Palladium metallic interdiffusion

For example, effective intermediate layers have been developed that create a smoother support surface to minimize defect density and reduce metallic interdiffusion. The following sections of this chapter examine the history, background, and applications of palladium membranes, including recent advances in fabrication methods and performance. 

Juda W, Krueger CW, Bombard TR. Method of producing thin palladium-copper and the like, palladium alloy membranes by solid-solid metallic interdiffusion, and improved membrane. United States Patent 6238465 2001. 

Hence, the decision to use a heated substrate with simultaneous evaporation of the component metals as an aid to homogenization requires consideration of whether or not it might have an adverse effect, i.e., causing preferential nucleation of one component, which interdiffusion may not be able to remedy. It was believed (60) that in preparing Pd-Rh alloys by simultaneous deposition on a substrate at 400°C, rhodium nucleated preferentially and that crystallites grew by the addition of palladium (and rhodium) atoms. The diffusion of palladium atoms into this kernel formed a phase with 88 =t 5% Rh (phase II). The outer shell of the crystallite, phase I, was in effect a solid solution deficient in rhodium compared with the overall film composition, and the Rh content of phase I therefore increased as the Rh flux was increased. 

Interdiflusion between the components of catalyst coatings and substrates can also lead to catalyst deactivation. If Nb, Ta, Ti, V or Zr diffuses through palladium or other noble metal protective layers and reacts on the outer surface to form stable oxides, carbides or nitrides, the catalytic dissociation of molecular hydrogen can be poisoned. Interdiffusion, linked to loss of hydrogen flux, has been reported by Edlund and McCarthy [47] and Pagheri et al. [56]. Membrane surfaces can also become depleted of palladium if palladium diffuses into the substrates. Apparent complete loss of palladium has been observed by Rothenberger et al. for 40 nm thick Pd films on Ta foils after 48 h use at 1173 K (900 °C) [41]. 

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