5 Werkstofftechnik
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Paper des Monats
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Particle size determination of a commercially available CeO2 nano powder - SOPs and reference data
(2023)
Compilation of detailed SOPs for characterization of a commercially available CeO2 nano powder including
- suspension preparation (indirect and direct sonication),
- particle size determination (Dynamic Light Scattering DLS and Centrifugal Liquid Sedimentation CLS) with reference data, respectively.
For sample preparation and analysis by Scanning Electron Microscopy (SEM) of this powder see related works (submitted, coming soon).
Als elektrische Durchschlagfestigkeit bezeichnet man die elektrische Feldstärke, bei der es zur Entladung durch ein isolierendes Medium kommt. Im Falle von Festkörpern ist dies ein zerstörender Prozess. Bei der messtechnischen Bestimmung der Durchschlagfestigkeit haben neben den verwendeten Messgeräten auch die eingesetzten Elektroden, die Form des Prüfkörpers und das Isoliermedium, in dem die Prüfung stattfindet, einen signifikanten Einfluss auf die ermittelten Messwerte. Im Vortrag werden die Einflüsse erläutert und anhand von Messreihen aus der Literatur und der eigenen Forschung quantifiziert. Aufgrund der vorgestellten Effekte wird klar, dass es sich bei elektrischer Durchschlagfestigkeit nicht um absolute Materialkennwerte handelt, sondern vielmehr um systemabhängige Größen.
Im Vortrag werden das Messprinzip einer Photozentrifuge erläutert und die Anforderungen der zugrundeliegenden Normen diskutiert. Die praktische Durchführung der Messung und insbesondere auch die vorbereitenden Arbeiten, sowie die Auswertung der Rohdaten bilden den Schwerpunkt des Vortrags. Gezeigt werden auch die Validierung sowie ein Beispiel zur regelmäßigen Verifizierung des Verfahrens. Nach Anwendungsbeispielen und Vergleichen zu Ergebnissen mit anderen Messverfahren, wird das Verfahren in einer Zusammenfassung bewertet.
Obtaining dense fine ceramics by the binder jetting additive manufacturing process is challenging. A slurry-based binder jetting process, such as the layerwise slurry deposition (LSD-print) process, can enable the printing of dense ceramic parts. This work describes a procedure to develop and qualify a suitable ink to manufacture silicon carbide green parts by LSD-print. Not only the printability but also the compatibility of the ink with the powder bed and the effect of the binding agent on the properties of the green parts are considered. Both aspects are important to obtain high green strength, which is necessary for printing large or thin-walled parts. Characterization methods, such as rheological and surface tension measurements, are applied to optimize three selected inks. The interplay between ink and powder bed is tested by contact angle measurements and by comparing the biaxial strength of cast and additively manufactured specimens.
Out of the three binding agents tested, a polyethyleneimine and a phenolic resin have a high potential for their use in the LSD-print of silicon carbide green bodies, whereas a polyacrylate binding agent did not show the required properties.
Laser melting manufacturing of large elements of lunar regolith simulant for paving on the Moon
(2023)
The next steps for the expansion of the human presence in the solar system will be taken on the Moon. However, due to the low lunar gravity, the suspended dust generated when lunar rovers move across the lunar soil is a significant risk for lunar missions as it can affect the systems of the exploration vehicles. One solution to mitigate this problem is the construction of roads and landing pads on the Moon. In addition, to increase the sustainability of future lunar missions, in-situ resource utilization (ISRU) techniques must be developed. In this paper, the use of concentrated light for paving on the Moon by melting the lunar regolith is investigated. As a substitute of the concentrated sunlight, a high-power CO2 laser is used in the experiments. With this set-up, a maximum laser spot diameter of 100 mm can be achieved, which translates in high thicknesses of the consolidated layers. Furthermore, the lunar regolith simulant EAC-1A is used as a substitute of the actual lunar soil. At the end of the study, large samples (approximately 250 × 250 mm) with interlocking capabilities were fabricated by melting the lunar simulant with the laser directly on the powder bed. Large areas of lunar soil can be covered with these samples and serve as roads and landing pads, decreasing the propagation of lunar dust. These manufactured samples were analysed regarding their ineralogical composition, internal structure and mechanical properties.
3D printing or additive manufacturing in space is of great value for long-term human spaceflight missions and space stations, conveniently offering access to a ‘virtual warehouse’ of tools and spare parts on the push of a button. The process only needs one type of feedstock such as powder or filament and only as much material as the final part requires, giving it a huge weight benefit over traditional subtractive methods.
While 3D printers are already operational on the ISS since 2014, the utilized processes are only capable of manufacturing relatively low strength parts from polymers not suitable for many tools or critical components. To gain access to high quality metal prints, a modified Laser Powder Bed Fusion (LPBF) process was developed to stabilize the critical powder bed in microgravity through a gas flow [2]. This setup was able to generate a (miniature) steel wrench during parabolic flights, but a reliable layer deposition has raised challenges due to the combination of gas flow parameters with microgravity conditions. Furthermore, the quality and density of the powder bed, which is critical for the process, cannot be examined afterward on the ground. This is due to hyper gravity phases during the flight that are influencing the properties of the powder bed.
In this paper, the challenges of the layer deposition are revised, and the subsequent evolution of the recoating system explained. Later, the challenges of an in-situ quality control, evaluation, and quantification of the properties of the powder bed are examined. As a solution, a high-resolution line-scanner is proposed and its implementation int the compact LPBF system demonstrated. Its ability to measure common defects such as ridges in the deposited layer is shown in experiments at normal gravity. As an illustration, Figure 1 shows an extreme case of the formation of ridges.