Relationships between process, microstructure and properties of molded zirconia micro specimens

Due to size effects the mechanical behavior of micro-components with dimensions in the range of some 100 μm and structure details of about 10 μm differs markedly from those of larger components. This is a crucial aspect for the design of micro-components for applications where demands for high strength are critical. The present study, which was performed in the frame of the Collaborative Research Centre 499 (SFB 499), approaches this issue by investigating the relationship between production process, microstructure and the mechanical properties of micro-specimens made from zirconia using two different feedstocks. The specimens were produced by a sintering process. The sintering temperature was varied between 1,300 and 1,500°C. Mechanical and tribological behavior of the specimens was determined by three-point bending tests as well as static and sliding friction tests, respectively. Properties derived from these tests were then correlated to the surface states in the specimens such as porosity, edge radius and roughness. The strength of the micro-specimens was found to be significantly influenced by these surface features. Whilst low porosity alone is not sufficient for high strength, notch effects resulting from pores as well as surface roughness can lower the strength. With increasing edge radius the strength of the material also increases. The porosity, edge radius and surface roughness were mathematically correlated with the strength to allow for a forecast. Within the SFB 499 feedstocks with specific properties were designed and reliable processes were developed to guarantee desirable surface roughness and porosity in the specimens. A characteristic bending strength of about 2,000 MPa is realizable in the micro-specimens within a good statistical reliability. The tribological tests revealed that the wear properties of the zirconia micro-components are strongly dependent on the quality of the feedstock.     

Ceramic micro parts produced by micro injection molding: latest developments

Powder injection molding is a preferred technology for the production of micro parts or microstructured parts. Derived from the well known thermoplastic injection molding technique it is suitable for a large-scale production of ceramic and metallic parts without final machining. To achieve good surface quality and control the part size and distortions is an important goal to allow mass production. This means that all process steps like part design adjusted for MIM/CIM-technology, appropriate choice of powder and binder components and injection molding simulation to design the sprue are required. Concerning the injection molding itself high quality mold inserts, high-precision injection molding with suitable molding machines like Battenfeld Microsystem50 or standard machine with special equipment like variotherm or evacuation of the molding tool and an adjusted debinding and sintering process have to be available. Results of producing micro parts by powder injection molding of ceramic feedstock will be presented.     

High-efficiency binary phase-transmission-grating using e-beam lithography

Abstract

Rigorous coupled-wave analysis indicates that diffraction efficiencies greater than 99% are feasible for dielectric phase-gratings with a rectangular profile. The use of rectangular rather than blazed profiles implies simplified fabrication techniques, since deep-etch submicrometre structuring techniques can be utilized. We identify several parameter combinations with high diffraction efficiencies using rigorous coupled wave analysis, demonstrate experimentally diffraction efficiencies of 94% in a Bragg mount configuration at a wavelength of 543 nm and discuss the influence of substrate thickness on the transmitted light intensities. A direct writing electron-beam lithography fabrication process gives wide flexibility in design realization.     

Electrophoretic deposition for fabrication of ceramic microparts

Electrophoretic deposition (EPD) is mostly used for producing moulds and layers. The present work shows the fabrication of ceramic microparts by the use of structured electrodes. As electrode structures euro coins and spinning nozzles were used. Additionally a cost effective and simple method was developed, which allows preserving the original master mould by using microstructured silicone moulds as substrate. This was enabled by coating the silicone moulds with graphite to obtain an electrically conductive surface, required for electrophoretic deposition.     

Fabrication of diamond micro tools for ultra precision machining

State of the art diamond tools for metal-cutting manufacturing are handcrafted by polishing and grinding of natural diamonds. Tools fabricated by these means are serially made unique copies with a limited variety of shapes. Furthermore, manual fabrication leads to deviation from ideal geometry. We present a novel technique for parallel fabrication of diamond micro tools with high contour accuracy by using lithographic methods followed by a modified ASE-process.     

Occurrence of perfluoroalkyl sulfonates and carboxylates in German drinking water sources compared to other countries.

Different homologues of C4 to C8 perfluoroalkyl carboxylates (PFCAs) and perfluoroalkyl sulfonates (PFASs) were detected in German surface waters, bank filtrates, artificially recharged groundwaters, and drinking waters. If no point sources are located nearby, the typically measured levels are in the low ng/L range. In the presence of point sources, such as a fluorochemical production site, a leaching agricultural fertilizer contaminated with PFCAs and PFASs, or drained PFC containing fire-fighting foams, much higher concentrations in the microg/L range occur. This situation is similar in Germany and other countries.