Role of cyclic ether and solvent in a non-alkoxide sol-gel synthesis of yttria-stabilized zirconia nanoparticles

The effects of cyclic ether (epoxide versus oxetane), solvent, and drying method were examined for a non-alkoxide sol-gel synthesis of yttria-stabilized zirconia (YSZ). YSZ sol-gel materials, from 3 to 25 mol % Y2O3, were successfully prepared with either propylene oxide (PO) or trimethylene oxide (TMO) in both aqueous and mixed ethanol-water solutions of Zr4+ and Y3+ chlorides. Supercritical drying (aerogels) produced fine, nanoparticulate networks, whereas drying under ambient conditions (xerogels) resulted in heterogeneous micrometer-sized hard agglomerates. The resulting materials were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption/desorption analysis, and elemental analysis by inductively coupled plasma-atomic emission spectroscopy. The cyclic ether and solvent were found to be critical factors in the resulting as-prepared aerogel surface area and morphology. For a given solvent, aerogels prepared with PO had higher surface areas than did those prepared with TMO. For example, the surface areas of aerogels prepared in water were 453 and 295 m(2)/g for PO and TMO, respectively. Following calcination to 550 degrees C, however, the crystallized YSZ powders were similar, consisting of homogeneous nanoparticles (similar to 10 nm) with spherical morphologies and high surface areas (> 100 m(2)/g). Elemental analysis, XRD, and electron microscopy indicated that Y2O3 and ZrO2 formed a homogeneous nanostructure over a wide range of Zr/Y ratios, corresponding to 3-25 mol % Y2O3.