Combinatorial screening of Pd-Ag-Ni membranes for hydrogen separation

As an effort to reduce Pd content, a combinatorial study was carried out on Pd-Ag system with the addition of Ni as a third element. A magnetron sputtering system was used to create a thin film material library using three sputter targets arranged in a triangular fashion. A total of 21 glass discs were used as a substrate onto which membranes typically 3 µm thick were deposited, each with a different composition covering a wide compositional field in Pd-Ag-Ni ternary phase diagram. Membranes produced were screened by a four probe resistivity measurement in terms of a reactivity index, defined as the ratio of resistivity under hydrogen to that under argon in the same conditions. Mapping based on the resistivity measurements indicated three alloys, namely Pd33Ag59Ni8, Pd55Ag28Ni17 and Pd76Ag18Ni6 where the reactivity index were relatively high, implying that they could be possible membrane compositions. Foils were prepared with matching compositions by melting and casting followed by rolling to ≈100 µm in thickness. This has shown that a permeability value of 6.50×10−10 mol/m s Pa1/2 could be obtained at 400 °C in Pd55Ag28Ni17 where Pd content is nearly two thirds of the commercial alloy Pd77Ag23.