Rotation-coalescence of confined particles in Ni 1– xO/NiAl 2O 4 composites

Abstract

The Ni 1– x O/NiAl 2O 4 powders of specified molar ratios (1:9, 32:1, 69:1, designated as N 1S 9, N 32S 1, N 69S 1) were sintered and annealed at 1873 K for 1–80 h and studied by transmission electron microscopy with regard to the orientation change of the intragranular particles. It was found that the N 1S 9 and N 32S 1 specimens contains only intergranular particles; whereas the N 69S 1 specimen contains both inter- and intragranular particles in the late stage of sintering. In N 69S 1 specimen, the intergranular spinel particles, either isolated or slightly coalesced as sausage-like chains, were able to detach from the Ni 1– x O grain boundaries and became parallel-epitaxial with respect to the host Ni 1– x O grains upon annealing. The orientation change can be ascribed to Brownian rotation and coalescence of the particles, and the rotation of the particles mostly proceeds over non-specific contact planes due to the dragging effect in the coalescence process. The epitaxial spinel particles could possibly be preserved in the Ni 1– x O grains when the intergranular particles were coalesced to a larger size to suppress grain boundary separation.