Effect of intermetallic diffusion between Pd and Ti–Al alloy on the performance of Pd/Ti–Al alloy composite membranes

The Ti–Al alloy possesses very desirable properties such as having a low density, high specific strength, good oxidation resistance at high temperatures, good acid or alkali resistance, and easy to process. Therefore, the use of porous Ti–Al alloys for the support of palladium composite membranes is an attractive alternative compared to stainless steel and ceramics. However, information on the intermetallic diffusion between Pd and the Ti–Al alloy at high temperatures is not yet available. In this work, the intermetallic diffusion between Pd and the Ti–Al alloy at high temperatures was studied using backscattered electron microscopy (BSE), EDX cross-sectional line scans, and electron probe microanalysis (EPMA). The results showed that neither diffusion of palladium nor diffusion of titanium and aluminum was observed after 40 h of treatment at 500 °C in hydrogen, which proved that the Ti–Al alloy effectively avoided the diffusion of metals compared to stainless steel. However, extensive intermetallic diffusion occurred between the Pd and the Ti–Al alloy after 40 h of treatment at 700 °C in hydrogen. Ti and Al atoms diffused from the metal-support interface into the Pd membrane layer. Pd also diffused into the Ti–Al alloy support. Significantly, the flux decline and the formation of pinholes on membrane surface correlated to the degree of intermetallic diffusion, and intermetallic diffusion would intensify leak formation.