Investigation of the Chemical Behavior between Platinum Rhodium and the Rocket Engine Propellants Monomethylhydrazine and Dinitrogen Tetroxide

The development and construction of spacecraft components depends on many different factors of influence. Since many missions run over several years it is necessary that the applied materials show an exceptional corrosion resistance and high temperature strength. That is the reason why noble metals are applied in many aerospace applications due to their advantageous properties. Especially platinum group metals feature enhanced characteristics, like superior high temperature and corrosion resistance.

One of the applications of platinum alloys is their use to manufacture combustion chamber parts for small bipropellant reaction control thrusters or apogee engines. These engines are widely used for boost an on-orbit maneuvering of large satellites and deep space probes. These engines are usually hypergolic bipropellant thrusters and use the storable propellants Monomethylhydrazine MMH as fuel and pure Dinitrogen Tetroxide N₂O₄, or Mixed Oxides of Nitrogen (MON-1, MON-3) as oxidizer.

The aim of this study is the analysis of the chemical behavior between platinum rhodium and the propellants MMH and N₂O₄. It is well known, that the uncoated surface of the platinum alloy is almost insensitive to oxidation. But for a better understanding of the whole reaction chain and for a better handling of the group of alloys with propellants exposure tests were performed. Here, samples were stored at different time periods in MMH and N₂O₄ (minimum 24 h; maximum 6 months). To analyze the samples before and after the exposure tests different research methods were used. Scanning electron microscopy (SEM) was performed to analyze the surface and the morphology of the samples. The chemical composition of the sample surface was detected by x-ray photoelectron spectroscopy (XPS).

These investigations will give information about the chemical behavior during exposure tests and what it means for the whole reaction chain of applied platinum alloys in connection with the propellants MMH and N₂O₄.