Early stages of reduction of nickel oxide single crystals: An investigation by transmission electron microscope

Abstract

Because of the practical importance of the reaction, a great deal of work has been done on the reduction of metallic oxides to metals. In this laboratory all stages of the reduction of nickel oxide to nickel are being studied using a transmission electron microscope. Small, pre-thinned single crystals of nickel oxide have been reduced outside the microscope in a hydrogen atmosphere and the reduction temperatures and times were varied. The resulting foils were then examined in a Phillips 301 100 kV electron microscope and the relationships between the nickel metal particles and the nickel oxide single crystal matrix were established. During the early stages of the reduction both epitaxial and non-epitaxial nuclei were observed, the latter becoming predominant as reduction time progressed. The nuclei were frequently separated from the nickel oxide matrix by a fissure and as they impinged and coalesced, a large scale structure resulted with internal porosity as often seen by optical microscopy.