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 α-Fe₂O₃ phase from the milling media results in a colour gradient (white to reddish) in the nanocrystalline ZrSiO₄ phase.