Microstructure characterization of nanocrystalline ZrSiO4 synthesized by ball-milling and high-temperature annealing

Microstructure characterization and phase transformation kinetics of a high-energy ball-milled and post-annealed stoichiometric (1:1 mol%) m-ZrO2 and amorphous (a-) SiO2 powder mixture have been investigated by Rietveld analysis of X-ray powder diffraction data. The experimental results reveal that the ball-milling of stoichiometric powder results in the formation of c-ZrO2/t-PSZ phases only. The ZrSiO4 phase was not found to form even after 30 h of milling. However, an almost stoichiometric ZrSiO4 (commercially known as zircon) phase is found to form even when a sample that was ball-milled for 5 min was post-annealed at 1473 K for 1 h. It appears that the intermediate t-PSZ phase plays an important role in zircon phase formation. The content of ZrSiO4 phase increases very sharply within 15 min of milling and remains almost unchanged after 30 h of ball-milling. It is also found that nanocrystalline zircon particles are almost free from lattice strain. Contamination by an alpha-Fe2O3 phase from the milling media results in a colour gradient (white to reddish) in the nanocrystalline ZrSiO4 phase.