Investigation of degradation mechanism of palladium–nickel wires during oxidation of ammonia

The process of oxidation of ammonia proceeds in 800–900 °C with high reactivity hydrogen discharge. Extremely aggressive environment and temperature require using the most chemically resistant materials with catalysis properties. One of the main groups of those materials is palladium–nickel alloys. In our investigation we focused on analysis of PdNi5 degradation during catalysis process. The investigation was performed on 78 μm diameter wires after long exposition to chemically aggressive environment. The samples were prepared with focused ion beam (FIB) system. The observations of surface and wire cross sections were executed using a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) device, which allowed defining chemical composition. The effect of a grain orientation on sensitivity to reaction with ammonia gas was tested by mapping with electron backscatter diffraction (EBSD) techniques. Significant change of wire cross section after long exposition was determined by 3D X-ray computer tomography (XCT). The obtained results can be basis of further investigation on improvement of strength of PdNi alloys in high temperature chemical application.

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► We focused on analysis of PdNi5 gauzes degradation during nitrogen reduction.
► Samples were analyzed using FIB, SEM, EDS, EBSD and micro-XCT techniques.
► Significant change of gauzes morphology and chemical composition was observed.
► FIB/SEM analysis shows that degradation of PdNi5 wires occurs deep into the material.
► Degradation is related to the diffusion of Ni and intense etching of grain boundaries.