Structural and microstructural changes in monoclinic ZrO2 during the ball-milling with stainless steel assembly

High-energy ball-milling of monoclinic (m-)ZrO2 was performed in air using the planetary ball mill with a stainless steel milling assembly. Structural and microstructural changes during the ball-milling were monitored using X-ray powder diffraction (XRD), Raman spectroscopy (RS), Mössbauer spectroscopy, field emission scanning electron microscopy (FE SEM) and energy dispersive X-ray spectrometry (EDS). The results of line broadening analysis indicated a decrease in the crystallite size and an increase in the micro-strains with the ball-milling time increased up to ~150 minutes. The results of quantitative phase analysis indicated the presence of a very small amount of tetragonal (t-) ZrO2 phase in this early stage of ball-milling. The onset of m-ZrO2→ t-ZrO2 transition occurred between 10 and 15 hours of ball-milling, which resulted in a complete transition after 20 hours of ball-milling. Further ball-milling caused a decrease of the t-ZrO2 lattice parameters followed by a probable transition into c- ZrO2. Combined results of precise lattice parameters measurements, SEM/EDS and Mössbauer spectroscopy showed that the stabilization of t- and c-ZrO2 polymorphs at RT can be attributed to the incorporation of aliovalent cations (Fe2+, Fe3+ and Cr3+) introduced into the sample due to the wear and oxidation of the milling media.