Novel coalescence-driven grain-growth mechanism during annealing/spark plasma sintering of NiO nanocrystals

A novel oriented attachment growth mechanism of nanograins has been suggested for spark plasma sintering and annealing of NiO nanopowder. A hierarchical microstructure built by cube-shaped nanograins was observed during pressure-less spark plasma sintering at temperatures above 1000 degrees C and when the powders were annealed in ambient atmosphere at and above 700 degrees C. Irrespective of the processing method used, a rotation assisted grain attachment of irregularly shaped nanocrystals results in such a microstructure with parallel epitaxy, twinning or line defects at the grain interface. The unique microstructural features and the governing factors for the attachment process have been discussed. Crown Copyright (C) 2017 Published by Elsevier Ltd. All rights reserved.