Ž . Journal of Non-Crystalline Solids 225 1998 120–124 Synthesis and sintering of zirconium oxide aerogel A. Lecomte ) , F. Blanchard, A. Dauger, M.C. Silva, R. Guinebretiere ` Laboratoire de Materiaux Ceramiques et Traitements de Surface, UPRESA CNRS no. 6015, ENSCI, 47 a 73 AÕenue Albert Thomas, ´ ´ ` 87065 Limoges, France Abstract Crystalline zirconium oxide aerogel was synthesised by supercritical drying of a precursor gel prepared in the zirconium n-propoxide, n-propanol, acetylacetone and water system. This aerogel retained the initial fractal structure of the gel state. Aerogel samples were heated at moderate temperatures and studied by X-ray diffraction and small angle X-ray scattering. Small angle X-ray scattering results strongly suggested that the structural modifications follow the linear Cahn’s theory for spinodal decomposition. Upon higher temperature annealing, the low-q intensity maximum, present on small angle X-ray scattering curves, began to move towards higher-q vectors before moving back to smaller angles. The aerogel sintering mechanism changed and crossed from sintering of crystalline mass fractal aggregates towards the conventional behaviour. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Zirconium oxide aerogel; Small angle X-ray scattering; Sintering 1. Introduction Chemically pure or doped zirconia materials have been widely investigated due to interest arising from their physical properties. However, the sol–gel meth- ods have renewed research interest in ZrO materi- 2 als. Indeed, by varying the gelation, ageing, drying or sintering processes, the sol–gel route allows preparation of a wide range of nanostructures among which the aerogels probably exhibit the most origi- nal. This nanostructure gives them many unique and interesting properties and, in many cases, the funda- mentals of the sintering process must be understood wx 1 . Such information is crucial for nano-engineering these materials and their structure–property relation- ships. ) Corresponding author. Tel: q33-5 55 45 22 22; fax: q33-5 55 79 09 98; e-mail: a.lecomte@enscidns.ensci.fr. The most intensively studied sintering behaviour w x w x is that of silica 2–6 or silicate 7,8 aerogels in the viscous flow mechanism domain. Despite foresee- able different behaviour, few studies have been de- voted to aerogels partially crystallized or susceptible wx to rapid crystallization under heat treatment 9 . X-ray diffraction and small angle X-ray scattering Ž . SAXS were carried out in order to determine the thermal behaviour of a fractal crystalline ZrO aero- 2 gel. By heating at temperatures in the 3508 to 6008C range we were able to follow structural evolution, particle growth and sintering. 2. Experimental procedures w x As described elsewhere 10 , the zirconia precur- sor gels were prepared in the zirconium n-propoxide, Ž . n-propanol, acetylacetone acacH and water system. 0022-3093r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0022-3093 98 00107-0