Structural and microstructural changes in monoclinic ZrO 2 during the ball-milling with stainless steel assembly

Abstract

High-energy ball-milling of monoclinic ZrO 2 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, Raman spectroscopy, Mössbauer spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectrometry. The results of line broadening analysis indicated a decrease in the crystallite size and an increase in the microstrains with the ball-milling time increased up to ∼150 min. The results of quantitative phase analysis indicated the presence of a very small amount of tetragonal ZrO 2 phase in this early stage of ball-milling. The onset of m-ZrO 2 → t-ZrO 2 transition occurred between 10 and 15 h of ball-milling, which resulted in a complete transition after 20 h of ball-milling. Further ball-milling caused a decrease of the t-ZrO 2 lattice parameters followed by a probable transition into c-ZrO 2. It was concluded that the stabilization of t- and c-ZrO 2 polymorphs at RT can be attributed to the incorporation of aliovalent cations (Fe 2+, Fe 3+ and Cr 3+) introduced into the sample due to the wear and oxidation of the milling media.