Palladium membranes are widely used to separate hydrogen from other gases in order to avoid contamination of fuel-cells. To improve the efficiency of the purification process, and thus decrease the size of the hydrogen separation component, it is needed to increase the operating temperature. But, it was frequently reported that the thin palladium metallic membrane can suffer from leakage after long term exposure to high temperature. Different type of defects has been described in the literature, in most cases it has been concluded that long term annealing of palladium in hydrogen rich atmospheres leads to the development of porosity.
In this work, careful observations of thin palladium membranes (20 µm) aged about 150 hours at 600°C under pure hydrogen, allow us to detect many cracks along grain boundaries. This kind of defects was not expected for a ductile metal as palladium.
Measurements of intergranular chemistry of aged membranes using Auger microscopy showed that some boundaries were significantly contaminated by sulfur. This is a direct evidence that sulfur segregates at palladium grain boundaries. Sulfur is well known to embrittle grain boundaries in many metals and alloys such as nickel, copper, thus it is reasonable to estimate that this mechanism can be, at least partially, responsible for live time limitations of palladium membranes in such applications. Moreover, Auger analysis suggest that sulfur comes from the inconel porous subtrate that supports the membrane, although its sulfur nominal concentration is as low as 100 wt ppm