Statik und Dynamik von ferromagnetischen Nanostrukturen

Der Eigenschaften kleiner ferromagnetischer Strukturen auf Halbleiteroberflächen stehen im Brennpunkt des Interesses der sog. "Magneto-Elektronik", weil man sich von solchen Strukturen sowohl im Hinblick auf die "Informationsspeicherung" (=statische Eigenschaften) als auch im Hinblick auf die "Informationsverarbeitung" (=dynamische Eigenschaften, Schaltprozesse) viel verspricht. In dieser Arbeit wird die Statik und Dynamik flacher zirkularer Permalloy Nanomagneten mit magnetischer Vortex- oder eindomäniger Konfiguration mit Hilfe mikromagnetischer Simulationen untersucht. Es gibt 4 äquivalente Vortexzustände, da die Vortizität (im oder gegen den Uhrzeigersinn) und die Polarität der Vertikalkomponente ("up" oder "down") unabhängig voneinander sind. Die Möglichkeit, bei diesen Vortexstrukturen zwei Bits unabhängig voneinander und reproduzierbar zu speichern und zu schalten, macht diese Strukturen sehr interessant

Exergy Analysis as a Developed Concept of Energy Efficiency Optimized Processes: The Case of Thermal Spray Processes

AbstractGiven the global economic growth and the rapid manufacturing development, the energy and resource efficiency will become an increasingly competitive factor and scope for the companies in the road of sustainability. Among energy efficiency optimization approaches, thermodynamics methodologies contribute toward the improvement of energy efficiency in manufacturing processes. Besides energy balance, exergy has been recently considered as a practical thermodynamics method for system's energy evaluation. From the exergy analysis, merging both exergy efficiency and exergy destruction highlights the energy inefficiencies within a system and provides useful information to the managers and decision makers for prioritizing the improvement potentials. Exergy analysis is generally an applicable method for the comparison of the alternative processes for a given purpose.In this study, thermal spray process techniques (APS, SPS, HVOF, HVSFS) as energy intensive manufacturing processes are analyzed and compared on the basis of exergy and energy analysis methods. For a comprehensive evaluation, energy efficiency as well as exergy efficiency and exergy destruction are proposed as the indicators.This work concludes with a discussion of the advantages of the exergy analysis method in comparison with a conventional energy efficiency evaluation by validation of the results for the case of thermal spray processes

Funktionsschichten für industrielle Anwendungen : Energieeinsparung durch neue Glaskeramikkochsysteme, Leichtmetallwerkstoffe im Fahrzeugbau, Schichtverbundstrukturen für Implantate

Das komplexe Anforderungsprofil moderner ingenieur- und werkstofftechnischerAufgabenstellungen bedingt in zunehmendem Maße den Einsatz von Werkstoffkombinationen in Form von Verbundmaterialien und Verbundbauweisen. Ein Einzelwerkstoff kann in seiner Funktion den gestellten Anforderungen im Allgemeinen nicht mehr gerecht werden

Influence of heat treatments on YSZ electrolyte for sofc manufactured by HVSFS

High-velocity suspension flame spraying (HVSFS) is a promising technology to manufacture yttria stabilized zirconia (YSZ) as solid electrolyte for solid oxide fuel cells (SOFC). In this paper isothermal ageing and thermal cycling have been carried out in order to evaluate their microstructural and mechanical stability. X-ray diffraction (XRD), scanning electron microscopy (SEM) and focused ion beam (FIB) techniques have used to analyze the microstructure of YSZ electrolyte before and after ageing at high temperature. Elastic modulus has been monitored by nanoindentation, while scratch tests have been performed in order to estimate the influence of ageing on the interface electrolyte/anode adhesion.Postprint (published version

Plasma Spraying of a Microwave Absorber Coating for an RF Dummy Load

The European fusion reactor research facility, called International Thermonuclear Experimental Reactor (ITER), is one of the most challenging projects that involves design and testing of hundreds of separately designed reactor elements and peripheric modules. One of the core elements involved in plasma heating are gyrotrons. They are used as a microwave source in electron–cyclotron resonance heating systems (ECRH) for variable injection of RF power into the plasma ring. In this work, the development and application of an alumina-titania 60/40 mixed oxide ceramic absorber coating on a copper cylinder is described. The cylinder is part of a dummy load used in gyrotron testing and its purpose is to absorb microwave radiation generated by gyrotrons during testing phase. The coating is applied by means of atmospheric plasma spraying (APS). The absorber coating is deposited on the inner diameter of a one-meter cylindrical tube. To ensure homogeneous radiation absorption when the incoming microwave beam is repeatedly scattered along the inner tube surface, the coating shows a varying thickness as a function of the tube length. By this it is ensured that the thermal power is distributed homogeneously on the entire inner tube surface. This paper describes a modeling approach of the coating thickness distribution, the manufacturing concept for the internal plasma spray coating and the coating characterization with regard to coating microstructure and microwave absorption characteristics

Deposition of Fluoresceine-Doped HAp Coatings via High-Velocity Suspension Flame Spraying

In current medicine, joint revision surgery plays an important role in the treatment of degenerative joint diseases. Infections of the artificial joints are an iatrogenic, accompanying symptom after joint replacement procedures. A new approach is to functionalize the bioactive coatings of the implants by infiltrating them with anti-inflammatory drugs. This work aims at a one-step approach in manufacturing drug-doped, porous hydroxyapatite coatings by high-velocity suspension flame spraying (HVSFS). Thermal exposure of the temperature-sensitive drugs is critical. Therefore, a new process setup, combining one axial and one radial suspension line, is used for coating deposition. The lower dwell time of the suspension in the flame through radial injection helps in controlling the temperature exposition of the contained drug to the flame. Additionally, the influence of the powder morphology, used as a carrier for the drug in the suspension, is investigated by carrying out spray experiments with suspensions from three different granule types. To analyze the temperature exposition within the coating process, fluoresceine was used as a model drug, as the decomposition of the organic, fluorescing molecules can be easily controlled by fluorescence intensity measurements. It could be shown that the deposition of temperature-sensitive organic molecules is possible without degrading the molecular structure by a modified HVSFS process. This knowledge offers new possibilities in the cost-effective one-step manufacturing of functionalized, anti-inflammatory bioceramic coatings on orthopaedic implants

Deposition of 3YSZ-TiC PVD Coatings with High-Power Impulse Magnetron Sputtering (HiPIMS)

Optimized coating adhesion and strength are the advantages of high-power impulse magnetron sputtering (HiPIMS) as an innovative physical vapor deposition (PVD) process. When depositing electrically non-conductive oxide ceramics as coatings with HiPIMS without dual magnetron sputtering (DMS) or mid-frequency (MF) sputtering, the growing coating leads to increasing electrical insulation of the anode. As a consequence, short circuits occur, and the process breaks down. This phenomenon is also known as the disappearing anode effect. In this study, a new approach involving adding electrically conductive carbide ceramics was tried to prevent the electrical insulation of the anode and thereby guarantee process stability. Yttria-stabilized zirconia (3YSZ) with 30 vol.% titanium carbide (TiC) targets are used in a non-reactive HiPIMS process. The main focus of this study is a parameter inquisition. Different HiPIMS parameters and their impact on the measured current at the substrate table are analyzed. This study shows the successful use of electrically conductive carbide ceramics in a non-conductive oxide as the target material. In addition, we discuss the observed high table currents with a low inert gas mix, where the process was not expected to be stable

Microstructural and Tribological Investigation of High-Velocity Suspension Flame Sprayed (HVSFS) Al2O3 Coatings

Al2O3 coatings were manufactured by the high-velocity suspension \ufb02ame spraying (HVSFS) technique using a nanopowder suspension. Their structural and microstructural characteristics, micromechanical behavior, and tribological properties were studied and compared to conventional atmospheric plasma sprayed and high-velocity oxygen-fuel-sprayed Al2O3 coatings manufactured using commercially avail- able feedstock. The HVSFS process enables near full melting of the nanopowder particles, resulting in very small and well \ufb02attened lamellae (thickness range 100 nm to 1 lm), almost free of transverse microcracking, with very few unmelted inclusions. Thus, porosity is much lower and pores are smaller than in conventional coatings. Moreover, few interlamellar or intralamellar cracks exist, resulting in reduced pore interconnectivity (evaluated by electrochemical impedance spectroscopy). Such strong interlamellar cohesion favors much better dry sliding wear resistance at room temperature and at 400 \ub0C