Chemically Reactive Crystal Defects in Electrodeposited Nickel

Abstract

Crystal structures and distribution of chemically reactive areas have been studied about the electrodeposited nickel having (211), (210) and (110) orientations by means of electron microscopy. In case of nickel electrodeposited on the mechanically polished substrate, characteristic preferred orientations occur in the specimens having the thickness of more than a few μ. A special procedure of the transmission electron microscopy is devised in order to observe directly the structure of thin top layer of the thick deposits having the preferred orientation.
The surface of the nickel deposits with the (211) orientation is covered by many hillocks twinned on a (111) plane perpendicular to the (211) orientation plane. Twin and grain boundaries in these deposits are chemically reactive and dissolved preferentially in a corrosive solution. In the electrodeposited nickel with the (210) orientation, in which the density of twin boundaries and stacking faults is low, these crystal defects are dissolved during immersion in the corrosive solution. In the deposits having the (110) orientation, twinning is seldom observed, and these deposits do not show particularly chemically reactive areas except grain boundaries. When prepared by the present electrodepositing conditions, the nickel deposits with the (211) orientation appear to be chemically more reactive than the deposits having other orientations, because of high density of chemically reactive crystal defects.