Monitoring the chemical changes in Pd induced by hydrogen absorption using microcantilevers.

The reactivity of the palladium shaped as a microcantilever is investigated as a function of the hydrogen stoichiometry. A small cell holding the microcantilever is designed to monitor the deflection and the flexural resonance response from high vacuum to a hydrogen gas pressure of several bars. The measurements show that the Young's modulus is accurate if the cantilever is thick enough to be described by a continuum mechanics approach. The orientation distribution function of the palladium grains determined by X-ray diffraction enables to correlate Young's modulus measured using microcantilevers with the elastic constant tensor issued from the literature. The surface stress induced by the dissociation of H2 in palladium surface depends mainly on the cantilever cross-section. Cantilever response was found to be extremely sensitive to both the palladium lattice expansion induced by the insertion of hydrogen atoms into octahedral sites of palladium and the electronic affinity between palladium and hydrogen.