In situ high temperature study of ZrO2 ball-milled to nanometer sizes

Nanostructured ZrO2 was prepared by high-energy ball-milling under different conditions and sintered at high temperatures. Structural and microstructural changes during the ball-milling were monitored using Raman spectroscopy (RS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The sintering process was monitored in situ at high temperature (300–1400 8C) by RS and XRD. The results of RS showed that the ball-milling had little or no influence on the transition from the starting monoclinic ZrO2 to the hightemperature tetragonal ZrO2. It was concluded that a partial transition from monoclinic to tetragonal polymorph, observed in some earlier ball-milling experiments, can be attributed to the stabilizing influence of impurities introduced due to the wearing of the milling media. In the present experiment ZrO2 ball-milling assembly was used, which reduced the influence of an additional material. The results of the line broadening analysis, performed using Rietveld refinements of the ball-milling products with powder-to-ball weight ratio (R) 1:10, indicated a decrease in the crystallite size and an increase in the microstrains with an increase in the ball-milling time up to 3 h. Further increase in the ball-milling time up to 10 h had a very small influence on the size and strain of the obtained m-ZrO2 products. A difference between the results of in situ RS and XRD analysis of the samples subjected to prolonged ball-milling was attributed to the chemical and microstractural differences between the surface and the bulk of the ZrO2 particles during the sintering at high temperatures. q 2004 Elsevier B.V. All rights reserved