Al 3+-stabilized c-ZrO 2 nanoparticles at low temperature by forced hydrolysis of dispersed metal cations in water

Abstract

A mixed aqueous solution (0.2–0.5 M) of ZrOCl 2·8H 2O and AlCl 3·6H 2O has a controlled forced hydrolysis to form an amorphous Zr 1−2 x Al 2 x O(OH) 2−2 x · αH 2O precursor on adding NH 4OH (in water) dropwise in a controlled manner at room temperature or preferably lower. X-ray diffraction of four halos at 19.2, 28.5, 39.2, and 57.0 nm −1 wavevectors ( x=0.05) characterizes the amorphous structure of the precursor. It undergoes a self-controlled reconstructive thermal decomposition into stabilized c-ZrO 2 of nanoparticles in Fm3 m cubic crystal structure at temperature as low as 200 °C. The process involves a predominant endothermic signal with a total of ∼60% loss in the precursor mass. It controls the local temperature and in turn governs moderate nucleation and grain growth in nanocrystals. The x=0.02–0.10 Al 3+additives cultivate stabilized c-ZrO 2 crystallites in 6–12 nm confined size ( d) on heating the precursor at 200–800 °C for 2–5 h. A reconstructive c→t/m-ZrO 2 phase transformation appears at extended temperature as 1000 °C as per the Al 3+additives. A pure m-phase, d∼26 nm, results at 1200 °C (800 °C otherwise at x=0). The lattice parameters vary as the x-value. The results of c-ZrO 2 formation and its stability and phase transformation are studied with X-ray diffraction, microstructure and thermal analysis of representative specimens.