Modulating the composition of a metal/oxide interface and using hydrogen as a probe

Solid Solutions of Hydrogen in Complex Materials

“…15 for the analogous case of Ag/MgO). Calculating Gibbs free energy of the reaction and the volume change yields data for the trapping energy and partial molar volume of H which are in agreement with experimental findings [90,91]. Thus the formation of a Mg(OH) 2 layer at the interface gives rise to a remarkable volume change which is about two times as much as for H-atoms dissolved in octahedral sites of Pd.…”

“…The concept of varying soichiometry is in agreement with experimental findings, where dependent on the oxygen activity during sample annealing treatments "irreversible" and reversible trapping of hydrogen was observed [90,91]. The term irreversible trapping was used because the corresponding part of trapped hydrogen could not be removed by prolonged anodic polarization of the sample, i.e.…”

“…Hydrogen trapping at metal/ceramic interfaces has been studied extensively [89,90,91] because of its relevance in the area of hydrogen embrittlement of high strength steels, where hydrogen is trapped at the metal/carbide interface [92]. Due to the large H-solubility and the ease of measuring chemical potentials palladium alloys are used as model alloys again.…”

Diffusivity and solubility of oxygen in solid palladium

“…By using the same technique, measurements of the diffusivity of oxygen in palladium were carried out by the same authors [5]. However, like the solubility values the ones for the diffusion coefficients are very low and, therefore, are in conflict with the well-known kinetics of internal oxidation of palladium during annealing in oxygen or air [6][7][8][9][10][11][12]. This has also been shown in the previous work of the present authors [13], where rapid internal oxidation of Pd-Mg alloys was observed and the resulting microstructures were analysed by using scanning electron microscopy [14,15].…”

Evidence of oxygen segregation at Ag/MgO interfaces

“…Moreover, quantitative volumetric measurements (sorption and desorption of oxygen) [25] and a special electrochemical technique applicable to the matrix metal palladium (high hydrogen permeability) have been employed [25± 27]. The varying oxygen coverage at the metal/ oxide interface gives rise to varying hydrogen segregation, which was studied extensively by Huang et al for palladium alloys [26,27]. There, the excess oxygen forming an oxide with the more noble matrix metal leads to irreversible trapping of hydrogen at the interface, which precedes water formation during the reduction of less noble oxides.…”