Global ETD Search

1	Development of a silica scaling test rig. Sinclair, Luke Alexander January 2012 (has links) One of the most significant problems faced in the geothermal power industry is that of scaling due to amorphous silica. The silica can deposit out of super-saturated brine in monomeric form and as colloidal particles. Deposition can occur at problematic rates on pipe surfaces and in the rocks of the re-injection wells. Currently there are a number of methods for controlling deposition but the fundamental mechanisms that govern the transport and attachment of silica are not well understood. Many field experiments on silica scaling have been conducted but, due to differences in brine chemistry and operational conditions, the results are hard to compare. Many laboratory experiments have also been performed but these are difficult to correlate with the field experiments. Previous research has found that hydrodynamics are important for the deposition of colloidal particles and inertial impaction was proposed to be the dominant transport mechanism. These results were analysed and, in contradiction, the dominant transport mechanism of the particles was theoretically expected to be that of diffusion. A series of experiments were planned that could test the effect of hydrodynamics on colloidal silica deposition in cylindrical pipe flow. Three parameters were to be varied in the experiment: particle size (10nm and 100nm), Reynolds number (750 - 23,600) and viscous boundary layer thickness (0.06 - 0.38mm). To perform this experimentation, a Silica Scaling Test Rig was designed, built and commissioned. A method for producing synthetic brine was developed which can provide sols that are stable for at least one month and have a particle size of 10-20nm. Silica deposition has successfully been obtained in three preliminary experiments using the rig. Without the exclusion of air from the rig significant corrosion occurs in the mild steel test piece. Protrusions that were likely to be silica deposits were found to be co-located with the corrosion, suggesting that one process promotes the other. Neither deposition nor corrosion was found on the pipe’s weld seam and heat affected zone. Corrosion was prevented using an oxygen exclusion system and two amorphous silica deposition structures were observed: a flat plate-like structure and a globular structure that consisted of 1-5μm diameter globules that built up on each other. Other field and laboratory experiments have produced globular structures similar to those found in this research. To perform the planned experimentation, future work is required: the silica deposition rate must be increased, colloidal silica sol stability must be improved, and some modifications must be made to the rig. Silica deposition colloidal silica hydrodynamics
2	Morphogenesis and Protein Composition of Valve Silica Deposition Vesicles from Diatoms Heintze, Christoph 05 April 2022 (has links) The silica-based cell walls of diatoms are outstanding examples of nature’s capability to synthesize complex porous structures with genetically controlled patterns from the nanometer scale to the range of hundreds of micrometers. Formation of the cell wall building blocks (valves and girdle bands) occurs in membrane-bound compartments, termed silica deposition vesicles (SDVs), which are unique organelles in silica-forming protists. Isolation of the SDVs has not yet been achieved, which has severely hampered the efforts to understand the mechanisms of biological silica morphogenesis. The present thesis aimed to address this shortcoming. The foundation was the development of an improved cell cycle synchronization and a fluorescence labeling method for the model diatom Thalassiosira pseudonana that enabled rapid identification of valve SDVs in a cell lysate. Correlative fluorescence and electron microscopy allowed visualizing the development of valve silica with unprecedented spatio-temporal resolution. Elemental analysis and demineralization of immature valves provided the first direct chemical evidence that silica morphogenesis is an interplay of inorganic and organic molecules inside the valve SDVs. Cryo TEM imaging of valve SDVs indicated the formation of organic patterns that precede silica depostion. From these observations, an organic biomolecule dependent, liquid-liquid phase separation based model for pore formation in the diatom T. pseudonana was proposed. The second part of this thesis was focused on the enrichment of valve SDVs from T. pseudonana and the subsequent proteomics based identification of more than 40 potential valve SDV proteins. Among these, three diatom-specific proteins contained conserved protein protein interaction domains (ankyrin-repeats) and were surprisingly predicted to be located in the cytoplasm. The fluorescent tagging of the three proteins (termed dANK1-3) confirmed their association with the valve SDVs. When the respective dank genes were knocked out by CRISPR/Cas9, the valves displayed permanent anomalies in the quantity and the pattern of ~22 nm sized pores. Double knockout mutants lacking both dank1 and dank3 were almost completely devoid of pores. The analysis of valve morphogenesis in the single and double knockout mutants revealed phenotypic changes that were consistent with the liquid-liquid phase separation based model for pore pattern formation in diatom biosilica. The work of this thesis has provided for the first time direct access to valve SDVs, which has opened entirely new possibilities for studying the composition, properties, and working mechanism of an organelle that forms a complex shaped mineral. info:eu-repo/classification/ddc/570 ddc:570
3	Modification électrochimique de l'interface liquide - liquide avec de la silice mésoporeuse / Electrochemical modification of the liquid - liquid interface with mesoporous silica Poltorak, Lukasz 25 September 2015 (has links) Ce travail combine l'électrochimie à l'interface liquide - liquide avec le procédé sol - gel pour la modification interfaciale avec de la silice mésoporeuse. Dans la première partie de ce travail, l’interface liquide – liquide macroscopique a été utilisée pour séparer la solution aqueuse de l'espèce de précurseur de silice hydrolysées (tétraéthoxysilane (TEOS)) de l'agent tensioactif cationique (cethyltrimethylammonium (CTA+) qui a agi comme un template et a été dissous dans le dichloroéthane. Le dépôt de matériau de silice a été déclenchée par le transfert du CTA+ à partir de la phase organique vers la phase aqueuse. CTA+ qui a transféré à la phase aqueuse a catalysé la réaction de condensation de la silice sur l’interface liquide – liquide. Le dépôt de silice à des interfaces liquide – liquide miniaturisées était la deuxième partie de ce travail. Les dépôts stables sur le côté de l'interface ont été synthétisés in situ par voie électrochimique. La stabilité mécanique des dépôts de silice permis un traitement thermique de la silice. Basé sur les techniques d’imagerie (par exemple SEM) il a été constaté que les dépôts forment des hémisphères pour des temps plus long. La réaction interfaciale a également été suivie in situ par spectroscopie Raman confocale. Caractéristiques moléculaires de l'interface ont été modifiées de manière spectaculaire une fois les espèces CTA+ ont été transférés à la phase aqueuse. Les interfaces liquide – liquide miniaturisés et modifiés ont également été évaluée avec le transfert voltampérométrique / This work combines the electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) with the Sol – Gel process of silica leading to an interfacial modification with mesoporous silica using soft template. In the first part of this work the macroscopic liquid – liquid interface was employed to separate the aqueous solution of the hydrolyzed silica precursor species (tetraethoxysilane (TEOS)) from the cationic surfactant (cethyltrimethylammonium (CTA+)) dissolved in the dichloroethane. The silica material deposition was controlled by the electrochemical CTA+ transfer from the organic to the aqueous phase. Template transferred to the aqueous phase catalyzed the condensation reaction and self-assembly resulting in silica deposition at the interface. Silica deposition at the miniaturized ITIES (membranes supporting array of micrometer in diameter pores were used in this regard) was the second part of this work. Silica interfacial synthesis performed in situ resulted in stable deposits growing on the aqueous side of the interface. Mechanical stability of the supported silica deposits allowed further processing – silica material was cured. Based on imaginary techniques (e.g. SEM) it was found that deposits forms hemispheres for longer experimental time scales. Interfacial reaction was also followed with in situ confocal Raman spectroscopy. Molecular characteristics of the interface were changed dramatically once CTA+ species were transferred to the aqueous phase. Array of microITIES modified with silica was also assessed by ion transfer voltammetry Tetraethoxysilane Interface liquide – liquide Ities Silice mésoporeuse Procédé Sol – Gel Cetyltrimethylammonium Tetraethylammonium Tetramethylammonium Tetrabuthylammonium Voltammétrie cyclique Spectroscopie Raman confocale Tamis moléculaire Modification interfaciale Dépôt de silice Voltammétrie de transfert d’ions 4-Octylbenzenesulfonate Miniaturisation MicroITIES Μities Membrane à base de silicium mésoporeux Tetraethoxysilane Liquid – liquid interface Ities Mesoporous silica Sol – Gel process Soft template Cetyltrimethylammonium Worm like structures Tetraethylammonium Tetramethylammonium Tetrabuthylammonium PAMAM dendrimers Cyclic voltammetry Confocal Raman spectroscopy Molecular sieving Interfacial modification Silica deposition Ion transfer voltammetry 4-Octylbenzenesulfonate Miniaturization MicroITIES Μities Mesoporous silicon wafers 541.37 660.297

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