Al3+-stabilized c-ZrO2 nanoparticles at low temperature by forced hydrolysis of dispersed metal cations in water

A mixed aqueous solution (0.2–0.5 M) of ZrOCl2·8H2O and AlCl3·6H2O has a controlled forced hydrolysis to form an amorphous Zr1−2xAl2xO(OH)2−2x·αH2O precursor on adding NH4OH (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-ZrO2 of nanoparticles in Fm3m 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 Al3+additives cultivate stabilized c-ZrO2 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-ZrO2 phase transformation appears at extended temperature as 1000 °C as per the Al3+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-ZrO2 formation and its stability and phase transformation are studied with X-ray diffraction, microstructure and thermal analysis of representative specimens.