This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour. Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present. Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly. To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation. <b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM

Im Rahmen dieser Arbeit wurde ein modulares Nukleinsäure-basiertes System zur Immobilisierung von verschiedenen bioaktiven Molekülen untersucht. Zur Verankerung nutzt das System komplementäre Nukleinsäurestränge. Einer der beiden Stränge wird durch anodische Polarisation partiell in die anodische Oxidschicht eingebaut, an den komplementären Strang wird das biologische Molekül konjugiert. Der Vorteil des hier weiter entwickelten Immobilisierungssystems bildet dessen Vielseitigkeit. Es kann auf alle titanbasierenden Implantate übertragen werden und dadurch, dass ein universelles Verankerungssystem verfügbar ist, können verschiedene bioaktive Moleküle aufgebracht werden. Für die Übertragung des Nukleinsäure-basierten Immobilisierungssystems auf reale Implantatoberflächenzustände konnten optimale Prozessbedingungen festgelegt werden. Weiterhin konnten verschiedene Ankerstrangsequenzen hinsichtlich ihres Einflusses auf Adsorption und Hybridisierungseffizienz beurteilt werden. In der vorliegenden Arbeit konnte eine Methode entwickelt werden, die es ermöglicht, das Immobilisierungssystem mit 25 kGy Standarddosis Gammastrahlung zu sterilisieren. Hierbei wurden verschiedene Strategien (Trocknung, Schutzgas, Opferstränge) untersucht und hinsichtlich ihrer Ankerstrangschutzfähigkeit bewertet. In Zell- und Tierversuchen konnte die biologische Aktivität der über das Immobilisierungssystem aufgebrachten Wachstumsfaktoren VEGF und BMP-2 gezeigt werden. Zusammenfassend konnte mit der vorliegenden Arbeit ein wichtiger Beitrag zur Weiterentwicklung eines Nukleinsäure-basierten Immobilisierungssystems im Hinblick auf eine klinische Anwendung geleistet werden.

<p>This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour.</p><p>Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present.</p><p>Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly.</p><p>To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation.</p><p><b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM</p>

No description available.

Nous avons étudié la spectroscopie et la dynamique d’excitation d’un système hybride constitué de molécules et de nanoparticules (NP) sur couche isolante, qui est aussi un catalyseur modèle (NP de Pd épitaxiées sur une couche mince de MgO sur Ag(100)). Nous avons mis en évidence le rôle de la forme et de la taille des NP ainsi que de l’épaisseur de la couche d’oxyde sur l’interaction entre NP et molécule de CO, par des expériences fondamentales capables de différentier les sites d’adsorption (spectroscopie laser vibrationnelle par somme de fréquences (SFG)). De plus, des expériences pompe-sonde nous ont permis de sonder la dynamique d’interaction des électrons excités dans les NP avec les molécules. Une analyse combinée par LEED et STM nous a permis de déterminer les meilleures conditions de croissance du film de MgO. Par la suite des NP de palladium ont été épitaxiées sur ce film avec une densité et une distribution de taille satisfaisantes. Les spectres SFG montre une forte dépendance de la fréquence de vibration avec la taille des NP et le taux de couverture en CO. Le modèle d’interaction dipolaire que nous avons développé met en évidence le fait que le déplacement de la fréquence de CO avec le taux de couverture et la taille des NP a deux causes : l’interaction dipolaire entre molécules d’une part, qui est modélisable, et d’autre part la variation de la liaison chimique molécule-substrat quand la couverture en adsorbats varie. Le modèle nous a permis de montrer que la polarisabilité vibrationnelle de CO varie d’environ 40 % dans notre gamme de taille de nanoparticule. La diminution de la force de la liaison chimique se traduit par la décroissance de la fréquence à couverture nulle avec la taille des NP. Ces variations vont dans le sens de la littérature : quand la taille des NP diminue, la densité d’états électroniques diminue, les liaisons Pd-Pd se contractent et l’énergie d’adsorption des molécules de CO diminue. L’excitation des électrons des NP et du substrat d’Ag se manifeste par une réponse spectroscopique et par la photodésorption de CO. On observe le découplage de l’excitation produite dans l’argent quand l’épaisseur de la couche d’oxyde dépasse quelques plans atomiques. On observe clairement un effet de taille sur l’efficacité de l’excitation électronique des NP sur les molécules de CO, qui diminue avec la taille des NP. Ceci montre que le confinement des électrons dans la particule a davantage pour effet d’augmenter la vitesse de relaxation électronique vers les phonons, que d’exciter plus efficacement les molécules adsorbées. Un modèle optique de double couche (NP/oxyde) sur un substrat d’argent et un modèle à trois températures (électrons, phonons et adsorbats) ont été développés dans le but d’interpréter quantitativement ces observations. Le modèle optique fait apparaître des variations très fortes de l’absorption par la couche de nanoparticules avec son épaisseur équivalente : les variations du coefficient de réflexion et l’effet des interférences multiples ne sont pas négligeables. Les résultats du modèle à trois températures montrent que la température électronique d’une couche continue est deux fois plus importante que celle des NP de taille finie. / We have studied the spectroscopy and excitation dynamics of a hybrid system consisting of molecules and nanoparticles (NPs) on insulating layer, which is also a model catalyst (Pd NPs grown on a thin layer of MgO on Ag(100)). We have highlighted the role of the shape and the NPs size as well as the thickness of the oxide layer in the interaction between NPs and CO molecules, by fundamental experiments allowing to differentiate the adsorption sites (Sum Frequency Generation (SFG)). In addition, pump-probe experiments allowed us to probe the dynamics of interaction between the photoexcited electrons bath in the NPs and the molecules. A combined study by LEED and STM allowed us to determine the growing conditions of MgO film. Subsequently palladium NPs were grown on this film with satisfying density and distribution size. The SFG spectra show a strong dependence of the vibrational frequency with the NPs size and the CO coverage. A dipole interaction model was developed showing that the CO frequency shift with the coverage and the NPs size has two causes: the dipolar interaction between molecules on the one hand, which is modeled, and on the other hand the variation of the molecule-substrate chemical bond when the adsorbate coverage varies. The model has allowed us to show that the vibrational polarizability of CO changes by 40 % in our range of NPs size. The decrease in the strength of the chemical bond results in the decrease of the frequency at zero coverage when the NPs size decreases. These variations are consistent with the literature: upon a decrease in the particle size, the electronic DOS decreases, the Pd-Pd bonds contract and the adsorption energy of CO molecules decreases. The electronic excitation of the NPs and the silver substrate manifested by the spectroscopic response and the CO photodesorption. We observed the decoupling of the electronic excitation produced in silver when the thickness of the oxide layer exceeds a few atomic planes. There is a clear size effect on the efficiency of electronic excitation of NPs on the CO molecules, which decreases as the NPs size decreases. This shows that the effect of electrons confinement in the particle rather consists in an increase in the relaxation rate of electrons to phonons, than in a more efficient excitation of the adsorbed molecules. A double-layer optical model (NP/oxide) on a silver substrate and a three-temperature model (electrons, phonons and adsorbates) have been developed to quantitatively interpret these observations. The optical model results show a very strong variation of the absorption intensity by the layer with its equivalent thickness: variation of the reflection and the effect of multiple interference are not negligible. The three temperatures model results show that the electronic temperature of a continuous layer is two times more important than in the case of finite size NPs.

Electrochromic devices are based on the intercalation processes to the active layer mostly WO3. The optical properties of active layer are changed by intercalation ions from the electrolyte. For that purpose are used Li ions. The mass of thin layer can be observed by the QCM method. This method is based on the changes of the resonance frequency of a quartz crystal resonator. The investigated substance is deposited on the surface of the resonator. Various metals (Pt, Au, Ag) and their compounds should be plated on the resonator. Most frequently, the resonators for the frequency 5,0 MHz are used. This frequency change is used for the detection of chemical changes of the electrode surface and is very sensitive.

Durch elektrochemische Impedanzspektroskopie während der anodischen Oxidation von Aluminium werden in der vorliegenden Arbeit die elektrochemischen Vorgänge während der Oxidbildung quantitativ und zeitabhängig untersucht. Es wird ein Modell vorgeschlagen und diskutiert, welches das Impedanzverhalten während der anodischen Oxidation in Schwefel-, Oxal- und Phosphorsäure über einen großen Bereich von Konzentrationen und Stromdichten abbilden kann. Aus den gewonnenen Ergebnissen werden die kapazitive Wirkung der Sperrschicht am Porengrund, der Eintritt von Ladungsträgern in die Sperrschicht, der Ionentransport durch die Sperrschicht sowie die Oxidbildungsreaktion selbst als wesentlich für das Impedanzverhalten identifiziert. Die ermittelten Zusammenhänge und Konstanten können als Grundlage für Modellvorstellungen dienen, welche das Verhalten elektrischer Prozessgrößen und die Ausbildung der charakteristischen Oxidstruktur bei der anodischen Oxidation von Aluminium verknüpfen. / In the present work, the electrochemical subprocesses of the oxide formation on aluminium by anodic oxidation are investigated using electrochemical impedance spectroscopy. The time dependence of the impedance behaviour and the quantitative relations between the process parameters and the impedance behaviour are considered. A model for the representation of the electrochemical behaviour during the anodic oxidation in sulphuric, oxalic and phosphoric acid is proposed and discussed for a wide range of anion concentrations and current densities. On the basis of the obtained results, the capacitive effect of the barrier layer, the charge transfer resistance of the barrier layer, the ion transport within the barrier layer and the oxide formation are identified as the dominating effects for the impedance behaviour. The established relations can serve as a basis for models, which interrelate both the electrochemical behaviour and the geometrical formation of the characteristic pore structure.

Metal surface cleaning is highly required in different fields of modern industry. Nuclear industry seeks for new methods for oxidized surface decontamination, and thermonuclear installations require the cleaning of plasma facing components from tritium-containing deposited layer. The laser ablation is proposed as an effective and safe method for metal surface cleaning and decontamination. The important factor influencing the laser heating and ablation is the in-depth distribution of laser radiation. The model of light propagation in a scattering layer on a metal substrate is developed and applied to analyse the features of light distribution. To simulate the contaminated surfaces, the stainless steel AISI 304L was oxidized by laser and in a furnace. Radioactive contamination of the oxide layer was simulated by introducing europium and/or sodium. The decontamination factor of more than 300 was demonstrated with found optimal cleaning regime. The decreasing of the corrosion resistance was found after laser cleaning. The ablation thresholds of ITER-like surfaces were measured. The cleaning productivity of 0.07 m2/hour∙W was found. For mirror surfaces, the damage thresholds were determined to avoid damage during laser cleaning. The possibility to restore reflectivity after thin carbon layer deposition was demonstrated. The perspectives of further development of laser cleaning are discussed.

Ein Schlüsselfeld der gegenwärtigen Biomaterialforschung ist die Modifizierung von Oberflächen mit Bestandteilen der extrazellulären Matrix (EZM) oder Molekülen, die bestimmte Funktionen nachahmen. Trotz einer Reihe positiver Ergebnisse in vitro und in vivo ist es mit den gegenwärtig zur Verfügung stehenden Immobilisierungsmethoden nicht möglich, unterschiedliche Komponenten in einem Prozessschritt zu immobilisieren, definierte Freisetzungscharakteristika für gleiche und/oder unterschiedliche Moleküle zu realisieren und die Beschichtung der Oberflächen nach Sterilisation der Implantate vorzunehmen, um empfindliche bioaktive Substanzen, wie Proteine, vor Schädigung zu bewahren. An diesem Punkt setzt die vorliegende Arbeit mit dem Ziel an, ein nukleinsäurebasiertes Immobilisierungssystem für Titanwerkstoffe zu entwickeln. Es wird zunächst am Beispiel eines Peptids mit der Aminosäuresequenz Arginin–Glyzin–Asparaginsäure (RGD) nachgewiesen, dass an der Grenzfläche Passivschicht/Elektrolyt von Titanwerkstoffen vorliegende Moleküle in durch anodische Polarisation verdickte Oxidschichten partiell eingebaut werden können und dabei ihre Funktionalität erhalten bleibt. Diese Immobilisierungsmethode wird zum Immobilisierungssystem erweitert, indem Nukleinsäureeinzelstränge mit der beschriebenen Methode als Ankerstränge (AS) in anodisch formierte Oxidschichten fixiert und in einem zweiten Prozessschritt mit komplementären Gegensträngen (GS) hybridisiert werden. In der Arbeit wird gezeigt, dass das Peptid in einem weiten Parameterbereich der elektrochemischen Bedingungen immobilisiert werden kann. Demgegenüber führen im Falle des nukleinsäurebasierten Immobilisierungssystems die Bildung reaktiver Sauerstoffspezies, die Photoaktivität der Oxidschicht sowie mehrfache Trocknungen und Wiederbenetzungen zu einer Schädigung gebundener AS bis hin zu einem vollständigen Verlust der Hybridisierbarkeit. Durch Zugabe von Ethanol in hoher Konzentration während des Immobilisierungsschritts, Arbeit unter Lichtausschluss sowie Vermeidung mehrerer Trocknungen und Wiederbenetzungen können die Nebenwirkungen soweit eingeschränkt werden, dass alle immobilisierten AS hybridisierbar sind. Nach dessen Etablierung im Rahmen dieser Arbeit ist es in nachfolgenden Projekten möglich, das nukleinsäurebasierte Immboilisierungssystem zu einem modularen, nukleinsäurebasierten Immobilisierungssystem zu erweitern, um die eingangs beschriebenen Grenzen etablierter Methoden zu umgehen. Dazu müssen im zweiten Prozessschritt Konjugate aus GS und bioaktiven Molekülen, wie z. B. Peptide oder Wachstumsfaktoren, eingesetzt werden. Weiterhin können durch die Nutzung verschiedener Längen und Basensequenzen die Hybridstabilität und damit die Freisetzungskinetik beeinflusst werden. / Surface functionalization with bioactive molecules is a main field in current biomaterial research. However, in vitro and in vivo results are heterogeneous. This may be at least partially attributed to the limits of the applied immobilization methods. With established immobilization methods possibilities are limited to immobilize different molecules in one step, to implement defined release kinetics for similar and/or different substances, or to carry out the immobilization after sterilization of the implant to save sensitive molecules from damage. Therefore in this thesis a nucleic acid based immobilization system for bioactive molecules is developed for titanium based materials. Using a peptide with the amino acid sequence arginine–glycine–aspartic acid (RGD) it is demonstrated at first, that small molecules, being present at the interface electrolyte/passive layer, can be immobilized by their partial incorporation in anodically formed oxide layers. The immobilization can be carried out in a wide range of electrochemical parameters and the peptide preserves its biological function under all conditions. This immobilization method is enhanced by utilizing single-stranded nucleic acids as anchor strands (AS), which can be hybridized by complementary strands (CS) in a second step. Contrary to the peptide, bound AS are damaged by the formation of reactive oxygen species during anodic polarization of the substrate, the photoyctivity of the titanium oxide layer and multiple drying and wetting cycles. These side effects must be constrained by adding ethanol in a high concentration to the electrolyte during the immobilization procedure, excluding light during preparation and avoiding multiple drying and wetting cycles. Applying these conutermeasures, a 100% hybridization of immobilized AS can be achieved. After establishing the nucleic acid based immobilization system it can be developed further to a modular, nucleic acid based immobilization system to overcome limitations of established immobilization methods. At first, conjugates of CS and bioactive molecules, such as peptides or growth factors, should be used in the hybridization step for a true functionalization of the surface. Furthermore, hybrid stability and thus release kinetics can be adjusted by using CS of different length and base sequences.

Solar cells based on organohalide perovskites (PSCs) have made rapid progress in recent years and are a promising emerging technology. An important next evolutionary step for PSCs is their up-scaling to commercially relevant dimensions. The main challenges in scaling PSCs to be compatible with current c-Si cells are related to the limited conductivity of the transparent electrode, and the processing of a uniform and defect-free organohalide perovskite layer over large areas. In this work we present a generic and simple approach to realizing efficient solution-processed, monolithic solar cells based on methylammonium lead iodide (CH₃NH₃PbI₃). Our devices have an aperture area of 25 cm² without relying on an interconnected strip design, therefore reducing the complexity of the fabrication process and enhancing compatibility with the c-Si cell geometry. We utilize simple aluminum grid lines to increase the conductivity of the transparent electrode. These grid lines were exposed to an UV-ozone plasma to grow a thin aluminum oxide layer. This dramatically improves the wetting and film forming of the organohalide perovskite junction on top of the lines, reducing the probability of short circuits between the grid and the top electrode. The best devices employing these modified grids achieved power conversion efficiencies of up to 6.8%.