ZrO_2 nanoparticles are synthesized, well-dispersed in decane, via a modified emulsion precipitation (MEP) method. This method starts with preparing two thermally stable water-in-oil emulsions with nonylphenol tetrathyleneglycol ether (Arkopal-40) as the main surfactant, didodecyldimethylammonium bromide (DiDAB) as the co-surfactant, decane as the continuous oil phase, and a zirconium salt solution or hexamethylenetetramine (HMTA) precipitation reagent solution as the dispersed water phase. The two emulsions are mixed and the pH of the water droplets is increased by decomposition of HMTA to induce the formation of metal hydroxide inside the droplets. After water removal by azeotropic distillation, a transparent dispersion of ZrO_2 nanoparticles in the oil phase is obtained and the particles are stabilized with a polymeric stabilizer poly-octadecyl methacrylate (PODMA). Characterization by transmission electron microscopy (TEM) shows that the ZrO_2 nanoparticles are non-agglomerated, spherical, and have a uniform particle size distribution of 5 nm in diameter. A purification process is conducted to remove the precipitation reaction byproduct and excess surfactants from the nanoparticle dispersions. Nanostructured ZrO_2 coatings can be made by spin-coating or drop deposition of the purified nanoparticle dispersion on substrates, followed by drying at room temperature and 200 deg C. The ZrO_2 layers can then be crystallized to obtain a dense tetragonal ZrO_2 with 10 nm grains by heating at 600 deg C.
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