Synthesis of spherical (30 nm) and rod-like (200 nm) zirconia co-reinforced mullite nanocomposites

The objective of this research is to study microstructure and phase evolution of zirconia-mullite (ZM) nanocomposites which were synthesized by the direct transformation from amorphous precursor monoliths. The monolithic precursors were heat treated at 950-1250 degrees C to obtain ZM composites. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were employed to investigate the microstructure of the composites. A unique nano- and submicron-zirconia co-reinforced mullite composite microstructure was obtained after a controlled crystallization. The nano tetragonal zirconia (t-ZrO2) grains (<50 nm) were spherical and embedded in the mullite lattice. The unconfined zirconia grains showed a preferred growth direction along < 1 0 0 > direction of t-ZrO2, and formed submicron grains (< 650 nm) with bar-like shape. The precursor derived ZM composites also demonstrated enhanced mechanical properties comparing with the conventional powder processed ZM composites. (C) 2013 Published by Elsevier Ltd and Techna Group S.r.l.