uma provável ineficiência no processo de separação. Numa segunda etapa foram realizadas análises dos grãos de ilmenita com o uso de um Microscópio Eletrônico de Varredura (MEV) acoplado a um Espectrômetro de Dispersão de Energia (EDS), para permitir a determinação de elementos químicos na amostra. Esta análise teve como objetivo verificar a existência de inclusões de monazita nos grãos de ilmenita. Porém, o que se observou foi a existência de algumas inclusões de quartzo e de alguns vazios deixados, provavelmente, por inclusões arrancadas durante o processo de preparação das amostras. Alguns destes vazios apresentaram formas semelhantes a de cristais de monazita, indicando a possibilidade da existência de inclusões deste mineral. Entretanto, a quantidade de grãos com possíveis inclusões de monazita é muito pequena, sendo insignificante como contaminante do concentrado final. Embora alguns vazios se assemelhem à forma da monazita, nenhum dos resultados do EDS identificou vestígios de sua presença. Ao final deste estudo ficou evidente que a principal fonte de contaminação do concentrado final de ilmenita corresponde à monazita, a qual se encontra liberada neste concentrado. Desta forma, há a necessidade de se melhorar o processo de separação dos minerais, de modo que a quantidade de monazita no concentrado final seja a menor possível, não prejudicando o rendimento da recuperação de ilmenita.

Synthesis and characterization of lanthanum- and yttrium-doped Fe2O3 pigments

MELO, D. M. A. et al. Synthesis and charactezarion of lanthanum and yttrium doped Fe2O3 pigments. Cerâmica, São Paulo, v. 53, p. 79-82, 2007.