Local order of the precursor gel for the synthesis of ZrO2-Y2O3 nanopowders by gel-combustion routes

I.O. FÁBREGAS; L.M. ACUÑA; D.G. LAMAS; R.J. PRADO; M.C.A. FANTINI

2007 Activity Report of the Brazilian Synchrotron Light Laboratory

Laboratorio Nacional de Luz Sincrotrón (LNLS)

Año: 2008 p. 1075 - 1075

1518-0204

ZrO2-Y2O3 ceramics have been intensely investigated because of their excellent electric and mechanical properties. In particular, TZP (tetragonal zirconia polycrystals) ceramics exhibit high ionic conductivity at intermediate temperatures and high fracture toughness. Unfortunately, the tetragonal phase is unstable and it can only be retained if the grain size is smaller than a critical value, which is in the range of 0.2-1 µm depending on the composition. For this reason, these materials are prepared from nanocrystalline powders, which also retain the tetragonal phase if the crystallite size is small enough. These nanopowders can be synthesized by a number of wet-chemical routes. Among them, gel-combustion routes are interesting because of their simple procedure and low-cost raw compounds. They are based on the preparation of an initial gel by thermal concentration of an aqueous solution of nitrates of the desired cations, followed by an autocombustion process. The reaction between nitrate ions and the organic fuel is strongly exothermic. The large volume of gases produced during the combustion reaction promotes the disintegration of the precursor gel, resulting in a ultrafine powder, with some organic residues, which are eliminated by calcination at moderate temperatures. In this work, we have investigated the local order of the precursor gel for several gel-combustion routes since it can play an important role in the retention of the tetragonal phase.