Available online at www.sciencedirect.com Journal of the European Ceramic Society 30 (2010) 3377–3387 Follow-up of zirconia crystallization on a surface modified alumina powder V. Naglieri a,b , L. Joly-Pottuz b , J. Chevalier b,∗ , M. Lombardi a , L. Montanaro a a Dept. Mater. Sci. and Chem. Eng., INSTM LINCE Lab., Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy b Université de Lyon, INSA de Lyon, MATEIS UMR CNRS 5510, Bât. Blaise Pascal, 7 Av. Jean Capelle, 69621 Villeurbanne, France Received 18 February 2010; received in revised form 4 July 2010; accepted 16 July 2010 Available online 19 August 2010 Abstract Here we report how thermal treatments of a surface modified -alumina powder on which a zirconium oxide precursor was grafted can be tailored so as to obtain an alumina–zirconia composite powder with well-controlled phase distribution and size. The transformation of the zirconia precursor from a starting amorphous phase to zirconia nano-grains bonded to the alumina particles surface was followed by X-ray diffraction (performed at room temperature on different thermally treated powders, as well as in situ at high-temperature) and by both conventional and high resolution transmission electron microscopy (TEM and HRTEM). Phase and nanostructure evolutions were followed on a large temperature span. The crystallization kinetics were analysed in terms of nucleation-growth mechanisms by exploiting Avrami–Johnson–Mehl–Kolmogorov formalism. Based on the above investigations, a tentative description of nucleation and growth features is proposed. This knowledge-based step represents a first approach towards nanopowders engineering. © 2010 Elsevier Ltd. All rights reserved. Keywords: Calcination; Sintering; Grain growth; Nanocomposites; Microstructure-final; Microstructure-prefiring 1. Introduction Alumina–zirconia composites are used as grinding media and cutting-tools, wear parts 1 and biomedical implants, 2,3 since they exhibit high hardness, strength and high fracture toughness due to transformation toughening mechanisms. 4–7 Especially, they are raising interest in orthopaedics, since they exhibit a larger crack resistance than alumina and a lower sensitivity to aging than zirconia. However, the content and the distribution of zir- conia grains inside the alumina matrix have a strong impact on their performances. 2 In particular, micro-nano-composites in which nano-zirconia particles are embedded in micron sized alu- mina matrix are expected to exhibit improved slow crack growth resistance and stability. 8 To achieve the control of microstruc- tural features at different scales, each step of the process, from powder synthesis to sintering, must be carefully set up. Alumina–zirconia powders can be prepared by various strate- gies, from the simple powder-mixing 2 to chemically based routes, like sol–gel, 4,9,10 co-precipitation, 11 and mixed-salts thermal decomposition. 12,13 Torrecillas and co-workers recently ∗ Corresponding author. E-mail address: jerome.chevalier@insa-lyon.fr (J. Chevalier). proposed a sophisticated and effective approach based on the powder–alkoxide mixture, 14 in which a zirconium alkoxide is grafted to the surface of alumina grains. After thermal treat- ments, zirconia nanocrystals, strongly bonded to the alumina surface, are developed. Such promising route has been applied and simplified by working in aqueous medium with inor- ganic zirconium salts. 15 These powders offer the opportunity to develop dense composite materials with very fine and homo- geneous microstructures, which represent a robust approach towards real nanostructured ceramic materials with promising properties. However, to our knowledge, there is still a lack of investigation concerning the intermediate steps between the starting amorphous phase on the alumina surface and the final developed microstructure, whereas a strict control of the nucle- ation and growth of zirconia crystals is needed to really achieve fully tailored microstructures. Here, this aim was pursued, by a precise follow-up of zirco- nia crystallization at the surface of alpha alumina grains during thermal treatments via X-ray diffraction (XRD) analysis and TEM observations. The final goal of the present work was to propose a possible nucleation-growth scenario able to support the choice of a suitable powder treatment to tailor phase distri- bution and size in the alumina–zirconia composite powder and consequently on sintered bodies. 0955-2219/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2010.07.029