Use of intense heat elimination during crystallization and cooling to improve the properties of steels

Institute of Casting Problems, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 45–49, September, 1988.     

PdAgAu alloy with high resistance to corrosion by H2S

PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd₈₃Ag₂Au₁₅ and Pd₇₄Ag₁₄Au₁₂, were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000H₂S/H₂ at 623 K for periods of 3 and 30 h. The microstructure, morphology and bulk composition of both non-exposed and H₂S-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 Pd₄S phase on the Pd foil during H₂S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H₂S 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 H₂S 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 H₂S 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 H₂ permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H₂S than pure Pd.