Papers by Author: Eberhard Müller

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Authors: Grit Hüttl, Dirk Beyer, Eberhard Müller
Authors: Beate Fankhänel, Eberhard Müller, Torsten Fankhänel, Winfried Siegel
Authors: Eberhard Müller, Dirk Kurtenbach, Gerhard Roewer, Erica Brendler, Brian S. Mitchell
Authors: H.-P. Martin, Dirk Kurtenbach, Eberhard Müller, Gerhard Roewer
Authors: Kirsten Moritz, Eberhard Müller
Abstract: The electrophoretic deposition (EPD) of AlN, Al2O3 and SiC, respectively, from ethanolic suspensions stabilised by suitable organic additives has been investigated. A main topic of this paper is the EPD in the direction of the gravitational force. Using an AlN suspension, the deposit weight depending on the experimental parameters was determined. The deposition was carried out under constant voltage or constant current conditions. Several factors influencing the effective electric field strength will be discussed. It could be shown that the conductivity of the suspension results mainly from the free ionic species. By EPD from the different suspensions, green bodies with monomodal pore size distributions were produced. The electrophoretic deposition of alumina from an ethanolic and from an aqueous suspension of the same composition led to similar results regarding the homogeneity of the particle packing in the deposits. The SiC suspension was also used for infiltrating woven carbon fibre mats by EPD in order to fabricate ceramic matrix composites.
Authors: Tanja Damjanović, Christos Argirusis, B. Jokanović, Günter Borchardt, Kirsten Moritz, Eberhard Müller, R. Herbig, Roland Weiss
Abstract: Combining sol-gel synthesis of 3/2 mullite through hydrolysis and condensation of tetraethoxysilane and aluminum-tri-sec-butylate with electrophoretic deposition (EPD) yields sufficiently thick and homogeneous layers which transform into mullite at T ≥ 1000 °C. The characterisation of the mullite precursor during synthesis was performed through electroacustic measurements. The protectiveness of the deposited mullite layers was tested in air in the temperature range 1200 °C ≤ T ≤ 1550 °C by means of isothermal thermogravimetric analysis for up to 200 hours. Comparing the oxidation rate of mullite coated C/C-Si-SiC samples to that of uncoated reference samples clearly demonstrated that mullite offers a significant improvement to the oxidation resistance of the uncoated material. At temperatures above 1600 °C the protectiveness of the deposited layer is reduced due to the existence of a liquid phase and the formation of CO bubbles above the cracks in the SiC layer. In order to prolong the protectiveness of our mullite layers at higher temperatures we deposited an additional layer from a suspension of mullite precursor with 5 wt. % of Al2O3 powder. The protectiveness of so obtained mullite and mullite/ Al2O3 layers was also tested under cyclic conditions at 1500 °C and 1550 °C. These experiments clearly demonstrated that all samples withstood at least for 4-10 cycles which were performed subsequently in different time intervals (from 2-3 days to 1 h).
Authors: G. Michel, G. Staupendahl, G. Eberhardt, Eberhard Müller, Ch. Oestreich
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