Diffusion bonding of Pd-Ag rolled membranes

Cold-rolled and annealed Pd-Ag 25% at. foils of thickness 50 mum have been joined by diffusion bonding in order to obtain permeator tubes used in laboratory applications for hydrogen separation and purification. The tubes produced present a sound and effective joint along the generatrix line: particularly, this procedure has shown better performance than arc welding, responsible for formation of thermally stressed zones and embrittlement of permeators. Based on the high diffusion of the Ag atoms, the joining procedure of the tubes consists of a thermal treatment at 1100degreesC for 1 h under controlled atmosphere (Ar-H 5%), where the overlapped limbs of the metal foil have been compressed in a special device. This joint obtained by diffusion bonding has shown absence of defects and good chemical and physical stability after thermal and hydrogenation cycling of the permeator tubes under their operating conditions. Characterization tests carried out in the temperature range 300 - 400degreesC on these membrane tubes have given hydrogen permeability values according to the literature. (C) 2004 Kluwer Academic Publishers.