TY - CHAP A1 - Freudenmann, Dominic A1 - Stollenwerk, Manfred A1 - Döhring, Thorsten A1 - Stadtmüller, Johannes A1 - Negri, Michele A1 - Lauck, Felix T1 - Combustion efficiency of iridium coated pellets for environmentally friendly space propulsion T2 - 14th Pico- and Nanosatellite Workshop, Würzburg, Germany N2 - Most of the satellite engines still uses critical fuels such as hydrazine, which is chemically aggressive, toxic and carcinogenic. New developments for satellite engines try to avoid such critical propellants. One promising approach is the usage of rocket-grade hydrogen peroxide [H2O2] in mono- and bipropellant driven rocket engines. Catalysts in the rocket engines convert the hydrogen peroxide by an exothermic catalytic reaction; the resulting hot gases oxygen and water vapor provide the thrust. Currently used catalysts are, for example, Al2O3 pellets impregnated with platinum. Within a joint research project of Aschaffenburg University and the German Aerospace Center new catalysts are developed. They consist of ceramic pellets coated with iridium using the magnetron sputtering process. Thereby the surface structure of the iridium layers strongly depends on the used sputtering process conditions [1]. After optimization of the sputtering parameters, it was demonstrated in laboratory experiments that the catalytic effect (measured by the volume of released gas) can be increased by a factor of four compared to platinum impregnated pellets [2]. In first hot firing tests at the test bench complex M11 at the DLR- Institute of Space Propulsion, these new, iridium-based catalysts have been used in a model combustion chamber for hydrogen peroxide decomposition. For this purpose, the reaction chamber was filled with iridium pellets in the high-altitude simulation chamber of the M11.2 test bench. The model chamber was equipped with numerous measuring devices like temperature and pressure sensors (e.g. Tcat, pcat). With the help of the mass flow and the herein obtained data, performance characteristics of the propellant system were accessible. High-concentrated hydrogen peroxide was used in the experiments as monopropellant (~ 87-wt.% H2O2). During the experiments, the combustion chamber was operated in pulse mode and in continuous mode. Aim of this campaign called MoCa (“Monopropellant Catalytic Demonstrator”) is the demonstration of functionality and the performance evaluation of this iridium-based monopropellant system. Recent experimental results will be presented. References: [1] A. Büttner et al., Thin Solid Films 2018, 662: 41–46 [2] M. Stollenwerk et al., Journal of Materials Science 2021, 56(16), 9974-9984 KW - Satellitentechnik KW - Katalysator KW - Iridium Y1 - 2021 ER - TY - JOUR A1 - Stollenwerk, Manfred A1 - Döhring, Thorsten A1 - Freudenmann, Dominic A1 - Schäfer, Tobias A1 - Stadtmüller, Johannes A1 - Röcke, Nicole T1 - Sputtered highly effective iridium catalysts: a new approach for green satellite propulsion JF - Journal of Materials Science N2 - This work demonstrated the large potential of sputtered iridium metal for catalytic reactions shown by the example of decomposition of hydrogen peroxide (H2O2) for space propulsion systems. For this purpose, iridium was coated onto Al2O3 pellets by a sputter process under varied process parameters. Depending on previously selected parameters, the obtained metal-loaded pellets offer closed- and/or open-shell structures. Catalytic productivity of these first-generation iridium-sputtered catalysts was estimated in laboratory experiments and compared to platinum-loaded pellets. Under optimized sputter-process conditions, the reactivity is significantly improved compared to the platinum-impregnated pellets. The better catalytic productivity can be explained by the increased active surface area of the iridium layers on the pellets. The surface morphology and the microstructure of the iridium coating can be actively controlled by the sputter pressure. The results are in accordance with the sputtering process pressure tendency described by the Thornton Structure–Zone Model. KW - Iridium KW - Katalysator KW - Satellitentechnik Y1 - 2021 U6 - https://doi.org/https://doi.org/10.1007/s10853-021-05897-z VL - 2021 IS - 2021 SP - 1 EP - 11 ER - TY - GEN A1 - Döhring, Thorsten A1 - Stollenwerk, Manfred A1 - Stadtmüller, Johannes A1 - Freudenmann, Dominic A1 - Röcke, Nicole T1 - Nanostructured iridium catalysts for effective hydrogen peroxide decomposition T2 - EuroNanoForum N2 - The EU intends to restrict the use of critical fuels in space propulsion systems. These propellants like hydrazine are chemically aggressive, toxic and carcinogenic. Space propulsion of the future should be environmentally friendly, inexpensive, and easy to handle. Aschaffenburg University and DLR are currently developing environmentally friendly technologies for future satellite engines. Thereby rocket-grade hydrogen peroxide, which is foreseen as a substitute, is converted to uncritical water vapour and oxygen by an exothermic catalytic reaction on nanostructured iridium layers. The resulting hot gases provide the required amount of thrust. The iridium catalyst layers are coated onto ceramic pellets, using RF magnetron sputtering technology. The catalytic functionality was tested afterwards at the chemical laboratories of DLR. First experimental results show a significantly higher catalytic activity for nanostructured iridium surfaces than for smoother crystalline layers. N2 - Poster KW - satellite KW - propulsion KW - catalyst KW - iridium KW - hydrogen peroxide KW - Iridium KW - Katalysator KW - Satellitentechnik Y1 - 2021 VL - 2021 ER - TY - JOUR A1 - Wissel, Julian A1 - Freudenmann, Dominic A1 - Cichocka, Magdalena Ola A1 - Pöhl, Almut A1 - Stephan-Hofmann, Iris A1 - Röcke, Nicole A1 - Pérez, Nicolás A1 - Döhring, Thorsten A1 - Stadtmüller, Johannes A1 - Stollenwerk, Manfred T1 - Microstructure of highly effective platinum–iridium alloys as catalysts for hydrogen peroxide decomposition JF - Research on Chemical Intermediates KW - Iridium KW - Katalysator KW - Raumfahrttechnik KW - Antrieb, Technik KW - Wasserstoffperoxyd Y1 - 2024 U6 - https://doi.org/10.1007/s11164-024-05412-4 SN - 0922-6168 VL - 50 IS - 11 SP - 5385 EP - 5397 PB - Springer Science and Business Media LLC ER -