Monoclinic Zirconia Bodies by Thermoplastic Ceramic Extrusion

Two ultrafine, undoped ZrO₂ powders with median primary particle sizes of 9 and 25 nm were used to prepare ceramic suspensions for thermoplastic extrusion. The organic vehicle consisted of an industrial-grade poly(ethylene- co -vinyl acetate) (EVA) or polyethylene (PE-HD) and decanoic acid as a dispersing agent. The powder volume loadings achieved were 44% and 52% by volume for the two powders, respectively. The amount of dispersant needed was calculated from a new model based on available chemisorption sites on the powder surface. Mixing and extrusion were conducted using a conventional modular plastic processing unit. Green bodies were dewaxed up to 450°C in an inert atmosphere and sintered to full density in air at 1060° and 1100°C, respectively. Analysis of the ceramic phase content and the microstructure of the bodies is presented.     

Monitoring the degradation of a solid oxide fuel cell stack during 10,000 h via electrochemical impedance spectroscopy

A 5-cell solid oxide fuel cell stack was tested during 10,000 h of continuous operation with simulated reformate gas as fuel (71 vol.% H₂, 20.7 vol.% CO₂ and 8.3 vol.% steam) under high fuel utilization (73%) and constant current load (0.5 A cm^?2 or 25 A) at 750 °C. In situ electrochemical impedance spectroscopy was used to monitor the evolution of ohmic and polarisation resistances of individual cells in the stack without interrupting the current load. Impedance spectra were recorded on each cell periodically (every 1000 h) or after uncontrolled incidents happened with the test setup. It has been found that the stack degradation is mainly attributed to the increased ohmic resistance, pointing to possible causes such as interconnect corrosion and reduced effective contact areas between cells and interconnects. The degradation rate during the first 5000 h was about 1% kh^?1, but increased afterwards up to 1.5% kh^?1 due to the impact of incidents. Both types of incidents (fuel supply fluctuations and overloading failure of the electronic load) were complicated by inhomogeneous fuel distribution among cells, leading to most probably partial re-oxidation of the anode, accelerating the stack degradation.     

Mechanical properties and morphology of papers prepared from single-walled carbon nanotubes functionalized with aromatic amides

Carbon nanotube papers (CNT papers, also referred to as “buckypapers”) prepared from chemically functionalized single-walled CNTs are being investigated for their mechanical tensile properties. While the Young’s moduli are unaffected by the functionalization with diazonium salts of aniline or aromatic mono- and bis-amides tensile strengths of CNT papers are found to increase with a growing degree of functionalization, and more pronounced with a growing number of amide groups capable of hydrogen bonding. The importance of hydrogen bonding becomes evident after its inhibition through N-methylation of the amide groups, resulting in a distinct reduction of strength values. Scanning electron micrography indicates that a high degree of functionalization or a high number of amide group results in the formation of domains with aligned CNTs.     

Distortion-free laser beam shaping for material processing using a digital micromirror device

Digital micromirror devices (DMD) are increasingly used in laser-based manufacturing for a maskless beam shaping in order to realize simultaneous 2D/3D material processing. Thereby, the DMD has to be irradiated under a sharp angle to achieve acceptable projection quality with negligible distortion phenomena. In this article, we present a novel setup for DMD-based laser material processing. It enables the irradiation under large angles (up to 60\(^{\circ }\)), the reduction of optical elements as well as machine size. Occurring optical distortions during the amplitude-based laser beam shaping are characterized. To eliminate these phenomena, we implement an optical modelling of the DMD patterns, taking into account the propagation through the tilted interfaces. The resulting imaging of different desired shapes is verified experimentally for its geometrical properties such as length, radius and aspect ratio. Thereby, an angle-dependent correction and high shape accuracy of the image projection is shown. This novel arrangement may have applications in direct laser writing and photochemical machining.