Hydrogen permeation through internally oxidized Pd alloys

Hydrogen diffusivity and solubility were determined by electrochemical hydrogen permeation tests in samples of Pd_0.97 Al_0.03 and Pd_0.97 Ce_0.03 in the as received and internally oxidized conditions. Internal oxidization caused the appearance of nanosized oxide precipitates in the Pd matrix. The shape and size of precipitates and also the coherence between the precipitates and the matrix were observed by transmission electron microscopy (TEM). Electrochemical hydrogen permeation tests revealed that the presence of oxides increases the apparent hydrogen solubility, S _app, but decreases the hydrogen diffusivity, D _app. The values of D _app were 2.0 × 10⁻¹¹ m² s⁻¹ for vacuum heat treated Pd_0.97 Al_0.03 alloy and 4.0 × 10⁻¹² m² s⁻¹ for internally oxidized Pd_0.97 Al_0.03 alloy. However, the concentration of trapped hydrogen was 49 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the vacuum heat treated condition and 403 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the internally oxidized condition. Both heat treatments were performed at 1073 K for 24 h. The influence of the nature, size and distribution of the precipitates on the hydrogen permeation parameters are discussed in this paper.