Le plutonium est produit dans les centrales nucléaires à partir de l’oxyde d’uranium utilisé comme combustible. Cet élément peut être détecté dans l’environnement du fait des essais nucléaires, accidents industriels, sous-marins nucléaires et déchets radioactifs. Le Pu peut ainsi être dispersé sous la forme de particules présentant différentes compositions chimiques et morphologiques, et plus particulièrement sous la forme colloïdale. La connaissance de la structure et de la réactivité de ces espèces s’avère primordiale pour la compréhension et la prédiction de leur éventuelle migration dans l’environnement. Dans ce contexte, la sonochimie est envisagée comme voie de synthèse innovante pour la préparation de suspensions colloïdales modèles de Pu. Dans un premier temps, les cinétiques de formation sonochimique de H2O2 dans l’eau pure et l’acide nitrique ont été étudiées en prévision des expérimentations en présence de Pu. L’étude du comportement du Pu(VI) en solution aqueuse sous ultrasons a, par la suite, permis de préparer des solutions de Pu(V) relativement pures et stables qui ont pu être rigoureusement caractérisées (XAFS, RMN, DFT, UV-vis, etc.). Par ailleurs, la sonolyse de solutions aqueuses de Pu(III) conduit à la formation d’un complexe polynucléaire de Pu(IV) hydrosoluble jamais reporté dans la littérature. Enfin, les études réalisées en milieu hétérogène solide-liquide ont permis de développer une voie de synthèse de colloïdes de Pu intrinsèques. Les colloïdes formés par sonolyse de PuO2 dans l’eau pure ont été comparés à des colloïdes hydrolytiques et autoradiolytiques à l’aide de nombreuses techniques de caractérisation (MET-HR, XAFS, STXM, NEXAFS, etc.). Le mécanisme de formation proposé implique la dispersion et la réduction de taille des particules d’oxyde suivi, de mécanismes rédox permettant l’accumulation de colloïdes. Les observations permettent de décrire ces colloïdes comme des particules nanométriques quasi-sphériques (7 nm sous ultrasons, contre 3 nm par hydrolyse) et monodisperses présentant une structure de type cœur/coquille composée d’un cœur de PuO2 cristallin et d’une surface de Pu(IV) hydrolysé. / Plutonium is a radioactive chemical element produced in nuclear power plants by uranium oxide fission reactions. This element has been found in the environment due to, for example, nuclear weapon testing, nuclear submarines and radioactive accidents. Pu has been dispersed under particle forms with various chemical compositions and morphologies and can potentially migrate under colloidal forms. The knowledge of the structure and reactivity of this species is of paramount importance to understand and predict their eventual migration into the environment. In this context, sonochemistry is considered as an innovative approach for the preparation of pattern Pu colloid suspensions. First, sonochemical kinetic formations of H2O2 in pure water and nitric media have been studied in prevision of experimentations with Pu. Pu(VI) behavior in sonicated aqueous solution has then been investigated for the preparation of relatively pure and stable Pu(V) solutions which have been rigorously characterized (XAFS, NMR, DFT, UV-vis, etc.). Besides, sonication of Pu(III) aqueous solutions lead to the formation of a hydrosoluble polynuclear complex of Pu(IV) never reported in the literature. Studies carried out in heterogeneous solid/liquid systems allowed to develop a synthesis method for the preparation of Pu intrinsic colloids. Colloids resulting from PuO2 sonolysis in pure water have been compared to hydrolytic and autoradiolytic colloids thanks to several characterization techniques (HR-TEM, XAFS, STXM, NEXAFS, etc.). The proposed formation mechanisms involves the dispersion and reduction of oxide particle sizes followed by redox reactions leading to accumulation of Pu colloids. Colloids can be described as quasi-spherical, monodisperse and nanometric particles (7 nm under ultrasound against 3 nm for hydrolysis) with a core/shell structure composed of a crystalline PuO2 core covered by a hydrolyzed Pu(IV) surface.

Orientador: João Sinézio de Carvalho Campos / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T04:59:19Z (GMT). No. of bitstreams: 1 RicchiJunior_ReinaldoAlberto_D.pdf: 3389529 bytes, checksum: 30c41e1272f73cf9094e8b6aac68ea93 (MD5) Previous issue date: 2013 / Resumo: A versatilidade do polifluoreto de vinilideno (PVDF) abriu um grande número de possibilidades de pesquisa para este trabalho. Após uma completa revisão bibliográfica sobre as aplicações deste material, o transdutor ultrassônico de PVDF, acoplado a um reator e a um microreator do elastômero polidimetilsiloxano (PDMS), foi o sistema escolhido para esta tese. Tal sistema acelerou reações de Morita-Baylis-Hillman (MBH). O primeiro teste foi realizado em um reator "macroscópico" de PDMS para analisar o comportamento da reação MBH com este material. Em seguida, após o aprofundamento dos estudos, foi realizada uma reação MBH no interior do microreator, também de PDMS, e os resultados mostraram que o fenômeno de cavitação é significativamente maior neste caso, abrindo perspectivas para trabalhos futuros. Análises de espectroscopia de ressonância magnética nuclear (RMN) e de cromatografia gasosa (CG) comprovaram a eficácia do transdutor ultrassônico. Também foram fabricadas microestruturas de PVDF pela técnica de Litografia Macia por um novo processo, abrindo novas perspectivas de pesquisa / Abstract: The versatility of polyvinylidene fluoride (PVDF) has opened a lot of possibilities for this research work. After a literature review about the applications of this material, the PVDF ultrasonic transducer coupled to a reactor and a microreactor of the elastomer polydimethylsiloxane (PDMS) was the system chosen for this thesis. Such system has accelerated reactions Morita-Baylis-Hillman (MBH). The first test was conducted in a "macroscopic" PDMS reactor to analyze the behavior of the MBH reaction with this material. Then, after further studies, the MBH reaction was performed inside the microreactor, also of PDMS, and the results showed that the phenomenon of cavitation is significantly higher in this case, opening perspectives for future work. Analysis of nuclear magnetic resonance spectroscopy (NMR) and gas chromatography (GC) demonstrated the effectiveness of the ultrasonic transducer. PVDF microstructures were also fabricated by Soft Lithography by a new process, opening new perspectives of research / Doutorado / Ciencia e Tecnologia de Materiais / Doutor em Engenharia Química

Yes / Sonochemistry, i.e., the application of mechanical energy in the form of sound waves, has recently been recognised for its similarity to mechanochemistry and is now included under the umbrella term of mechanochemistry. Typically, due to the hypothesised cavitation mechanism, a liquid medium is considered as a necessity for a process to take place as a result of ultrasonic irradiation. In view of this, condensation reactions between solid reagents in the complete absence of solvent were carried out successfully by ultrasonic irradiation with the importance of particle size being highlighted. This work increases the potential of sonochemistry in the drive towards a sustainable future. / EPSRC (EP/L019655/1)

Contrairement aux effluents aqueux issus du procédé PUREX, les effluents issus des procédés de séparation poussée actuellement en développement pour séparer les actinides mineurs contiennent des réactifs organiques en quantité importante. Afin de minimiser l'impact de ces composés sur les étapes en aval du procédé et pour respecter les normes de rejet, la destruction de ces composés est indispensable. De par des conditions opératoires et de sûreté adaptées au domaine du nucléaire, la voie sonochimique apparaît comme une solution très prometteuse pour l'élimination des espèces organiques. La propagation d'une onde ultrasonore dans un milieu liquide se traduit par l'apparition de bulles de cavitation qui vont croître et imploser, engendrant ainsi des conditions locales de température et pression extrêmes. Chaque bulle de cavitation peut être alors considérée comme un microréacteur à haute température et haute pression capable de détruire, sans ajout de réactifs spécifiques, les molécules organiques. Les premières études portant sur l'influence de la fréquence ultrasonore sur la sonolyse et la sonoluminescence de l'acide formique ont montré que la dégradation de l'acide formique se déroule à l'interface liquide/bulle quelle que soit la fréquence ultrasonore. La différence notable entre les ultrasons basse et haute fréquence réside principalement dans l'initiation de réactions secondaires observées seulement entre 200 et 1057 kHz. Malgré une activité sonochimique bien plus importante à haute fréquence, l'utilisation des ultrasons seuls pour traiter les effluents issus des procédés de séparation avancée ne peut être envisagée de par la concentration élevée en acides carboxyliques. Afin d'augmenter l'efficacité des réactions sonochimiques, l'ajout de catalyseurs à base de platine supporté a donc été étudié. Dans ces conditions, il s'avère que le couplage ultrasons/catalyseurs permet une augmentation considérable des cinétiques de dégradation des acides carboxyliques. / Unlike aqueous effluents from the PUREX process, aqueous effluents from advanced separation processes developed to separate the minor actinides (Am, Cm) contain organic reagents in large amounts. To minimize the impact of these organic compounds on the next steps of the process, and to respect standard discharges, it is necessary to develop new techniques of degradation of organic compounds. Sonochemistry appears as a very promising solution to eliminate organic species in aqueous nuclear effluents. Indeed, the propagation of an ultrasonic wave in a liquid medium induces the appearance of cavitation bubbles which will quickly grow and implode, causing local conditions and extreme temperatures and pressures. Each cavitation bubble can then be considered as a microreactor at high temperature and high pressure able to destroy organic molecules without the addition of specific reagents. The first studies on the effect of ultrasonic frequency on sonoluminescence and sonolysis of formic acid have shown that the degradation of formic acid occurs at the bubble/liquid interface. The most striking difference between low-frequency and high-frequency ultrasound is that the sonolysis of HCOOH at high ultrasonic frequencies initiates secondary reactions not observed at 20 kHz. However, despite a much higher sonochemical activity at high frequency, highly concentrated carboxylic acids in the aqueous effluents from advanced separation processes cannot be destroyed by ultrasound alone. To increase the efficiency of sonochemical reactions, the addition of supported platinum catalysts has been studied. In these conditions, an increase of the kinetics of destruction of carboxylic acids such as oxalic acid is observed.

A tecnologia de nanocompósitos é aplicável a uma vasta gama de polímeros termoplásticos e termofixos. A utilização de subprodutos da cana de açúcar tem sido extensivamente estudada como fonte de reforços para os nanocompósitos. O bagaço da cana é largamente utilizado na cogeração de energia e, como resultado da queima deste material, são produzidas milhões de toneladas de cinzas. Para este trabalho, sílica contida nas cinzas do bagaço da cana de açúcar foi extraída por método químico e método térmico. O método térmico se mostrou mais eficiente levando a uma pureza de mais de 93 % em sílica, enquanto o método químico gerou sílica bastante contaminada com cloro e sódio provenientes dos reagentes da extração. As partículas de sílica obtidas foram avaliadas por espalhamento de luz dinâmico (DSL) e apresentaram tamanho médio de 12 μm. Estas partículas foram submetidas à moagem em moinho de bolas e na sequência a tratamento sonoquímico em meio líquido. As partículas de sílica tratadas no processo sonoquímico a 20 kHz, potência de 500 W e 90 minutos tiveram suas dimensões reduzidas a escala nanométrica da ordem de dezenas de nanômetros. A nanossílica obtida foi então incorporada como reforço em polietileno de alta densidade (HDPE). Ensaios mecânicos e termo-mecânicos mostram ganhos de propriedades mecânicas, com exceção da propriedade de resistência ao impacto. O ensaio de deflexão térmica (HDT) mostrou que a incorporação deste reforço no HDPE levou a um pequeno aumento nesta propriedade relação ao HDPE puro. A cristalinidade dos nanocompósitos gerados foi avaliada por meio de calorimetria exploratória diferencial (DSC) e observou-se um decréscimo de cristalinidade do material quando a incorporação de reforço foi de 3%. O material irradiado a 250 kGy com feixe de elétrons mostra ganhos acentuados na principais propriedades do mesmo, principalmente devido ao alto nível de reticulação do HDPE irradiado. / The nanocomposite technology is applicable to a wide range of thermoplastic and thermoset polymers. The use of sugar cane byproducts has been extensively studied as a source of reinforcement for nanocomposites. The bagasse is widely used in cogeneration and as a result of the burning of this material, millions of tons of ash are produced. For this work, silica contained in the ashes of bagasse from sugarcane was extracted by chemical method and thermal method. The thermal method is more efficient leading to a purity of more than 93% of silica, while the chemical method generated silica contaminated with chlorine and sodium from the extraction reagents. The silica particles obtained were evaluated by dynamic light scattering (DSL) and presented an average size of 12 micrometers. These particles were submitted to grinding in a ball mill and then to a sonochemical treatment. Silica particles treated by the sonochemical process ( 20 kHz, 500 W and 90 minutes) had its dimensions reduced to nanometric scale of tenths of nanometers. The nanossílica obtained was then used as reinforcement in high density polyethylene (HDPE). Mechanical and thermo-mechanical properties were assessed and gains were shown for mechanical properties , except for the impact resistance. The distortion temperature (HDT) showed that the incorporation of the reinforcement in HDPE led to a small increase in this property compared to pure HDPE. The crystallinity of the nanocomposites generated was evaluated by differential scanning calorimetry (DSC) and it was observed a decrease of crystallinity in the material when the reinforcing incorporation was 3%. The material irradiated to 250 kGy with electron beam showed important property gains, mainly due to the high level of crosslinking of irradiated HDPE.

A tecnologia de nanocompósitos é aplicável a uma vasta gama de polímeros termoplásticos e termofixos. A utilização de subprodutos da cana de açúcar tem sido extensivamente estudada como fonte de reforços para os nanocompósitos. O bagaço da cana é largamente utilizado na cogeração de energia e, como resultado da queima deste material, são produzidas milhões de toneladas de cinzas. Para este trabalho, sílica contida nas cinzas do bagaço da cana de açúcar foi extraída por método químico e método térmico. O método térmico se mostrou mais eficiente levando a uma pureza de mais de 93 % em sílica, enquanto o método químico gerou sílica bastante contaminada com cloro e sódio provenientes dos reagentes da extração. As partículas de sílica obtidas foram avaliadas por espalhamento de luz dinâmico (DSL) e apresentaram tamanho médio de 12 μm. Estas partículas foram submetidas à moagem em moinho de bolas e na sequência a tratamento sonoquímico em meio líquido. As partículas de sílica tratadas no processo sonoquímico a 20 kHz, potência de 500 W e 90 minutos tiveram suas dimensões reduzidas a escala nanométrica da ordem de dezenas de nanômetros. A nanossílica obtida foi então incorporada como reforço em polietileno de alta densidade (HDPE). Ensaios mecânicos e termo-mecânicos mostram ganhos de propriedades mecânicas, com exceção da propriedade de resistência ao impacto. O ensaio de deflexão térmica (HDT) mostrou que a incorporação deste reforço no HDPE levou a um pequeno aumento nesta propriedade relação ao HDPE puro. A cristalinidade dos nanocompósitos gerados foi avaliada por meio de calorimetria exploratória diferencial (DSC) e observou-se um decréscimo de cristalinidade do material quando a incorporação de reforço foi de 3%. O material irradiado a 250 kGy com feixe de elétrons mostra ganhos acentuados na principais propriedades do mesmo, principalmente devido ao alto nível de reticulação do HDPE irradiado. / The nanocomposite technology is applicable to a wide range of thermoplastic and thermoset polymers. The use of sugar cane byproducts has been extensively studied as a source of reinforcement for nanocomposites. The bagasse is widely used in cogeneration and as a result of the burning of this material, millions of tons of ash are produced. For this work, silica contained in the ashes of bagasse from sugarcane was extracted by chemical method and thermal method. The thermal method is more efficient leading to a purity of more than 93% of silica, while the chemical method generated silica contaminated with chlorine and sodium from the extraction reagents. The silica particles obtained were evaluated by dynamic light scattering (DSL) and presented an average size of 12 micrometers. These particles were submitted to grinding in a ball mill and then to a sonochemical treatment. Silica particles treated by the sonochemical process ( 20 kHz, 500 W and 90 minutes) had its dimensions reduced to nanometric scale of tenths of nanometers. The nanossílica obtained was then used as reinforcement in high density polyethylene (HDPE). Mechanical and thermo-mechanical properties were assessed and gains were shown for mechanical properties , except for the impact resistance. The distortion temperature (HDT) showed that the incorporation of the reinforcement in HDPE led to a small increase in this property compared to pure HDPE. The crystallinity of the nanocomposites generated was evaluated by differential scanning calorimetry (DSC) and it was observed a decrease of crystallinity in the material when the reinforcing incorporation was 3%. The material irradiated to 250 kGy with electron beam showed important property gains, mainly due to the high level of crosslinking of irradiated HDPE.

This research exploits mild sonication in a thin layer electrochemical cell to enhance rates of reaction in systems under voltammetric perturbation. Sound waves propagate through a thin layer of condensed fluid to provide energy to the electrode solution interface in the form of pressure and temperature. The sonic energy provided in three dimensions can be exploited to enhance rates of heterogeneous electron transfer as the energy is harnessed at the two dimensional electrode interface. Enhanced rates of heterogeneous electron transfer are of interest both for fundamental reasons and for exploitation in electrochemical energy systems. The initial pilot studies were directed at demonstrating the impact of acoustic energy on heterogenous electron transfer. Redox couples with different electron transfer rates were evaluated. Whereas compounds with reversible electron transfer kinetics demonstrated little improvement, redox couples such as ferric ion (Fe3+) with slow electron transfer kinetics exhibited an increase in the standard heterogeneous electron transfer rate constant, k0 with an increase in acoustic energy. The reduction of oxygen is a complex four proton, four electron process that is of technological importance. Slow kinetics of the oxygen reduction is a primary loss of efficiency in electrochemical power sources. Much like the ferric ion, oxygen kinetic rats improve. Preliminary studies in the oxidation of methanol demonstrated a sonocatalyic effect in methanol electrolysis that is of particular interest for the development of liquid based fuel cells. Sonication can both clean and destroy surface materials. The cleaning power inherent in sonication improves electrocatalysis and removes deposits and oxides from the electrode surface.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 167-174).

This century has seen a phenomenal growth in energy demands and environmental pollution, which has given rise to a worldwide awareness for the need to address these issues immediately. / This thesis focuses on the fabrication of high performance electrocatalysts applied in fuel cells and developing appropriate advanced oxidation processes for environmental remediation. It has been shown that ultrasonic irradiation is a promising method of synthesizing nanometre sized metal colloids with specific properties. Sonophotocatalysis has proved to be an effective process for the degradation of organic pollutants / The synthesis of platinum monometallic and platinum-ruthenium bimetallic nanoparticles was successfully achieved by using sonochemical irradiation. A chemical method and a hybrid method were used to reveal and understand the process of Ru(III) reduction by sonochemistry. TEM images of the Pt and PtRu monometallic/bimetallic particles indicate typical diameters of less than 10 nm. An effort was made to investigate the influence of two different methods, namely simultaneous and sequential sonochemical reduction, on the structure and formation of PtRu bimetallic nanoparticles. It has been shown that the sequential reduction method produces a relatively higher yield of core-shell nanoparticles than the simultaneous reduction method. It has been concluded that Pt nanoparticles, which are formed first, play an important role in catalysing the formation of Ru nanoparticles. / A number of methods including chemical, sonochemical and radiolytic synthesis were used to fabricate platinum and platinum-ruthenium monometallic/bimetallic nanoparticles. Furthermore, the evaluation of the electrocatalytic performance of these particles was performed by using cyclic voltammetry. Simultaneous and sequential methods for the synthesis of PtRu were adopted to investigate their influence on the electrocatalytic performance of these bimetallic nanoparticles. thas been shown that simultaneous reduction is an effective means of fabricating high performance electrocatalytic PtRu catalysts. A number of experiments with different ratios of platinum to ruthenium ions in precursor solution were carried out to study the effect of the ruthenium composition in platinum-ruthenium electrodes. It has been found that the methanol oxidation ability of platinum-ruthenium bimetallic nanoparticles can change with the alternation of ratio of Pt(II) to Ru(III) in the precursor solution. Simultaneous radiolytic reduction has the potential to fabricate higher performance electrocatalytic bimetallic nanoparticles. / Although both photo-oxidation and sono-oxidation techniques are fascinating solutions to the environmental problems at hand, the critical limit of these individual processes is their low efficiency of environmental remediation. In my project, sonolysis and photocatalysis (sonophotocatalysis) have been simultaneously employed to degrade selective organic pollutants in aqueous environments, such as methyl orange, p-chlorobenzoic acid, p-aminobenzoic acid and p-hydroxybenzoic acid. Experiments have been carried out in order to improve the efficiency of sonophotocatalytic reactions to ensure that a substantial amount of the electrical energy is utilized in degrading the organic pollutants. / Methyl orange, an azo dye, was selected as the degradation target for sonophotocatalysis. An orthogonal array analysis method was employed to clarify the correlation between the efficiencies of sonolysis, photocatalysis and sonophotocatalysis and the various operation conditions studied. Emphasis was placed on investigating the influence of pH and the ultrasound parameters on these three advanced oxidation processes. It was of interest to find that the degradation of methyl orange originates from hydroxylation and demethylation processes preceding aromatic ring-opening. / Sonophotocatalysis was also applied in the degradation of three aromatic carboxylic acids, p-chlorobenzoic acid, p-hydroxybenzoic acid and p-aminobenzoic acid. Experiments were carried out in order to get a thorough understanding of the synergy effects produced by combining the two oxidation techniques. A number of advanced analytical techniques, such as HPLC and Q-TOF MS/LC, were employed to comprehensively monitor and analyse the sonophotocatalytic degradation process. It has been found that synergistic effects of the combined system have been identified with respect to the parent organic pollutant as well as its degradation products. Additionally, products were quantitatively analysed by a kinetic simulation method in order to understand the reaction mechanism. This method also allowed us to quantify the synergy effects. It was observed that the solution pH played a key role in determining the degradation rate and controlling the direction of the degradation reaction. Based on the analytical data gathered, the sonophotocatalytic degradation pathway of the aromatic carboxylic acids was established. The experimental results suggest that the sonophotocatalytic technique is likely to lead to a complete mineralization of organic pollutants in aqueous solutions.

Thesis (M.S.)--Baylor University, 2008. / Includes bibliographical references (p. 63-64).