PdAgAu alloy with high resistance to corrosion by H2S

Abstract PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd 83 Ag 2 Au 15 and Pd 74 Ag 14 Au 12 , were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000H 2 S/H 2 at 623 K for periods of 3 and 30 h. The microstructure, morphology and bulk composition of both non-exposed and H 2 S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD and SEM analysis revealed time-dependent growth of a bulk Pd 4 S phase on the Pd foil during H 2 S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H 2 S exposure. In agreement with the XRD and SEM results, sulfur was not detected in the bulk of either ternary alloy samples by EDS, even after 30 h of H 2 S exposure. X-ray photoelectron spectroscopy (XPS) depth profiles were acquired for both PdAgAu alloys after 3 and 30 h of exposure to characterize sulfur contamination near their surfaces. Very low S 2p and S 2s XPS signals were observed at the top-surfaces of the PdAgAu alloys, and those signals disappeared before the etch depth reached ∼10 nm, even for samples exposed to H 2 S for 30 h. The depth profile analyses also revealed silver and gold segregation to the surface of the alloys; preferential location of Au on the alloys surface may be related to their resistance to bulk sulfide formation. In preliminary tests, a PdAgAu alloy membrane displayed higher initial H 2 permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H 2 S than pure Pd.