Microstructure evolution of an equimolar powder mixture of ZrO2-TiO2 during high-energy ball-milling and post-annealing

High-energy dry ball-mill and post-anneal processing were applied to synthesise ZrTiO4 oxide powder from an equimolar TiO2-ZrO2 powder mixture. X-ray diffraction was used to identify structural changes in the milled and the subsequently post-annealed samples. Applied milling assemblies, vials and balls made of WC-Co hard-metal and also of agate materials, were successful in such way that a fully amorphous structure appeared in the samples if milling lasted long enough. The milling time required for complete disordering was almost five times longer with the agate assembly (about 50 h) in comparison with the WC-Co one (about 10 h). Also, the hard-metal assembly incorporated in the milled samples some amount of a WC impurity due to contamination, whereas contamination of samples by agate material was not observed by XRD. The preparation of the crystalline ZrTiO4 powder phase from the amorphous one, was possible if the samples were exposed to a subsequent heat treatment. The structural transformations occurring during heating the samples went in two different ways depending upon the previously used milling assembly. In the first case annealing of samples performed for 1 h at 650 degreesC caused a structural transformation of the WC phase into the WO3 phase, whereas this temperature was not high enough to allow the crystallisation of the amorphous ZrTiO4. Annealing of the samples at 900 degreesC for 1 h caused complete crystallisation of the amorphous powder into the crystalline ZrTiO4 phase, without any evidence of the presence of the former W-base phases. Apparently this temperature favoured the formation of the solid solution of the WO3 phase in the ZrTiO4 crystalline phase. The crystallisation of the amorphous ZrTiO4 phase in samples milled in an agate assembly was possible even at 650 degreesC, although at this temperature it was a very slow process, and prolonged annealing time was necessary. If the samples, milled in an agate assembly up to 50 h, were heated at 900 degreesC for 1 h, they can fully transform into the crystalline ZrTiO4 phase. (C) 2001 Elsevier Science B.V: All rights reserved.