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Nanomatériaux pour applications thermoélectriques / Nanomatetials for thermoelectric applicationsVo, Thi Thanh Xuan 17 September 2015 (has links)
Les nano-composés de type Sn1-xTaxO2 (0 ≤ x ≤ 0,03) ont été étudiés en vue de leurs propriétés thermoélectriques. Une méthode de co-précipitation a été utilisée pour synthétiser des nano-poudres ayant une taille des grains moyenne d’environ 3 nm. L’étude structurale et microstructurale a suggéré une limite de solubilité pour le Ta de 0,008 ≤ x < 0,010. Ces nano-poudres ont été ensuite densifiées par Spark Plasma Sintering, avec des compacités atteignant ~ 95%. Le dopage en Ta a permis une amélioration des propriétés thermoélectriques du SnO2 et, en accord avec la limite de solubilité, une valeur maximale du facteur de mérite de 4,7x10-5 K-1 a été observée pour l’échantillon x = 0,008. De plus, nous avons démontré qu’une diminution de la taille des grains permettait d’améliorer le coefficient Seebeck, de diminuer la conductivité thermique, mais conduisait à une diminution de la conductivité électrique. La stabilité des oxydes, notamment à l'échelle nanométrique, est remise en question par des caractérisations physico-chimiques. Partant de ces matériaux à base de SnO2, un nano-composite (ZnO-SnO2) a été étudié. Le composé Zn1-xGdxO (0 ≤ x ≤ 0,03) a été préparé par la méthode de Péchini et caractérisé en comparant avec d’autres matériaux à base de ZnO. Un premier test de nano-composite M30 (30% en masse Sn0.996Ta0.004O2 et 70% en masse Zn0.997Gd0.003O) a été mené. Le résultat obtenu a montré qu’une concentration de nano-inclusion Sn0.996Ta0.004O2 de 30 % ne permettait pas d’améliorer les propriétés thermoélectriques du nano-composite M30, par rapport aux matériaux de départ. / The nano-compound Sn1-xTaxO2 (0 ≤ x ≤ 0.03) was studied with a view to their thermoelectric properties. A method of co-precipitation was used to synthesize nano-powders having an average grain size of about 3 nm. The structural and microstructural study suggested a solid solubility limit of 0.008 ≤ x < 0.010. These nano-powders were then densified by Spark Plasma Sintering, with density reaching ~ 95%. The doping of Ta improved the thermoelectric properties, and in good agreement with the solubility limit, a maximum value of the factor of merit of 4.7x10-5 K-1 was observed for the sample x = 0.008. The stability of oxides, particularly at the nanoscale, is questioned by physicochemical characterizations. From these SnO2-based materials, a nano-composite (ZnO-SnO2) was studied. The compound Zn1-xGdxO (0 ≤ x ≤ 0.03) was prepared by the method of Pechini and characterized by comparing with other ZnO-based materials. A first test of nano-composite M30 (30 wt% Sn0.996Ta0.004O2 and 70 wt% Zn0.997Gd0.003O) was conducted. The result showed that a concentration of 30% nano-inclusion Sn0.996Ta0.004O2 did not allow to improve the thermoelectric properties of nano-composite M30, compared to the starting materials.
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Biocatalytic Production, Preparation and Characterization of Large-ring CyclodextrinsMokhtar, Mohd Noriznan 26 January 2009 (has links)
Cyclodextrins (CD) are cyclic oligosaccharides composed of six to more than sixty
glucose units. Large-ring cyclodextrins (LR-CD) are novel CD comprised of more than eight
glucose units with cavity structures and sizes different from that of commercially available
CD<sub>6</sub> – CD<sub>8</sub>. LR-CD may offer unique molecular recognition properties and can be produced
biocatalytically from starch using cyclodextrin glucanotransferase (CGTase, E.C. 2.4.1.19) in
a short reaction time. LR-CD were isolated from glucose, CD<sub>6</sub> – CD<sub>8</sub> and other compounds by
complexation of CD<sub>6</sub> – CD<sub>8</sub> as well as precipitation techniques. The yield of LR-CD (degree
of polymerization from 9 to 21) was optimized using central composite design. Addition of
polar organic solvents to the synthesis resulted in higher yields of LR-CD. LR-CD composed
of 9 to 21 glucose units were successfully separated using reversed-phase of ODS-AQ
chromatography and normal-phase of polyamine II chromatography. Maintaining optimized
reaction conditions aided in a high yield of CD<sub>9</sub>; it could be separated with reasonable yield
using a single step of polyamine II chromatography. A co-grinding method helped to obtain
higher solubilization levels of glibenclamide, vitamin A acetate and vitamin D<sub>3</sub> in CD<sub>13</sub>, CD<sub>10</sub>
and CD<sub>11</sub>, respectively when compared to other CD. Vitamin K<sub>1</sub> was solubilized in distilled
water with CD<sub>6</sub> – CD<sub>13</sub> using a co-precipitation method. When compared with other CD, CD<sub>9</sub>
was seen to be the best solubilizer. The analysis of complexes using ESI MS showed
spironolactone and glibenclamide complexed with CD<sub>9</sub> and CD<sub>13</sub>, respectively.
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[en] PRODUCTION AND CHARACTERIZATION OF MAGNETITE STRUCTURES: NANOPARTICLES, THIN FILMS AND LITHOGRAPHED ARRAYS / [pt] PRODUÇÃO E CARACTERIZAÇÃO DE ESTRUTURAS DE MAGNETITA: NANOPARTÍCULAS, FILMES FINOS E PADRÕES LITOGRAFADOSGERONIMO PEREZ 29 October 2021 (has links)
[pt] Este trabalho pode ser dividido em três etapas principais: síntese das nanopartículas, deposição de filmes finos e litografia por feixe de elétrons. As nanopartículas magnéticas foram sintetizadas pelo método de co-precipitação a partir de sulfato de ferro II (FeSO4), cloreto férrico (FeCl3) e hidróxido de amônia (NH4OH) à temperatura ambiente. Para prevenir a formação de agregados, foi adicionado nitrato de sódio (NaNO3) em pequenas quantidades, que se mostrou bastante eficiente. Em seguida foram produzidos filmes de magnetita utilizando o sistema de pulverização catódica usando fonte de radiofrequência (sputtering RF). Os alvos foram produzidos por compactação das nanopartículas de magnetita produzidas anteriormente. Os filmes finos foram depositados em substrato de silício. A formação de magnetita durante a deposição foi confirmada por difração de raios-x e magnetômetro de amostra vibrante. Uma vez controlados os parâmetros de deposição, foram produzidos arranjos de magnetita. A litografia por feixe de elétrons foi produzida em substrato de silício recoberto com máscara de PMMA (polimetilmetacrilato) de 250 nm de espessura. Foram produzidos arranjos periódicos de formas básicas a modo de testar a técnica de litografia: quadrados de 1 μm e círculos de 1 μm, 500 nm e 250 nm de diâmetro formados de um filme de magnetita de 80 nm de espessura. A espessura do filme, forma, tamanho e separação das figuras que compõem os padrões litografados influenciam na facilidade com que será retirada a mascara de PMMA. / [en] This work can be divided into three main steps: synthesis of nanoparticles, thin film deposition and electron beam lithography. The magnetic nanoparticles were synthesized by co-precipitation method from iron II sulfate (FeSO4), ferric chloride (FeCl3) and ammonium hydroxide (NH4OH) at room temperature. A small amount of sodium nitrate (NaNO3) was added to avoid the cluster formation, which was very efficient. Then the magnetite thin films were produced using the sputtering RF (radio frequency source) system. The targets were produced by compression of magnetite nanoparticles previously produced in the first step. The thin films were deposited on a silicon substrate. The formation of the magnetite after the deposition was confirmed by x-ray diffraction and vibrating sample magnetometer. The arrays of magnetite were made once the deposition parameters were controlled. The electron beam lithography has been produced on silicon substrate covered of PMMA (polymethylmethacrylate) resist 250 nm thick. Were produced periodic arrays of basic forms a way to test the technique of lithography, a square micron circles 1 μm, 500 nm and 250 nm in diameter formed of a magnetite film 80 nm thick. The film thickness, shape, size and separation of the figures which comprise standards lithographed can influence the ease with which the mask is withdrawn from PMMA.
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