A palladium alloy composite membrane for the purification of hydrogen isotopes

Abstract

In this study, experimental investigations were carried out on the deposition of Pd–Ag25at.% alloy on porous 316-type stainless steel substrate from ammoniacal solution by pulse electroplating, in order to prepare Pd–Ag alloy selective H-permeable membranes. The effects of the pulse electroplating conditions on the silver content, composition, morphology, and metallographical structure of the plated layers were studied. The film was evaluated by x-ray diffraction analysis. Besides the Pd–Ag alloy, there was a small amount of free silver ions in the layers that could be alloyed through annealing at 600°C. The silver content in the plated layers decreased with increase in the average current density and the conduction time. A high silver concentration in the plating solution was favorable for plating high silver content layers. Plated layers with silver content below 26 at.% had a bright appearance. The alloy phase featured with single and steady face centered cubic structure, and with the preferred orientation crystal face, being the lowest energy face (111). The results showed that the deposition rates of Pd–Ag alloy and silver were controlled by the mass transfer process of silver ammino complex. The Pd–Ag (25.7±0.3)at.% alloy selective H-permeable membranes with 8 μm thickness were prepared using the pulse electroplating technology and the annealing method that developed in the experiments. At 300 and 350°C, the hydrogen permeability per unit area of this membrane was 27.6 and 28.5 mL(STP)/min cm2, respectively, which was about 8.8 and 9.1 times higher than that of the commercial Pd–Ag25at.% alloy membranes, respectively, under the same condition with the operating pressure being 0.1 MPa. By using the prepared membrane, hydrogen of high purity could be obtained. After passing through this membrane, the He content in the gas mixture of 15%He–85%H2(V/V) was reduced to as small as 0.03%. The results indicated that the clearing factor of this membrane was 375 for 3He, and was higher than 500 for all the other impurity-gases. In summary, the prepared Pd–Ag alloy selective H-permeable membrane is potentially applicable for purifying the fusion fuel and for producing ultra-high pure hydrogen.