Comparative study of thermal desorption and pumping performance for TiZrV-, Pd-, or Pd/TiZrV-coated copper tubes

Abstract

TiZrV, Pd, and Pd/TiZrV (Pd-overcoated TiZrV) films are prepared and evaluated to clarify the effect of overcoated Pd layers on the film thermal desorption and pumping performance. In thermal desorption experiments after CO dosing, the Pd/TiZrV films release the sorbed CO, but the TiZrV films do not. This difference in behavior indicates that the Pd layers limit the accumulation of carbon on or near the surface. The Pd/TiZrV films show H2 sticking probabilities more than three times greater than those for the TiZrV films because of the superior H2 dissociation and diffusion properties of Pd. However, Pd exhibits a higher H2 equilibrium pressure than TiZrV; thus, the Pd/TiZrV films exhibit a lower pumping rate than the TiZrV films at H2 pressures close to the H2 equilibrium pressure. In addition, the Pd layers are confirmed to effectively protect the underlying TiZrV films during atmospheric exposure, resulting in a long operating life.