Analysis of the nanopores produced in nickel and palladium by high hydrogen pressure

Abstract

Samples of pure nickel and palladium were submitted to a high hydrogen pressure (HHP) of 3.5 GPa at 800 °C for 5 h. Analysis of the resulting structural modification was performed using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and small-angle X-ray scattering (SAXS), the latter specifically for Ni. The formation of superabundant vacancies (SAVs) was observed in the structure in both cases. For Pd, the pores, which formed by the coalescence of vacancies, had dimensions of 20–30 nm when present in the interior of the metal and 1–3 μm when condensed at the surface. The pores were seen to be dispersed homogeneously across the surface of Pd. For Ni, however, pores were created preferentially at the grain boundaries, which promoted significant decohesion in the metal. The distribution of pores induced by heat treatment of Ni subjected to HHP was determined by SAXS analysis and two populations of pores, with population mean diameters of 50 and 250 Å, were observed.