Autor: Loreen Wermuth

Due to new private space companies the competition in the space business has changed considerably over the past years. The pressure of competition leads to the fact that the production and the missions themselves must always be made more cost-effective. In addition to these two aspects, the focus is also on the development of new innovations and technologies. However, in this connection the requirements are constant quality and highest reliability. Based on extreme external conditions the applied components have to meet stringent requirements within the space business. That is the reason, why materials play an essential role. In this connection very good temperature and media resistance are required. Due to their advantageous properties platinum rhodium alloys are preferentially used, e.g. in the field of small rocket engines. To achieve a maximum performance, highest reliability and durability, the selected materials have to be compatible to the applied fuels. Within this thesis, the interactions between the propellant components MMH and NTO with the platinum alloy PtRh 90-10 and the connected high temperature behaviour in small rocket engines should be characterized and described. First of all a simulation was performed for a better basic understanding of the combustion mechanism of MMH and NTO within a small rocket engine. The simulation shows that a varying temperature field depends on the formed liquid cooling film and the hypergolic combustion reaction. The main combustion species are CO₂, CO, CH₄, N₂, NO₂, H₂, CO, HCN, H₂O, OH and H. The concentration of these species can vary over the combustion chamber profile due to the prevailing temperature and the partial reactions taking place in detail. However, it should be considered that due to the different temperatures and the varying concentrations of the main combustion species, various high-temperature interactions with the combustion chamber material can occur. As shown within this work, the interaction between both propellant components and the alloy system in a temperature range of 400 °C to 550 °C leads to a material change. This interaction is based on a combination of erosion, sublimation and condensation. The results of the analyses for the temperature ranging from 700 °C to 900 °C clarify that the interactions lead to a change in the material, which is caused by a mechanism similar to metal dusting of nickel base alloys. The reason for that is that the carbon-rich atmosphere leads to the formation of graphite. The high temperature interaction between the Platinum-Rhodium 90-10 alloy and both propellants Monomethylhydrazine and Dinitrogen tetroxide depend on the one hand on the prevailing temperature field and on the other hand on the current status of the combustion reaction with the corresponding species. For the development of future engines the combustion mechanism has to be fully understood in detail to prevent undesirable interactions. In this context, the use of an alternative or newly developed propellant should be considered. Furthermore, the applied materials as well as the design/construction of future engines should be further developed in order to make them even more innovative, efficient and reliable.