CONFINED ZRO2 PARTICLES IN NIO.NAL2O3 SPINEL

Microstructures of confined ZrO2 particles in NiO-nAl2O3 (n = 1.67) sp inel and residual strain of the spinel matrix were studied by transmis sion electron microscopy. The intragranular ZrO2 particles in NiO-nAl2 O3 spinel are sometimes slightly faceted following the crystallographi c planes {111} of the latter. Similar to that in the non-cubic matrice s (e.g. Al2O3 and mullite) the transformation of the tetragonal-ZrO2 ( t-ZrO2) particles either intragranular or intergranular resulted in th e formation of monoclinic ZrO2 (m-ZrO2) twins which appeared mosaic li ke within the particle, but secondary deformation twins occurred near the grain boundary. In the vicinity of the intragranular ZrO2 particle s the spinel matrix was anisotropically strained, both dilatational an d compressional, by the t-ZrO2 and m-ZrO2 phases respectively.