Nanocrystalline Pd and PdH0.7 prepared by heavy plastic deformation under pressure

The method proposed for the formation of a nanocrystalline structure in some metals having a tendency to adsorb hydrogen involves heavy plastic deformation under pressure and subsequent complete or partial dehydrogenation. The formation of a nanocrystalline structure in the palladium-hydrogen system was studied. The coarse-grained disklike palladium specimens 6 mm in diameter and 0.3 mm in thickness were electrolytically hydrogenated to a level ensuring the formation of β hydride PdH 0.7 . Then the palladium specimens and the specimens containing α-PdH x (x = 0.01) + β-PdH 0.7 were deformed by shear wider pressure to E = 7-8 at 20 and -196°C. The deformation of the initial palladium specimens to e = 7 decreases their grain size to 50-100 nm, and the deformation of the specimens containing hydrides to e = 7-8 both at 2() and at -196°C decreases their grain size to 15-20 nm and, in some regions, to 3-5 nm. Annealing at 180°C for I h or holding at room temperature for more than seven days causes partial dehydrogenation of the hydrogenated deformed nanocrystalline palladium specimens (n-Pd). The grain size of n-Pd was shown by electron microscopy to be unaffected by dehydrogenation, remaining unchanged at 3-20 nm.