Borohydride synthesis and stabilization of flake-like tetragonal zirconia nanocrystallites

Flake-like particles of tetragonal zirconia (t-ZrO₂) were synthesized using ZrOCl₂·8H₂O as zirconium precursor, and sodium borohydride (NaBH₄) and cetyltrimethylammonium bromide (CTAB) as precipitating agent and surfactant, respectively. Small-sized nuclei, which formed during the borohydride synthesis, play an important role in the formation of small sized crystallites (5 nm) even at 600 °C and stabilization of t-ZrO₂ in both the samples synthesized with and without surfactant. In the sample synthesized without CTAB, a minor m-ZrO₂ phase (5 vol.%) along with the major t-ZrO₂ phase having a crystallite size of 20 nm, was observed at 700 °C. However, the use of surfactant leads to the formation of stabilized t-ZrO₂ nanoparticles with a smaller crystallite size of 15 nm. SEM micrographs of t-ZrO₂ show elliptical as well as elongated shaped flake-like morphology. The formation of small sized crystallites and slow growth of nucleation embryo play an important role in stabilizing the t-ZrO₂ up to as high temperature as 700 °C.