Development of an image based paticle diagnostics for the examination of Thermal Spraying processes

In der vorliegenden Arbeit ist die Entwicklung der Partikeldiagnostik Particle Shape Imaging (PSI) dargestellt. Dieses bildgebende Verfahren wurde speziell für die Untersuchung eines Industrieprozesses zur Oberflächenbeschichtung ausgelegt, der allgemein unter dem Namen Thermisches Spritzen bekannt ist. Die Prinzipien könne aber auch auf Partikeluntersuchungen in anderen technischen Bereichen übertragen werden. Mit PSI werden am individuellen Partikel im Spritzstrahl die relevanten Eigenschaften Form, Größe und Geschwindigkeit berührungslos, simultan und mit hoher Ortsauflösung bestimmt. Hierbei sind folgende extreme Bedingungen, die speziell beim Plasmaspritzen auftreten zu berücksichtigen: Eigenleuchten des Plasmas (optische Störquelle), Mindestabstand (10cm) des Diagnostiksystems zum Meßvolumen im Plasmaspritzstrahl (thermische Belastung), Kleinheit der Partikel (Durchmesserbereich von 5µm bis 100µm) und geringe Partikeldichten (namp;quot;0,03mm-3). Um diesen Anforderungen zu begegnen, wird bei der PSI Diagnostik eine extrem sensitive Bildverstärkerkamera (ICCD-Kamera) mit Belichtungszeiten im Nanosekundenbereich, ein hochauflösendes Fernmikroskopie-System und ein Dauerstrichlaser hoher Intensität eingesetzt. Verfahrenstechnisch ist die PSI-Diagnostik durch folgende Eigenschaften charakterisiert: - Auf der Grundlage einer stereoskopischen Durchlichtbeleuchtung können die Partikel mit hoher Ortsauflösung in einem eng begrenzten Meßvolumen lokalisiert werden. Diese Technik löst auch das "Problem der Tiefenschärfe". - Durch die Kombination mit einem System zur Triggerung der Bildaufnahmen kann die PSI-Meßtechnik auch bei niedrigen Partikeldichten erfolgreich eingesetzt werden. Die Triggerung ermöglicht zusätzlich eine elektronische Vorauswahl von Partikeln, die wegen ihrer Nähe zur Gegenstandsebene der abbildenden Optik in den aufgenommenen Bildern mit hoher Schärfe und gutem Kontrast erscheinen. Als Folge ergeben sich gesteigerte Genauigkeit und Effizienz der Bildauswertung. - Eine speziell auf das PSI-Verfahren abgestimmte Bildverarbeitungstechnik identifiziert die Partikel in den aufgenommenen Bildern. Durch die Anwendung eines Klassifizierungsverfahrens, das auf einem Ellipsenvergleich basiert, werden trotz der Formenvielfalt der Partikel statistisch auswertbare Ergebnisse erzielt. - In PSI wurde ein vollständiges Laser Doppler Anemometrie Meßverfahren integriert, das die Sendeseite der PSI-Diagnostik zur Objektbeleuchtung verwendet. Dadurch wird der Vergleich mit einem bereits etablierten Meßverfahren möglich. Darüber hinaus kann experimentell eine Zuordnung zwischen den Streulichtsignalen und den Form- und Größenmerkmalen der Partikel hergestellt werden. - Die an unterschiedlichen Meßorten (scannender Meßmodus) aufgenommenen statistischen Partikeldaten werden für PSI und LDA nach einem einheitlichen Prinzip ausgewertet und graphisch dargestellt. - Die komplexe optische Abbildungstechnik des Particle Shape Imaging Verfahrens wird über ein Modell auf Basis der skalaren Wellentheorie in ihren wesentlichen Eigenschaften beschrieben. Über die Umsetzung dieses Modells in eine Computersimulation gelingt eine Verbindung zwischen den Systemkenngrößen und den zu erwartenden Bildergebnissen.In this work the development of an image based particle diagnostics called Particle Shape Imaging (PSI) is described. Its application is focused on the examination of an industrial coating technology well-known as thermal spraying. The underlying principles can be used for particle diagnostics in other technical fields, too. With PSI it is possible to determine important particle properties like shape, size and velocity in-flight and within a plasma spray jet. The results are obtained with high spatial resolution on a statistically representative number of individual particles. In the development of PSI typical conditions of plasma spraying technology had to be taken into account: strong radiation of the plasma in the visible range (optical distortions), necessary safety distance (10cm) to the plasma spray jet (thermal load), particle diameter range (5µm to 100µm) and low particle density (namp;quot;0,03mm-3). To meet these requirements for PSI a sensitive, intensified Camera (ICCD) with exposure times in the nanosecond range, a high resolution long-distance-microscope and a high intensity cw-laser are used. The PSI principle can be characterized by the following properties: - Based on a stereoscopic laser-beam-illumination, particles can be localized with high resolution in a well defined measuring volume. This helps to avoid problems arising from the small depth of focus of high resolution optics. - The combination with a trigger-system extends the application range of PSI towards low particle densities. Additionally an electronic preselection is provided which allows to acquire only those particles which are near the focal plane. Thus particles are imaged sharply with high contrast. The subsequent image processing can be performed efficiently and with high accuracy . - The image processing is aligned to the particularities (stereoscopic illumination) of PSI. The identified particles of arbitrary shape are classified by corresponding ellipses. This leads to a quantitative description of particle properties which can be used for a statistical representation of the obtained measuring data. - A Laser-Doppler-Anemometry (LDA) system is integrated into the PSI diagnostics. It is using the PSI sender module for particle illumination. Thus PSI results can be directly compared to a well established technique and additionally it is possible to associate experimentally obtained stray light signals to size and shape information. - Particle properties are measured at different spatial locations (scanning mode). For PSI and LDA a common principle was found to visualize the statistically reprocessed data. - A mathematical model of the PSI imaging technique was found on the basis of scalar waves. With the help of this description a computer simulation was realized to predict the obtainable imaging results for various experimental set-ups

Influence of Oxygen Partial Pressure during Processing on the Thermoelectric Properties of Aerosol-Deposited CuFeO2

In the field of thermoelectric energy conversion, oxide materials show promising potential due to their good stability in oxidizing environments. Hence, the influence of oxygen partial pressure during synthesis on the thermoelectric properties of Cu-Delafossites at high temperatures was investigated in this study. For these purposes, CuFeO2 powders were synthetized using a conventional mixed-oxide technique. X-ray diffraction (XRD) studies were conducted to determine the crystal structures of the delafossites associated with the oxygen content during the synthesis. Out of these powders, films with a thickness of about 25 µm were prepared by the relatively new aerosol-deposition (AD) coating technique. It is based on a room temperature impact consolidation process (RTIC) to deposit dense solid films of ceramic materials on various substrates without using a high-temperature step during the coating process. On these dense CuFeO2 films deposited on alumina substrates with electrode structures, the Seebeck coefficient and the electrical conductivity were measured as a function of temperature and oxygen partial pressure. We compared the thermoelectric properties of both standard processed and aerosol deposited CuFeO2 up to 900 °C and investigated the influence of oxygen partial pressure on the electrical conductivity, on the Seebeck coefficient and on the high temperature stability of CuFeO2. These studies may not only help to improve the thermoelectric material in the high-temperature case, but may also serve as an initial basis to establish a defect chemical model

A compact, multi-pixel parametric light source

The features of a compact, single pass, multi-pixel optical parametric generator are discussed. Several hundreds of independent high spatial-quality tunable ultrashort pulses were produced by pumping a bulk lithium triborate crystal with an array of tightly focussed intense beams. The array of beams was produced by shining a microlenses array with a large pump beam. Overall conversion efficiency to signal and idler up to 30% of the pump beam has been reported. Shot-to-shot energy fluctuation down to 3% was achieved for the generated radiation.Comment: 11 pages, 6 figures, submitted to "Optics Communications

Diffraction microtomography with sample rotation: influence of a missing apple core in the recorded frequency space

Diffraction microtomography in coherent light is foreseen as a promising technique to image transparent living samples in three dimensions without staining. Contrary to conventional microscopy with incoherent light, which gives morphological information only, diffraction microtomography makes it possible to obtain the complex optical refractive index of the observed sample by mapping a three-dimensional support in the spatial frequency domain. The technique can be implemented in two configurations, namely, by varying the sample illumination with a fixed sample or by rotating the sample using a fixed illumination. In the literature, only the former method was described in detail. In this report, we precisely derive the three-dimensional frequency support that can be mapped by the sample rotation configuration. We found that, within the first-order Born approximation, the volume of the frequency domain that can be mapped exhibits a missing part, the shape of which resembles that of an apple core. The projection of the diffracted waves in the frequency space onto the set of sphere caps covered by the sample rotation does not allow for a complete mapping of the frequency along the axis of rotation due to the finite radius of the sphere caps. We present simulations of the effects of this missing information on the reconstruction of ideal objects.Comment: 7 pages, 11 figures, presented at Focus On Microscopy 200

Optical correlation techniques for the investigation of colloidal systems

This review aims to provide a simple introduction to the application of optical correlation methods in colloidal science. In particular, I plan to show that full appraisal of the intimate relation between light scattering and microscopy allows designing novel powerful investigation techniques that combine their powers. An extended version of this paper will appear in "ColloidalFoundations of Nanoscience", edited by D. Berti and G. Palazzo, Elsevier (ISBN 978-0-444-59541-6). I am very grateful to the publisher for having granted me the permission to post this preprint on arXiv.Comment: 19 pages, 5 figure

A Hardware Implementation of MAYO Signature Scheme

We present a hardware implementation for the MAYO post-quantum digital signature scheme, which is submitted to the American National Institute of Standards and Technology’s call for diversification of quantum-resistant public key cryptographic standards. The scheme is based on the Unbalanced Oil and Vinegar signature scheme, which operates on the fact that solving systems of multivariate polynomial equations is NP-complete. MAYO utilizes a unique whipping technique in combination with emulsifier maps to offer a significant reduction in key size compared to other Unbalanced Oil and Vinegar signature schemes. In this paper, we demonstrate how to design a hardware architecture for the MAYO post-quantum signature scheme. We also provide a comprehensive analysis and propose multiple optimization techniques to reduce resource utilization and accelerate computation on hardware platforms